This is a description of how I built a solar power system
- Solar Cells. I bought 40 12.5cm x 12.5 cm panels from eBay, costing about EUR80. Each panel generates about 3W at 0.5V, so if I use 40 of them I should get around 100W on a good day, at around 15V or 20V, sufficient to push electrons into a 12V battery. These cells are not sealed in epoxy, so while they are cheap and very light, they are very brittle, and need to be mounted on a stiff board
- Solar Controller. This cost about EUR10 from eBay. It is for regulating the charging of lead acid batteries from solar panels. It has some LED indicators
- Ammeter / Voltmeter. This was EUR3 from Ebay and allows me to see what is coming out of the panels
- Lead acid battery. This was EUR18 from a local electrical shop. It is suitable for alarms, and has a capacity of 7 Amp Hours. This is a "deep cycle battery" meaning it has a small number of thick plates, suitable for slow charge and discharge
- Plywood board and some clear plastic school book cover or polythene sheet
The battery has a capacity of 7Ah. This means it will supply for example 12W for 7 hours, or in my application, could power a 3W LED lighting system for 28 hours, although it would be a bad idea to run down the battery too much as it causes damage. Lead acid batteries always take a few hours to charge, and for this small battery, that means I can charge at a maximum rate of 1 Amp. At 12 V that means a rate of 12W. The panel can supply 100W maximum, so a battery of greater capacity might be more suitable for this panel and for my lighting application.
The panel is made from a pieces of plywood. I soldered the cells together using a special metal ribbon for solar cells. Each piece of ribbon joins the backside of one cell to the front side of the next, so that the cells are arranged in series. There are two tracks on each cell so I soldered both tracks. The cells might crack as they are very brittle, so it's a good idea to solder all of the terminals on the cells for redundancy. You can see in the picture below that I wasn't too careful and broke some of the cells.
The panels are covered with a clear plastic intented to cover school books. It is attached to the back of the board by duck tape. This is necessary to protect the wood and the panels from the elements.
I made a control panel to mount the controller, ammeter / voltmeter and battery. Here you can see that in the shade on a sunny October morning in Ireland, the panel is generating about 1.5W. On a cloudy afternoon with direct sun it might produce 3W.