Buying used solar equipment can be a reliable and inexpensive option, but the buyer should make a physical inspection before purchasing. Solar panels should be free of obvious damage such as cracks and condensation under the glass.
Little data exists regarding the longevity of a solar panel because so many original panels are still in use. Used solar panels typically put out up to 10 percent less power than new panels, as some degradation of equipment is caused by sunlight. Stored panels that have not been in the sun show little to no degradation.
A used solar panel should be tested with a multimeter in full sunlight to ensure functionality. Used equipment, such as batteries, is less reliable than panels and should only be purchased from a reputable source.