What Is Renewable Energy Definition

Renewable energy refers to energy generated from natural resources that are continuously replenished, such as sunlight, wind, water, and geothermal heat. These renewable resources can be used to generate electricity, provide heating and cooling, and power transportation.

Renewable energy is a key part of efforts to transition away from fossil fuels like coal, oil, and natural gas, which produce greenhouse gas emissions that drive climate change. Expanding renewable energy can also improve energy access, energy security, and air quality. According to the UN, renewable energy has become increasingly cost-competitive and provides reliable energy services for sustainable development.

Renewable energy accounted for 12.6% of total U.S. energy consumption and 17.5% of electricity generation in 2019, with the largest renewable sources being hydropower, wind, and solar. There is potential for further growth to help meet energy needs while reducing environmental impacts. Understanding the benefits, challenges, and future potential of renewable energy is important as communities, companies, and countries work to transition toward sustainable energy systems.

Sources: https://www.epa.gov/statelocalenergy/local-renewable-energy-benefits-and-resources, https://www.un.org/en/climatechange/raising-ambition/renewable-energy

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Types of Renewable Energy

There are several major types of renewable energy sources that are commonly used today.

Solar Energy

Solar energy comes directly from the sun and is converted into electricity or heat. Solar panels convert sunlight into electricity, while solar thermal collectors capture heat from the sun. Solar is one of the fastest growing renewable energy sources today. Source

Wind Energy

Wind energy captures the natural wind flow using large wind turbines and converts it into electricity. Wind farms consisting of many turbines are increasingly being used around the world. Source

Hydropower

Hydropower uses flowing water like in dams or rivers to spin large turbines and generate electricity. It’s one of the oldest and most established renewable energy sources.

Geothermal Energy

Geothermal energy taps into the natural heat beneath the earth’s surface to produce steam or hot water that can drive turbines to create electricity.

Biomass Energy

Biomass energy uses organic matter like plants, wood, or waste to produce heat and electricity. It can also be converted into biofuels for transportation.

Solar Energy

Solar energy comes from capturing photons from sunlight and converting them into electricity or heat. It is considered a renewable energy source because the sun will continue shining for billions of years. There are two main ways to harness solar energy:

Solar photovoltaics (PV) convert sunlight directly into electricity using semiconducting materials like silicon. When sunlight hits the PV cells, electrons are knocked loose and can be captured as direct current electricity. PV panels can be installed on rooftops or ground-mounted to generate electricity for homes, businesses, and utilities.

According to source, solar PV capacity grew at an average annual rate of 49% between 2006-2011 as costs declined dramatically. By 2020, global solar PV capacity reached 760 gigawatts.

Solar thermal systems use sunlight to heat a fluid like water or oil to create steam to drive a turbine and generate electricity. They can also be designed as solar hot water systems to provide hot water for buildings. Solar troughs, towers and dishes can all be used for utility-scale solar thermal plants.

Solar energy is well-suited for residences because rooftop PV systems can reduce or even eliminate monthly electricity bills. Community solar projects allow households to share costs and benefits of a larger solar installation. Utility-scale solar provides clean renewable energy to the grid through large ground-mounted PV and concentrating solar plants.

Wind Energy

Wind energy is one of the fastest growing renewable energy sources in the world. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce electricity. Most wind turbines have three blades that face into the wind; the wind turns the blades around a rotor which spins a shaft connected to a generator (IEA).

How much electricity a turbine generates depends on its size and the wind’s speed through the rotor. Most turbines operate at wind speeds between 13 and 56 mph. As wind passes over the blades, the rotor spins; this rotational energy is converted into electricity (IEA). Turbines typically start generating electricity at wind speeds of about 9 to 10 mph.

Wind farms can be built on land (onshore) or offshore in bodies of water. Onshore wind is the most established technology while offshore wind is a fast growing industry. At the end of 2021, global installed wind power capacity was 837 GW, with onshore wind making up 70% of installations and offshore wind accounting for the remaining 30% (IEA).

The global onshore market grew by close to 90 GW to reach 578 GW in 2021. China accounted for nearly half of global additions. The United States and Brazil more than doubled their onshore capacity additions compared to 2020 (IEA).

Offshore wind capacity grew by 21 GW in 2021 to reach 57 GW. China led in new capacity followed by the United Kingdom and the Netherlands. Forecasts estimate offshore wind capacity will reach 380 GW by 2030 as more offshore projects come online in Europe, China, and the United States (IEA).

Hydropower

Hydropower is one of the most widely used forms of renewable energy and generates electricity by using the power of moving water. In 2021, global hydropower capacity reached approximately 1,397 gigawatts (GW) [1]. The three main types of hydropower systems are dams, run-of-river, and pumped storage.

Dams are the most common type of hydropower plant. They store large reservoirs of water behind a dam which is released to spin turbines and generate electricity. China has the highest installed capacity of dam-based hydropower in the world at over 350 GW [2].

Run-of-river hydropower channels a portion of a river through a canal or penstock to spin turbines. It requires less infrastructure than dams but generates less power. Run-of-river is used more often for micro hydropower projects under 10 MW of capacity.

Pumped storage hydropower works by pumping water uphill into a reservoir when electricity demand is low and releasing it to generate power during high demand periods. Pumped storage provides grid reliability and helps integrate intermittent renewables like solar and wind.

Micro hydropower systems generate under 1 MW of electricity and provide decentralized renewable power for isolated communities. They have minimal environmental impact compared to large dams.

