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I'd like to run my raspberry pi via solar energy. I have a 12v 20w solar panel with the following charge controller:

https://www.amazon.co.uk/gp/product/B0197ZNWLM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

The following 5v regulator:

https://www.amazon.co.uk/gp/product/B00RGK5G3I/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

My problem is I don't know what kind of battery to use for this set up.

Can anyone suggest and explain the kind of battery that can supply power to the raspberry pi and at the same time be charged from the solar charge controller?

Many thanks,

Paul

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closed as too broad by Scott Seidman, Andy aka, Daniel Grillo, uint128_t, KyranF Apr 29 '16 at 20:43

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ So, you have a charger. Because you have a charger you then know what battery type you need. It's probably written somewhere in the product info. Only you have any idea where you live so only you can work out how much sunlight you are going to receive and what down time is acceptable. However, you are asking to know what kind of battery you can use. Will it surprise you if I vote to close this question? \$\endgroup\$ – Andy aka Apr 29 '16 at 16:21
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Most solar charge controllers are for 12-24v lead acid batteries, and I suppose that yours is also intended for this process. Therefore, you can use pretty much any 12v-24v lead acid battery you choose.

If you want a battery that will be able to power your raspberry pi throughout the night as well then a proper sized battery must be picked.

A Raspberry Pi uses around 700mA maximum, but to be safe lets assume it will draw 1A at 5v. Since we are most likely going to be using a 12v battery, we need to figure out how much current it will draw at 12 volts, which turns out to be 0.42 amps. Assuming the solar panel is only on 8 hours a day, we need to have a battery for the other 16 hours. That means we would roughly a 7Ah battery which are pretty common. (If you have questions about the calculations then comment, because I don't know how to use the equation thing on this site)

Next is to check that the amount of sunlight that your panel gets daily is enough to power the pi and battery for the night, again to be safe let's say 8 hours. Since your panel is 12v and 20w, it gives out about 1.7 amps. Subtract the 0.42 amps for the raspberry pi current and there is 1.28 amps left over for charging the battery, over an 8 hour period, it will put in 10.24 amps. This should be more than enough and it gives headroom for cloudy days and winter.

So in conclusion, you should use a 12v 7Ah lead acid battery hooked up to your solar system and regulator, which will allow you to run your pi 24/7 with a bit of headroom for inefficiency and weather conditions.

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    \$\begingroup\$ I would say there is almost zero headroom for inefficiency and weather. The rated 20W at 12V is probably extremely good conditions, I would down-rate the capability to an average of half of this. You can never predict how long a bad weather spell will last for, so nothing will really help if there is a sustained overcast condition for a week or two. But if reliability is key, I would double the battery capacity. \$\endgroup\$ – KyranF Apr 29 '16 at 15:30
  • \$\begingroup\$ Well, I meant under optimal conditions there would be a little headroom. For example a cloud passing over for an hour or two, or if the circuit has only something like 85% efficiency it would still work. \$\endgroup\$ – Laessen Apr 29 '16 at 15:41
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    \$\begingroup\$ You also failed to allow for shitty efficiency on the buck converter, it's safe to assume 80% efficiency on that. So 0.42A + 20% for conversion losses. \$\endgroup\$ – KyranF Apr 29 '16 at 16:13
  • \$\begingroup\$ @Tullio_IRL If you found my response helpful please upvote it. \$\endgroup\$ – Laessen Apr 29 '16 at 19:40
  • \$\begingroup\$ @KyranF I think what you are saying is that he should increase both his battery size and solar array because it is barely able to power it, and I don't disagree with that but his system (with the limited info we know) should be capable as it is. \$\endgroup\$ – Laessen Apr 29 '16 at 19:43

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