To calculate land use requirements for different kinds of power production, it is essential to know the relevant area-specific power densities. Smil estimates that the average area-specific power densities for biofuels, wind, hydro and solar power production are 0.30 W/m2, 1 W/m2, 3 W/m2 and 5 W/m2, respectively (power in the form of heat for biofuels, and electricity for wind, hydro and solar). The average human power consumption on ice-free land is 0.125 W/m2 (heat and electricity combined), although rising to 20 W/m2 in urban and industrial areas. The reason for the low area-specific power density for biofuels is a combination of low yields and only partial utilization of the plant when making liquid fuels (for instance, ethanol is typically made from sugarcane's sugar content or corn's starch content, while biodiesel is often made from rapeseed and soybean's oil content).