Geothermal Energy

Geothermal energy taps into the natural heat from the earth’s core to generate power. This renewable energy source utilizes steam or hot water from geothermal reservoirs located deep underground. According to ThinkGeoEnergy, the top geothermal power generation countries in 2022 were the United States, Indonesia, Philippines, Turkey, and New Zealand.

There are three types of geothermal power plants: dry steam, flash, and binary. Dry steam plants use steam directly from the reservoir to turn turbines and generate electricity. Flash plants pull hot water into low pressure tanks, causing the water to boil and produce steam for energy. Binary cycle plants transfer the reservoir’s hot water heat to another liquid with a lower boiling point that vaporizes to drive the turbines.

In addition to electricity generation, geothermal energy has many direct use applications. The earth’s natural warmth can be used directly for heating buildings, greenhouses, fish farms and other facilities. Geothermal heat pumps leverage stable ground temperatures for space heating and cooling. Hot water from geothermal reservoirs can also be used for bathing, aquaculture, and industrial processes requiring heat.

Biomass Energy

Biomass energy refers to the renewable energy derived from plant and animal waste as well as from organic matter. Some of the most common forms of biomass energy include:

Plant waste – This includes agricultural residues like corn stalks and sugarcane waste, as well as forest debris and dead trees.
Animal waste – Manure from cows, pigs, chickens, and other animals is used to produce methane gas that can generate electricity.
Landfill gas – The organic waste decomposing in landfills releases methane gas that is captured and utilized as an energy source.

Ethanol – This liquid biofuel is produced by fermenting the sugars in crops like corn and sugarcane. It can replace gasoline in vehicles.
Biodiesel – Produced from vegetable oils, animal fats, and recycled cooking grease, this fuel can replace or be blended with diesel in vehicles.

According to the International Energy Agency (IEA), biomass accounted for about 10% of global primary energy consumption in 2019 [1]. In some countries like Finland and Sweden, biomass contributes 20-30% of the total energy supply. Biomass is a versatile energy source that can be used for electricity generation, transportation, and heating homes and buildings.

Benefits of Renewable Energy

Renewable energy provides many important benefits compared to fossil fuels. Some key benefits include:

Reduces greenhouse gas emissions – Renewables like wind, solar, and hydropower produce little to no global warming emissions when operating, so they help lower the carbon footprint of our electricity system (UCSUSA). Expanding renewables can help reduce the impacts of climate change.

Energy independence and security – Local renewable energy sources reduce our dependence on imported fuels, increase domestic energy supply, and improve national security. This makes our energy system more resilient and reliable.

Cost reductions – The costs of renewables like wind and solar have declined rapidly. In many cases renewables are now the lowest-cost option for new electricity generation. Widespread renewables lower electricity prices for consumers.

Job creation – Expanding renewable energy creates well-paying jobs in manufacturing, installation, and more. The renewable energy industry employs hundreds of thousands of Americans across all 50 states (DOE).

Challenges of Renewable Energy

While renewable energy has many clear benefits, there are also some significant challenges facing its widespread adoption. Some of the main challenges include:

Intermittency: Many renewable energy sources like solar and wind are intermittent, meaning they are not available on demand and rely on weather conditions. This can make integrating high levels of renewables onto the electric grid difficult (https://sustainablereview.com/challenges-in-renewable-energy/).

High upfront costs: The upfront capital costs of building renewable power plants and transmission infrastructure can be significant. Although costs are falling, renewables require substantial upfront investments that fossil fuels do not (https://regenpower.com/what-are-the-problems-faced-by-renewable-energy/).

Land use constraints: Renewable projects like bioenergy and solar/wind farms require large amounts of land area for crops or siting. Finding adequate available land with appropriate conditions can be challenging, especially compared to fossil fuel plants.

Transmission infrastructure needs: New transmission lines need to be built to transport renewable power from source to end-users. Upgrading and expanding transmission is expensive and faces siting challenges (https://www.iea.org/reports/renewable-energy-market-update/challenges-and-opportunities-beyond-2021).

Future of Renewable Energy

The future of renewable energy looks bright, with several reports projecting rapid growth in the coming decades. According to the U.S. Energy Information Administration (EIA), renewable generation will supply 44% of U.S. electricity by 2050, up from 21% today. The EIA projects that much of this growth will come from solar and wind power. The International Renewable Energy Agency (IRENA) is even more bullish, projecting renewables will supply 85% of global electricity by 2050, compared to 25% today.

This massive growth will be driven by several key factors. First, costs for wind and solar power continue to decline rapidly, making them increasingly cost-competitive with fossil fuels. Second, emerging technologies like battery storage, smart grids, and electric vehicles will enable higher penetrations of variable renewables like wind and solar on the grid. Third, many countries have implemented ambitious renewable energy targets and policies, like carbon pricing, clean electricity standards, and financial incentives. According to the International Energy Agency (IEA), achieving net zero emissions globally by 2050 will require clean energy investment to triple to $4 trillion per year by 2030.

While solar and wind currently dominate renewable capacity additions, emerging technologies may grab market share in the coming decades. These include offshore wind, floating solar, geothermal, tidal, advanced biofuels, green hydrogen, and newer solar technologies like perovskites. However, not without challenges. Integration, transmission, permitting, and financing issues must be solved for renewables to reach their full potential. With supportive policies and sustained technological progress, renewables appear well on their way to displacing fossil fuels this century.