Renewable energy can be defined as energy that is replenished at a higher rate than it is used. Fossil fuels do not qualify as renewable energy sources under this definition because they are spent more quickly than they are naturally restored. Sunlight, wind, geothermal, and hydropower energies, though, are renewable. Sunlight, wind, geothermal, and hydropower sources are virtually inexhaustible; we will never deplete the global supply. Furthermore, these four energies have fewer related greenhouse gas emissions than traditional fossil fuels.

Solar Energy Renewable

Sunlight is the most abundant source of energy available on Earth. Sunlight can be cheaply acquired and has extremely low emissions outputs. Capturing energy from the sun is accomplished with solar panels. When sunlight impinges on a solar panel, the photovoltaic silicon cells convert light energy into usable electricity. Solar panels’ energy generation process is itself 100% greenhouse gas emissions free. Manufacturing solar panels are, however, associated with some carbon dioxide emissions; according to a study in Nature, solar panels produce emissions as low as 20g CO2 equivalent per kilowatt-hour over their lifetime.

The main disadvantage to solar power: it’s not consistently available at all times, in all places. Sunlight energy varies depending on the time of day, season and year, and geographic location. On the other hand, if installed in the right place and stored properly, the electric energy from solar panels can provide energy to people living in remote areas, without the need for larger energy networks. Therefore, purchasing solar panels could save your household money on its monthly energy bill!

Wind Energy Renewable

Wind energy comes from turbines. The force created by the motion of air turns the turbine’s blades around a rotor, which spins a generator to create electricity. Simply put, the kinetic energy from the wind is collected by wind turbines, converted to electricity, and then stored for later use. The wind is an inexhaustible resource, it will never run out. Though, like sunlight, the wind is not equally available at all times and in all places. The ideal locations for wind turbine installation are windy areas, that have little wildlife, and are far away from populations of people, as wind turbines can be noisy.

Wind turbines are usually hundreds of feet tall and are often installed in groups, referred to as wind farms. Turbines work better in groups so that sufficient amounts of wind energy can be captured over a large distance. For the most part, greenhouse gas emissions from wind energy are quite low, especially relative to those of fossil fuel combustion. The emissions associated with wind energy are a result of manufacturing their parts and materials.

Hydropower Renewable

Hydropower facilities come in four different forms: impoundment, diversion, offshore (seawater), and pump and storage. In each case, the principle is the same, water is energy created by the movement of flowing water which pushes against the blades of a turbine to spin a turbine. Hydropower plants operate similarly to wind farms, in that they convert kinetic energy to electric energy.

Renewable Geothermal

Geothermal energy is heat continuously produced inside Earth. Most of this internal heat is brought on by the spontaneous process of unstable atomic nuclei transitioning into more stable versions of themselves; radioactive decay. The decay of radioactive elements results in a release of heat and happens perpetually in the Earth’s core, meaning that this energy can never be exhausted.

Earth’s internal energy heats up underground sources of water, which rises up to the surface as underwater hydrothermal vents geysers, steam vents, and hot springs. This energy too can be made to turn a turbine generator and generate electricity.

Renewable Biomass

Biomass is an organic source of energy, that is, it’s the material of or from living organisms. Common biomass materials include agriculture feedstocks, grasses, wood, algae, animal manure, and human sewage. Organic material is consistently available and can, in theory, be used indefinitely. The energy contained in biomass comes partly from the carbohydrates that photosynthetic plants have synthesized using sunlight, carbon dioxide, and water. The carbohydrates from plants and animals can be transformed into usable energy when burned (direct combustion) or converted.

Biomass technically qualifies as a renewable source of energy, but when burned, biomass emits carbon dioxide at rates comparable to fossil fuels for the same amount of generated energy. Unlike burning fossil fuel burning, which releases carbon that’s been stored underground for millions of years or more, biomass burning releases carbon that’s been stored in living organisms, i.e plants, animals, and organic wastes. The carbon dioxide from burned biomass is not moved back into the biosphere as quickly as it is expelled, meaning that biomass combustion is not a carbon-neutral means of energy production.