What Are 7 Renewable Energy Sources?

Renewable energy sources are becoming increasingly important as we work to combat climate change and reduce our reliance on fossil fuels. Renewable energy comes from natural sources that are constantly replenished, such as sunlight, wind, water, plants, and geothermal heat. Switching to renewable energy is a key strategy to reducing greenhouse gas emissions and avoiding the worst impacts of climate change. Unlike fossil fuels, renewable energy sources are inexhaustible and much better for the environment.

Some of the main renewable energy sources include solar, wind, hydropower, bioenergy, geothermal energy, ocean energy, and hydrogen energy. Each has unique advantages and plays an important role in transitioning away from fossil fuels. This article will provide an overview of 7 major renewable energy sources, their benefits, and why they are critical for building a sustainable future.

Solar

Solar energy comes directly from the sun and is captured and converted into electricity or heat. There are two main types of solar energy technologies:

• Solar photovoltaics (PV) convert sunlight directly into electricity using semiconducting materials. PV panels are commonly seen on rooftops to generate electricity for homes and businesses.
• Solar thermal technologies use mirrors or lenses to concentrate solar energy to produce heat. This heat can then be used to produce electricity via a steam turbine or heat engine. Solar thermal is also used for water and space heating in homes and buildings.

According to recent statistics from Anationofmoms.com, solar energy accounts for just over 2% of electricity generation in the United States, but its usage is growing rapidly. The solar industry employs over 250,000 people in the U.S. Federal tax credits have helped drive growth, and costs continue to fall making solar more affordable.

Solar energy offers a clean, renewable source of power from an abundant resource – the sun. PV panels work even on cloudy days and can be installed on homes, businesses and at utility-scale solar farms. With solar thermal, the heat from the sun can pasteurize water and provide heating and cooling in addition to electricity generation. Solar will continue to grow as a major renewable energy source for the future.

Wind

Wind power harnesses the wind to generate electricity using wind turbines. Wind turbines convert the kinetic energy in wind to mechanical power through rotating blades connected to a rotor. This rotational energy spins a generator to create electricity (Windenergy.gov, 2022, https://www.energy.gov/eere/wind/how-do-wind-turbines-work).

Multiple wind turbines are usually installed together in groups called wind farms or wind power plants to generate larger amounts of electricity. The world’s largest offshore wind farm is Hornsea 1 in the UK, which has 174 turbines with a total capacity of 1.2 gigawatts (GW) (Windenergy.gov, 2022, https://www.energy.gov/eere/wind/articles/hornsea-1-worlds-largest-offshore-wind-farm-complete).

As of 2021, global installed wind capacity was 837 GW, led by China with 302 GW, the US with 134 GW, and Germany with 63 GW (Global Wind Energy Council, 2022, https://gwec.net/global-figures/global-statistics/). Wind power accounted for around 6% of total global electricity generation in 2019 (Our World in Data, 2022, https://ourworldindata.org/renewable-energy#wind-energy).

Hydropower

Hydropower generation accounts for over 15% of global electricity production and over 85% of global renewable electricity generation as of 2017 (Hydropower Status report 2017). Most hydropower is generated using dammed reservoirs, where water released from the reservoir flows through turbines to generate electricity. Pumped storage hydropower works by pumping water uphill into a reservoir when electricity demand is low so that it can be released to generate power at times of high electricity demand.

As of 2016, global installed hydropower capacity was 1,246 GW, generating over 4,100 TWh of electricity annually which accounted for over 16% of global electricity generation (hydropower status report). Hydropower is a renewable energy source that offers flexibility to meet peak electricity demands, making it an important part of the renewable energy mix.

Bioenergy

Bioenergy is energy generated from organic matter or waste biological material known as biomass. Biomass can be sourced from plants, residues from agriculture or forestry, and organic components of municipal and industrial wastes. Bioenergy comes in various forms including biofuels like ethanol and biodiesel used for transportation, biogas generated from organic waste through anaerobic digestion and used for heating and power, and solid biomass like wood chips or pellets burned to produce electricity and heat.¹ Biomass resources provide about 5% of global primary energy demand today.²

Bioenergy production offers environmental benefits by reducing greenhouse gas emissions compared to fossil fuels. However, large-scale production can also have negative impacts like deforestation, increased water use, and threats to biodiversity and land conservation. Sustainable practices are needed to ensure bioenergy provides more benefits than costs to the environment.³ Overall, bioenergy from waste streams and sustainable biomass presents a renewable, carbon-neutral energy source that can help meet energy demands while transitioning from fossil fuels.

Geothermal

Geothermal energy utilizes the natural heat from the Earth’s core to generate electricity and provide direct heating and cooling. To extract geothermal energy, wells are drilled into underground reservoirs to tap into hot water and steam. The hot water can either be used directly to provide heat, or it can be pumped to the surface to power geothermal power plants and generate electricity.

At geothermal power plants, the hot water is pumped under high pressure to drive a turbine connected to a generator. The steam that results from the hot water flashing to a lower pressure is used to spin the turbine blades. The moving turbine then converts the mechanical energy into electrical energy. In 2021, the leading geothermal energy producing states were California and Nevada, which together accounted for 95% of U.S. geothermal capacity¹.

Direct heating uses for geothermal energy include district heating systems, greenhouse heating, industrial processes, and heating and cooling buildings through geothermal heat pumps. Ground-source heat pumps transfer heat between the ground and a building by circulating water or antifreeze solution through pipes laid in the ground. In winter, the fluid collects heat from the Earth and carries it indoors. In summer, the system reverses and takes heat from the indoor air and transfers it to the ground¹. Geothermal direct heating is clean, reliable, and cost effective.

