8 ms·

SolarPi experiment 2: Finally something that works

125 points by marbu 3y ago

thebears5454 3y ago
I like that this guy has been struggling with this for so long lol Just some random guy that I'm connected to via his frustrations
- dylan604 3y ago
  I too feel the pain of starting a project possibly because someone feels they can do something for cheaper than a retail version. When pricing all of the components, this often looks to be the case. Oh how many times have I then had to buy things a second time or decide something else is needed once elbow deep into the project and many weekends later. If everything was calculated to include the amount of time invested, it would have been so much easier to just buy the thing. But something about pride or some such just won't allow that to happen. We could wax poetically about the act of accomplishment and the self learning blah blah, but it's pride. Edit: Just wanted to add the relevant quote: "My only regret is that you can’t power the raspberry from frustration, because my levels are lately spiking so high, that I am continually wondering why isn’t reality bending around my hate."
  - Eisenstein 3y ago
    > If everything was calculated to include the amount of time invested, it would have been so much easier to just buy the thing. But then when that thing breaks you can't fix it with the knowledge and spare parts you have on hand.
    - dylan604 3y ago
      That's okay since right to repair doesn't really exist. The owner of the product would just sue you for breech of licensing. er...
    - thebears5454 3y ago
      I wonder how big your spare parts drawer/box is
      - deleted 3y ago
        [deleted]
      - Eisenstein 3y ago
        Most hobbiest electronics these days are multi-multi-use. A raspi and some solar panels, batteries, and charge controllers could be parts in a million different saturday projects.
  - verinus 3y ago
    and it's also about the learning experience!
  - Bystroushaak 3y ago
    I mean, I have nothing against the retail version of this, if there was any. If you have something in mind, post it here. I've tried the PiJuice first, in hopes that it will be sufficiently retail and will work for this usecase, and it didn't.
conorh 3y ago
Is there a cheap(ish) solar regulator like the one he is using that does have the ability to output data somewhere for logging purposes?
- louwrentius 3y ago
  The entry-level Victron mppt (I recommend an mppt charger) is the 75/10 by Victron. You also need their ve.direct cable which is not cheap, but if you are willing, you can make your own.
  - hallz 3y ago
    The Basic Victron SmartSolar has bluetooth built-in (no cable needed) and a mobile app with realtime charge monitoring and history. The ve.direct cable is for doing more complex things. https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf https://www.victronenergy.com/upload/documents/Datasheet-Sma...
dragontamer 3y ago
1. Lead Acid is far cheaper, though its bigger and heavier than LiFePo. 12V @12Ah is only $35 from a brand-name (https://batteryinthecloud.com/products/ps-12120 https://batteryinthecloud.com/products/ps-12120), and closer to $25 from no-name brands on Amazon. 2. Modules to charge LeadAcid are so cheap, they don't even make them. This specified PS-battery hsa a 13.5V to 13.8V "standby" voltage, meaning that 13.65V from the Solar Panel is all you need to have a UPS. Connect the 13.65V source from the Solar-panels to the + and - leads of the 12V battery, and volia. You get 13.65V when solar is available, and 12V from the battery when the solar cuts off. The end. Isn't that easy? 3. Grid-tie should be similarly easy, though I don't have too much experience with it myself. IMO, buy a professional AC->DC converter, probably at 19V or some other suitable voltage and then get a DC-DC buck converter to go from 19V to 14.35V, and then a diode (0.7V dropoff) to hook up to your batteries in parallel. You'll also need a diode in your Solar-panels cause you don't want your Grid-tie system "charging your solar panels" (that'd probably create a fire and/or damage them...). Hobbyists should NOT deal with main-power themselves, but there's a gross-many number of AC-to-DC converters available from $10 to $40. 4. Don't battery balance. Just buy bigger batteries. If 12Ah isn't enough, buy a 20Ah battery. If 20Ah isn't enough, buy a 33Ah battery, etc. etc. The limit is whatever you're comfortable with (the bigger batteries give more current which can be more dangerous)
- louwrentius 3y ago
  Don’t do lead acid. I say this from experience. Lead acid charges too slow. You want a battery that can capture every ray of sunshine - especially with intermittent sunlight - and charge at full speed. Lifepo4 can do this. Lead acid can’t.
