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Why a Typical Home Solar Setup Does Not Work with the Grid Down

443 points by cesarb 8y ago

deleted 8y ago
[deleted]
gnicholas 8y ago
Super useful. Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires. In the article I read, they mentioned that even home solar wouldn't work, which seemed crazy. I can now see why this is the case, and what folks should do (get a transfer switch and generator) to be able to power their home with their solar panels.
- tlrobinson 8y ago
  > Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires Huh, where can I read about this?
  - rconti 8y ago
    Even just going to pge.com i get an interstitial about it, but no detail. A couple links: https://yubanet.com/regional/pge-shutting-off-power-during-high-wildfire-threats-what-does-it-mean/ https://yubanet.com/regional/pge-shutting-off-power-during-h... https://www.mercurynews.com/2018/06/12/pge-could-shut-off-power-on-purpose-amid-fire-hazards/ https://www.mercurynews.com/2018/06/12/pge-could-shut-off-po...
  - mcpherrinm 8y ago
    TLDR: Power lines are a cause of wildfires, and PG&E may shut down power on some transmission lines in times of extreme fire danger. https://www.sfchronicle.com/business/article/For-PG-E-cutting-power-could-prevent-fires-save-13019005.php https://www.sfchronicle.com/business/article/For-PG-E-cuttin... https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power/ https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power...
    - joering2 8y ago
      Interesting fact: years ago it was designed to build electric infrastructure above the ground because air friction addsup about 20% of electricty, free. It wouldnt be possible underground. But then, you know, whole State of amedium size country like California, would have no power interruptions in heat spikes.
  - gnicholas 8y ago
    I read about it in The Almanac [1]. Also, note that the map that shows higher and lower risk zones doesn't actually indicate what locations may be affected by outages. They only show where the affected lines are, but those apparently feed homes/buildings that appear to be in the clear. 1: https://www.almanacnews.com/news/2018/07/25/pge-may-cut-power-in-extreme-weather https://www.almanacnews.com/news/2018/07/25/pge-may-cut-powe...
- EGreg 8y ago
  Can you please elaborate about the transfer switch and generator - how to use them? What about just using batteries?
  - TheSpiceIsLife 8y ago
    Typical grid-tied solar system would still require a transfer switch, either auto or manual, they're called break-before-make transfer switches because they disconnect the mains supply before switching over to the battery + inverter system or generator. These transfer switches are mechanically interlocked so it's not possible to have both supplies connected simultaneously as this would generally be release-the-magic-smoke catastrophic. Typical auto transfer switches are fast enough that computer equipment etc won't notice. Edited to add: if you want truly uninterruptible power then you should do what data centres do: everything runs off the UPS all the time (well, all the computers, maybe not all the cooling system), the only thing that changes is the supply: either mains, batteries, solar, or generator. Or some combination of batteries + the other three.
    - btbuilder 8y ago
      There's another UPS-source option, which is also my favorite, flywheel! Back in the 00s I visited a DC that two very large flywheel UPS that were being trialed to replace the battery room.
      - pas 8y ago
        Flywheels are alive and well in the DC industry. They are used for those crucial seconds while the generator starts up. And as a backup for the UPS-es. (After all, those batteries might not be in top shape all the time.) Though I imagine eventually battery tech will take over.
        TheSpiceIsLife 8y ago
        If the flywheel can be integrated in to the generator design then generator startup can be almost instantaneous. Synchronisation would still take a few moments. I don’t know if anyone is building systems like that though?
- bacon_waffle 8y ago
  Unfortunately, adding a generator and a transfer switch will probably not enable you to get power from the solar panels. You'll also need an inverter that's designed to operate off grid; the anti-islanding feature on a normal grid tie inverter will prevent it from providing power when the grid is gone. There are a few ways that anti-islanding systems can work, but it's reasonable to imagine that the inverter is measuring the impedance between its output and a nominal AC source: the power grid. If that impedance is too high - and it will be unless you've got a rather large generator - then the inverter will not source power.
Johnny555 8y ago
During 2017, I saw a lot of news articles talking about how the Evil Power Companies were being Meanie McMean by not letting people with solar panels use them when the grid was down. The implication (in many news articles) was that these powerless people with solar panels could use them to power their home while the grid was down, if only the evil power company didn't require that solar not work if the grid was down. I don't remember seeing any articles that blame the power company for home solar not working off-grid... I do remember seeing articles saying that most home solar installations won't work if the power grid is down, but nothing that implied that the power companies were behind it.
- 0xCMP 8y ago
  In Florida it was popular around hurricane season after we lost power. I'm glad I finally understand why because all that I'd seen reported was the solar systems installed must be turned off. I'd always assumed all these systems (many of which are meant to be used in a storm + lower electricity costs) had a transfer switch.
- PJDK 8y ago
  Here's one example https://boingboing.net/2017/09/18/rep-ray-rodrigues.html https://boingboing.net/2017/09/18/rep-ray-rodrigues.html
tlrobinson 8y ago
> To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while It doesn't seem like a battery or capacitor to handle blips like an airplane flying overhead would need to be very large?
- derefr 8y ago
  No, but using a small battery means using a battery that get heavily charged/discharged by such events, and therefore has a short lifespan (less than a year, probably, if you used the kind of battery that's in a UPS.) The reason the battery banks for solar are so large isn't just to capture the entire daytime output for night-time use, but also so that they can have a lifespan closer to that of the solar array itself.
  - foota 8y ago
    That's interesting! Is it like an SSD where you plan for a certain amount of cells to fail or does it reduce load on the cells so they last long individually?
    - TheSpiceIsLife 8y ago
      Generally speaking, lead acid batteries, and lithium batteries, last longer if they are never (rarely?) deeply discharged. If you need 100Ah from your batteries you’re better off provisioning as many times more up to some cost-benefit analysis.
    - derefr 8y ago
      The latter. Whenever your battery gets super discharged, picture this happening inside it: https://www.youtube.com/watch?v=r-YbQN_twpw https://www.youtube.com/watch?v=r-YbQN_twpw Notice how running the current the other way will break up the formed crystals, but it won't actually re-dissolve them. That's what it means for a battery to wear out. (Battery electrolytes are chosen specifically to be resistant to this, so the effect is mainly visible as a thin "rust" of deposited crystals on the battery's anode, rather than the full-scale crystals seen here.) A similar but distinct process occurs when overcharging a battery, where, instead of splitting the electrolyte molecules apart, you're reacting and bonding them together to form new molecules or molecular complexes, with the reaction usually being one-way rather than an equilibrium reaction. (For lithium batteries this process is exothermic and catalyzed by the presence of the product—thus lithium battery explosions.) It's much better for the life of the battery if it basically just hovers around 40-60% charge for its whole useful life, since then you're just generating tiny seed crystals (on discharge) and then re-dissolving them (on charge), where those crystals are small enough that they can be fully re-absorbed. And this is true even in battery-cell technologies that require a "deep charge cycle" to erase their "battery memory." Battery memory is basically the electrolyte causing enough crystalline rust specifically on the anode to increase its resistance. A deep discharge can capture and erase this rust—but it still shortens the battery's lifespan, because you're still producing non-reabsorbable large crystals within the electrolyte.
bacon_waffle 8y ago
There are all sorts of issues with using a regular grid-tied inverter in an off-grid situation; there are regulatory issues besides the anti-islanding (which is a complicated topic all on its own), and technical challenges too. A lot of the technical challenges go back to the inverter effectively being a thing that bolts on to the existing house wiring; I think that if they could be more of a pass-through thing (like a UPS) then the picture would be a lot simpler. An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution. Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect. Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated. What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again. Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!
ghubbard 8y ago
