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How much battery storage does a solar PV system need?

24 points by martinald 11y ago

deleted 11y ago
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- jacquesm 11y ago
  The one thing you don't do when you're off the grid is run an airconditioning system. The way to cover a gap longer than a few days is with a genset.
  - deleted 11y ago
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phire 11y ago
Battery storage is simply not meant to cover that kind of gap. It's intended more to cover the overnight period, when you have no sun, or maybe for a few days with bad weather. You need to spec your system so at the very least it generates enough power on the worst days of the year to cover your needs, and surplus power on good days. You also should have a second means of power generation, wind works nicely as it's uncommon to have a day that isn't either windy or sunny.
- codecamper 11y ago
  The OP does not have a single clue about actually using solar. His price per KWH is about 1 order of magnitude off (and then some). I've used 100% solar for the past 2 years and there has not been a single day that I needed a second source of power. Also my system is quite modest. Just 500W of panels and about 600Wh of lithium ion battery (lifepo4) energy storage. The 500W of panels is plenty. Most days I charge my batteries fully before noon. The 600Wh of batteries is enough to get me through 3 days of heavy cloud weather ( you get about 10% of your maximum generation on a heavily clouded day ). This system is for two people using our computers and 3g wireless for the entire day. LED lights at night which are bright and warm, water pump, food processor, stereo, iPad, hella gadgets, raspberry pi backup server, etc etc If I changed something, I'd double the batteries that I use.. going to 24V. You get more of the rated power of the solar panel when using a 24V system. I am considering getting an electric bike & storing extra power there. The total cost of the system was about $800. In the summer I can generate about 2 kWh / sunny day -- I only need about 400Wh / day though. You do the math for the cost per kWh. It's damn cheap.
  - jacquesm 11y ago
    > The OP does not have a single clue about actually using solar. Exactly. It's a total nonsense proposition to offset seasonal swing using battery power. Running a PV system is about conservation first and foremost and some planning second. Your battery is for the day/night cycle and overcast days, not for seasonal variations. Maybe he should run a PV system for a while before writing articles like these.
    - raesene4 11y ago
      I think the original article was looking at the proposition of off-grid energy use using purely solar, in which scenario seasonal variations matter From the article "Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation."
      - jacquesm 11y ago
        > Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation. If you go off grid on purely solar your backup is not a battery, your backup is a genset. It's a nonsense proposition leading to nonsense conclusions based on nonsense numbers. Very tiring.
        raesene4 11y ago
        I'd agree, I was just pointing out the basis that the author was coming from which was the reason why he was considering seasonal variations in battery calculations. With that said, from reading some articles about off-grid living, it's not outwith the bounds of possibility that people are looking at pure solar (or pure renewable anyway) off-grid living, for priniple-based reasons , rather than a more pragmatic rationale.
        11y ago
ra 11y ago
The amount of battery storage required for a household on-grid is much smaller when you can think of the grid as a load balancing device. Of course we'd need to get away from the huge mismatch between feed-in tariffs and consumption tariffs. Ideally the difference would be a small spread (like in a currency exchange rate) and a nominal daily connection fee. In which case a 10KW Tesla powerwall is a pretty handy size.
- crdoconnor 11y ago
  >Of course we'd need to get away from the huge mismatch between feed-in tariffs and consumption tariffs. Maybe first we could nationalize the whole outfit and run it on a cost-plus basis. There is way too much profit being made from being a monopoly grid operator. That probably has more to do with why solar is such a good deal than the green energy subsidies do.
  - maxerickson 11y ago
    In the US I'm under the impression that generation and transmission are pretty heavily regulated. Do you have a favorite example company that makes egregious profits?
- ZeroGravitas 11y ago
  In an optimally operating power grid, household storage should be pointless. If it makes economic sense for you to deploy batteries then you're probably dealing with a poorly regulated, or underperforming grid. The latter may simply be a matter of geography, but even then unless you live in a cabin in the woods then I believe e.g. in Australia some utilities are creating solar/battery/genset microgrids for remote communities, rather than try to maintain long power lines from the main grid.
jacquesm 11y ago