  - dragontamer 3y ago
    A 12V 12Ah battery is 144Wh. I'm fairly certain that Lead-acid can accept 0.3C, and you're right in that a 60W panel is slightly more than the 43W that Lead-acid can accept. But sizing 12V 20Ah (ie: 240 Wh), and now 0.3C is 72W or 6A of safe charging (less than 0.3C). ------------- See #4: just buy a bigger battery if you need a bigger battery. Bigger battery provides more power and energy proportionally for the chemistry. And a 12V 20Ah lead-acid is just $40 on Amazon. --------- I guess your overall point is that "Trickle-charge" isn't enough for Solar? Which is something I admit I didn't think about earlier (trickle-charge just doesn't send as much current to the battery due to the lower voltage). But I guess there's a "simplicity of circuit" advantage of trickle-charging. A more complex state-of-charge circuit (likely a microcontroller keeping tabs on the battery) is needed to safely send 0.3C down to the Lead Acid. EDIT: On the other hand, having your "charge controller" just be like, two power diodes, is a gross benefit to simplicity. Its something you can do with Lead-Acid that's fully impossible with LiFePo (and is why LiFePo4 needs expensive charge controllers to work). For hobbyist purposes, there's something to be said about using simpler technologies, even if their specs are worse (and I'm not entirely sure if Lead-Acid has worse specs than LiFePo4 in this use case).
louwrentius 3y ago
I started out like the author of the blog post with a 60Watt panel and a cheap non-mppt solar controller. My balcony orientation was shit and that didn’t work out. Since then I upgraded “quite a bit”… The challenge is more difficult than it seems. A raspberry pi 4b does ~3.4 watt idle so that’s 84 watt-hour per day. This may not sound like a lot, but for battery-powered devices it quite a bit. Microcontrollers can run months on that amount of energy, but they aren’t as convenient as the Pi. The 12v 12ah battery used, contains 144 watt hour. Only enough to cover less than two full days with little to no sunlight. The 50 watt panel is already small, but the non-mppt controller makes it even more inefficient. With good sunlight, the panel can easily run the pi and charge the battery during daytime. The “real” challenge is to keep the Pi online during days of overcast weather. A 150 watt panel may only do 4-8 watt under those circumstances and that’s not enough. But I always love these projects none the less.
- dragontamer 3y ago
  I know Rasp. Pi is all the rage these days, but if I were to make a solar-server, it'd be off of Beaglebone Black instead. * Beaglebone Black uses slightly less power and is slower than Rasp. Pi. Lower power is a big benefit however. * Beaglebone has the "Programmable Realtime Unit" (a microcontroller-like hard-realtime subsystem with GPIO pins). * These PRU subsystems can probably (???) be utilized for the battery-state-of-charge and possibly even provide a software-control for mppt solar chargers. Theoretically of course, but... I have to imagine that a Cortex M4 has enough MHz to handle these kinds of calculations. * If not, the Beaglebone Black has a built in ADC that could be used as the basis of power calculations. Worst case, add in a proper uC to handle power / build my own MPTT / Battery charger.
  - tiagod 3y ago
    At least on MCUs, being slower can counter-act the lower active power, as you'll take longer to do whatever you want to do and go back to deep sleep. I'd like to know if this also happens with these SBCs, or if they even have any aggressive power saving features that can be employed.
znpy 3y ago
I remember tuning down the clock speed of the raspberry pi cpu when playing with flashrom, maybe that could also be used to reduce its power consumption? Not sure what rPi version the author is using, i think i remember i was using the original one ? It was 700mhz by default i think i clocked down to 200mhz and 50mhz. Granted, it was mostly unusable (bye bye openssh) at 50 mhz.
- folmar 3y ago
  There are also a lot of different optimizations and their impact discussed in https://ieeexplore.ieee.org/abstract/document/7811590 https://ieeexplore.ieee.org/abstract/document/7811590
sleepytimetea 3y ago
