What Types Of Renewable Energy Are There?

Renewable energy comes from natural sources that are constantly replenished, such as sunlight, wind, water, heat from the earth’s core, and plant materials. Switching to renewable energy is extremely important as we work to combat climate change and reduce greenhouse gas emissions globally. The burning of fossil fuels like coal, oil and natural gas account for over 80% of the world’s energy use, but also produce pollutants and greenhouse gases that are warming the planet. Renewable resources are readily available across the planet and are clean sources of energy that produce little to no global warming emissions.

There are several major types of renewable energy we will cover in depth here including solar, wind, hydropower, geothermal, bioenergy and wave/tidal power. Understanding the key characteristics, benefits and challenges of each renewable energy type is crucial as we transition our energy dependence away from fossil fuels and toward clean, sustainable sources.

Table of Contents

Solar

Solar power is one of the most promising renewable energy sources, utilizing the sun’s energy and converting it into useful electricity. The main technologies for harnessing solar power include photovoltaics and concentrating solar power.

Photovoltaics (PV) use solar panels containing silicon cells to convert sunlight directly into electricity. As of 2021, global installed PV capacity reached over 827 GW, with Asia leading in solar installations, followed by Europe and North America (Source). PV systems come in different applications like rooftop solar on homes and businesses or utility-scale solar farms.

Concentrating solar power (CSP) systems use mirrors to concentrate sunlight to drive traditional steam turbines or engines. CSP allows energy storage by heating molten salt to generate power when direct sunlight is unavailable. The global installed CSP capacity reached 6.5 GW in 2021, with Spain and the United States having the most capacity (Source). Major CSP projects are located in sunny, arid regions like the southwest United States, North Africa, the Middle East, and Australia.

Solar thermal systems use solar energy for direct heating applications like heating water. China leads the world in installed solar thermal capacity with over 373 GW, used for residential and industrial applications (Source).

Wind

Wind is one of the most popular forms of renewable energy source and there has been immense growth in wind power generation globally. According to the Global Wind Energy Council, wind power capacity increased by 17% in 2020 with 94 GW added. China, the US, India, Germany and Spain are the top countries for wind energy production currently

There are two main types of wind energy – onshore and offshore. Onshore wind farms are located on land and make up most of the wind installations globally. The wind turbines are usually around 100 meters in height. Offshore wind farms are located in bodies of water, usually oceans, and have larger wind turbines than onshore ones that can capture stronger winds. They are more expensive to build than onshore but provide more energy.[1]

Modern wind turbines are designed to operate for 20-25 years. The wind turns the blades of the turbines, which spin a shaft connected to a generator to produce electricity. Some key components include the rotor blades, gearbox, generator and transformer.[2] Wind energy is a clean and renewable source that helps reduce greenhouse gas emissions and air pollution when displacing fossil fuels.

Hydropower

Hydropower is one of the most widely used forms of renewable energy and generates electricity by using water’s flow or height to spin a turbine connected to a generator (1). It accounted for around 16% of total global electricity generation in 2021, making it the largest source of renewable power. There are several types of hydropower facilities (2):

Dams – Most hydropower is generated using dams which store water in a reservoir and control its flow. The Three Gorges Dam in China is currently the world’s largest hydroelectric dam.

Pumped storage – Water can be pumped uphill into a reservoir during periods of low electricity demand and then released through turbines to generate power during high demand times.
Run-of-river – Power is generated from the natural flow of rivers without the need for a large dam or reservoir.
Tidal – Tidal barrage systems capture the energy from the rise and fall of ocean tides to generate electricity.

Major hydropower generating countries include China, Canada, Brazil, the United States, and Russia (1). Norway generates the most hydroelectricity in Europe, followed by France and Sweden (2).

(1) IEA – Key hydropower statistics

(2) Statista – Hydropower generation in Europe 2022

Geothermal

Geothermal energy is derived from the heat coming from beneath the Earth’s surface. It is a renewable energy source that does not create greenhouse gas emissions.

One of the most common uses of geothermal energy is for electricity generation, with countries like Kenya having significant geothermal capacity. Geothermal power plants use steam from reservoirs of hot water found a couple of miles or more below the Earth’s surface to turn turbines and generate electricity.

Geothermal energy can also be used directly for heating and cooling purposes. Geothermal heat pumps can tap into shallow ground warmth in the winter to heat buildings and the cooler temperatures in the summer to provide air conditioning. The geothermal gradient means that temperature increases with depth, which geothermal systems utilize.

Natural hot springs have emerged where geothermal energy seeps up to the Earth’s surface. Humans have used these hot springs for bathing, cooking, and heating for thousands of years. Today, hot springs are still used for relaxation and health purposes.

