What Are Five Renewable Energy Sources Technologies?

Renewable energy comes from natural sources that are constantly replenished, such as sunlight, wind, water, and geothermal heat. Renewable energy technologies harness these flows of energy to generate electricity, provide heat, or mechanical power with a much lower environmental impact than conventional technologies relying on finite resources like coal, oil, and natural gas. The importance of renewable energy comes from both environmental and economic viewpoints. Renewable energy allows electrical generation without fossil fuel combustion, reducing pollutants that contribute to problems like climate change and poor air quality. Renewables can also provide energy locally, improving energy security and access. Economically, renewable electricity costs have dropped dramatically in the last decade, becoming cost-competitive with conventional sources. The transition from fossil fuels to renewables is a crucial step in building a sustainable energy system.

Solar Power

Solar power is generated by capturing sunlight and converting it into electricity. This is done through the photovoltaic effect, in which solar cells contain materials that absorb photons from sunlight and release electrons. The electrons flow through the material to produce electric current.

Most solar power systems today use solar photovoltaic (PV) panels made up of silicon solar cells. Solar PV systems can be installed on rooftops of buildings, or ground-mounted over large areas to form utility-scale solar farms. Residential rooftop solar typically generates 3-8 kilowatts, while solar farms can generate hundreds of megawatts and provide power for thousands of homes.

Solar thermal technologies use mirrors to concentrate sunlight to heat a fluid like water or oil, which then generates steam to spin a turbine and generator. Concentrated solar power plants allow solar energy to be stored as heat and provide electricity even when the sun isn’t shining.

Solar energy offers a clean, renewable source of electricity that produces no air or water pollution. Solar only works during daylight hours, so energy storage or supplementing with other sources is important for 24/7 reliability. The cost of solar has dropped dramatically in recent years, leading to rapid growth in residential, commercial and utility-scale installations. The U.S. had over 100 gigawatts of solar capacity in 2021.

Sources: “How does solar power work? – National Grid”, “How does solar power work? – KinectSolar”

Wind Power

Wind power harnesses the wind to generate electricity using wind turbines. Wind turbines work by converting the kinetic energy in wind into mechanical power that runs a generator (National Grid, 2022). There are two main types of wind farms: onshore and offshore.

Onshore wind farms are located on land, while offshore wind farms are located in bodies of water, usually oceans, lakes, and rivers. Offshore wind turbines tend to be larger in capacity and more efficient than onshore turbines due to higher wind speeds and consistency in wind direction offshore (National Grid, 2022). However, offshore wind farms are more expensive to construct and maintain than onshore farms.

Today’s new wind power projects utilize wind turbines with capacities in the 3-4 MW range onshore and 8-12 MW offshore (IRENA, 2022). Global wind power capacity reached 743 GW by the end of 2019, with 60% from onshore farms and 40% from offshore farms (CSS, 2022). The energy return on investment (EROI) for wind power is estimated to be between 18-20, meaning that for every unit of energy invested in wind power, 18-20 units of energy are generated (CSS, 2022).

Hydropower

Hydropower is one of the oldest and most widely used renewable energy sources. It generates electricity by using the power of moving water. There are several types of hydropower technologies:

Dams and reservoirs are the most common type of hydropower plant. A dam is constructed to create a large reservoir, and the water flowing through turbines in the dam generates electricity. Major advantages of reservoir hydropower include the ability to store water for electricity generation when needed.¹

Run-of-river hydropower captures the energy from rivers or streams with little or no reservoir capacity. These systems rely on the steady flow of the river to generate electricity.²

Pumped storage hydropower plants can pump water uphill into a reservoir during times of low electricity demand and release it through turbines to generate power during high demand. This allows energy storage for later use.³

Micro hydropower systems have a generating capacity up to 100 kilowatts and can provide power for isolated homes, farms, or small communities.¹

Geothermal

Geothermal energy utilizes the natural heat from the Earth’s interior to generate electricity and provide heating and cooling. The geothermal gradient, which is the rate of temperature increase with depth in the Earth, drives geothermal energy systems. On average, the geothermal gradient is about 25–30°C/km of depth (Source). However, in some areas with high geothermal activity, the gradient can be much higher, allowing geothermal power plants to operate more efficiently.

There are three main types of geothermal power plants (Source):

• Dry steam plants that use steam from a geothermal reservoir to directly drive a turbine generator.
• Flash steam plants that pull deep, high-pressure hot water into lower pressure tanks and use the resulting flashed steam to drive a turbine.
• Binary cycle plants that pass geofluid through a heat exchanger to heat a secondary fluid with a lower boiling point that is vaporized to drive a turbine.

Geothermal systems can provide constant baseload power and serve as a sustainable alternative to fossil fuels. However, geothermal power is restricted to areas with sufficient geothermal resources and accounts for a small fraction of total global electricity generation.

Biomass

Biomass energy comes from organic matter such as plants, wood, agricultural waste, urban waste, and animal waste. It can be converted into useful energy through various processes like combustion, fermentation, anaerobic digestion, and gasification (https://www.eia.gov/energyexplained/biomass/). Biomass is considered a renewable energy source because the organic materials can be replenished on a human timescale.

