Energy is the foundation of life. We can no longer afford to treat energy generation as the vague realm of benign public utilities and powerful corporations beyond our control. We must educate ourselves about this fundamental part of life and society, and literally retake the power for the people. This article gives a brief overview of renewable energy sources. Renewable energy currently constitutes 3.4% of US total energy supply, the vast majority of which is generated by biomass.
Energy from the sun is the foundation of renewable energy. Technically, sunlight, wind, and biomass are all forms of energy from the sun. Although both solar and wind are extremely promising renewable energy sources, they account for only 0.4% of the US primary energy supply, and a smaller fraction of our electricity generation.
Photovoltaic (PV)cells use the sun\’s energy to generate electricity; the electricity can be used directly, to charge batteries for later use, or to generate hydrogen from water by electrolysis/ PV cells are only about 15% efficient; more research must be done to increase the efficiency and make PV generated electricity less expensive. PV cells, particularly when paired with hydrogen fuel cells, hold great promise for a decentralized, clean energy system.
The sun can also be used to directly heat water, buildings, and to provide ventilation.
Heat from the sun warms air, causing the air movement we call wind. Wind energy is very successful in several European countries, especially Denmark, where it accounts for 3.5% of their primary energy. More than 75% of Danish wind turbines are owned collectively; turbines are operated singly or in small groups. Denmark also has a number of off-shore wind farms. In contrast, the US and the UK have concentrated on large land-based wind farms which have not been as successful.
There are a number of tricky issues with wind turbines, such as the maintenance associated with so many moving parts and buffeting by strong/varied wind speeds. Wind power has essentially no emissions. It is estimated that 30% of European electricity demand may be met by wind by 2030.
Hydrogen is a good way to store energy. The gas can be produced from water by electrolysis powered by photovoltaic panels or wind turbines, or from natural gas, methanol or biomass with added heat. Hydrogen can be recombined with oxygen in a fuel cell to generate extremely clean electricity, or burned as fuel. When coupled with wind/solar technology, hydrogen is a potentially very decentralized, clean way to generate electricity and heat.
Caution: Hydrogen could also be used in a way requiring a large transportation infrastructure similar to that of natural gas (the \’hydrogen economy\’). This is the industry\’s goal.
Biomass involves using organic matter (manure, dedicated energy crops, agricultural waste, liquid/solid/gaseous fuels (like biodiesel, hydrogen, ethanol, etc.), heat and chemicals.
Biomass accounts for 3% of both US total energy supply and electrical supply. Biomass emits little carbon and can reduce nitrous and sulfur dioxides and other air pollutants.
Concerns: What kind of land should be dedicated to producing energy crops? Also, organic matter can be used to produce certain plastics and chemicals that would be superfluous in a truly sustainable society (think Archer Daniel Midland, DuPont, etc.)
Geothermal energy employs steam or very hot water coming form the earth to power turbines and generate electricity.
Geothermal energy meets only a tiny fraction of the US electricity demand.
Current technology is very reliable (>95%) and emits almost no carbon. Geothermal energy is not cost competitive with current fossil fuel technology, because the US government is not interested in investing in technology/exploration. Total possible generating capacity is not know but estimated to be large with the right technology.
Folks like to talk about capturing energy from tides, waves, magma within the earth, and other wacky sources. Right now these are not technically feasible options, and will not be needed if we commit to using less energy.