Renewable energy is a source of power generation that does not rely upon the burning of fossil fuels, but rather the ‘fuel’ is a natural resource that is not only plentiful and freely available, but replenishable. Most people these days are familiar of renewable energy, and in the eco-conscious era in which we live they are aware of the suite of benefits an energy mix that’s higher in renewable energy brings: reduced pollution of water and air, elimination of carbon emissions that are causing climate change, and a general push towards environmentally-friendly and sustainable energy use.
However, when discussing renewable energy most people will simply think of solar energy and wind energy. After hydropower, solar and wind are the most common renewable energy sources used across the United States, so it’s not surprising these are the renewable sources with which people are most familiar. According to the United States Energy Information Administration (EIA), hydropower, solar energy, and wind power account for 15% of all U.S. electricity and 89% of all U.S. renewable electricity. While that demonstrates just how important these energy sources are, the data show that there were 73 billion kilowatthours (kWh) of renewable electricity generated in the United States in 2018 from other renewable energy sources; that’s enough energy to power over 6.5 million U.S. homes for the year. So while it’s understandable hydro, solar, and wind are the main events, the other renewable energy sources out there are contributing a whole lot. So what are these other less discussed renewables?
The same EIA data shows that geothermal power was used to generate 16 billion kWh of electricity in the United States in 2018, 0.4% of all U.S. electricity. As defined by the International Renewable Energy Agency (IRENA):
Geothermal energy is heat derived within the sub-surface of the earth. Water and/or steam carry the geothermal energy to the Earth’s surface. Depending on its characteristics, geothermal energy can be used for heating and cooling purposes or be harnessed to generate clean electricity.
The advantage that geothermal energy has is that the heat is already coming from the earth, all we need to do is drill down to tap into it! But the downside is that not every part of the planet is suitable for geothermal energy. Some areas don’t have the natural heat nor the ability to drill down, and because of this geothermal energy is a sustainable energy source that is terrific for those who live in appropriate areas to go green, but it’s not widely scalable as a renewable solution across the globe.
Biomass energy is an umbrella term that covers numerous types of renewable energy generation. While the EIA data show biomass totaled 58 billion kWh of electricity generation in 2018 (good for 1.4% of total U.S. electricity), that’s broken out into wood (41 billion kWh), landfill gas (11 billion kWh), and municipal solid waste (7 billion kWh).
Generally speaking, biomass (according to EIA) is an organic material that comes from plants and animals and it contains stored in it energy from the sun. Thinking back to your high school biology classes, you’ll remember that plants absorb the sun’s energy via photosynthesis and then anything that consumes those plants or uses those plants take on that energy. The idea of biomass energy it to take these sources of biomass and burn them to create heat, either to heat an area of generate electricity.
As mentioned above, biomass can take a number of different forms. Wood energy is when trees, wood waste, or other lumber products are burned for energy. Landfill gas takes all of our organic waste-- food scraps, wood products, animal waste, etc.-- and uses bacteria to brake those organic sources of biomass down and release methane. We then capture that methane (which if we didn’t capture would be a potent greenhouse gas) and then use it as a source of renewable energy. Municipal solid waste, or waste-to-energy, is a similar source of energy but instead of breaking down the waste into gas with bacteria will burn them at special waste-to-energy plants.
Geothermal and biomass are just two of the most prevalent sources of renewable energy outside of hydro, solar, and wind today, but others continue to be developed, studied, and implemented. These sources that may become a bigger source in the future include tidal energy, hydrogen energy, wave energy, and more.