I have recently gone down the solar panel rabbit hole too but I never tried the "fancy portable mini panels" cause they seem to weak and overpriced. Instead, I acquired two large 140W panels that had been removed from an old installation for the princely sum of $20 (USD). After struggling with trying to find connectors that I could pair with the MC3 connectors (remember, these panels came off an old installation), I bought a dozen MC4 and just cut off the old MC3 connectors...MC4 is the way to go these days. Next came the surprise at finding out about "MPPT" - in all my years looking at solar panels on roofs, I never knew they were so finicky about voltage vs current curves...real MPPT charge controllers start at $70 for a Victron 15Amp and I decided to try my luck with Chinese sellers on AliExpress...turns out the charger was a PWM fake sold as a MPPT charge controller. Anyway, I also needed a battery since the charger doesn't work without a battery source. That's another saga but short story - I built my own 3S battery pack out of 18650s.
- louwrentius 3y ago
  What are you planning to power with your solar setup? You may be aware and this is 100% redundant but lifepo4 is a safer chemistry and small cells are becoming more affordable by the day. If there’s no risk of those 18650s overheating it’s fine I guess.
  - IshKebab 3y ago
    18650 is just a shape. You can get LiFePo4 18650s.
gh02t 3y ago
I've been looking for the same sort of mini charge controller with grid backup that is mentioned in the problems and challenges also with no luck. Is this really not a product that exists? I've long wanted to do a sort of small scale migration to solar. Offset the load from my home server with a few solar panels and source any excess power needed from the grid while also charging the batteries/providing power from solar when the sun is up. I could probably engineer something myself but doing things right on high power circuits is not worth the effort/risk. Any suggestions?
- colechristensen 3y ago
  Just grid tie a few panels with microinverters (one small independent inverter per panel), and forget the battery. Recommended Enphase https://enphase.com/ https://enphase.com/ As long as your solar capacity production is not often more than your usage at the same time, batteries won’t be of any particular use … they have to be fairly large to have any great utility in your home anyway, battery backup and solar production are orthogonal goals until you are producing a lot of power. If you do want battery backups on a small scale, just get a UPS the same as you would without solar.
- turtlebits 3y ago
  Look for "solar inverter" - Growatt, MPP Solar are popular brands - they will come with inverters though, but have grid backup/passthrough.
roughly 3y ago
I did a similar project a while back with a Pi Zero W, which has the perk of maxing at like 1w. Still, my takeaway was "whatever you think you need for a panel, triple it, and whatever you think you need for a battery, multiply it by like 10." Cloudy days tend to come together, the power output for your panel will drop off way more than you think, and your battery won't charge nearly as fast as you're hoping.
- rambambram 3y ago
  > Cloudy days tend to come together You probably have no idea how philosophical this sounds.
  - avidiax 3y ago
    It's also a mathematical tautology. There's only a few ways to evenly space the cloudy days. There's exponentially more ways to clump them.
- yomlica8 3y ago
  I've been thinking about trying to make a game/trail camera out of a Pi Zero which is a similar sort of problem. My idea it was only on part of the night I wouldn't need much power. But this thread is making me think things are going to be more complicated!
  - roughly 3y ago
    I think you’re better using simpler hardware for this - adafruit sells a dozen different varieties of microcontroller board with Wi-Fi, all of those will be much easier to keep powered.
vanillax 3y ago
Solar Shed mega hobbyist. Finally a HN topic I can contribute to. I've spent last few years trying to build out my solar shed mainly to have auxilary power to charge weed whacker, leaf blower, power lights, power a camera, etc. Just basic 12v power. The number one lesson is to 4x your power needs. 4x your watts and 4x your battery amp hours. Don't cheap out on charge controllers. There's never enough sun light to fully charge your batteries and your panels are never at the right angle to maximize sunlight. Especially in less solar friendly areas like Michigan. Lead acid is fine if you over compensate with panels. Lead acid will last longer in the cold than LiFEP04. Die hards will say you cant charge LiFEP04 in winter but I do. I accept the fact that my batteries will degrade faster. When you can build your own packs, its a lot easier to find which single set of cells went out and cheaper to replace. Its a risk I accept. If you are starting out, get a 200 Ah/hr LiFEP04 battery and 400 watts solar. Its a very good starting point for 12v and gives room for expandability. Avoid foldables. Avoid Harbor Freight. Avoid Jackery Solar Panels. You need Quality Panels. If you wanna learn more, check out Will Prowse https://www.youtube.com/@WillProwse https://www.youtube.com/@WillProwse
