Since some batteries are rechargeable they are more likely be used in conjunction with another form of alternate power, such as windmills or solar collection. Geothermal power is generated below the Earth's surface wherever water comes in contact with heated rocks. When the heated rocks are located close enough to the surface, we can drill and pump the hot water and steam to the surface where it is used to generate power. Engineers will pump water into the ground if heated rocks are present, but no water. Bolivia, Iceland, Italy, Japan, the Philippines, New Zealand, and the United States have developed and use geothermal power plants to produce energy.
Spacecraft use fuel cells to produce electricity by combining hydrogen and oxygen.
While the fuel cells are extremely efficient, the current technology is expensive. Solid and liquid wastes can also provide energy. By burning trash we can produce heat energy and electric energy and reduce landfill mass at the same time. Many paper and lumber mills use the waste wood that is not useful to fuel boilers which in turn generate steam for running machinery in the plants. Liquids like sewage can be used to produce methane, and the use of a process called bioconversion converts organic animal and plant waste into liquid fuels such as methanol.