Solar system for charging tablets at rural African Schools

Hi all,
I work for onebillion, a nonprofit educational software publisher. We make apps to teacher maths to young chldren around the world. We want to bring this transformational learning to every child in Malawi via our oneclass initiative.

Getting to the point, we have a locally-made cabinet in each school with a 20A Tracer MPPT charge controller and 2x 100Ah 12V lead-acid batteries in series. This is hooked up to a 200W panel on the roof. At night, this system charges 32 iPad Minis and continuously powers a Raspberry Pi with WiFi and 3G.

While the system works well, it's not easy to scale to other schools quickly, which is the stage we're at now.

So…

We're making a wall-mountable unit (essentially a 12U server cabinet) with everything built in. We think it's right to go for a LiFePO4 battery due to weight, efficiency and lifespan.
Could any of you fine people suggest a suitable combination of parts for this:

- 24V 40Ah LiFePO4 battery + BMS
- 20A MPPT charge controller suitable for the battery (I've seen specific Lithium charge controllers)

We'd also like to be able to charge the battery from an AC power brick as an option.
While we want reliable parts, cost really is a major factor.

Any ideas much appreciated!


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Comments

  • solar_davesolar_dave Solar Expert Posts: 2,343 ✭✭✭✭
    Re: Solar system for charging tablets at rural African Schools

    If you have utility power then use it to charge the devices, off grid solar is going to be way more expensive.
  • onebilliononebillion Registered Users Posts: 2
    Re: Solar system for charging tablets at rural African Schools
    solar_dave wrote: »
    If you have utility power then use it to charge the devices, off grid solar is going to be way more expensive.

    95% of Malawian schools have no grid electricity, hence why I'm asking for help on this forum.
    The AC input is for the 5% that do.
  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Solar system for charging tablets at rural African Schools

    None of this appears to be a diy project, so in that case, I'd look into these guys that can provide the lifepo4 batteries along with other infrastructure, and possibly end-user support:

    http://www.elitepowersolutions.com/packages.html

    While primarily directed towards EV users, they have some turnkey stuff, and possibly some end-user support.

    Just be prepared for sticker shock up front.

    On a personal charging standpoint away from school, perhaps something as simple as the folding panels from Anker might do (careful there is a lot of junk out there - so only Anker and Powerfilm for me!) :
    http://www.ianker.com/support-c7-g263.html

    While this will charge an iPad directly, you probably don't want to do so in direct sun, so tack on a larger li-ion battery (these are NOT lifepo4, but usually linmc) to be charged separately and used whenever needed. Again, from the Anker Astro line:
    http://www.ianker.com/External-Batteries/category-c1-s1#2nd%20Gen%20Astro

    Just keep your expectations about lifepo4 in line with reality and sometimes mere availability. Don't get suckered into buying off-brand junk. GBS, CALB, Winston, are the major players. Think carefully as you may find that merely replacing your existing batteries a much better deal.
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