Bioenergy

Bioenergy refers to renewable energy derived from organic matter, known as biomass. The most common types of bioenergy are biomass, biogas, and biofuels. Biomass energy is generated by burning wood, plants, biodegradable waste, or other organic materials. Global bioenergy use was around 60 EJ in 2020, with biomass accounting for about 80% of total bioenergy use. The largest share of biomass is utilized for heating purposes, followed by electricity generation. Biogas is produced from anaerobic digestion or fermentation of organic matter like manure, sewage, municipal waste, green waste, plant material, and crops. It is primarily composed of methane and carbon dioxide and can be used to generate electricity and heat, or can be processed into renewable natural gas and transportation fuels. Biofuels refer to liquid fuels such as ethanol and biodiesel that are made from biomass feedstocks. In 2020, biofuels made up around 16% of total global bioenergy consumption. First generation biofuels use food crops like corn, sugar cane, or vegetable oils as feedstocks while second and third generation biofuels utilize non-food crops, agricultural residues, municipal solid waste, and algae as feedstocks.

Wave & Tidal

Tidal stream generators and wave energy converters are two promising types of renewable energy from ocean waves and tides. Tidal stream generators utilize underwater turbines that are powered by tidal currents, similar to how wind turbines capture energy from moving air. The turbines are placed in areas with fast tidal flows, such as straits between land masses or around headlands.

According to one study, global ocean energy capacity projections for tidal power are estimated at over $900-1,000 billion through 2050, representing an average investment of over $2.2 billion per year (Source). Tidal stream generators have advantages such as predictability and consistency of power generation.

Wave energy converters capture the energy of ocean surface waves and convert it into electricity. Various techniques are used, such as floating structures that rise and fall with waves or buoyant paddles that generate power as waves push past them. Although not yet widely commercialized, wave energy has potential for future expansion, especially in coastal regions with sufficient wave activity.

Hydrogen

Hydrogen can be used as a renewable energy source when it is produced via electrolysis using electricity from renewable sources like solar or wind. The process of electrolysis uses an electric current to split water molecules (H2O) into hydrogen and oxygen. The renewable hydrogen produced can then be stored and used to generate electricity in a fuel cell, releasing only water vapor and heat as byproducts.

Fuel cells powered by renewable hydrogen have potential applications in transportation, including fuel cell electric vehicles, ships, trains, and planes. Fuel cell vehicles using compressed hydrogen can provide driving ranges over 300 miles on a full tank and can be refueled in under 5 minutes. The only tailpipe emissions are water vapor. Hydrogen fuel cell buses and other larger vehicles are already being deployed in some cities.

Large scale production, storage, and distribution infrastructure for renewable hydrogen is still being developed. Some key challenges include reducing the costs of electrolysis and fuel cells and finding effective ways to store and transport large quantities of hydrogen gas. Underground salt caverns are one potential method for bulk hydrogen storage. As the hydrogen economy expands, renewable hydrogen is expected to play an important role in decarbonizing the transportation, power generation, and industrial sectors.

(Sources: https://www.sciencedirect.com/science/article/pii/S030626192301632X, https://www.linkedin.com/pulse/hydrogen-energy-storage-market-type-application-key)

Storage

Energy storage is a critical component of renewable energy systems. Storage helps overcome the intermittent nature of renewable sources like solar and wind by capturing excess energy when production is high and discharging it when production is low. There are several main types of energy storage used with renewables:

Batteries are one of the most widespread forms of storage. Lithium-ion batteries in particular have become popular for pairing with solar energy systems. Utility-scale lithium-ion installations reached over 1,600 megawatt-hours in 2018, and projections estimate continued strong growth in the coming years (Integration – Book chapter – IOPscience – Institute of Physics).

Pumped hydro storage involves pumping water uphill to a reservoir during times of excess renewable generation, then releasing it through hydroelectric turbines when power is needed. This is currently the predominant form of energy storage worldwide. Pumped hydro allows storage of large amounts of energy, but requires specific terrain and has high upfront costs.

Compressed air energy storage compresses air in underground caverns or pipes during low demand. The compressed air is then heated and expanded through a turbine to generate electricity when required. While not yet widely adopted, compressed air offers another large-scale storage option.

Conclusion

The types of renewable energy are varied and growing, with solar, wind, and hydropower leading globally in capacity added so far. However, other sources like geothermal, bioenergy, wave and tidal, and hydrogen hold promise for further diversifying and decentralizing energy production. Although renewable energy is seeing record growth, there is still a need to accelerate deployment to reach climate goals. Key next steps will be continuing to improve technologies and bring down costs, building out vital infrastructure like transmission lines, implementing supportive policies, and mobilizing investment. If the world can fully tap into the potential of renewables by scaling them up across the energy system, they hold great promise for delivering secure, affordable, low-carbon energy globally.