Great article, lots of technical details. A simple answer to the 'Why' can be found in the middle under the 'Off Grid Without Batteries' headline. > If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,
- raverbashing 8y ago
  "there's no waveform to sync with" is technically correct and a very poor excuse A residential no-break has no waveform to sync with as well. Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)
  - TheSpiceIsLife 8y ago
    When the grid goes back up the system would check the grid frequency and phase, and slowly match that waveform over a few minutes by making light changes. When the two are aligned within a good-enough tolerance the system will switch back to it's regular state of mains + solar ( + batteries + wind + generator + etc / whatever). These are all solved problems with commercial off the shelf components.
    - zaarn 8y ago
      Are these commercial off the shelf components as cheap as a microinverter?
      - TheSpiceIsLife 8y ago
        I just typed microinverter in to Google and clicked on shopping. It looks to me like microinverters are a commercial off the shelf product? Will a microinverter do all of the things a multi-component phase-syncing system with automatic transfer switches do? I don't see why a microinverter can't be built with these components integrated. I can't tell you if such a unit exists as I'm not well versed in the product range. As far as a price comparison goes, I guess it only makes sense to compare a like-for-like system?
CaliforniaKarl 8y ago
I've read the detailed reports for outages in the West and the North-East, and they touch on alot of the same concepts that were in this (awesome) article. Does anyone know, what's a good resource for learning more about power generation, grid regulation, etc.? The relationship between frequency/voltage and available vs. demanded current, frequency sync, grid maintenance, etc.…
- throwawaycanada 8y ago
  If you have a reasonable electrical background I would suggest this textbook: Electrical Machines, Drives and Power Systems by Theordore Wildi
ggm 8y ago
We found that even a well made Honda petrol genset was highly unstable feeding volts into a UPS for a machineroom. They are good at lights. They are good at a cooker. They suck at anything which expects regulated, non-noisy volts. Lots of homebrew 'you can plug this magick cable I made' methods to supply volts across the fence to neighbours houses when the power goes down are really bad: behind the meter is just as lethal as in front of the meter, if you get it wrong. TL;DR if you need to read a website like this for clue how to avoid losing power, you are putting your life at risk if you don't follow code, and don't know what you're doing.
- driverdan 8y ago
  Inverter generators like the popular Hondas are not good for surges. If you run them at a steady draw they'll give you nice, clean power. If you your demand fluctuates significantly they will stall or cut out and the voltage during or after the stall may be dirty. You have to read the specs carefully to make sure they are a good match for your use.
  - ggm 8y ago
    Fridge. Surge load. Washing machine. Huge torque surge load. Airconditioning. That's basically a fridge? So.. "home" solar setup.. home.. like fridges, aircon and washing machines... Do you see where this is going?
    - thinkythought 8y ago
      The solution here is inverter drive appliances. I had a cheapo but great thrift store inverter microwave. My cheapo junk 3000w inverter could run it off a few hundred Ah of batteries without issue, still spitting out clean power on the other outlets. A regular microwave(with a lower run wattage in theory, by about 1/3rd) would instantly blow the thing up and set off its obnoxious alarm. With some carefully selected appliances you would probably be fine. This stuff used to be super pricey, but now even the cheaper brands are putting out inverter drive ACs for example. Not window units, but mini splits and home systems
bunkydoo 8y ago
youre all somewhat ignorant if you think that solar is even remotely a solution. if humans could get along for more than 2 weeks we could have unlimited clean power through nuclear. even jeff bezos has articulated this.
modeless 8y ago
So much complexity to deal with synchronizing AC frequency. I wonder if DC wouldn't be a better choice for a modern power grid?
- sooper 8y ago
  The costs to refit would be enormous. I think there are some issues on longer lines with things like inductance, cable size requirements, etc as well.
- rollulus 8y ago
  High-voltage DC [1] is being used to transport power over longer distances because it can be cheaper and there's less power loss. Like a sibling commented here, the costs would be enormous to convert an AC grid into a DC grid. AFAIK are there two reasons that the grid is AC: generators produce AC, and AC is so easy to transform up and down. That transforming is essential since you want to transport energy at high voltages [2] but you don't want 380kV in someone's house. [1]: https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current [2]: https://en.wikipedia.org/wiki/Electric_power_transmission#Advantage_of_high-voltage_power_transmission https://en.wikipedia.org/wiki/Electric_power_transmission#Ad...
  - avianlyric 8y ago
    Your right that AC is super easy to transform. But it’s quite easy to build generators that produce DC. They’re frequently called dynamos and you find them on old bikes to power the lights. With modern electronics doing DC-DC transforming is pretty easy (because modern electronics is basically magic). And the reason why high voltage DC transmission is a thing, is because you can get way more power down the same wire with DC compared to AC. Many high voltage DC lines used to be high voltage AC that was converted to increase the transmission capacity without building more cables.
  - gmueckl 8y ago
    But, apart form installation costs, a low voltage DC power network inside homes might make sense (e.g. 12V or 24V). There's a lot of modern electronics that doesn't depend on the regular powerline voltage anymore. Unifying their power supplies into a central unit should have some benefits.
taneq 8y ago
> Backfeeding the power grid, according to some lineworkers I've talked to, is really not a big concern for two reasons. First, lineworkers assume lines are live until proven otherwise. And, second, no residential system is going to successfully backfeed a large dead section of grid. [...] it's really not that big a concern from a technical/safety perspective. This is wrong and dangerous. Suddenly energising a section of grid which has been isolated from all known power sources could easily kill someone working on it. Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested. Yes, your inverter will probably overload and trip out before putting too much voltage into your local section of the grid, depending on where it's isolated. No, it's not OK to bet a random stranger's life on it.
- TheSpiceIsLife 8y ago
  I like to always highlight the difference between a technically correct statement and a public health and safety policy statement. A thing may be technically correct, but for the health and safety of the public at large we need to adhere to a consistent policy with what we say in the public sphere. Mains voltage is dangerous and kills kills kills. Never connect anything to the mains power supply unless you are licensed to do so, or employ someone who is licensed to do so. Always assume a circuit is live unless you-personally have checked and locked out the breaker with your own personal lockout device that only you have the key to.
  - maxerickson 8y ago
    You are supposed to have a license to plug a TV into the wall? I'm being silly, but you are going on about how the wording of statements matters.
    - jjeaff 8y ago
      Funny enough, if you've ever done a tradeshow at a venue that has union labor, they will literally make you fill out a request and wait for a licensed union electrician to come and plug your TV (or phone charger or anything with a plug). You will then receive a bill for their time. And if you plugged in your TV yourself, and they find out, you just unplug it immediately and wait for the licensed union electrician to come plug it in for you again.
WalterBright 8y ago
I'm curious why a large capacitor or inductor cannot be used to provide momentary power for things like electric motor starts, and to smooth out events like a plane briefly occluding the sun. I built an audio amplifier in college that had a couple of huge capacitors on the power supply (about the size of a can of soda). It would keep the amp running a few seconds after I shut off the power.
- PinguTS 8y ago
  Capacitors are for DC. You but them in your amplifier after the supply, when you have DC. Electric motors, especially the simple ones found in compressors for cooling, are running from AC. You can't put a capacitor into the AC path. You can only convert it to DC, charge the capacitor and then convert it back to AC. Where we are back to the original problem.
  - Dylan16807 8y ago
    The real problem is having insufficient power to provide AC, not the need to use slightly better logic in the inverters.
  - WalterBright 8y ago
    > Capacitors are for DC. The output of solar panels is DC, too. The capacitors would be placed in the DC side.
- mindslight 8y ago
