The conversion efficiency of energy is the ratio of the amount of energy produced by conversion to the amount of energy consumed or the available energy of the equipment. The sun emits a lot of energy in a very wide spectrum, but we can only rely on photovoltaic technology to capture a very small part of that spectrum. Today, commercial PV systems have conversion efficiencies of between 7 and 17 percent. By comparison, a typical fossil-fuel generator has an efficiency of around 28 percent. Under laboratory conditions, however, some photovoltaic cells can convert up to 40 percent of the energy contained in sunlight into electricity.