> 1. Household consumption is 5,000 kWh/year. (About right for Western Europe, low for the US, high for most of the rest of the world.) So, to stick with HN's tradition of making negative comments about articles: This author is totally clueless, that's not at all how you size a PV system (and the battery to go with it). Battery power in a solar system is not used to offset seasonal variation but the day/night cycle and a possible overcast day (or two). Then the first line listing the assumptions made starts from the average household but a PV system designer that is designing an actual system rather than a theoretical one will start with throwing everything out that you can miss, the household will be anything but 'average'. Electric heat, AC and a whole raft of other big consumers get thrown right out before you even start to think about what your consumption will be. No romantic array of incandescent spots for you, and no baseboard heat. Everything you can save you won't have to generate and store and that's your first gain. This will cut the consumption in half or even better and then you can start wondering about how much PV you need, if you're going to have wind or water to augment that, what size you genset will have to be (in case all of the above aren't available for a longer period) and what kind of storage battery you need. (And of course what size inverter(s) to convert your DC back to AC tied into the distribution panel of your house, you really don't want to run your household on DC) A good rule of thumb for battery storage for a system that is off-grid and totally self-reliant is to have 5 days worth of consumption leading to 33% or 20% of battery discharge depending on how nice you want to be to your batteries. That's a whopping large battery, most likely larger than what your friendly car company can sell you in one chunk so you'll need multiple units ganged together via some kind of bus system. When you go off-grid your life can depend on the working of the system, if you're snowed in and you can't get fuel, the sun lets you down and there is no wind then you fire up your trusty genset (preferably a diesel, you might be running it for a week straight in an emergency) to put some much needed charge into your batteries. Of course you anticipated this and you have two weeks worth of fuel stored. Also, in very cold weather battery capacity tends to be reduced. So, in short design your house and your life around your energy budget and even then you'll find you need a rather very large battery.
- codecamper 11y ago
  It's a true & bit of a bummer fact: most homes are incredibly energy inefficient. Especially when it comes to heating. But people must change & figure out how to do it. (hint: 50 cent per watt solar and cheaper.. you just may be able to heat with solar. storing energy as heat... you don't need a battery. You need concrete.) Evolve or die. BTW, lithium batteries do not off gas hydrogen (like lead acid batteries do). Therefore, you just keep your batteries inside with you. They'll work just as efficiently and any of their 5% inefficiency will become heat.
ghouse 11y ago
How many 9s of reliability do you want to pay for? Speaking only regarding residential energy: In North America, other than Hawaii as of a couple weeks ago, solar generation banks credit for electricity exported to the grid. In effect, a 100% efficient, and free, battery. In Austrlia, exported power receives credit only equal to the offset generation -- less than 1/3 of the total price of electricity. In those cases, there is an economic evaluation. Otherwise, batteries are for reliability. And apparently there are more residential backup generators in the US than there are residential rooftop solar.
- jacquesm 11y ago
  Going off-grid when the grid is present and reliable is dumb. Even without net-metering being 100% as long as you cover your own use 90% of the time it is still much cheaper than battery power (charge/discharge costs more than what power from the grid costs, batteries have a life-span). So in that situation you try to cut your consumption when you generate little power or you take the hit by paying for grid power. The larger chunk of your bill in that case will be the termination fees, the electricity bill typically has two components, one where you pay a fixed fee for the connection whether you use it or not and another you pay per used KWh. The first component can handily outstrip the second making those very expensive KWs, especially when you're close to running of your own power most of the time. Still, if you think of it as a replacement for both your genset and your very large battery it may make economic sense to do this anyway. It all depends on the location and reliability of the grid. Where I lived our PV system was many times more reliable than the local grid so we ended up ditching the hookup but that's a very exceptional situation.
  - chris_wot 11y ago
    That's what this doesn't take into account. If you install batteries, you use them for only part of the time to make up for times the PV doesn't generate electricity. This offsets costs of drawing from the grid. But when you need to draw from the grid, you do so.
shalmanese 11y ago
In this hypothetical scenario, instead of investing so much in batteries, why not just double the size of your solar array so you're not storing 6 months worth of power in batteries? That would only cost ~20K instead of the ~500K for batteries.
- jacquesm 11y ago
  You use the battery to offset the times when the sun does not shine so more solar power does not work. You don't use batteries to offset the summer/winter cycle, you use them to offset the day/night cycle and to store a bit more in case the next couple of days are overcast. The whole winter/summer storage thing is nonsense, nobody sizes a PV system like that.
  - raesene4 11y ago
    well nobody apart from people looking for an off-grid lifestyle of course. What I took from the article is that pure solar off-grid is impractical away from equatorial latitudes.
    - jacquesm 11y ago