  Fundamentally, the size involved. Your amplifier's capacitors were extremely large for the power the amplifier was using, as their purpose was to reduce the ripple voltage from the power supply. One of those "1 Farad" car stereo caps (not the classiest example) can store 72 joules (watt-seconds). So to handle a 1kW excursion for 5 seconds, would take over 70 of them. Possible, yes. But probably not worthwhile. The frustrating thing about this article is that it keeps conflating fundamental physical problems (like needing to store energy to deal with peaks), with the limitations of currently-productized circuit topologies. It's not hard to imagine an inverter that would do something similar to MPPT without needing to pull/dump the maximum power possible, would manage a small bit of local storage (a combination of caps and abused batteries), and could intelligently load shed (with "kind" brownouts) on multiple outlets. It's also not hard to imagine an inverter (brushless motor) air conditioner that would be a lot kinder of a load, and could even operate at variable power. But of course with the current state of homebuilding, these are bespoke ideas better filed as "off the grid". Which is the entire larger point - an "off the grid" system fundamentally costs more in materials and also presently application engineering time, than the on-grid systems being sold to homeowners. (Although I do have to wonder about adding a piece to the current puzzle that would generate/manage a local grid frequency, and shed excess power using off-the-shelf electric heaters.)
parimm 8y ago
The solution to this is to use Hybrid inverters+batteries with a auto disconnect on the mains.
alkonaut 8y ago
My cheap and simple 15-minute UPS device has waveform generation (?) and a battery. Surely with solar you often have to have huge batteries? In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.
- mcny 8y ago
  > In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining. Not a subject matter expert by any means but depending on how much sun you get, there are probably better options than solar for you (solar might not be the right choice for you).
  - alkonaut 8y ago
    Solar is increasingly popular around here though (latitudes 60-65) which I only assumed also meant that storage was also handled with batteries. Seasonal storage is probably not, but at least generation during the day and use during the night must be. I learned from the article that lower temps helps efficiency, so perhaps our climate with short days and subzero temps for 5-7 months is still viable because of higher efficiency?
    - namibj 8y ago
      Keep in mind that thermal storage is cheap compared to electrical, just not efficiently reversible. E.g. you heat up a block of paraffin in a tub of water and it takes a lot of energy without large temperature changes due to the phase change. The output temperature would require rather large radiators or floor/wall heating. At this temperature you could even dump waste heat of a computer (well, CPU and GPU, maybe DRAM, not the rest) into this thermal storage.
Allower 8y ago
Home solar setup is the wrong phrase to describe these setups. maybe "distributed solar grid" is better. When i think about a "Home solar setup" I'm thinking of an off-grid, battery powered operation. Otherwise there is nothing 'home' about your setup besides the location, which is ridiculous and disingenuous imho
SigmundA 8y ago
My dad has a 7kw system with the SMA inverter with emergency power outlet for 1.5kw. Works ok, as said the main issue without batteries to buffer is stability. I have a Magnum 3000w Hybrid inverter in my RV with 320w of solar with a MPPT solar controller. The solar controller feeds the batteries and the inverter draws from batteries or charges them with UPS grade change over. Magnum hybrids can do interesting things like if the sun is out and I am running the air conditioner off generator or shore power it will pull batteries down to float voltage and invert excess power to lower draw, I usually get about 1 amp reduction with 320w of panels. You can also dial in your shore amps and if a load needs more the inverter will step in and provide the overage from the batteries. Nice if you driveway surfing and only have a 15 amp outlet but want to run the microwave or whatever. The RV is basically a giant UPS with generator.
- mikestew 8y ago
  Having just finished a 450W solar system on our RV, along with new big-ass 200ah battery, I was shocked to find out that house systems have no battery backing. Because I have had to explain to everyone that asks “can it run...?” that you can run anything you want if the battery can handle it, the solar is just a battery charger and doesn’t directly run anything. But as one who is considering residential solar, I guess there’s more research to do as home solar apparently doesn’t work that way at all (though it probably will when I do it). Side note: thanks for the inverter mention. That’s next on the list, and the Magnum sounds to be worth a look.
  - rbritton 8y ago
    I went the Victron route on my setup, primarily because they make whole systems that can talk with each other. I had originally been looking at the Magnum, though.
    - mikestew 8y ago
      I guess in all of my searching when buying, I never discovered that Victron makes inverters, despite having one of their charge controllers (seems like Xantrex gets all the mentions for high-end inverters). I'll check them out, thanks.
jefftk 8y ago
> The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet). It's not ideal, but this is so much better than what most installs are built with (nothing).
- test6554 8y ago
  I thought there were shutoff devices that could detect a grid outage and instantly disconnect your home from the grid allowing your inverter to power your house until grid power is restored. I assumed something like this would be $10K but well worth it, as basically the whole point of battery-backed solar is energy independence.
  - imglorp 8y ago
    Look for "transfer switch".
  - ianburrell 8y ago
    From the article, the problem isn't the transfer switch but that the microinverters used on most systems don't work without the grid. If the grid goes down or is disconnected, the microinverters stop providing power. It is possible to get inverter that will work independently, and batteries to buffer the load, but the off-grid system is a lot more expensive than normal rooftop solar system.
CNJ7654 8y ago
Interesting. Around where I live (NH), it's very rare to see home solar setups that don't have the ability to operate independent from the grid. In fact, it's far more normal to see solar solutions that aren't even connected to the grid due to the cost of having power run to the property.
gwbas1c 8y ago
That article is TLDR for the target audience. The end part that basically says, 'solar panels need batteries and a more expensive inverter to run without the grid" needs to be at the beginning of the article.' The details of power curves then come for those who want more details about why.
foxhop 8y ago
It's also not safe for line workers who think power is off to a main and get zapped by a small fleet of home solar in The neighborhood.
tzs 8y ago
I've been looking into backup solutions to keep my fridge and well pump [1] going during outages. Anyone tried something like the following? The obvious approach is a propane generator. Propane rather than gasoline because we only get a small number of outages a year, and most are fairly short, but there is occasionally one that is 10+ hours. I'd want to store enough fuel for at least 10 hours of generator use, but most years would only actually use a fraction of that, and so I'd have to be constantly rotating the fuel (probably into my car, as the only other gas powered thing I have, my lawn mower, only uses about a gallon a year) to keep it fresh enough to still work for the generator. Propane does not go bad, so storing 10 hours worth of propane for years is no problem. But both of the things I want to power (fridge and pump) are very intermittent loads. I don't want the generator running all the time during an outage, wasting fuel, just to be ready when the fridge or pump needs to actually run. Even idling the generator will be consuming fuel. I could leave the generator off except when I need to actually have the fridge or well run, but that would be quite annoying as I'd have to go outside to start and stop the generator--and power failures are usually when it is quite unpleasant outside. So what I've been thinking of is having a dedicated battery and inverter for the fridge, and a dedicated battery and inverter for the well pump. When power fails, I can start watching the fridge temperature (it has a battery powered wireless temperature monitor, so I can see the temperature without opening the door). When it warms up to the high end of its normal variation, I can unplug it from the wall outlet, plug it into the inverter, and start the inverter running off the battery. When the fridge cools back down, turn off the inverter. Repeat throughout the outage. Similar for well pump. When I run out of water, go run the pump from the inverter and battery until the tank is full. I'd still have the generator, but now it would be used to recharge batteries, not power any house circuits or devices. Over time, I'd probably add batteries, eventually reaching a point where I have enough that I can get through most outages without needing the generator. (Actually, I'd probably do the well directly from the generator instead of inverter and battery. When I go out to turn on the generator to recharge batteries, I'd also plug the well pump into the generator to refill the well). I could start with one inverter and a battery or two, without a generator. This would probably get me through a large fraction of the outages. Then over time I could add more batteries, more inverters, and the generator to extend the number of things I can use during an outage and how long an outage I can get through, in a nice budget friendly way. [1] I probably don't actually need the well pump--as soon as an outage starts I fill a couple water bottles to have drinking water, and fill the bath tub to have water for flushing the toilet, and that will almost always be good enough. Why immediately fill things instead of just leaving the water in the well tank and hot water heater until I actually need it? Because I have no idea how much water I have. The outage could have happened right after the pump finished filling the tank, or it could be just before the pump was going to start and fill a nearly empty tank. Filling the water bottles and bathtub right away lets me know what I've got.
