How Solar Yard Lights Work
A solar yard light uses standard solar cells in a very straightforward application. A single solar cell produces a maximum of 0.45 volts and a varying amount of current depending on the size of the cell and the amount of light striking the surface. Therefore, in a typical yard light you need four cells wired in series in order to produce 1.8 volts and a maximum of about 100 milliamps in full, bright sunlight.
The solar cells are wired directly to the battery through a diode (which prevents the battery’s current from flowing back through the solar cell at night). The battery is a completely standard AA Nicad battery.
A battery like this produces about 1.2 volts and can store a maximum of approximately 700 milliamp-hours. During the day, the battery charges, reaching maximum charge except on shorter winter days or days when there is heavy overcast. At night, the solar cells stop producing power while the photoresistor turns on the LED.
Thanks howstuffworks.com for this great solar energy info.