      If that's what you too from the article then you're right 'pure solar' is impractical (anywhere). You always need a battery and you always need some kind of backup. But if you're going to think like that grid power is also impractical anywhere, since it too could fail. Power is so important that no single source should be relied on anywhere. In inner cities of course your only chance of getting power is the local electricity company hookup, but if that should fail for any extended period of time such a city would rapidly become a place where you could no longer live, especially at latitudes where it tends to get very cold in the winter. So, nobody (in their right mind, at least) will do a 'pure' photovoltaic system. There will always be some kind of backup-power mechanism, either the grid, a wind-turbine, a battery to tide you over, a pelton wheel fed from a stream, grid power or any combination of the above.
      - 11y ago
chris_wot 11y ago
5,000kW per year is low in the U.S.? That is extraordinarily wasteful. In most of Australia the average is about 2300kW per quarter, and even that is probably a high estimate. But if 5000kW is low then I'm assuming the average has to be 6000kW, or 6500kW! That a HUGE amount of power! What on earth are people in America using?!?
- zurn 11y ago
  You might have mixed per-quarter and per-year numbers there. According to http://shrinkthatfootprint.com/average-household-electricity-consumption http://shrinkthatfootprint.com/average-household-electricity... the average (in MWh/a) is 11.7 for USA and 7.2 for Australia, both at the high end of first-world countries. It's 3.5 for Germany for instance. I always wondered why we measure consumption in those units, instead of just using average power directly. 11.7 MWh/a = 1.33 kW.
  - chris_wot 11y ago
    No, not at all. I'd like to know where they got those figures! In NSW, Australia's largest state, IPART (the Independent Pricing and Regulatory Tribunal) who until about a year ago set electricity prices, gives different figures for 2010: "Households with 1-2 residents use about 1,400 kWh of electricity per quarter Households with 3-4 residents use about 2,100 kWh of electricity per quarter, and Households with 5 or more residents use at least 2,700 kWh of electricity per quarter." http://www.ipart.nsw.gov.au/Home/For_Consumers/Compare_Energy_Offers/Typical_household_energy_use http://www.ipart.nsw.gov.au/Home/For_Consumers/Compare_Energ... Edit: I must be tired. My calculations are way off. Sorry about that.
alephnil 11y ago
One thing this article shows, is how different solar is on high vs low latitudes. Up to around 40 degrees, solar is practical, and you only need to take the nights and possibly cloud cover into account, at 60 degrees, the seasonal variation is too high to be stored in a parctical way, even with his assumption of flat consumption through the year, which is quite unrealistic with the short days and low temperatures at high latitudes. It means that off the grid solar is unrealistic in Northern Europe, but it can be a possibility many other places in the world.
- jacquesm 11y ago
  I ran an off-the-grid fairly normal house in Northern Canada, solar was > 70% of our power. Seasonal variations are not leveled by batteries but by properly dimensioning the system and reduced consumption. So off the grid solar is very realistic in higher latitudes, especially if you take into consideration that panels will generate a lot more power when they're cold than when they are warm. The most power I ever saw generated instantaneously was on a terribly cold day in February (but that was exceptional). Sure the days are shorter but you adapt to the reduced energy budget fairly easily. Off the grid solar is unpractical the world over if you don't adapt your consumption.
  - codecamper 11y ago
    Wow that is great that you were 70% solar in North Canada. Yes I've heard that panels can output actually more than their rated capacity when sunny & cold. I think the big problem people have with going PV, is that there isn't a good manual on how to go solar. & much of it is changing and improving as we speak.
    - jacquesm 11y ago
      There may not be a manual simply because every situation is different (and it's a personal thing too), but there is a huge community of renewable energy enthusiasts at http://www.otherpower.com/ http://www.otherpower.com/ , they have a discussion board at http://www.fieldlines.com/ http://www.fieldlines.com/ . Collectively they have a huge amount of knowledge about anything related to renewables and anybody considering going off grid could do a lot worse than to become a member and to start reading forum threads. They range all the way from people interested but not actually doing anything to people operating fair sized solar and wind farms and everything in between.
crdoconnor 11y ago
IIRC the Tesla batteries are actually really pricey for what you get because of the brand. I think you can get something from a 'lesser' brand for about 2/3 the price, possibly even less. In other news, name brand sneakers are also expensive and probably not really worth it.
- ghshephard 11y ago
  I'd love to see a citation. All I recall people saying when the Tesla Batteries came out was, "How can they sell the system for so little money?" and that "There was nothing out there at that price point" http://www.forbes.com/sites/jeffmcmahon/2015/05/05/why-tesla-batteries-are-cheap-enough-to-prevent-new-power-plants/ http://www.forbes.com/sites/jeffmcmahon/2015/05/05/why-tesla...
nkurz 11y ago
The author wrote followup article in which he estimates costs for a more reasonable system that is sized for winter production rather than annual storage: A Potential Solution to the Problem of Storing Solar Energy – Don’t Store It. http://euanmearns.com/a-potential-solution-to-the-problem-of-storing-solar-energy-dont-store-it/ http://euanmearns.com/a-potential-solution-to-the-problem-of... As commenters here and on the blog suggest, this is a much more cost effective approach (although still prohibitively expensive in extreme latitudes).