Plant-based biomass includes wood, grasses, algae, and other plants that harness energy from the sun via photosynthesis. These feedstocks can be directly burned for heating and electricity generation. They can also be converted into liquid biofuels like ethanol and biodiesel. Agricultural residues like corn stover, sugarcane bagasse, and wheat straw are abundant sources of plant biomass (https://bmcenergy.biomedcentral.com/articles/10.1186/s42500-019-0004-7).

Waste-to-energy conversion utilizes organic waste streams like municipal solid waste, agricultural waste, and animal manure. Technologies like anaerobic digestion produce biogas from organic matter, while processes like pyrolysis and gasification generate synthesis gas. These gases can be used to generate electricity, heat, or transportation fuels (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7738282/). Converting waste into energy reduces landfill volumes and provides a sustainable energy supply.

Hydrogen

Hydrogen is a promising renewable energy source that can be produced through electrolysis and then used to generate electricity in fuel cells. Electrolysis uses electricity to split water into hydrogen and oxygen. This process can utilize electricity from renewable sources like solar or wind to produce carbon-free hydrogen fuel (1).

Fuel cells then convert the hydrogen back into electricity, with water as the only byproduct. Fuel cells are more efficient than combustion engines and eliminate harmful emissions (2). The hydrogen fuel can be used in fuel cell vehicles or to store energy from renewables. Hydrogen has a high energy density by weight, though it has a low density by volume compared to other fuels (3).

Effective hydrogen storage and transportation is an important area of research. Hydrogen is typically stored as a compressed gas or cryogenic liquid. Storage tanks strong enough to contain the high-pressure gas are large and heavy. Materials like metal hydrides and carbon nanotubes are being investigated to maximize hydrogen storage density (2). Developing safe, high-capacity, affordable hydrogen storage is key to unlocking its full potential.

(1) https://www.energy.gov/eere/fuelcells/hydrogen-production-electrolysis

(2) https://www.energy.gov/eere/fuelcells/hydrogen-storage

(3) https://www.sciencedirect.com/topics/engineering/hydrogen-energy-storage

Wave & Tidal Energy

Wave and tidal energy are sustainable renewable energy sources that harness the kinetic energy of ocean waves and tides. Tidal stream generators and wave energy converters are two promising technologies being developed in this field.

Tidal stream generators, also known as tidal turbines, are underwater rotors that extract energy from moving tidal currents in a similar way that wind turbines capture energy from wind. The kinetic motion of the tides turns the rotors, which powers an electrical generator. Tidal stream generators can provide predictable and reliable clean energy, as the tides are highly predictable. However, the technology faces challenges around turbine durability in harsh ocean environments. ¹

Wave energy converters capture energy from the up-and-down motion of ocean waves using floating or submerged devices. Different designs include oscillating water columns, point absorbers, and oscillating wave surge converters. Wave power holds enormous energy potential but can be intermittent and difficult to capture efficiently. Continued innovation and economies of scale could enable wave energy to become a major renewable electricity source. ²

Comparison

When comparing renewable energy sources, some of the key factors to consider are cost, capacity factor, land use needs, and the pros and cons of each technology.

In terms of cost, hydropower is often the cheapest at around $0.05/kWh, followed by onshore wind, solar PV, geothermal and biomass which are typically below $0.10/kWh. Offshore wind remains more expensive at around $0.08/kWh (1). However, costs vary greatly based on location, resource quality, project size and other factors.

Capacity factors also differ significantly. Geothermal and hydropower facilities often achieve capacity factors of 90% or higher, meaning they can generate nearly their full potential output. Wind and solar PV have lower capacity factors of 25-50% due to intermittency. Biomass plants can achieve 60-80% capacity factors (2).

Land use needs also vary. Hydropower requires large areas flooded behind dams. Solar and onshore wind need substantial land areas. Offshore wind, geothermal and biomass have smaller footprint requirements (3).

Each renewable energy source has pros and cons. Hydropower provides inexpensive, reliable baseload power but has high upfront costs and environmental impacts. Wind and solar offer emissions-free power but intermittency requires integration. Geothermal and biomass provide consistent renewable power but have limited suitable locations. There is no single perfect energy source, so diversifying renewables is optimal.

(1) IRENA – Renewable Power Generation Costs in 2022

(2) EIA – Electric Power Annual

(3) NREL – Land-Use Requirements for Solar Power Plants in the United States

Conclusion

Renewable energy sources play an important role in mitigating climate change and transitioning to clean energy. Given the variability of renewable energy sources, a diverse energy portfolio is crucial to ensure reliability and resiliency. Renewable energy has enormous growth potential and the capacity to supply 100% of global energy demand by 2050 (https://www.un.org/en/climatechange/raising-ambition/renewable-energy). With supportive policies, falling costs, and technological advances, renewable energy can expand rapidly while reducing carbon emissions. Switching to renewable energy across power, heating, cooling, and transport sectors is a key strategy to limit global warming. Tapping renewable sources also reduces air pollution and enhances energy access and security. In summary, renewable energy plays a pivotal role in building sustainable and equitable energy systems for the future.