Ocean

The ocean has immense potential for renewable energy generation. The open waters are constantly in motion from tides, currents, and waves which can be harnessed to produce electricity. There are several ocean energy technologies being utilized and developed including tidal power, wave power, ocean thermal energy conversion (OTEC), and others.

Tidal power harnesses the rise and fall of ocean tides to spin turbines. Tidal barrages are essentially dams built across tidal areas that force water through turbines as the tide comes in and out. Tidal stream generators are underwater turbines that use tidal currents to generate electricity. Some advantages of tidal power are its predictability and reliability. However, it is limited to coastal regions with high tidal ranges. Some potential environmental impacts need to be carefully managed as well such as effects on marine life migration and sediment transport (“The USA’s ocean energy generation potential. Source”).

Wave power uses the kinetic energy from ocean surface waves to drive turbine generators. Various designs like oscillating water columns, point absorbers, and overtopping devices are used. Wave power potential is abundant but it has proved challenging to develop cost-effective and durable technology that can withstand harsh ocean conditions. Environmental effects such as noise and seabed disturbance also need to be considered.

OTEC uses temperature differences between warmer surface water and colder deep water to run a heat engine and produce electricity. This can work in tropical regions where surface water is around 25°C or more and 1000+ meters deep the water is around 5-10°C cooler. OTEC systems can be land-based or floating offshore. OTEC is powerful in theory but comes with engineering challenges. The cold water pipes need to be extremely large. Environmental impacts, especially from discharging the cold deep water, must be carefully managed.

The ocean offers tremendous renewable energy potential with minimal associated greenhouse gas emissions. Continued research and development can help overcome technical challenges and expand the use of ocean energy sources.

Hydrogen

Hydrogen is considered a renewable energy source when it is produced from renewable sources like wind and solar power. Hydrogen gas releases energy when reacted with oxygen in a fuel cell to generate electricity. Fuel cells create electricity through a chemical reaction, not combustion, so emissions depend on the hydrogen production method.

Hydrogen fuel cells are emerging as a clean energy technology for vehicles, stationary power, and portable applications. Fuel cell electric vehicles powered by hydrogen emit no harmful tailpipe pollutants like particulate matter or ozone-forming emissions. Renewable hydrogen production is key for hydrogen fuel cells to provide emissions reductions compared to conventional vehicles.

Methods for producing renewable hydrogen include electrolysis powered by renewable electricity from solar and wind, biomass gasification, and photobiological water splitting. Water electrolysis uses electricity to split water into hydrogen and oxygen. Electrolyzers can rapidly respond to fluctuations in renewable power generation.

According to the International Energy Agency, global renewable hydrogen production could reach over 200 million tonnes by 2027, more than double the 2020 level. Widespread adoption of hydrogen fuel cell vehicles and growth in renewable hydrogen production capacity will be needed to tap into hydrogen’s potential as a versatile, clean energy carrier.

(https://www.iea.org/reports/how-much-will-renewable-hydrogen-production-drive-demand-for-new-renewable-energy-capacity-by-2027)

Comparison

When comparing renewable energy sources, there are several factors to consider including pros and cons, costs, and capacity factors. Each source has its own advantages and disadvantages.

Solar power is clean and renewable, but dependent on sunny weather. The capacity factor of solar PV is around 15-30%. Costs have fallen dramatically in the past decade making solar energy competitive with fossil fuels. However, solar still requires energy storage solutions for 24/7 power (Thompson, 2022).

Wind power is a mature technology capable of large-scale generation, but subject to variation based on wind conditions. Wind capacity factors range from 35-55%. While costs have declined, wind turbines require large land areas and some view them as visually unappealing (NEFUSA, 2023).

Hydropower offers consistent and reliable output, but opportunities for new major dams are limited due to topography and environmental concerns. Existing hydro capacity factors can exceed 50%. Costs are relatively low, but dependent on geographical constraints and rainfall levels (NEFUSA, 2023).

Bioenergy provides a use for agricultural waste, but has limitations around sustainable sources and supply chains. Capacity factors for bioenergy range from 40-80%. While costs are competitive, sourcing sufficient sustainable biomass for large-scale generation poses challenges (NEFUSA, 2023).

Geothermal taps into continuous heat beneath the surface, but viable locations are geographically limited. Capacity factors range from 45-90%. Drilling costs are high, but once built, geothermal offers low operating costs (Thompson, 2022).

Ocean energy like tidal are renewable and predictable, but technology is still under development. Capacity factors can reach 40%. Costs remain prohibitively high currently, requiring further R&D to become commercially viable (Thompson, 2022).

Hydrogen, produced via electrolysis with renewables, is a clean fuel but requires very low costs to be competitive. As a storage medium, hydrogen offers high efficiency but requires new infrastructure. Costs are still high but dropping as production scales up (Thompson, 2022).

Conclusion

In summary, it is clear that there are many promising renewable energy sources available to transition our society away from fossil fuels. Solar, wind, hydropower, bioenergy, geothermal, ocean, and hydrogen energy can all play a role in creating a more sustainable future. While fossil fuels have powered society for decades, their severe environmental impacts necessitate a shift to clean, renewable options for our energy needs. The technologies highlighted here – from massive offshore wind turbines to rooftop solar panels – demonstrate the incredible innovation and potential of renewable energy. What is needed now is the societal and political will to accelerate the transition. With the right policies, investments, and public engagement, a clean energy economy is within reach. The environmental, health, and economic benefits of such a transition would be enormous. The time to act is now.