- ZeroGravitas 11y ago
  Across two epically long blog posts, that's a lot of words, numbers and graphs to say "it's sunnier nearer the equator" and "electric grids are handy, don't abandon them for no reason", all delivered with a lot of attitude for no obvious reason. Is there some context outside of these two posts that makes them reasonable things for someone to have spent so much time and effort on?
knappador 11y ago
Let's look at chemical storage with hydrocarbons in the mix, allowing some as-yet non-commercial (air-metal & combined cycle home generators) to make good food for speculation. A consumer to operate a small gas turbine and store their energy in the form of hydrocarbons. If this is to be sensible, then 43MJ/kg would have to be enough, because that's what they're going to get with kerosene/jet fuel. Now let's consider lithium. The problem with metal-air batteries has mostly been poisoning by unwanted gases. Let's assume for a moment that a membrane material is developed that only allows high purity oxygen through, but suffers low throughput. This is no problem for our off-grid solution because we're talking about large storage relative to power, similar to some flow battery applications. Using some method of specific ion or biological style solution, such a membrane is not implausible. Lithium-air weighs in at 40MJ/kg specific energy. How much does it cost? Given that a metal-air battery uses lithium oxide, the lithium carbonate and lithium hydroxide prices are not quite valid guides, but the price of $7/kg is obtainable for the carbonate of "battery grade." If the pure oxide can be the material used in manufacture, then possibly the $7 value is in the ballpark. Jet-A is $0.45 per kilogram. 1.41 $/gal / 3.78541 l/gal / 0.820 kg/l Higher efficiency must be allowed because even with combined cycle at high latitudes where it's cold, we're looking at 90% round-trip for a battery vs ~75% for our Brayton cycle + home heating. There are external costs to a large tank of kerosene and a pile of lithium carbonate. One requires a gas turbine and the other requires a battery & significant manufacturing. Excepting those two things, we're left with a roughly 7:1 factor of cost for the raw material, so a seven year payoff it is. Lithium might not be the cheapest rechargeable precursor. It might be great for EV's (high power output is a requirement) and maybe something else will show up as the cheapest energy storage without requiring off-grid people to rely on ARES gravity trains. Perovskites (new paper just suggested that hot-carrier phonons can be used to raise theoretical efficiency to 66%) throw yet another wrinkle into solar. Both energy storage and generation could become quite a bit cheaper. All hypothetical, yes, but my napkin does tell me not to rule out off-grid, not that I'm sympathetic to off-grid, anti-social Ayn Rand acolytes =D Whatever matters for off-grid matters for a ton of settings, such as places where there is no grid still. It's tough to say definitively that a straight-renewable energy source won't become cost-competitive even in grid areas of high latitude within the decade. Source on Jet A specific heat: http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelSpecifications2005.pdf http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelS... Source on Lithum Air theoretical specific energy: https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery Jet A price: http://www.indexmundi.com/commodities/?commodity=jet-fuel http://www.indexmundi.com/commodities/?commodity=jet-fuel Lithium Carbonate Price (ev grade): http://www.globalstrategicmetalsnl.com/_content/documents/405.pdf http://www.globalstrategicmetalsnl.com/_content/documents/40...
anovikov 11y ago
Of course the example is wrong because for most of the places it is resolved by simply having a larger PV array so that even winter generation is sufficient. That will probably not work for 60N, but easily for 40N: an array about the size calculated for 60N, used at 40N, will not require any seasonal storage. And of course, nobody uses storage like that. Off-grid system must combine solar and wind, wind typically gets stronger in winter, plus about 24 hour worth of energy consumption in storage (a couple Tesla systems), and finally a diesel generator for a few percent of the total generation for the unlucky days when sun doesn't shine and the wind doesn't blow.
aexaey 11y ago
You really shouldn't plan battery storage for winter/summer cycle. Batteries are for day/night cycle. If stretched a bit, then maybe batteries will cover "that rainy day, when I need to do laundry" and similar. But not much more, as you've seen yourself - this is prohibitively expensive. For winter/summer cycle, if you're south of 40° N (and north of 40° S) just oversize PVs. Otherwise, you need a second power source - grid, wind or geothermal. Not to mention that having a second source is really good if you ever plan for maintenance or emergency repairs.
orasis 11y ago
Troll post.
Johnythree 11y ago
The usual approach is to take a conventional house design, and then design a solar supply to meet its needs. This results in a crazy large system due to our appalling wasteful house designs (which in turn are due to historically cheap electricity). A better approach is to decide how much you can spend on solar, then design a house which will function within that limitation. To succeeded you will need to change house designs, select different type and size of appliances, and most importantly, make some personal sacrifices. If you can live within these limits, then yes, you will enjoy having Solar. If not, you would be better to continue with your existing expensive lifestyle.