- carapace 3y ago
  > Avoid Harbor Freight. Why? I'm just starting out with solar power and I got a 100W panel set (4 x 25W with a charge controller) and 35Ah battery from HF just to try it out and so far it seems fine.
  - tiahura 3y ago
    The cheap junk on Amazon is much better.
    - eyegor 3y ago
      This is not generally true. Amazon is plagued by drop shippers now and as a result most of their solar junk is many years old warehouse stock. Harbor freight tends to be better. Ex: https://youtu.be/W-fgI6Kyy2I https://youtu.be/W-fgI6Kyy2I
  - naikrovek 3y ago
DavidGetchel 3y ago
Nice to see solar projects like this. We have 4 solar setups on the property currently. One for main house. Another for the pump house. A temporary garage setup and one for a studio. A good way to learn to manage your own power generation and setting up systems.
daotoad 3y ago
There are some really handy databases with detailed insolation data available for sizing your solar projects. https://nsrdb.nrel.gov/ https://nsrdb.nrel.gov/ is one place to find this stuff. Years ago I worked on environmental monitoring systems for snow and ice management. One of the things I did was help spec out solar systems for remote installations in Alaska and Canada. The basic issue was "How much sun will there be in a typical summer?" combined with "How much power can we store in our batteries?" and "How much power can we draw from the lead acid batteries without them freezing?" (who knew that a discharged battery freezes at a lower temperature than a charged one? I sure didn't). It's a pretty straightforward process, actually. The company I worked for had a pretty detailed spreadsheet to help with bids, but essentially you: 1. look up the insolation data for the install site in one of the databases with that info (like https://nsrdb.nrel.gov/ https://nsrdb.nrel.gov/) 2. compute rate of loss over time for your installation (power consumption +_self-discharge) 3. look at the battery datasheets to determine how much you can discharge the battery at any given time based on anticipated temperature ranges 4. work out what your tolerances are for temperature and insolation variability Usually there would be a couple of options that were in the cost sweet spot where you had a bit more solar and bit less battery or vice versa. Some of these sites were up around the arctic circle, so battery was pretty important in those cases, since you're looking at months without appreciable sun combined with low temperatures. This wasn't even the major part of my job, but it was a small company and I wore a lot of hats.
turtlebits 3y ago
IME, a 50w panel is not enough. You'll never get full output, even in perfect alignment and a sunny day. I probably get an average of 70% or less from my 4x250w panels.
frankreyes 3y ago
> This means that the solar power cannot provide enough power to charge the battery, although I am using a 60W solar panel for ~5W Raspberry Pi. Just because there's "light" doesn't mean the panel will produce power. The sun has to shine BRIGHTLY. This is why solar power in Berlin or London is a waste of resources, because the sun doesn't shine BRIGHTLY there.
- pjc50 3y ago
  Objectively false: my system in Scotland (56 north) works quite nicely, and even on cloudy days you get a considerable amount of power. The power output is simply proportional to brightness. It is, after all, just a big flat photodiode.
  - frankreyes 3y ago
    Considerable does not translate into 100% efficiency. This is what the original article means. In your specific case you had to over provision your solar installation compared to , for example, Egypt.
hggh 3y ago
It's down right now. Archived version: https://web.archive.org/web/20230822000517/http://blog.rfox.eu/en/Hardware/SolarPi_experiment_2_Finally_something_that_works.html https://web.archive.org/web/20230822000517/http://blog.rfox....
GoToRO 3y ago
"the Raspberry is actually powered from the USB output of the controller" I don't know about his controller but these cheap controllers will power the USBs even on low battery. They will kill the battery (he even mentions this bellow). The right way to have USB output is to connect a car charger to the 12V output of the controller and then connect your load to that charger. That 12V output is cut when the battery is low and reconnected after it is charged. These voltages can be set in the controller. This way the battery will never discharge so much that the controller doesn't even recognize the type of battery (6V, 12V)

