Green Energy: An Overview and Breakdown of Green Energy Types

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green energy guide

The term green energy stands for energy generated from a variety of renewable energy sources, which is turned into more user-friendly forms of energy. In most cases it’s turned into electricity; other forms of green energy are heat, mechanical power, compressed air or chemicals generated from renewable sources. The main sources for green energy are the sun, the wind, water, heat and plants/animals.

In 2017, renewable energy contributed about 3,273.6 terawatt-hours (TWh) to the U.S. energy market, according to the Energy Information Agency (EIA). That is about 11% of the total U.S. energy consumption. Around 17% of U.S. electricity generation was from renewable energy sources.

Finding Green Energy

Clearly it’s important to find green energy because it can save you money on your energy bills. The question remain: how can you find green energy suppliers. There are many out there, so you need to make sure you compare energy providers and make sure you’re getting the best offer in your area.

Renewable Energy Versus Green Energy

Renewable energy is generated by the planet’s unlimited natural resources. These resources have in common that they either last indefinitely or they are continuously replenished, providing a sustainable flow of energy.

The term Green Energy is generally used for renewable energy generated by sources that aren’t affecting the environment, river flows, adversely while generating power. This is particularly true for hydropower, which often requires large dams and reservoirs. While hydropower is a renewable energy source it’s technically not a type of green energy, unless it’s generated by low impact hydro plants.

Types of Green Energy

Renewable energy is mainly used for electricity generation. While hydroelectric power is the biggest source of renewable electricity, biomass energy accounted for 45% of all renewable energy. Biomass is mainly used directly for heating or converted into solid, liquid or gasified biofuels such as pellets, ethanol or biogas.

The main sources for renewable electricity generation are hydroelectric power, wind power, solar power, biofuels, geothermal energy and less common sources such as tidal power or wave power.

Biomass Energy

Biomass energy or bioenergy is produced from any organic material originating from plants or animals, by converting biomass into more useful forms of energy such as heat, electricity, gas or liquid fuels. The most common forms of biomass used to generate energy are wood, crops and manure.

With a contribution of 1,489.97 TWh to U.S. energy consumption, biomass energy is by far the largest source of renewable energy.

Biomass can also be converted into methane gas, ethanol or biodiesel fuels. In 2016, 95% of gasoline sold in the U.S. was blended with 10% ethanol while cars and trucks that use “flexible-fuel” become more common. Flexible fuels usually contain up to 85% ethanol (E85).

Hydroelectric Power

The mechanical power from water is still being used in various types of watermills or to produce compressed air, but it’s mainly used to generate electricity in hydroelectric power plants.

Hydroelectric power plants are using the water from the stream of a river or a reservoir to drive a water turbine and generator to produce electricity. True green energy is coming from the smaller run-of-the-river plants without artificial reservoirs.

As the largest source for renewable electricity (43.74%) in the U.S., hydropower was generating a total of 300.3 TWh or around 7.4% of the country’s total electricity in 2017.

Wind Power

Wind power is used to generate electricity by converting kinetic energy into mechanical energy using wind turbines.

The second largest source of renewable energy (21%) in the U.S. is wind power, generating a total of 254.3 TWh or over 37% of the total electricity in 2017.

Solar Power

The sun’s power is generally harvested using three different technologies: solar photovoltaic (PV) and solar thermal to generate mainly electricity while low-temperature solar heating systems provide hot water to homes and businesses. Both electric power sources can use different technologies to generate electricity; the main difference is the size of the plants.

Large commercial sites, which are typically at least over 1 MW, are considered utility scale power plants. Small-scale systems, especially those on private homes, schools or businesses, are typically rooftop PV systems.

In 2017, solar power contributed some 77.28 MWh or 6% to the nation’s total renewable energy generation. While utility-scale solar electricity generation is well-documented, distributed power generation from smaller systems is not measured. The EIA estimated that in 2017, distributed small-scale PV systems generated about 23.99 TWh of the total 74 TWh of solar PV-system generated electricity,

Solar Thermal Power

High-temperature solar power plants use thermal collectors to absorb concentrated sunlight from mirrors or lenses to produce heat in Concentrated Solar Thermal (CST) or electricity in Concentrated Solar Power (CSP) plants.

According to the EIA, about 3.27 TWh of solar thermal energy was generated in the U.S. in 2017, which was 0.1% of the country’s total electricity generation.

Solar Photovoltaic

Solar photovoltaic (PV) systems absorb the sun’s light using solar panels and convert it into electricity. Typically, an inverter then changes the electric current from DC to AC and feeds it into the grid.

In 2017, the total generation from utility and small-scale facilities in the United States was 74,007 MWh. An estimated 23,990 MWh came from distributed small-scale generation.

Low-temperature Solar Water Heating

Another form of solar energy use is for low-temperature water heating. Solar water heaters are used to reduce the need for conventional water heating (and cooling), often as rooftop systems on homes, businesses, schools or gyms but also for outdoor and indoor pools.

Solar water heating is typically small scale. No recent numbers have been reported. According to the U.S. Department of Energy, over 1.5 million homes and businesses had an installed capacity of over 1,000 megawatts (MW) in 2006.

Geothermal Energy

Geothermal energy is the heat naturally created by the Earth itself, harvested mainly to heat (or cool) buildings or to generate electricity using a turbine and generator. Geothermal heat pumps tap into the ground just deep enough to where the Earth's surface maintains a temperature between 50° and 60°F using the energy for heating or cooling.

Geothermal power plants generated about 5.93 TWh in 2017, which represents 2% of the total renewable energy consumption in the U.S.

Other Green Energy Sources

Besides the major renewable energy sources there are other sources that currently have no significant role in U.S. power generation, such as tidal power or wave power, which are basically forms of hydropower. In some cases, waste to energy systems such as waste incinerators or landfill gas extraction are considered forms of green energy. When done right, they decrease the adverse effects of waste which is going to landfills or burned in other facilities anyway.

Not renewable but counting as a form of green energy is hydrogen if it’s produced using renewable primary energy. Hydrogen can be burned directly as a fuel or to power fuel cells to generate electricity. Burning hydrogen creates no pollution.