Solar powered project advice

Tags: #<Tag:0x00007fa496eaa5f0> #<Tag:0x00007fa496eaa4b0> #<Tag:0x00007fa496eaa370>
#1

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.

#2

Heya!

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%

https://www.batterystuff.com/kb/tools/solar-calculator.html

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!?

1 Like
#3

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:

#4

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…

1 Like
#5

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.

2 Likes
#6

You can work out dewpoint from humidity and temperature

2 Likes
#7

I got my solar powered shed finally installed a few weeks ago.

The barebones arduino triggers the fan using a transistor switch circuit. My arduino programme checks for the humidity and temperature every 10 seconds and if the reading is within 0.5 degrees of dewpoint, it switches on the extractor fan for 20 mins, followed by a pause of 30 mins. It is allowed to run up to four times every 24 hours.

The fan spec says it can shift 70 cubic feet of air per minute, which is a bit more than my shed contains.

Seem like reasonable settings? It seems to be working pretty well so far. I think the fan is mostly running in the early hours, then the battery recharges late morning, early afternoon.

One thing I wondered about is how to log fan runs without adding a lot more hardware and using a lot more energy? Any thoughts?

The whole thing is extreme overkill but it was fun getting it up and running.

1 Like
#8

Nice work! I think logging will give you the answer as to how quickly the humidity drops. I would go with an SD card as you already have SPI hardware https://randomnerdtutorials.com/guide-to-sd-card-module-with-arduino/ Make sure to provide the right voltage.

1 Like
#9

That looks perfect, thanks.