24 points by martinald 11y ago

deleted 11y ago

[deleted]

jacquesm 11y ago
The one thing you don't do when you're off the grid is run an airconditioning system. The way to cover a gap longer than a few days is with a genset.
- deleted 11y ago
  [deleted]

phire 11y ago

Battery storage is simply not meant to cover that kind of gap. It's intended more to cover the overnight period, when you have no sun, or maybe for a few days with bad weather. You need to spec your system so at the very least it generates enough power on the worst days of the year to cover your needs, and surplus power on good days. You also should have a second means of power generation, wind works nicely as it's uncommon to have a day that isn't either windy or sunny.

codecamper 11y ago
The OP does not have a single clue about actually using solar. His price per KWH is about 1 order of magnitude off (and then some). I've used 100% solar for the past 2 years and there has not been a single day that I needed a second source of power. Also my system is quite modest. Just 500W of panels and about 600Wh of lithium ion battery (lifepo4) energy storage. The 500W of panels is plenty. Most days I charge my batteries fully before noon. The 600Wh of batteries is enough to get me through 3 days of heavy cloud weather ( you get about 10% of your maximum generation on a heavily clouded day ). This system is for two people using our computers and 3g wireless for the entire day. LED lights at night which are bright and warm, water pump, food processor, stereo, iPad, hella gadgets, raspberry pi backup server, etc etc If I changed something, I'd double the batteries that I use.. going to 24V. You get more of the rated power of the solar panel when using a 24V system. I am considering getting an electric bike & storing extra power there. The total cost of the system was about $800. In the summer I can generate about 2 kWh / sunny day -- I only need about 400Wh / day though. You do the math for the cost per kWh. It's damn cheap.
- jacquesm 11y ago
  > The OP does not have a single clue about actually using solar. Exactly. It's a total nonsense proposition to offset seasonal swing using battery power. Running a PV system is about conservation first and foremost and some planning second. Your battery is for the day/night cycle and overcast days, not for seasonal variations. Maybe he should run a PV system for a while before writing articles like these.
  - raesene4 11y ago
    I think the original article was looking at the proposition of off-grid energy use using purely solar, in which scenario seasonal variations matter From the article "Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation."
    - jacquesm 11y ago
      > Even with these rough numbers it’s hard to see how anyone living any distance from the Equator is going to be able to justify the cost of installing enough batteries to go off-grid with a domestic rooftop solar PV installation. If you go off grid on purely solar your backup is not a battery, your backup is a genset. It's a nonsense proposition leading to nonsense conclusions based on nonsense numbers. Very tiring.
      - raesene4 11y ago
        I'd agree, I was just pointing out the basis that the author was coming from which was the reason why he was considering seasonal variations in battery calculations. With that said, from reading some articles about off-grid living, it's not outwith the bounds of possibility that people are looking at pure solar (or pure renewable anyway) off-grid living, for priniple-based reasons , rather than a more pragmatic rationale.
        11y ago

ra 11y ago

The amount of battery storage required for a household on-grid is much smaller when you can think of the grid as a load balancing device. Of course we'd need to get away from the huge mismatch between feed-in tariffs and consumption tariffs. Ideally the difference would be a small spread (like in a currency exchange rate) and a nominal daily connection fee. In which case a 10KW Tesla powerwall is a pretty handy size.

crdoconnor 11y ago
>Of course we'd need to get away from the huge mismatch between feed-in tariffs and consumption tariffs. Maybe first we could nationalize the whole outfit and run it on a cost-plus basis. There is way too much profit being made from being a monopoly grid operator. That probably has more to do with why solar is such a good deal than the green energy subsidies do.
- maxerickson 11y ago
  In the US I'm under the impression that generation and transmission are pretty heavily regulated. Do you have a favorite example company that makes egregious profits?
ZeroGravitas 11y ago
In an optimally operating power grid, household storage should be pointless. If it makes economic sense for you to deploy batteries then you're probably dealing with a poorly regulated, or underperforming grid. The latter may simply be a matter of geography, but even then unless you live in a cabin in the woods then I believe e.g. in Australia some utilities are creating solar/battery/genset microgrids for remote communities, rather than try to maintain long power lines from the main grid.

