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Solar Power

This is a description of how I built a solar power system

Materials:

Description

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.

Scaling

It is interesting to see how much it would cost to build a larger system. For example, for EUR1000, one could spend EUR400 on panels and EUR600 on batteries. For that investment, one could have panels capable of supplying maximum 400W. One could buy 6 x 70Ah batteries, costing about EUR100 each, and storing a total of 420Ah. That storage is equivalent to 5kWh or EUR1 of electricity from the grid.