stevewilhelm 8y ago
Install a Tesla Powerwall. Problem solved. https://www.tesla.com/powerwall https://www.tesla.com/powerwall
randyrand 8y ago
instead of shutting off when the current is exceeded- why can’t you just use a current limiting device and cap it? modern bench top power supplies can limit current
irrational 8y ago
What I would like to know is, if there was an emergency situation and the grid was going to be down for an extended period of time (I'm thinking 3+ weeks, months, years) would there be a way of altering the system so that the home could have electricity, at least during daylight hours?
- sounds 8y ago
  The article points out that the most cost-effective solution is to get an internal combustion generator.
driverdan 8y ago
As this article touches on the solar panels are the cheap part of a solar setup. If you want to run off grid the costs skyrocket. I live in an off grid bus. My whole electrical system cost in the US$9-10000 range with only 810W of solar. The other components cost a lot more: * ~$900 for 3x 270W Renogy solar panels * $1500 for 3.6kWh of LiFePO4 batteries (12 100A 3.6V cells) * $1600 for a Victron 3kW inverter / charger * $2000 for a Honda EU3000is generator to run my AC The rest was the Victron solar controller, color control panel (that runs Linux!), breakers, relays, transfer switch, fuses, cable, and all the other stuff you need to hook it together. This isn't at house scale either. The cost would go up significantly to support a house scale system.
- agumonkey 8y ago
  ICE bus ?
  - driverdan 8y ago
    ICE?
    - sprobertson 8y ago
      Internal combustion engine
  - driverdan 8y ago
    There are no practical electric buses. The bus itself is on the Chevy C4500 chassis with a diesel engine.
    - agumonkey 8y ago
      jehu garcia made an electric VW van, but i don't know much about it. a couple also made a solar powered van, but as people say, it's probably very short on mileage (basically move a bit and rest while it charges.
- VectorLock 8y ago
rdl 8y ago
Maybe this applies in normal markets, but in Puerto Rico the grid is both shit-tier reliability and horribly expensive. Rooftop solar and lithium batteries in an off-grid format are both far more reliable and far cheaper than the grid, assuming a 5% cost of capital. I might throw in some LP or diesel generation capacity too, but solar plus battery is an easy choice.
- nine_k 8y ago
  Are lithium batteries the best choice here? They have superior energy density, but IIRC there are choices that are heavier but cheaper (per kWh installed), like ready-made car acid-lead batteries, or industrial Ni-Cd batteries. What do people actually use?
  - vorpalhex 8y ago
    Not sure for Solar, but most HAMs using field radio setups still use deep cycle marine batteries as they withstand abuse and are much cheaper.
    - tjohns 8y ago
      The big benefit lead acid batteries have is that it's easy to find surplus SLA batteries from businesses, and even new cells aren't that expensive. That said, I've started seeing lithium batteries slowly catch on in amateur radio as the price on the LiFePo4 cells go down. Especially for portable setups.
  - rdl 8y ago
    Tesla PowerWall is only an Apple-level premium (and not a Vertu-level premium) for what it is. I would probably just go with 1-4 of those for residential unless getting something more capable. I don’t own a house yet, though. My ideal situation would be a microgrid with 10-20 homes (in a compound/neighborhood or condo building) and some commercial/office, which pushes all the electronics costs down to something more reasonable.
- RankingMember 8y ago
dublin 8y ago
A huge amount of the info on solar PV power on the net is absolute garbage. (I spent 5 years working on the most advanced solar performance optimization and monitoring system developed to date.) I haven't read all of this article, but so far, it looks dead on (you have no idea how rare that is!) Solar is not the panacea many people wish it was, simply due to the way God built the universe - and there's not a thing we can do about that. (And yes, the panels are now only a small part of the cost of a solar system, especially one capable of operating off-grid...)
- rebootthesystem 8y ago
  Looks like I great article. I'll have to defer reading it. During a quick scan I saw a mention of the SMA technology that allows for dedicated outlets to be powered-up in case of grid failure. I built a 13 kW ground-mount system feeding a pair of SMA inverters. I have tested this feature by disconnecting from the grid and enabling the outlets (one per inverter). I didn't quite get to the 2,000 W rating SMA claims but got close. Which means that with this size of an array and two inverters I get somewhere between 3kW and 4kW of power to run various devices while the sun is up. Considering that we might have a couple of power outages a year on average (if that), I felt this was a reasonable investment. Going with batteries is just too expensive and not justifiable at all given the reliability of the grid. One way to think about this is that the grid is your battery. A stretch, I know. Funny that there's a picture of a gasoline generator towards the end of the article. My guess is that I am likely to invest in a 5 kW to 6 kW generator before I ever add batteries to this system. Again, it's a matter of ROI. Also, I would not go with a gasoline powered generator at all. Gasoline degrades with time and could be a nightmare to maintain the system with sporadic use. I think a propane fueled generator might be a better idea. The fuel does not degrade. So long as you don't have leaks it'll be there ready to go when you need it. I know way too many people who have been mercilessly duped by these solar companies who come in, hook them on some kind of a lease, install inadequate systems and move on to the next victim. Lack of understanding on the side of consumers has created a situation where solar is equivalent to magic and unscrupulous actors can take advantage of them. That part is sad.
kingkawn 8y ago
Forgive my ignorance in advance; is there any viability to a system that pumps water uphill to a storage tank then it flows downhill later to let the current run a generator?
- modzu 8y ago
  you're basically describing a gravity battery https://en.m.wikipedia.org/wiki/Gravity_battery https://en.m.wikipedia.org/wiki/Gravity_battery
- taylortbb 8y ago
  Yes, in fact they're already in use. They're called pumped storage systems, https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
- OxO4 8y ago
  Yes, pumped-storage hydroelectricity is used extensively [0]. [0] https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
iamleppert 8y ago
This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. It used minimal components (& simple ones), no batteries, nothing fancy but was enough energy to supply a community of several single family homes in a completely off grid system.
- akeck 8y ago
  Fascinating. By chance, would you have a link or article for further reading?
- dragonwriter 8y ago
  > This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. So, your example of energy options other than solar is solar with hydro storage? Or did you mean “other than photovoltaic” when you said “othet than solar”.
  - iamleppert 8y ago
    Yeah, meant to say conventional PV solar.
HIPisTheAnswer 8y ago
Off grid power != AC power. Duh! Wtf do I want AC for? People think theyre all going to have a stupid fridge which opens from the side to let as much heat in as possible and with a highly inneficient compressor which is tucked behind it where the heat can only escape through it. Or a giant motor to shake their clothes in (electrically heated) water! Ahahah! I swear i keep telling people the KWh is going to cost 150-300 mg of gold (0.10 - 0.20 gold $) and their eyes just glaze over; they think it sounds nuts? If they had off grid power, they might be forced to agree. So the average person will be able to afford a couple or three KWh per month. Two low-powered computers and some lights. We light the whole place with less than 5w. The mere fact that we so often use measures like kilo watts is a good tell tale of the current power glut. The powergrid rate where we are is about 0.0015 gold $ per KWh, or 100 times below sensible prices.
segmondy 8y ago
Of course, if you want to run off the grid, the first thing is to minimize your electrical appliance. Get a laptop, the laptop will serve as your TV, computer, radio, etc. No TV, no Washer/Dryer (you will hand wash), No regular fridge, get a small 12v fridge. No microwave, use stove to heat up food. No A/C, design the space to not get hot, high windows, under the shade, facing away from the sun. Maybe a small fan. The biggest optimization begins with your appliances.

