In off-grid situations it’s easiest to start from the power requirements, but this might also be the most difficult since most people have no idea how much power is needed. The basics are the same for a small or a big project. It’s always good to start small ifyou aren’t that familiar with DIY solar projects.
A small shed/storage building will be solar powered:
- Some interiour and exteriour lighting
- Small low voltage accessoires like a radio, a laptop or a phone charger
Daily power use:
- Interiour lighting: 12V LED approx. 30W during 3 hours
- Exteriour lighting 12V LED approx. 10W (flooder for example) during 1 hour
- Accessoires 12V, 50W for 2 hours
This makes a total of 30×3+10×1+50×2 = 200Watts of daily use.
As mentioned before it would be nice is this is maximum 20% (group 27 batteries have this capacity.) of the battery capacity. So it would be nice to be able to store about 1000W. An 12V/85Ah battery can handle 1020Wh (12×85) so would be sufficient. Most
This battery should get a charge current between 1/12 an 1/8 of the Ah value,
In this case: 7.1 to 10.6 Amps.
A so-called 12 Volt solar panel (actually they supply 18V, but are used for charging 12V batteries) of 130 or 150 Wp would do.
Material list for this example:
- Battery 12V/85Ah
- Solar panel 130 or 150Wp
- Charge controller 12V / 10A
For testing you might just have a used car battery laying around that is a bit smaller, like 60Ah. In that case just use a smaller 100W panel (get it on Ebay for example)
The schematics would look like this. However the circuit breakers (must be DC Breakers) can easily be replaced bij regular glass orfuses. The advantage of a breaker is you can also use it as a switch. The charge controller also protects the output this prevents the level from the battery becoming to low. If the battery voltage drops too low the output is switched of.
Download the PDF
So what about the yield of the panel ?
In this example we talked about 200Watt usage. But taking out 200Watt means we have to put in about 50% more, so 300Watts. A 130Wp panel handles this in about 3 hours and 25 minuts of sunshine hours with a regular charge controller. An MPPT controller does better. Remember daylight also charges the battery just less than direct sunlight.