jacquesm 11y ago

> 1. Household consumption is 5,000 kWh/year. (About right for Western Europe, low for the US, high for most of the rest of the world.) So, to stick with HN's tradition of making negative comments about articles: This author is totally clueless, that's not at all how you size a PV system (and the battery to go with it). Battery power in a solar system is not used to offset seasonal variation but the day/night cycle and a possible overcast day (or two). Then the first line listing the assumptions made starts from the average household but a PV system designer that is designing an actual system rather than a theoretical one will start with throwing everything out that you can miss, the household will be anything but 'average'. Electric heat, AC and a whole raft of other big consumers get thrown right out before you even start to think about what your consumption will be. No romantic array of incandescent spots for you, and no baseboard heat. Everything you can save you won't have to generate and store and that's your first gain. This will cut the consumption in half or even better and then you can start wondering about how much PV you need, if you're going to have wind or water to augment that, what size you genset will have to be (in case all of the above aren't available for a longer period) and what kind of storage battery you need. (And of course what size inverter(s) to convert your DC back to AC tied into the distribution panel of your house, you really don't want to run your household on DC) A good rule of thumb for battery storage for a system that is off-grid and totally self-reliant is to have 5 days worth of consumption leading to 33% or 20% of battery discharge depending on how nice you want to be to your batteries. That's a whopping large battery, most likely larger than what your friendly car company can sell you in one chunk so you'll need multiple units ganged together via some kind of bus system. When you go off-grid your life can depend on the working of the system, if you're snowed in and you can't get fuel, the sun lets you down and there is no wind then you fire up your trusty genset (preferably a diesel, you might be running it for a week straight in an emergency) to put some much needed charge into your batteries. Of course you anticipated this and you have two weeks worth of fuel stored. Also, in very cold weather battery capacity tends to be reduced. So, in short design your house and your life around your energy budget and even then you'll find you need a rather very large battery.

codecamper 11y ago
It's a true & bit of a bummer fact: most homes are incredibly energy inefficient. Especially when it comes to heating. But people must change & figure out how to do it. (hint: 50 cent per watt solar and cheaper.. you just may be able to heat with solar. storing energy as heat... you don't need a battery. You need concrete.) Evolve or die. BTW, lithium batteries do not off gas hydrogen (like lead acid batteries do). Therefore, you just keep your batteries inside with you. They'll work just as efficiently and any of their 5% inefficiency will become heat.

ghouse 11y ago

How many 9s of reliability do you want to pay for? Speaking only regarding residential energy: In North America, other than Hawaii as of a couple weeks ago, solar generation banks credit for electricity exported to the grid. In effect, a 100% efficient, and free, battery. In Austrlia, exported power receives credit only equal to the offset generation -- less than 1/3 of the total price of electricity. In those cases, there is an economic evaluation. Otherwise, batteries are for reliability. And apparently there are more residential backup generators in the US than there are residential rooftop solar.

jacquesm 11y ago
Going off-grid when the grid is present and reliable is dumb. Even without net-metering being 100% as long as you cover your own use 90% of the time it is still much cheaper than battery power (charge/discharge costs more than what power from the grid costs, batteries have a life-span). So in that situation you try to cut your consumption when you generate little power or you take the hit by paying for grid power. The larger chunk of your bill in that case will be the termination fees, the electricity bill typically has two components, one where you pay a fixed fee for the connection whether you use it or not and another you pay per used KWh. The first component can handily outstrip the second making those very expensive KWs, especially when you're close to running of your own power most of the time. Still, if you think of it as a replacement for both your genset and your very large battery it may make economic sense to do this anyway. It all depends on the location and reliability of the grid. Where I lived our PV system was many times more reliable than the local grid so we ended up ditching the hookup but that's a very exceptional situation.
- chris_wot 11y ago
  That's what this doesn't take into account. If you install batteries, you use them for only part of the time to make up for times the PV doesn't generate electricity. This offsets costs of drawing from the grid. But when you need to draw from the grid, you do so.

shalmanese 11y ago

In this hypothetical scenario, instead of investing so much in batteries, why not just double the size of your solar array so you're not storing 6 months worth of power in batteries? That would only cost ~20K instead of the ~500K for batteries.

jacquesm 11y ago
You use the battery to offset the times when the sun does not shine so more solar power does not work. You don't use batteries to offset the summer/winter cycle, you use them to offset the day/night cycle and to store a bit more in case the next couple of days are overcast. The whole winter/summer storage thing is nonsense, nobody sizes a PV system like that.
- raesene4 11y ago
  well nobody apart from people looking for an off-grid lifestyle of course. What I took from the article is that pure solar off-grid is impractical away from equatorial latitudes.
  - jacquesm 11y ago
    If that's what you too from the article then you're right 'pure solar' is impractical (anywhere). You always need a battery and you always need some kind of backup. But if you're going to think like that grid power is also impractical anywhere, since it too could fail. Power is so important that no single source should be relied on anywhere. In inner cities of course your only chance of getting power is the local electricity company hookup, but if that should fail for any extended period of time such a city would rapidly become a place where you could no longer live, especially at latitudes where it tends to get very cold in the winter. So, nobody (in their right mind, at least) will do a 'pure' photovoltaic system. There will always be some kind of backup-power mechanism, either the grid, a wind-turbine, a battery to tide you over, a pelton wheel fed from a stream, grid power or any combination of the above.
    - 11y ago

chris_wot 11y ago

5,000kW per year is low in the U.S.? That is extraordinarily wasteful. In most of Australia the average is about 2300kW per quarter, and even that is probably a high estimate. But if 5000kW is low then I'm assuming the average has to be 6000kW, or 6500kW! That a HUGE amount of power! What on earth are people in America using?!?

