The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt.

One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions; such as, temperature specified.