Unfortunately, this energy flux is not quite as useful as it might at first appear. First, much of this solar flux falls on the oceans that cover roughly three quarters of the surface of the planet. The most efficient commercially available solar power collectors are only 28.5% efficient in producing DC electrical power so a space-based solar collector of this type can harvest only 380 watts of power, and when mounted at the surface of the earth a similar type solar array can harvest no more than about 280 watts of power. These highly efficient solar collector cells rely on expensive semiconductors using Germanium, Gallium Arsenide and Gallium Indium Phosphide, each of which absorbs solar energy at specific sets of wavelengths.