How Is Renewable Energy Generated?
Renewable energy is energy generated from natural sources that are constantly replenished, such as sunlight, wind, rain, tides, waves, and geothermal heat. The five main types of renewable energy are solar, wind, hydropower, bioenergy, and geothermal. Renewable energy provides around a fifth of the world’s electricity generation and plays an increasingly important role in energy systems as countries work to reduce greenhouse gas emissions and achieve energy security. According to the International Energy Agency, renewable energy could grow to provide almost 50% of global electricity by 2030.
Ramping up renewable energy is a key strategy for transitioning to clean energy systems that support climate targets and sustainable development. Renewable sources produce little to no greenhouse gas emissions, which is critical for mitigating climate change. Renewables can also strengthen energy security by relying on domestic sources rather than imported fossil fuels. Additionally, renewable energy creates jobs and other socioeconomic benefits as countries scale up technologies like solar PV, wind, and geothermal across the world.
Solar
Solar photovoltaic (PV) systems convert sunlight directly into electricity using semiconducting materials. PV cells are assembled into solar panels, which can be installed on rooftops or ground-mounted for utility-scale projects. As of January 2023, 73.5 gigawatts (GW) of utility-scale solar capacity was operating in the United States, about 6% of the U.S. total (U.S. Energy Information Administration).
Residential solar PV systems typically range from 5 to 15 kilowatts. Panels are installed on rooftops to generate electricity for home use, with any excess fed back to the grid. Commercial solar is similar but larger in scale, with systems sized according to business needs. In 2022, the U.S. installed 4.6 GW of residential solar PV and 2.1 GW of non-residential (Wikipedia).
Utility-scale solar farms can be over 1 gigawatt in size. These large installations feed power directly into the transmission grid. Utilities are increasingly adding solar to their generation portfolios to meet renewable targets and lower emissions. The U.S. currently has over 100 GW of total installed solar capacity (International Energy Agency).
Wind
Wind power is generated through wind turbines, which use blades to capture the wind’s kinetic energy and convert it into mechanical power to turn an electrical generator. The amount of power generated depends on the turbine’s size and the wind speed. Wind turbines come in all shapes and sizes, but the most common have three blades and sit atop tall towers. Commercial-scale turbines can reach over 600 feet tall.
Wind turbines are often grouped together in large clusters called wind farms. Onshore wind farms are located on land, while offshore wind farms are located in bodies of water, usually near coastal regions. According to the Global Wind Energy Council, the top countries for wind power capacity in 2021 were China, the United States, Germany, India, and Spain. China led with over 300 gigawatts of installed capacity.[1]
Offshore wind has become an increasingly important part of many countries’ renewable energy strategies. Floating offshore wind farms allow turbines to be installed in deeper waters farther from shore. While more expensive than onshore wind, offshore wind can provide higher wind speeds and more consistent power generation.[2]
Hydropower
Hydropower is one of the most common forms of renewable energy. It uses the natural flow of water or the force of falling or fast-moving water to generate electricity without the harmful byproducts associated with fossil fuels. There are three main types of hydropower facilities:
Hydroelectric Dams – Hydroelectric dams use a dam built across a large river to store water in a reservoir. The water flows through a turbine, spinning it, which in turn activates a generator to produce electricity. The height of water behind the dam creates hydraulic head, which determines the amount of electricity generated. Hydroelectric dams provide a stable, reliable source of electricity and now make up about 6% of U.S. electricity generation.
Run-of-River Systems – Run-of-river systems channel a portion of a river’s water through a canal or penstock to spin a turbine and generator. These systems do not require dams or water storage reservoirs, reducing their environmental impact. However, electricity generation depends on seasonal river flows and is less consistent than hydroelectric dams. Run-of-river provides about 5% of U.S. hydropower capacity.
Pumped Storage – Pumped storage facilities pump water uphill into a reservoir at times when electricity demand and prices are low. The water is then released through turbines to generate electricity when demand and prices are high. Pumped storage represents about 95% of utility-scale electricity storage in the U.S. and allows other renewable sources like wind and solar to connect to the grid by offsetting their intermittent nature.
Geothermal
Geothermal energy is derived from the heat within the earth. There are three types of geothermal power plants that convert geothermal heat into electricity – dry steam, flash, and binary cycle power plants. Dry steam plants utilize steam from geothermal reservoirs to directly turn turbines. Flash plants take high-pressure heated water from deep inside the earth and convert it into steam to drive turbines. Binary cycle plants transfer the internal heat from geothermal water to a secondary fluid which has a much lower boiling point. This causes the secondary fluid to flash to vapor which then drives the turbines. Enhanced geothermal systems (EGS) are a new technology that injects fluid into hot rock reservoirs to create geothermal resources in areas that lack natural geothermal activity.
