AC or DC
Decide whether to use existing alternating current (AC), which requires an inverter, or direct current (DC) power for solar lighting--a major decision. Setting up lights in an outbuilding or small cabin where the necessary cable for connection is limited is ideal for DC, because no expensive inverter is needed for DC bulbs, and it also dampens the downfall of DC requiring more expensive cables. Commercial solar photovoltaic panel kits are available that use LED lights, which can light a small outbuilding for a couple of hours at a time.
Converting to Solar-powered Light
To power one or two lights, get DC, light-emitting diode (LED) or compact fluorescent lamp (CFL) bulbs and a small solar array with a rating of about 10 watts. According to the U.S. Department of Energy, LED's "offer better light quality than incandescent bulbs, last 25 times as long and use even less energy than CFLs." Converting all lighting to solar in an average-size home will likely require an inverter and a charge controller, which can get expensive. If you are running the rest of your electricity needs from your utility power source, get a qualified electrician to connect your solar power to your meter.
Solar Power Needs
Determine the amount of watt hours per day needed by multiplying the number of watts by the average hours used per day. Using an average solar insolation map for your area, find the average number of hours of sunlight expected and divide this number into the number of watt hours per day needed for your solar light(s). This will total the watts that a given number of photovoltaic cells need to generate to operate the lights.
If the lights must operate on demand, either a grid connection or a battery will be necessary. The size of the battery is based on the amp hour rating. Different methods are used to estimate the size of the battery bank needed for solar-powered lights, though the calculation is generally based on watt hours per day, depth of battery discharge, ambient temperature of where the batteries will be stored and the total system voltage.
It can be a daunting task to convert the lighting of an entire home to solar power. Start small in order to learn the ins and outs before attempting to do a full-scale change. Of course, if you have the money, you can always hire professionals to do it all for you.