443 points by cesarb 8y ago

deleted 8y ago

[deleted]

Super useful. Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires. In the article I read, they mentioned that even home solar wouldn't work, which seemed crazy. I can now see why this is the case, and what folks should do (get a transfer switch and generator) to be able to power their home with their solar panels.

tlrobinson 8y ago
> Pacific Gas & Electric (which powers much of CA) recently announced that they may pre-emptively shut off power to certain parts of Silicon Valley out of concern for potential fires Huh, where can I read about this?
- rconti 8y ago
  Even just going to pge.com i get an interstitial about it, but no detail. A couple links: https://yubanet.com/regional/pge-shutting-off-power-during-high-wildfire-threats-what-does-it-mean/ https://yubanet.com/regional/pge-shutting-off-power-during-h... https://www.mercurynews.com/2018/06/12/pge-could-shut-off-power-on-purpose-amid-fire-hazards/ https://www.mercurynews.com/2018/06/12/pge-could-shut-off-po...
- mcpherrinm 8y ago
  TLDR: Power lines are a cause of wildfires, and PG&E may shut down power on some transmission lines in times of extreme fire danger. https://www.sfchronicle.com/business/article/For-PG-E-cutting-power-could-prevent-fires-save-13019005.php https://www.sfchronicle.com/business/article/For-PG-E-cuttin... https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power/ https://sacramento.cbslocal.com/2018/06/25/pge-cutting-power...
  - joering2 8y ago
    Interesting fact: years ago it was designed to build electric infrastructure above the ground because air friction addsup about 20% of electricty, free. It wouldnt be possible underground. But then, you know, whole State of amedium size country like California, would have no power interruptions in heat spikes.
- gnicholas 8y ago
  I read about it in The Almanac [1]. Also, note that the map that shows higher and lower risk zones doesn't actually indicate what locations may be affected by outages. They only show where the affected lines are, but those apparently feed homes/buildings that appear to be in the clear. 1: https://www.almanacnews.com/news/2018/07/25/pge-may-cut-power-in-extreme-weather https://www.almanacnews.com/news/2018/07/25/pge-may-cut-powe...
EGreg 8y ago
Can you please elaborate about the transfer switch and generator - how to use them? What about just using batteries?
- TheSpiceIsLife 8y ago
  Typical grid-tied solar system would still require a transfer switch, either auto or manual, they're called break-before-make transfer switches because they disconnect the mains supply before switching over to the battery + inverter system or generator. These transfer switches are mechanically interlocked so it's not possible to have both supplies connected simultaneously as this would generally be release-the-magic-smoke catastrophic. Typical auto transfer switches are fast enough that computer equipment etc won't notice. Edited to add: if you want truly uninterruptible power then you should do what data centres do: everything runs off the UPS all the time (well, all the computers, maybe not all the cooling system), the only thing that changes is the supply: either mains, batteries, solar, or generator. Or some combination of batteries + the other three.
  - btbuilder 8y ago
    There's another UPS-source option, which is also my favorite, flywheel! Back in the 00s I visited a DC that two very large flywheel UPS that were being trialed to replace the battery room.
    - pas 8y ago
      Flywheels are alive and well in the DC industry. They are used for those crucial seconds while the generator starts up. And as a backup for the UPS-es. (After all, those batteries might not be in top shape all the time.) Though I imagine eventually battery tech will take over.
      - TheSpiceIsLife 8y ago
        If the flywheel can be integrated in to the generator design then generator startup can be almost instantaneous. Synchronisation would still take a few moments. I don’t know if anyone is building systems like that though?
bacon_waffle 8y ago
Unfortunately, adding a generator and a transfer switch will probably not enable you to get power from the solar panels. You'll also need an inverter that's designed to operate off grid; the anti-islanding feature on a normal grid tie inverter will prevent it from providing power when the grid is gone. There are a few ways that anti-islanding systems can work, but it's reasonable to imagine that the inverter is measuring the impedance between its output and a nominal AC source: the power grid. If that impedance is too high - and it will be unless you've got a rather large generator - then the inverter will not source power.

Johnny555 8y ago

During 2017, I saw a lot of news articles talking about how the Evil Power Companies were being Meanie McMean by not letting people with solar panels use them when the grid was down. The implication (in many news articles) was that these powerless people with solar panels could use them to power their home while the grid was down, if only the evil power company didn't require that solar not work if the grid was down. I don't remember seeing any articles that blame the power company for home solar not working off-grid... I do remember seeing articles saying that most home solar installations won't work if the power grid is down, but nothing that implied that the power companies were behind it.

0xCMP 8y ago
In Florida it was popular around hurricane season after we lost power. I'm glad I finally understand why because all that I'd seen reported was the solar systems installed must be turned off. I'd always assumed all these systems (many of which are meant to be used in a storm + lower electricity costs) had a transfer switch.
PJDK 8y ago
Here's one example https://boingboing.net/2017/09/18/rep-ray-rodrigues.html https://boingboing.net/2017/09/18/rep-ray-rodrigues.html

tlrobinson 8y ago

> To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while It doesn't seem like a battery or capacitor to handle blips like an airplane flying overhead would need to be very large?

derefr 8y ago
No, but using a small battery means using a battery that get heavily charged/discharged by such events, and therefore has a short lifespan (less than a year, probably, if you used the kind of battery that's in a UPS.) The reason the battery banks for solar are so large isn't just to capture the entire daytime output for night-time use, but also so that they can have a lifespan closer to that of the solar array itself.
- foota 8y ago
  That's interesting! Is it like an SSD where you plan for a certain amount of cells to fail or does it reduce load on the cells so they last long individually?
  - TheSpiceIsLife 8y ago
    Generally speaking, lead acid batteries, and lithium batteries, last longer if they are never (rarely?) deeply discharged. If you need 100Ah from your batteries you’re better off provisioning as many times more up to some cost-benefit analysis.
  - derefr 8y ago
    The latter. Whenever your battery gets super discharged, picture this happening inside it: https://www.youtube.com/watch?v=r-YbQN_twpw https://www.youtube.com/watch?v=r-YbQN_twpw Notice how running the current the other way will break up the formed crystals, but it won't actually re-dissolve them. That's what it means for a battery to wear out. (Battery electrolytes are chosen specifically to be resistant to this, so the effect is mainly visible as a thin "rust" of deposited crystals on the battery's anode, rather than the full-scale crystals seen here.) A similar but distinct process occurs when overcharging a battery, where, instead of splitting the electrolyte molecules apart, you're reacting and bonding them together to form new molecules or molecular complexes, with the reaction usually being one-way rather than an equilibrium reaction. (For lithium batteries this process is exothermic and catalyzed by the presence of the product—thus lithium battery explosions.) It's much better for the life of the battery if it basically just hovers around 40-60% charge for its whole useful life, since then you're just generating tiny seed crystals (on discharge) and then re-dissolving them (on charge), where those crystals are small enough that they can be fully re-absorbed. And this is true even in battery-cell technologies that require a "deep charge cycle" to erase their "battery memory." Battery memory is basically the electrolyte causing enough crystalline rust specifically on the anode to increase its resistance. A deep discharge can capture and erase this rust—but it still shortens the battery's lifespan, because you're still producing non-reabsorbable large crystals within the electrolyte.

bacon_waffle 8y ago

There are all sorts of issues with using a regular grid-tied inverter in an off-grid situation; there are regulatory issues besides the anti-islanding (which is a complicated topic all on its own), and technical challenges too. A lot of the technical challenges go back to the inverter effectively being a thing that bolts on to the existing house wiring; I think that if they could be more of a pass-through thing (like a UPS) then the picture would be a lot simpler. An off-grid capable inverter needs to handle several state transitions smoothly, and some of those are hard. For instance, starting up can be a lot harder when there's no mains voltage. An inverter will have a maximum output current, which is generally not too far from the maximum power output of the inverter divided by minimum mains voltage. If you have a load that presents as a constant resistance, like a water heater, then as the inverter's output voltage goes from 0 to 240V (120V for areas with weenie power) the current will smoothly go from nothing up to whatever the load normally draws, along with the voltage, and there's no problem. But! A lot of loads aren't resistive - things like computers, battery chargers, and inverter-driven motors (as newer appliances often have) will tend to look more like constant-power loads. So, once they decide it's OK to turn on, if the voltage happens to be half of nominal at that point, they will try to pull twice their nominal current. If that causes the total draw to exceed what the inverter can provide, it stops and maybe tries again. It's practically impossible to measure what the load characteristic of something like a house, from the perspective of an inverter, so the best you can do is something like guess-and-check, and that's not a great solution. Then, how to handle reconnection with the grid; you either need to re-synchronise before reconnecting, or ensure that the intrepid homeowner first shuts off the house before turning the switch to reconnect. Switches that can handle that job may need to be specified per-installation, and there are all sorts of regulations around how they work and where they can go. They are not cheap, as a rule. Some regions have the solar generation stuff on a separate export power meter from the import one. This means that the switch needs to be on he supply side of both meters, and that could be regulatorily complicated. What about multiple inverters? These things all need to play nice with each other when solo, or installed with others. Perhaps you didn't design those, and they might try to start up too, then fire up their anti islanding which should promptly trip out again. Remember this all has to work with variable input power available, and it needs to be packaged up so that installation is straightforward, and operation is basically hands-off. Oh, and inexpensive too!