The United States is the world’s largest producer of geothermal energy with over 3,900 MW of installed capacity as of 2023. Other top geothermal power countries include Indonesia, Philippines, Turkey, and New Zealand. Geothermal provides a stable baseload renewable power source in countries with high geothermal potential. Key factors enabling growth in the geothermal power market globally are supportive government policies, technology improvements, and rising electricity demand.
Bioenergy
Bioenergy refers to renewable energy produced from biological sources, primarily from biomass, and accounted for about 55% of renewable energy globally in 2021 according to the International Energy Agency (IEA). 1 Bioenergy’s main sources of generation include:
Biomass combustion – Burning biomass materials like wood, agricultural residues, and organic waste to generate electricity. The US Energy Department states biomass is the largest U.S. renewable energy source today. 2
Biogas from organic waste – Bacteria break down organic matter like crop residues, manure, and food waste anaerobically to produce a gas mixture called biogas. This biogas can be burned for heat and electricity generation. 3
Biofuels – Fuels like ethanol and biodiesel produced from biomass materials that can replace or blend with fossil-based fuels like gasoline and diesel for transportation.
Wave & Tidal
The ocean offers tremendous potential for renewable energy generation. Wave and tidal energy technologies harness the kinetic energy of ocean waves or the movement of ocean tides.
Tidal power can be generated in two main ways: tidal barrage and tidal stream. Tidal barrage involves building a dam-like structure to capture the energy as tides flow in and out of an estuary or bay. The movement of the tides turns turbines to generate electricity (Wave power – U.S. Energy Information Administration (EIA)). Tidal stream involves placing turbines directly in coastal waters or estuaries to capture energy from the ebb and flow of ocean currents.
Wave power utilizes floating or submerged structures that convert the kinetic energy of ocean waves into electricity. Common wave power technologies include point absorbers, oscillating water columns, and overtopping devices. It’s estimated that wave power alone could provide over 2,600 TWh per year in the United States (Science & Tech Spotlight: Renewable Ocean Energy).
Together, wave and tidal energy represent a largely untapped renewable resource that could play a growing role in a diversified energy portfolio as the technologies continue to mature.
Hydrogen
Hydrogen can be produced through a process called electrolysis, which uses electricity to split water into hydrogen and oxygen. This method has the potential to produce “green” hydrogen if the electricity comes from renewable sources like wind or solar. Electrolysis is seen as a promising method for large-scale production of hydrogen in the future (DOE).
Hydrogen is gaining attention as a clean energy carrier that could enable greater use of renewables. The idea is to produce hydrogen when there is excess renewable electricity, store it, and then use it in fuel cells or other applications when renewable output is lower. This provides a way to balance renewable energy supply and demand. With more advancement in production, storage and distribution, hydrogen could play a major role in a clean energy economy (EIA).
Storage
One of the main challenges with renewable energy sources like solar and wind is that they are variable and intermittent. Energy storage provides a solution to store excess renewable energy when it is abundant and dispatch it when renewable generation is lower. Large-scale energy storage also helps stabilize the grid and integrate higher shares of renewables. There are several main storage technologies used today including batteries, pumped hydro storage, compressed air energy storage, and thermal storage.
Lithium-ion batteries have emerged as a leading storage technology in recent years. According to the International Energy Agency, the United States had over 25 GW of utility-scale battery storage capacity in 2020, followed by China with over 4 GW. By 2026, the U.S. is projected to have nearly 50 GW of battery storage capacity (IEA). The global market for grid-scale battery storage is expected to expand rapidly in the coming years.
Pumped hydro storage is the most mature and widely used form of grid storage. This involves pumping water uphill into a reservoir when electricity demand is low and releasing it to generate power at times of peak demand. The United States has over 20 GW of pumped hydro storage, the most of any country (Guidehouse Insights). Compressed air energy storage is another technology that compresses air in underground caverns to be released later to turn a turbine. Thermal energy storage involves technologies like molten salt to store excess heat that can be used later to produce steam and generate electricity when needed.
Conclusion
In summary, the key renewable energy sources discussed include solar, wind, hydropower, geothermal, bioenergy, wave & tidal, and hydrogen. Solar and wind energy have seen the most significant growth in recent years and are projected to continue leading renewable capacity additions through 2030. However, all renewable sources will need to grow substantially to meet decarbonization goals. According to the IEA, renewable energy capacity must triple by 2030 to keep global warming below 1.5°C.
Renewable energy already accounts for over 26% of global electricity generation. With supportive government policies, falling technology costs, and increased private sector investment, the outlook is positive for renewable energy to supply over 50% of the world’s electricity by 2030. Key factors driving growth include improving competitiveness with fossil fuels, energy security and independence benefits, and the urgent need to reduce greenhouse gas emissions. While there are still challenges around integrating variable renewables, storage solutions and smart grids will enable higher penetrations. With renewables scaling up rapidly, the energy transition is underway but increased ambition will be required to fully decarbonize the world’s energy system.