zurn 11y ago
You might have mixed per-quarter and per-year numbers there. According to http://shrinkthatfootprint.com/average-household-electricity-consumption http://shrinkthatfootprint.com/average-household-electricity... the average (in MWh/a) is 11.7 for USA and 7.2 for Australia, both at the high end of first-world countries. It's 3.5 for Germany for instance. I always wondered why we measure consumption in those units, instead of just using average power directly. 11.7 MWh/a = 1.33 kW.
- chris_wot 11y ago
  No, not at all. I'd like to know where they got those figures! In NSW, Australia's largest state, IPART (the Independent Pricing and Regulatory Tribunal) who until about a year ago set electricity prices, gives different figures for 2010: "Households with 1-2 residents use about 1,400 kWh of electricity per quarter Households with 3-4 residents use about 2,100 kWh of electricity per quarter, and Households with 5 or more residents use at least 2,700 kWh of electricity per quarter." http://www.ipart.nsw.gov.au/Home/For_Consumers/Compare_Energy_Offers/Typical_household_energy_use http://www.ipart.nsw.gov.au/Home/For_Consumers/Compare_Energ... Edit: I must be tired. My calculations are way off. Sorry about that.

alephnil 11y ago

One thing this article shows, is how different solar is on high vs low latitudes. Up to around 40 degrees, solar is practical, and you only need to take the nights and possibly cloud cover into account, at 60 degrees, the seasonal variation is too high to be stored in a parctical way, even with his assumption of flat consumption through the year, which is quite unrealistic with the short days and low temperatures at high latitudes. It means that off the grid solar is unrealistic in Northern Europe, but it can be a possibility many other places in the world.

jacquesm 11y ago
I ran an off-the-grid fairly normal house in Northern Canada, solar was > 70% of our power. Seasonal variations are not leveled by batteries but by properly dimensioning the system and reduced consumption. So off the grid solar is very realistic in higher latitudes, especially if you take into consideration that panels will generate a lot more power when they're cold than when they are warm. The most power I ever saw generated instantaneously was on a terribly cold day in February (but that was exceptional). Sure the days are shorter but you adapt to the reduced energy budget fairly easily. Off the grid solar is unpractical the world over if you don't adapt your consumption.
- codecamper 11y ago
  Wow that is great that you were 70% solar in North Canada. Yes I've heard that panels can output actually more than their rated capacity when sunny & cold. I think the big problem people have with going PV, is that there isn't a good manual on how to go solar. & much of it is changing and improving as we speak.
  - jacquesm 11y ago
    There may not be a manual simply because every situation is different (and it's a personal thing too), but there is a huge community of renewable energy enthusiasts at http://www.otherpower.com/ http://www.otherpower.com/ , they have a discussion board at http://www.fieldlines.com/ http://www.fieldlines.com/ . Collectively they have a huge amount of knowledge about anything related to renewables and anybody considering going off grid could do a lot worse than to become a member and to start reading forum threads. They range all the way from people interested but not actually doing anything to people operating fair sized solar and wind farms and everything in between.

crdoconnor 11y ago

IIRC the Tesla batteries are actually really pricey for what you get because of the brand. I think you can get something from a 'lesser' brand for about 2/3 the price, possibly even less. In other news, name brand sneakers are also expensive and probably not really worth it.

ghshephard 11y ago
I'd love to see a citation. All I recall people saying when the Tesla Batteries came out was, "How can they sell the system for so little money?" and that "There was nothing out there at that price point" http://www.forbes.com/sites/jeffmcmahon/2015/05/05/why-tesla-batteries-are-cheap-enough-to-prevent-new-power-plants/ http://www.forbes.com/sites/jeffmcmahon/2015/05/05/why-tesla...

nkurz 11y ago

The author wrote followup article in which he estimates costs for a more reasonable system that is sized for winter production rather than annual storage: A Potential Solution to the Problem of Storing Solar Energy – Don’t Store It. http://euanmearns.com/a-potential-solution-to-the-problem-of-storing-solar-energy-dont-store-it/ http://euanmearns.com/a-potential-solution-to-the-problem-of... As commenters here and on the blog suggest, this is a much more cost effective approach (although still prohibitively expensive in extreme latitudes).