ghubbard 8y ago

Great article, lots of technical details. A simple answer to the 'Why' can be found in the middle under the 'Off Grid Without Batteries' headline. > If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with,

raverbashing 8y ago
"there's no waveform to sync with" is technically correct and a very poor excuse A residential no-break has no waveform to sync with as well. Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)
- TheSpiceIsLife 8y ago
  When the grid goes back up the system would check the grid frequency and phase, and slowly match that waveform over a few minutes by making light changes. When the two are aligned within a good-enough tolerance the system will switch back to it's regular state of mains + solar ( + batteries + wind + generator + etc / whatever). These are all solved problems with commercial off the shelf components.
  - zaarn 8y ago
    Are these commercial off the shelf components as cheap as a microinverter?
    - TheSpiceIsLife 8y ago
      I just typed microinverter in to Google and clicked on shopping. It looks to me like microinverters are a commercial off the shelf product? Will a microinverter do all of the things a multi-component phase-syncing system with automatic transfer switches do? I don't see why a microinverter can't be built with these components integrated. I can't tell you if such a unit exists as I'm not well versed in the product range. As far as a price comparison goes, I guess it only makes sense to compare a like-for-like system?

CaliforniaKarl 8y ago

I've read the detailed reports for outages in the West and the North-East, and they touch on alot of the same concepts that were in this (awesome) article. Does anyone know, what's a good resource for learning more about power generation, grid regulation, etc.? The relationship between frequency/voltage and available vs. demanded current, frequency sync, grid maintenance, etc.…

throwawaycanada 8y ago
If you have a reasonable electrical background I would suggest this textbook: Electrical Machines, Drives and Power Systems by Theordore Wildi

ggm 8y ago

We found that even a well made Honda petrol genset was highly unstable feeding volts into a UPS for a machineroom. They are good at lights. They are good at a cooker. They suck at anything which expects regulated, non-noisy volts. Lots of homebrew 'you can plug this magick cable I made' methods to supply volts across the fence to neighbours houses when the power goes down are really bad: behind the meter is just as lethal as in front of the meter, if you get it wrong. TL;DR if you need to read a website like this for clue how to avoid losing power, you are putting your life at risk if you don't follow code, and don't know what you're doing.

driverdan 8y ago
Inverter generators like the popular Hondas are not good for surges. If you run them at a steady draw they'll give you nice, clean power. If you your demand fluctuates significantly they will stall or cut out and the voltage during or after the stall may be dirty. You have to read the specs carefully to make sure they are a good match for your use.
- ggm 8y ago
  Fridge. Surge load. Washing machine. Huge torque surge load. Airconditioning. That's basically a fridge? So.. "home" solar setup.. home.. like fridges, aircon and washing machines... Do you see where this is going?
  - thinkythought 8y ago
    The solution here is inverter drive appliances. I had a cheapo but great thrift store inverter microwave. My cheapo junk 3000w inverter could run it off a few hundred Ah of batteries without issue, still spitting out clean power on the other outlets. A regular microwave(with a lower run wattage in theory, by about 1/3rd) would instantly blow the thing up and set off its obnoxious alarm. With some carefully selected appliances you would probably be fine. This stuff used to be super pricey, but now even the cheaper brands are putting out inverter drive ACs for example. Not window units, but mini splits and home systems

bunkydoo 8y ago

youre all somewhat ignorant if you think that solar is even remotely a solution. if humans could get along for more than 2 weeks we could have unlimited clean power through nuclear. even jeff bezos has articulated this.

modeless 8y ago

So much complexity to deal with synchronizing AC frequency. I wonder if DC wouldn't be a better choice for a modern power grid?

sooper 8y ago
The costs to refit would be enormous. I think there are some issues on longer lines with things like inductance, cable size requirements, etc as well.
rollulus 8y ago
High-voltage DC [1] is being used to transport power over longer distances because it can be cheaper and there's less power loss. Like a sibling commented here, the costs would be enormous to convert an AC grid into a DC grid. AFAIK are there two reasons that the grid is AC: generators produce AC, and AC is so easy to transform up and down. That transforming is essential since you want to transport energy at high voltages [2] but you don't want 380kV in someone's house. [1]: https://en.wikipedia.org/wiki/High-voltage_direct_current https://en.wikipedia.org/wiki/High-voltage_direct_current [2]: https://en.wikipedia.org/wiki/Electric_power_transmission#Advantage_of_high-voltage_power_transmission https://en.wikipedia.org/wiki/Electric_power_transmission#Ad...
- avianlyric 8y ago
  Your right that AC is super easy to transform. But it’s quite easy to build generators that produce DC. They’re frequently called dynamos and you find them on old bikes to power the lights. With modern electronics doing DC-DC transforming is pretty easy (because modern electronics is basically magic). And the reason why high voltage DC transmission is a thing, is because you can get way more power down the same wire with DC compared to AC. Many high voltage DC lines used to be high voltage AC that was converted to increase the transmission capacity without building more cables.
- gmueckl 8y ago
  But, apart form installation costs, a low voltage DC power network inside homes might make sense (e.g. 12V or 24V). There's a lot of modern electronics that doesn't depend on the regular powerline voltage anymore. Unifying their power supplies into a central unit should have some benefits.

taneq 8y ago

> Backfeeding the power grid, according to some lineworkers I've talked to, is really not a big concern for two reasons. First, lineworkers assume lines are live until proven otherwise. And, second, no residential system is going to successfully backfeed a large dead section of grid. [...] it's really not that big a concern from a technical/safety perspective. This is wrong and dangerous. Suddenly energising a section of grid which has been isolated from all known power sources could easily kill someone working on it. Yes, lineworkers will isolate and test lines before touching them. No, this won't protect them because your inverter could start outputting after they've tested. Yes, your inverter will probably overload and trip out before putting too much voltage into your local section of the grid, depending on where it's isolated. No, it's not OK to bet a random stranger's life on it.

TheSpiceIsLife 8y ago
I like to always highlight the difference between a technically correct statement and a public health and safety policy statement. A thing may be technically correct, but for the health and safety of the public at large we need to adhere to a consistent policy with what we say in the public sphere. Mains voltage is dangerous and kills kills kills. Never connect anything to the mains power supply unless you are licensed to do so, or employ someone who is licensed to do so. Always assume a circuit is live unless you-personally have checked and locked out the breaker with your own personal lockout device that only you have the key to.
- maxerickson 8y ago
  You are supposed to have a license to plug a TV into the wall? I'm being silly, but you are going on about how the wording of statements matters.
  - jjeaff 8y ago
    Funny enough, if you've ever done a tradeshow at a venue that has union labor, they will literally make you fill out a request and wait for a licensed union electrician to come and plug your TV (or phone charger or anything with a plug). You will then receive a bill for their time. And if you plugged in your TV yourself, and they find out, you just unplug it immediately and wait for the licensed union electrician to come plug it in for you again.

WalterBright 8y ago

I'm curious why a large capacitor or inductor cannot be used to provide momentary power for things like electric motor starts, and to smooth out events like a plane briefly occluding the sun. I built an audio amplifier in college that had a couple of huge capacitors on the power supply (about the size of a can of soda). It would keep the amp running a few seconds after I shut off the power.

