Solar powered project advice

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Hi, I have a metal bike shed which suffers from condensation inside. The concrete base probably needs a damp course, but let’s leave that aside for now.

I bought a solar panel and fan and fitted them to the shed to try to extract the damp air. The panel is about A4 size, specced as 18V, 10W. The fan is about 14cm square. Actually it came with two fans, one can pull air and the other can push, to generate air flow. For now I have fitted just one as an extractor.

So today, with medium sun at about 11.30am, the fan spun well, but had to be started with a push. It looks as though it will only self-start with really strong sunshine.

What I would like to do is set up a rechargeable battery which is charged by the panel, and then powers the fan at a set time every day for an hour or so, e.g. at dawn, or when the temperature change is biggest.

So I would need A) a charging circuit, and B) some kind of programmable low-energy microcontroller which can turn the power to the fan on and off according to a pre-programmed schedule.

The big question: is such a setup possible with a small solar panel like this? If so, any recommendations on which parts to use?

I did find battery powered solar extractors for sale, but they were out of stock until next year and had manual on/off switches. So I presume it might be possible in theory.


Start here to do some calculations:

  • Fan draw W -> how long you will run it = amp hrs needed
  • Solar output = size / number hours sun = amp hrs provided
  • Battery needed = Amp hours you need to store * 2 as you never want to discharge over 50%

If you are charging a battery from a solar panel you basically need a solar charge controller or it drains in reverse when it’s dark, or you risk overcharging the battery…

Hope that helps,
Bring your stuff to electronics night tomorrow 7pm!?

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That’s really useful, I will use that site to do some sums… Thanks.

I’ve bolted the solar panel to the shed so I can’t bring it in unfortunately :slight_smile:

No worries - come by and have a chat if you like! Find out the watts of the fan(s) and you should be able calculate what you need in terms of specs…

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Well I ordered a few bits and pieces.

  • Solar charge controller
  • 12V 5AH Battery
  • Pololu step down buck controller 12V -> 5V, for powering arduino from battery
  • Arduino bare-bones parts, for low energy operation. (Basically an Atmega328 and a few other bits.)
  • Humidity and temperature sensor

We’ll see how it goes! I will need to figure out when to trigger the fan. I think condensation will happen when there is a significant temperature drop, so I can use the sensor values for that.


You can work out dewpoint from humidity and temperature