Solar panels generate electricity from the sun and send that electricity in the form of direct current (DC) to the system. Solar panels are usually either monocrystalline, polycrystalline, or amorphous silicon (also referred to as “thin film”). Monocrystalline panels are made out of pure silicon wafers, and have an efficiency of around 18%, compared to around 14% for polycrystalline and 9% for thin film.