125 points by marbu 3y ago

I like that this guy has been struggling with this for so long lol Just some random guy that I'm connected to via his frustrations

dylan604 3y ago
I too feel the pain of starting a project possibly because someone feels they can do something for cheaper than a retail version. When pricing all of the components, this often looks to be the case. Oh how many times have I then had to buy things a second time or decide something else is needed once elbow deep into the project and many weekends later. If everything was calculated to include the amount of time invested, it would have been so much easier to just buy the thing. But something about pride or some such just won't allow that to happen. We could wax poetically about the act of accomplishment and the self learning blah blah, but it's pride. Edit: Just wanted to add the relevant quote: "My only regret is that you can’t power the raspberry from frustration, because my levels are lately spiking so high, that I am continually wondering why isn’t reality bending around my hate."
- Eisenstein 3y ago
  > If everything was calculated to include the amount of time invested, it would have been so much easier to just buy the thing. But then when that thing breaks you can't fix it with the knowledge and spare parts you have on hand.
  - dylan604 3y ago
    That's okay since right to repair doesn't really exist. The owner of the product would just sue you for breech of licensing. er...
  - thebears5454 3y ago
    I wonder how big your spare parts drawer/box is
    - deleted 3y ago
      [deleted]
    - Eisenstein 3y ago
      Most hobbiest electronics these days are multi-multi-use. A raspi and some solar panels, batteries, and charge controllers could be parts in a million different saturday projects.
- verinus 3y ago
  and it's also about the learning experience!
- Bystroushaak 3y ago
  I mean, I have nothing against the retail version of this, if there was any. If you have something in mind, post it here. I've tried the PiJuice first, in hopes that it will be sufficiently retail and will work for this usecase, and it didn't.

conorh 3y ago

Is there a cheap(ish) solar regulator like the one he is using that does have the ability to output data somewhere for logging purposes?

louwrentius 3y ago
The entry-level Victron mppt (I recommend an mppt charger) is the 75/10 by Victron. You also need their ve.direct cable which is not cheap, but if you are willing, you can make your own.
- hallz 3y ago
  The Basic Victron SmartSolar has bluetooth built-in (no cable needed) and a mobile app with realtime charge monitoring and history. The ve.direct cable is for doing more complex things. https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf https://www.victronenergy.com/upload/documents/Datasheet-Sma...

dragontamer 3y ago

1. Lead Acid is far cheaper, though its bigger and heavier than LiFePo. 12V @12Ah is only $35 from a brand-name (https://batteryinthecloud.com/products/ps-12120 https://batteryinthecloud.com/products/ps-12120), and closer to $25 from no-name brands on Amazon. 2. Modules to charge LeadAcid are so cheap, they don't even make them. This specified PS-battery hsa a 13.5V to 13.8V "standby" voltage, meaning that 13.65V from the Solar Panel is all you need to have a UPS. Connect the 13.65V source from the Solar-panels to the + and - leads of the 12V battery, and volia. You get 13.65V when solar is available, and 12V from the battery when the solar cuts off. The end. Isn't that easy? 3. Grid-tie should be similarly easy, though I don't have too much experience with it myself. IMO, buy a professional AC->DC converter, probably at 19V or some other suitable voltage and then get a DC-DC buck converter to go from 19V to 14.35V, and then a diode (0.7V dropoff) to hook up to your batteries in parallel. You'll also need a diode in your Solar-panels cause you don't want your Grid-tie system "charging your solar panels" (that'd probably create a fire and/or damage them...). Hobbyists should NOT deal with main-power themselves, but there's a gross-many number of AC-to-DC converters available from $10 to $40. 4. Don't battery balance. Just buy bigger batteries. If 12Ah isn't enough, buy a 20Ah battery. If 20Ah isn't enough, buy a 33Ah battery, etc. etc. The limit is whatever you're comfortable with (the bigger batteries give more current which can be more dangerous)