ZeroGravitas 11y ago
Across two epically long blog posts, that's a lot of words, numbers and graphs to say "it's sunnier nearer the equator" and "electric grids are handy, don't abandon them for no reason", all delivered with a lot of attitude for no obvious reason. Is there some context outside of these two posts that makes them reasonable things for someone to have spent so much time and effort on?

knappador 11y ago

Let's look at chemical storage with hydrocarbons in the mix, allowing some as-yet non-commercial (air-metal & combined cycle home generators) to make good food for speculation. A consumer to operate a small gas turbine and store their energy in the form of hydrocarbons. If this is to be sensible, then 43MJ/kg would have to be enough, because that's what they're going to get with kerosene/jet fuel. Now let's consider lithium. The problem with metal-air batteries has mostly been poisoning by unwanted gases. Let's assume for a moment that a membrane material is developed that only allows high purity oxygen through, but suffers low throughput. This is no problem for our off-grid solution because we're talking about large storage relative to power, similar to some flow battery applications. Using some method of specific ion or biological style solution, such a membrane is not implausible. Lithium-air weighs in at 40MJ/kg specific energy. How much does it cost? Given that a metal-air battery uses lithium oxide, the lithium carbonate and lithium hydroxide prices are not quite valid guides, but the price of $7/kg is obtainable for the carbonate of "battery grade." If the pure oxide can be the material used in manufacture, then possibly the $7 value is in the ballpark. Jet-A is $0.45 per kilogram. 1.41 $/gal / 3.78541 l/gal / 0.820 kg/l Higher efficiency must be allowed because even with combined cycle at high latitudes where it's cold, we're looking at 90% round-trip for a battery vs ~75% for our Brayton cycle + home heating. There are external costs to a large tank of kerosene and a pile of lithium carbonate. One requires a gas turbine and the other requires a battery & significant manufacturing. Excepting those two things, we're left with a roughly 7:1 factor of cost for the raw material, so a seven year payoff it is. Lithium might not be the cheapest rechargeable precursor. It might be great for EV's (high power output is a requirement) and maybe something else will show up as the cheapest energy storage without requiring off-grid people to rely on ARES gravity trains. Perovskites (new paper just suggested that hot-carrier phonons can be used to raise theoretical efficiency to 66%) throw yet another wrinkle into solar. Both energy storage and generation could become quite a bit cheaper. All hypothetical, yes, but my napkin does tell me not to rule out off-grid, not that I'm sympathetic to off-grid, anti-social Ayn Rand acolytes =D Whatever matters for off-grid matters for a ton of settings, such as places where there is no grid still. It's tough to say definitively that a straight-renewable energy source won't become cost-competitive even in grid areas of high latitude within the decade. Source on Jet A specific heat: http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelSpecifications2005.pdf http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelS... Source on Lithum Air theoretical specific energy: https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery https://en.wikipedia.org/wiki/Lithium%E2%80%93air_battery Jet A price: http://www.indexmundi.com/commodities/?commodity=jet-fuel http://www.indexmundi.com/commodities/?commodity=jet-fuel Lithium Carbonate Price (ev grade): http://www.globalstrategicmetalsnl.com/_content/documents/405.pdf http://www.globalstrategicmetalsnl.com/_content/documents/40...

anovikov 11y ago

Of course the example is wrong because for most of the places it is resolved by simply having a larger PV array so that even winter generation is sufficient. That will probably not work for 60N, but easily for 40N: an array about the size calculated for 60N, used at 40N, will not require any seasonal storage. And of course, nobody uses storage like that. Off-grid system must combine solar and wind, wind typically gets stronger in winter, plus about 24 hour worth of energy consumption in storage (a couple Tesla systems), and finally a diesel generator for a few percent of the total generation for the unlucky days when sun doesn't shine and the wind doesn't blow.

aexaey 11y ago

You really shouldn't plan battery storage for winter/summer cycle. Batteries are for day/night cycle. If stretched a bit, then maybe batteries will cover "that rainy day, when I need to do laundry" and similar. But not much more, as you've seen yourself - this is prohibitively expensive. For winter/summer cycle, if you're south of 40° N (and north of 40° S) just oversize PVs. Otherwise, you need a second power source - grid, wind or geothermal. Not to mention that having a second source is really good if you ever plan for maintenance or emergency repairs.

orasis 11y ago

Troll post.

Johnythree 11y ago

The usual approach is to take a conventional house design, and then design a solar supply to meet its needs. This results in a crazy large system due to our appalling wasteful house designs (which in turn are due to historically cheap electricity). A better approach is to decide how much you can spend on solar, then design a house which will function within that limitation. To succeeded you will need to change house designs, select different type and size of appliances, and most importantly, make some personal sacrifices. If you can live within these limits, then yes, you will enjoy having Solar. If not, you would be better to continue with your existing expensive lifestyle.