PinguTS 8y ago
Capacitors are for DC. You but them in your amplifier after the supply, when you have DC. Electric motors, especially the simple ones found in compressors for cooling, are running from AC. You can't put a capacitor into the AC path. You can only convert it to DC, charge the capacitor and then convert it back to AC. Where we are back to the original problem.
- Dylan16807 8y ago
  The real problem is having insufficient power to provide AC, not the need to use slightly better logic in the inverters.
- WalterBright 8y ago
  > Capacitors are for DC. The output of solar panels is DC, too. The capacitors would be placed in the DC side.
mindslight 8y ago
Fundamentally, the size involved. Your amplifier's capacitors were extremely large for the power the amplifier was using, as their purpose was to reduce the ripple voltage from the power supply. One of those "1 Farad" car stereo caps (not the classiest example) can store 72 joules (watt-seconds). So to handle a 1kW excursion for 5 seconds, would take over 70 of them. Possible, yes. But probably not worthwhile. The frustrating thing about this article is that it keeps conflating fundamental physical problems (like needing to store energy to deal with peaks), with the limitations of currently-productized circuit topologies. It's not hard to imagine an inverter that would do something similar to MPPT without needing to pull/dump the maximum power possible, would manage a small bit of local storage (a combination of caps and abused batteries), and could intelligently load shed (with "kind" brownouts) on multiple outlets. It's also not hard to imagine an inverter (brushless motor) air conditioner that would be a lot kinder of a load, and could even operate at variable power. But of course with the current state of homebuilding, these are bespoke ideas better filed as "off the grid". Which is the entire larger point - an "off the grid" system fundamentally costs more in materials and also presently application engineering time, than the on-grid systems being sold to homeowners. (Although I do have to wonder about adding a piece to the current puzzle that would generate/manage a local grid frequency, and shed excess power using off-the-shelf electric heaters.)

parimm 8y ago

The solution to this is to use Hybrid inverters+batteries with a auto disconnect on the mains.

alkonaut 8y ago

My cheap and simple 15-minute UPS device has waveform generation (?) and a battery. Surely with solar you often have to have huge batteries? In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining.

mcny 8y ago
> In hot climates you have some power use when the sun is up (cooling, pool heating,) but where I live I’d need my power most when the sun is absent in night and winter (power use is probably 80% heating). Any amount of solar power would be nearly useless if only available when the sun is shining. Not a subject matter expert by any means but depending on how much sun you get, there are probably better options than solar for you (solar might not be the right choice for you).
- alkonaut 8y ago
  Solar is increasingly popular around here though (latitudes 60-65) which I only assumed also meant that storage was also handled with batteries. Seasonal storage is probably not, but at least generation during the day and use during the night must be. I learned from the article that lower temps helps efficiency, so perhaps our climate with short days and subzero temps for 5-7 months is still viable because of higher efficiency?
  - namibj 8y ago
    Keep in mind that thermal storage is cheap compared to electrical, just not efficiently reversible. E.g. you heat up a block of paraffin in a tub of water and it takes a lot of energy without large temperature changes due to the phase change. The output temperature would require rather large radiators or floor/wall heating. At this temperature you could even dump waste heat of a computer (well, CPU and GPU, maybe DRAM, not the rest) into this thermal storage.

Allower 8y ago

Home solar setup is the wrong phrase to describe these setups. maybe "distributed solar grid" is better. When i think about a "Home solar setup" I'm thinking of an off-grid, battery powered operation. Otherwise there is nothing 'home' about your setup besides the location, which is ridiculous and disingenuous imho

SigmundA 8y ago

My dad has a 7kw system with the SMA inverter with emergency power outlet for 1.5kw. Works ok, as said the main issue without batteries to buffer is stability. I have a Magnum 3000w Hybrid inverter in my RV with 320w of solar with a MPPT solar controller. The solar controller feeds the batteries and the inverter draws from batteries or charges them with UPS grade change over. Magnum hybrids can do interesting things like if the sun is out and I am running the air conditioner off generator or shore power it will pull batteries down to float voltage and invert excess power to lower draw, I usually get about 1 amp reduction with 320w of panels. You can also dial in your shore amps and if a load needs more the inverter will step in and provide the overage from the batteries. Nice if you driveway surfing and only have a 15 amp outlet but want to run the microwave or whatever. The RV is basically a giant UPS with generator.

mikestew 8y ago
Having just finished a 450W solar system on our RV, along with new big-ass 200ah battery, I was shocked to find out that house systems have no battery backing. Because I have had to explain to everyone that asks “can it run...?” that you can run anything you want if the battery can handle it, the solar is just a battery charger and doesn’t directly run anything. But as one who is considering residential solar, I guess there’s more research to do as home solar apparently doesn’t work that way at all (though it probably will when I do it). Side note: thanks for the inverter mention. That’s next on the list, and the Magnum sounds to be worth a look.
- rbritton 8y ago
  I went the Victron route on my setup, primarily because they make whole systems that can talk with each other. I had originally been looking at the Magnum, though.
  - mikestew 8y ago
    I guess in all of my searching when buying, I never discovered that Victron makes inverters, despite having one of their charge controllers (seems like Xantrex gets all the mentions for high-end inverters). I'll check them out, thanks.

jefftk 8y ago

> The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet). It's not ideal, but this is so much better than what most installs are built with (nothing).

test6554 8y ago
I thought there were shutoff devices that could detect a grid outage and instantly disconnect your home from the grid allowing your inverter to power your house until grid power is restored. I assumed something like this would be $10K but well worth it, as basically the whole point of battery-backed solar is energy independence.
- imglorp 8y ago
  Look for "transfer switch".
- ianburrell 8y ago
  From the article, the problem isn't the transfer switch but that the microinverters used on most systems don't work without the grid. If the grid goes down or is disconnected, the microinverters stop providing power. It is possible to get inverter that will work independently, and batteries to buffer the load, but the off-grid system is a lot more expensive than normal rooftop solar system.

CNJ7654 8y ago

Interesting. Around where I live (NH), it's very rare to see home solar setups that don't have the ability to operate independent from the grid. In fact, it's far more normal to see solar solutions that aren't even connected to the grid due to the cost of having power run to the property.

gwbas1c 8y ago

That article is TLDR for the target audience. The end part that basically says, 'solar panels need batteries and a more expensive inverter to run without the grid" needs to be at the beginning of the article.' The details of power curves then come for those who want more details about why.

foxhop 8y ago

It's also not safe for line workers who think power is off to a main and get zapped by a small fleet of home solar in The neighborhood.

tzs 8y ago

I've been looking into backup solutions to keep my fridge and well pump [1] going during outages. Anyone tried something like the following? The obvious approach is a propane generator. Propane rather than gasoline because we only get a small number of outages a year, and most are fairly short, but there is occasionally one that is 10+ hours. I'd want to store enough fuel for at least 10 hours of generator use, but most years would only actually use a fraction of that, and so I'd have to be constantly rotating the fuel (probably into my car, as the only other gas powered thing I have, my lawn mower, only uses about a gallon a year) to keep it fresh enough to still work for the generator. Propane does not go bad, so storing 10 hours worth of propane for years is no problem. But both of the things I want to power (fridge and pump) are very intermittent loads. I don't want the generator running all the time during an outage, wasting fuel, just to be ready when the fridge or pump needs to actually run. Even idling the generator will be consuming fuel. I could leave the generator off except when I need to actually have the fridge or well run, but that would be quite annoying as I'd have to go outside to start and stop the generator--and power failures are usually when it is quite unpleasant outside. So what I've been thinking of is having a dedicated battery and inverter for the fridge, and a dedicated battery and inverter for the well pump. When power fails, I can start watching the fridge temperature (it has a battery powered wireless temperature monitor, so I can see the temperature without opening the door). When it warms up to the high end of its normal variation, I can unplug it from the wall outlet, plug it into the inverter, and start the inverter running off the battery. When the fridge cools back down, turn off the inverter. Repeat throughout the outage. Similar for well pump. When I run out of water, go run the pump from the inverter and battery until the tank is full. I'd still have the generator, but now it would be used to recharge batteries, not power any house circuits or devices. Over time, I'd probably add batteries, eventually reaching a point where I have enough that I can get through most outages without needing the generator. (Actually, I'd probably do the well directly from the generator instead of inverter and battery. When I go out to turn on the generator to recharge batteries, I'd also plug the well pump into the generator to refill the well). I could start with one inverter and a battery or two, without a generator. This would probably get me through a large fraction of the outages. Then over time I could add more batteries, more inverters, and the generator to extend the number of things I can use during an outage and how long an outage I can get through, in a nice budget friendly way. [1] I probably don't actually need the well pump--as soon as an outage starts I fill a couple water bottles to have drinking water, and fill the bath tub to have water for flushing the toilet, and that will almost always be good enough. Why immediately fill things instead of just leaving the water in the well tank and hot water heater until I actually need it? Because I have no idea how much water I have. The outage could have happened right after the pump finished filling the tank, or it could be just before the pump was going to start and fill a nearly empty tank. Filling the water bottles and bathtub right away lets me know what I've got.