louwrentius 3y ago
Don’t do lead acid. I say this from experience. Lead acid charges too slow. You want a battery that can capture every ray of sunshine - especially with intermittent sunlight - and charge at full speed. Lifepo4 can do this. Lead acid can’t.
- dragontamer 3y ago
  A 12V 12Ah battery is 144Wh. I'm fairly certain that Lead-acid can accept 0.3C, and you're right in that a 60W panel is slightly more than the 43W that Lead-acid can accept. But sizing 12V 20Ah (ie: 240 Wh), and now 0.3C is 72W or 6A of safe charging (less than 0.3C). ------------- See #4: just buy a bigger battery if you need a bigger battery. Bigger battery provides more power and energy proportionally for the chemistry. And a 12V 20Ah lead-acid is just $40 on Amazon. --------- I guess your overall point is that "Trickle-charge" isn't enough for Solar? Which is something I admit I didn't think about earlier (trickle-charge just doesn't send as much current to the battery due to the lower voltage). But I guess there's a "simplicity of circuit" advantage of trickle-charging. A more complex state-of-charge circuit (likely a microcontroller keeping tabs on the battery) is needed to safely send 0.3C down to the Lead Acid. EDIT: On the other hand, having your "charge controller" just be like, two power diodes, is a gross benefit to simplicity. Its something you can do with Lead-Acid that's fully impossible with LiFePo (and is why LiFePo4 needs expensive charge controllers to work). For hobbyist purposes, there's something to be said about using simpler technologies, even if their specs are worse (and I'm not entirely sure if Lead-Acid has worse specs than LiFePo4 in this use case).

louwrentius 3y ago

I started out like the author of the blog post with a 60Watt panel and a cheap non-mppt solar controller. My balcony orientation was shit and that didn’t work out. Since then I upgraded “quite a bit”… The challenge is more difficult than it seems. A raspberry pi 4b does ~3.4 watt idle so that’s 84 watt-hour per day. This may not sound like a lot, but for battery-powered devices it quite a bit. Microcontrollers can run months on that amount of energy, but they aren’t as convenient as the Pi. The 12v 12ah battery used, contains 144 watt hour. Only enough to cover less than two full days with little to no sunlight. The 50 watt panel is already small, but the non-mppt controller makes it even more inefficient. With good sunlight, the panel can easily run the pi and charge the battery during daytime. The “real” challenge is to keep the Pi online during days of overcast weather. A 150 watt panel may only do 4-8 watt under those circumstances and that’s not enough. But I always love these projects none the less.

dragontamer 3y ago
I know Rasp. Pi is all the rage these days, but if I were to make a solar-server, it'd be off of Beaglebone Black instead. * Beaglebone Black uses slightly less power and is slower than Rasp. Pi. Lower power is a big benefit however. * Beaglebone has the "Programmable Realtime Unit" (a microcontroller-like hard-realtime subsystem with GPIO pins). * These PRU subsystems can probably (???) be utilized for the battery-state-of-charge and possibly even provide a software-control for mppt solar chargers. Theoretically of course, but... I have to imagine that a Cortex M4 has enough MHz to handle these kinds of calculations. * If not, the Beaglebone Black has a built in ADC that could be used as the basis of power calculations. Worst case, add in a proper uC to handle power / build my own MPTT / Battery charger.
- tiagod 3y ago
  At least on MCUs, being slower can counter-act the lower active power, as you'll take longer to do whatever you want to do and go back to deep sleep. I'd like to know if this also happens with these SBCs, or if they even have any aggressive power saving features that can be employed.

znpy 3y ago

I remember tuning down the clock speed of the raspberry pi cpu when playing with flashrom, maybe that could also be used to reduce its power consumption? Not sure what rPi version the author is using, i think i remember i was using the original one ? It was 700mhz by default i think i clocked down to 200mhz and 50mhz. Granted, it was mostly unusable (bye bye openssh) at 50 mhz.

folmar 3y ago
There are also a lot of different optimizations and their impact discussed in https://ieeexplore.ieee.org/abstract/document/7811590 https://ieeexplore.ieee.org/abstract/document/7811590

sleepytimetea 3y ago

I have recently gone down the solar panel rabbit hole too but I never tried the "fancy portable mini panels" cause they seem to weak and overpriced. Instead, I acquired two large 140W panels that had been removed from an old installation for the princely sum of $20 (USD). After struggling with trying to find connectors that I could pair with the MC3 connectors (remember, these panels came off an old installation), I bought a dozen MC4 and just cut off the old MC3 connectors...MC4 is the way to go these days. Next came the surprise at finding out about "MPPT" - in all my years looking at solar panels on roofs, I never knew they were so finicky about voltage vs current curves...real MPPT charge controllers start at $70 for a Victron 15Amp and I decided to try my luck with Chinese sellers on AliExpress...turns out the charger was a PWM fake sold as a MPPT charge controller. Anyway, I also needed a battery since the charger doesn't work without a battery source. That's another saga but short story - I built my own 3S battery pack out of 18650s.

louwrentius 3y ago
What are you planning to power with your solar setup? You may be aware and this is 100% redundant but lifepo4 is a safer chemistry and small cells are becoming more affordable by the day. If there’s no risk of those 18650s overheating it’s fine I guess.
- IshKebab 3y ago
  18650 is just a shape. You can get LiFePo4 18650s.

gh02t 3y ago

I've been looking for the same sort of mini charge controller with grid backup that is mentioned in the problems and challenges also with no luck. Is this really not a product that exists? I've long wanted to do a sort of small scale migration to solar. Offset the load from my home server with a few solar panels and source any excess power needed from the grid while also charging the batteries/providing power from solar when the sun is up. I could probably engineer something myself but doing things right on high power circuits is not worth the effort/risk. Any suggestions?

colechristensen 3y ago
Just grid tie a few panels with microinverters (one small independent inverter per panel), and forget the battery. Recommended Enphase https://enphase.com/ https://enphase.com/ As long as your solar capacity production is not often more than your usage at the same time, batteries won’t be of any particular use … they have to be fairly large to have any great utility in your home anyway, battery backup and solar production are orthogonal goals until you are producing a lot of power. If you do want battery backups on a small scale, just get a UPS the same as you would without solar.
turtlebits 3y ago
Look for "solar inverter" - Growatt, MPP Solar are popular brands - they will come with inverters though, but have grid backup/passthrough.

roughly 3y ago

I did a similar project a while back with a Pi Zero W, which has the perk of maxing at like 1w. Still, my takeaway was "whatever you think you need for a panel, triple it, and whatever you think you need for a battery, multiply it by like 10." Cloudy days tend to come together, the power output for your panel will drop off way more than you think, and your battery won't charge nearly as fast as you're hoping.

rambambram 3y ago
> Cloudy days tend to come together You probably have no idea how philosophical this sounds.
- avidiax 3y ago
  It's also a mathematical tautology. There's only a few ways to evenly space the cloudy days. There's exponentially more ways to clump them.
yomlica8 3y ago
I've been thinking about trying to make a game/trail camera out of a Pi Zero which is a similar sort of problem. My idea it was only on part of the night I wouldn't need much power. But this thread is making me think things are going to be more complicated!
- roughly 3y ago
  I think you’re better using simpler hardware for this - adafruit sells a dozen different varieties of microcontroller board with Wi-Fi, all of those will be much easier to keep powered.

vanillax 3y ago

Solar Shed mega hobbyist. Finally a HN topic I can contribute to. I've spent last few years trying to build out my solar shed mainly to have auxilary power to charge weed whacker, leaf blower, power lights, power a camera, etc. Just basic 12v power. The number one lesson is to 4x your power needs. 4x your watts and 4x your battery amp hours. Don't cheap out on charge controllers. There's never enough sun light to fully charge your batteries and your panels are never at the right angle to maximize sunlight. Especially in less solar friendly areas like Michigan. Lead acid is fine if you over compensate with panels. Lead acid will last longer in the cold than LiFEP04. Die hards will say you cant charge LiFEP04 in winter but I do. I accept the fact that my batteries will degrade faster. When you can build your own packs, its a lot easier to find which single set of cells went out and cheaper to replace. Its a risk I accept. If you are starting out, get a 200 Ah/hr LiFEP04 battery and 400 watts solar. Its a very good starting point for 12v and gives room for expandability. Avoid foldables. Avoid Harbor Freight. Avoid Jackery Solar Panels. You need Quality Panels. If you wanna learn more, check out Will Prowse https://www.youtube.com/@WillProwse https://www.youtube.com/@WillProwse