stevewilhelm 8y ago

Install a Tesla Powerwall. Problem solved. https://www.tesla.com/powerwall https://www.tesla.com/powerwall

randyrand 8y ago

instead of shutting off when the current is exceeded- why can’t you just use a current limiting device and cap it? modern bench top power supplies can limit current

irrational 8y ago

What I would like to know is, if there was an emergency situation and the grid was going to be down for an extended period of time (I'm thinking 3+ weeks, months, years) would there be a way of altering the system so that the home could have electricity, at least during daylight hours?

sounds 8y ago
The article points out that the most cost-effective solution is to get an internal combustion generator.

driverdan 8y ago

As this article touches on the solar panels are the cheap part of a solar setup. If you want to run off grid the costs skyrocket. I live in an off grid bus. My whole electrical system cost in the US$9-10000 range with only 810W of solar. The other components cost a lot more: * ~$900 for 3x 270W Renogy solar panels * $1500 for 3.6kWh of LiFePO4 batteries (12 100A 3.6V cells) * $1600 for a Victron 3kW inverter / charger * $2000 for a Honda EU3000is generator to run my AC The rest was the Victron solar controller, color control panel (that runs Linux!), breakers, relays, transfer switch, fuses, cable, and all the other stuff you need to hook it together. This isn't at house scale either. The cost would go up significantly to support a house scale system.

agumonkey 8y ago
ICE bus ?
- driverdan 8y ago
  ICE?
  - sprobertson 8y ago
    Internal combustion engine
- driverdan 8y ago
  There are no practical electric buses. The bus itself is on the Chevy C4500 chassis with a diesel engine.
  - agumonkey 8y ago
    jehu garcia made an electric VW van, but i don't know much about it. a couple also made a solar powered van, but as people say, it's probably very short on mileage (basically move a bit and rest while it charges.
VectorLock 8y ago

rdl 8y ago

Maybe this applies in normal markets, but in Puerto Rico the grid is both shit-tier reliability and horribly expensive. Rooftop solar and lithium batteries in an off-grid format are both far more reliable and far cheaper than the grid, assuming a 5% cost of capital. I might throw in some LP or diesel generation capacity too, but solar plus battery is an easy choice.

nine_k 8y ago
Are lithium batteries the best choice here? They have superior energy density, but IIRC there are choices that are heavier but cheaper (per kWh installed), like ready-made car acid-lead batteries, or industrial Ni-Cd batteries. What do people actually use?
- vorpalhex 8y ago
  Not sure for Solar, but most HAMs using field radio setups still use deep cycle marine batteries as they withstand abuse and are much cheaper.
  - tjohns 8y ago
    The big benefit lead acid batteries have is that it's easy to find surplus SLA batteries from businesses, and even new cells aren't that expensive. That said, I've started seeing lithium batteries slowly catch on in amateur radio as the price on the LiFePo4 cells go down. Especially for portable setups.
- rdl 8y ago
  Tesla PowerWall is only an Apple-level premium (and not a Vertu-level premium) for what it is. I would probably just go with 1-4 of those for residential unless getting something more capable. I don’t own a house yet, though. My ideal situation would be a microgrid with 10-20 homes (in a compound/neighborhood or condo building) and some commercial/office, which pushes all the electronics costs down to something more reasonable.
RankingMember 8y ago

dublin 8y ago

A huge amount of the info on solar PV power on the net is absolute garbage. (I spent 5 years working on the most advanced solar performance optimization and monitoring system developed to date.) I haven't read all of this article, but so far, it looks dead on (you have no idea how rare that is!) Solar is not the panacea many people wish it was, simply due to the way God built the universe - and there's not a thing we can do about that. (And yes, the panels are now only a small part of the cost of a solar system, especially one capable of operating off-grid...)

rebootthesystem 8y ago
Looks like I great article. I'll have to defer reading it. During a quick scan I saw a mention of the SMA technology that allows for dedicated outlets to be powered-up in case of grid failure. I built a 13 kW ground-mount system feeding a pair of SMA inverters. I have tested this feature by disconnecting from the grid and enabling the outlets (one per inverter). I didn't quite get to the 2,000 W rating SMA claims but got close. Which means that with this size of an array and two inverters I get somewhere between 3kW and 4kW of power to run various devices while the sun is up. Considering that we might have a couple of power outages a year on average (if that), I felt this was a reasonable investment. Going with batteries is just too expensive and not justifiable at all given the reliability of the grid. One way to think about this is that the grid is your battery. A stretch, I know. Funny that there's a picture of a gasoline generator towards the end of the article. My guess is that I am likely to invest in a 5 kW to 6 kW generator before I ever add batteries to this system. Again, it's a matter of ROI. Also, I would not go with a gasoline powered generator at all. Gasoline degrades with time and could be a nightmare to maintain the system with sporadic use. I think a propane fueled generator might be a better idea. The fuel does not degrade. So long as you don't have leaks it'll be there ready to go when you need it. I know way too many people who have been mercilessly duped by these solar companies who come in, hook them on some kind of a lease, install inadequate systems and move on to the next victim. Lack of understanding on the side of consumers has created a situation where solar is equivalent to magic and unscrupulous actors can take advantage of them. That part is sad.

kingkawn 8y ago

Forgive my ignorance in advance; is there any viability to a system that pumps water uphill to a storage tank then it flows downhill later to let the current run a generator?

modzu 8y ago
you're basically describing a gravity battery https://en.m.wikipedia.org/wiki/Gravity_battery https://en.m.wikipedia.org/wiki/Gravity_battery
taylortbb 8y ago
Yes, in fact they're already in use. They're called pumped storage systems, https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...
OxO4 8y ago
Yes, pumped-storage hydroelectricity is used extensively [0]. [0] https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

iamleppert 8y ago

This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. It used minimal components (& simple ones), no batteries, nothing fancy but was enough energy to supply a community of several single family homes in a completely off grid system.

akeck 8y ago
Fascinating. By chance, would you have a link or article for further reading?
dragonwriter 8y ago
> This is exactly why people need to explore alternative energy options other than solar. The best off-grid setup I’ve seen is a bunch of conductive pipes lay over the ground that heated water from the sun, that in turn was used to generate enough energy to pump water to a storage tank during the day up a large hill. At night the tank was drained and water came back down and the resulting pressure was used to generate power, supply back to the grid. So, your example of energy options other than solar is solar with hydro storage? Or did you mean “other than photovoltaic” when you said “othet than solar”.
- iamleppert 8y ago
  Yeah, meant to say conventional PV solar.

HIPisTheAnswer 8y ago

Off grid power != AC power. Duh! Wtf do I want AC for? People think theyre all going to have a stupid fridge which opens from the side to let as much heat in as possible and with a highly inneficient compressor which is tucked behind it where the heat can only escape through it. Or a giant motor to shake their clothes in (electrically heated) water! Ahahah! I swear i keep telling people the KWh is going to cost 150-300 mg of gold (0.10 - 0.20 gold $) and their eyes just glaze over; they think it sounds nuts? If they had off grid power, they might be forced to agree. So the average person will be able to afford a couple or three KWh per month. Two low-powered computers and some lights. We light the whole place with less than 5w. The mere fact that we so often use measures like kilo watts is a good tell tale of the current power glut. The powergrid rate where we are is about 0.0015 gold $ per KWh, or 100 times below sensible prices.

segmondy 8y ago

Of course, if you want to run off the grid, the first thing is to minimize your electrical appliance. Get a laptop, the laptop will serve as your TV, computer, radio, etc. No TV, no Washer/Dryer (you will hand wash), No regular fridge, get a small 12v fridge. No microwave, use stove to heat up food. No A/C, design the space to not get hot, high windows, under the shade, facing away from the sun. Maybe a small fan. The biggest optimization begins with your appliances.