carapace 3y ago
> Avoid Harbor Freight. Why? I'm just starting out with solar power and I got a 100W panel set (4 x 25W with a charge controller) and 35Ah battery from HF just to try it out and so far it seems fine.
- tiahura 3y ago
  The cheap junk on Amazon is much better.
  - eyegor 3y ago
    This is not generally true. Amazon is plagued by drop shippers now and as a result most of their solar junk is many years old warehouse stock. Harbor freight tends to be better. Ex: https://youtu.be/W-fgI6Kyy2I https://youtu.be/W-fgI6Kyy2I
- naikrovek 3y ago

DavidGetchel 3y ago

Nice to see solar projects like this. We have 4 solar setups on the property currently. One for main house. Another for the pump house. A temporary garage setup and one for a studio. A good way to learn to manage your own power generation and setting up systems.

daotoad 3y ago

There are some really handy databases with detailed insolation data available for sizing your solar projects. https://nsrdb.nrel.gov/ https://nsrdb.nrel.gov/ is one place to find this stuff. Years ago I worked on environmental monitoring systems for snow and ice management. One of the things I did was help spec out solar systems for remote installations in Alaska and Canada. The basic issue was "How much sun will there be in a typical summer?" combined with "How much power can we store in our batteries?" and "How much power can we draw from the lead acid batteries without them freezing?" (who knew that a discharged battery freezes at a lower temperature than a charged one? I sure didn't). It's a pretty straightforward process, actually. The company I worked for had a pretty detailed spreadsheet to help with bids, but essentially you: 1. look up the insolation data for the install site in one of the databases with that info (like https://nsrdb.nrel.gov/ https://nsrdb.nrel.gov/) 2. compute rate of loss over time for your installation (power consumption +_self-discharge) 3. look at the battery datasheets to determine how much you can discharge the battery at any given time based on anticipated temperature ranges 4. work out what your tolerances are for temperature and insolation variability Usually there would be a couple of options that were in the cost sweet spot where you had a bit more solar and bit less battery or vice versa. Some of these sites were up around the arctic circle, so battery was pretty important in those cases, since you're looking at months without appreciable sun combined with low temperatures. This wasn't even the major part of my job, but it was a small company and I wore a lot of hats.

turtlebits 3y ago

IME, a 50w panel is not enough. You'll never get full output, even in perfect alignment and a sunny day. I probably get an average of 70% or less from my 4x250w panels.

frankreyes 3y ago

> This means that the solar power cannot provide enough power to charge the battery, although I am using a 60W solar panel for ~5W Raspberry Pi. Just because there's "light" doesn't mean the panel will produce power. The sun has to shine BRIGHTLY. This is why solar power in Berlin or London is a waste of resources, because the sun doesn't shine BRIGHTLY there.

pjc50 3y ago
Objectively false: my system in Scotland (56 north) works quite nicely, and even on cloudy days you get a considerable amount of power. The power output is simply proportional to brightness. It is, after all, just a big flat photodiode.
- frankreyes 3y ago
  Considerable does not translate into 100% efficiency. This is what the original article means. In your specific case you had to over provision your solar installation compared to , for example, Egypt.

hggh 3y ago

It's down right now. Archived version: https://web.archive.org/web/20230822000517/http://blog.rfox.eu/en/Hardware/SolarPi_experiment_2_Finally_something_that_works.html https://web.archive.org/web/20230822000517/http://blog.rfox....

GoToRO 3y ago

"the Raspberry is actually powered from the USB output of the controller" I don't know about his controller but these cheap controllers will power the USBs even on low battery. They will kill the battery (he even mentions this bellow). The right way to have USB output is to connect a car charger to the 12V output of the controller and then connect your load to that charger. That 12V output is cut when the battery is low and reconnected after it is charged. These voltages can be set in the controller. This way the battery will never discharge so much that the controller doesn't even recognize the type of battery (6V, 12V)