What Is Solar And Renewable Energy?

Renewable energy comes from natural sources or processes that are constantly replenished. This includes sunlight, wind, water, plants, and much more. Unlike fossil fuels which take millions of years to form, renewable energy is readily available with limited or no need for extraction, transportation, and processing just to generate electricity.

Transitioning to renewable energy is critical to combat climate change and build a sustainable future. The burning of fossil fuels like coal, oil, and natural gas releases greenhouse gases which trap heat and warm the planet. Renewable energy generates little to no global warming emissions. Widespread adoption of renewables along with energy efficiency can help us reach net-zero emissions and stabilize the climate.

There are many different types of renewable energy sources that are clean, sustainable, and in endless supply. The major forms of renewable energy include solar, wind, hydropower, bioenergy, geothermal, wave, and tidal power. Each has unique advantages and can play a significant role in decarbonizing electricity generation, heating, transportation, and more.

Table of Contents

Solar Energy

Solar energy is derived from the sun’s radiation and harnessed using various technologies such as solar photovoltaics, solar thermal energy, and concentrated solar power. Solar energy technologies convert sunlight into electricity and heat either directly using photovoltaics and solar thermal collectors, or indirectly using concentrated solar power systems.

How Solar Energy Works

Solar energy technologies harness the energy from the sun’s electromagnetic radiation to generate useful energy in the form of electricity and heat. Solar radiation can be converted to electricity using solar photovoltaics, concentrated into thermal energy using solar thermal collectors, or used to heat a working fluid to power turbines and generate electricity using concentrated solar power.

Solar Photovoltaics

Solar photovoltaic (PV) panels contain semiconductor materials that convert sunlight directly into electricity through the photovoltaic effect. PV panels do not need direct sunlight and can still generate some electricity on cloudy days. Individual PV cells are interconnected and assembled into solar panels and arrays of various sizes to generate power.

Solar Thermal

Solar thermal technologies use collectors such as lenses or mirrors to concentrate sunlight which is then converted to thermal energy or heat. The heat can be used directly for hot water heating in homes, commercial and industrial processes, and even electricity generation. Types of solar thermal collectors include flat plate collectors, evacuated tube collectors, solar air heaters, and concentrating collectors.

Concentrated Solar Power

Concentrated solar power (CSP) systems utilize mirrors to concentrate sunlight to heat a transfer fluid which produces steam to spin a turbine generator to produce electricity. CSP requires direct solar radiation and currently only operates in areas of high direct normal irradiance. CSP technologies include parabolic trough, linear Fresnel, power tower, and dish/engine systems.

Solar Applications

Solar energy can be used at both small and utility-scale applications. Small scale uses include solar water heating, solar pool heating, solar attic fans, solar lighting, solar ovens, and rooftop solar PV. Large scale solar power generation plants can range from a few megawatts to over 1 gigawatt using technologies such as PV power stations, CSP towers, and commercial solar thermal systems.

Wind Energy

Wind energy is one of the leading renewable energy sources worldwide. It harnesses the wind, caused by the uneven heating of the atmosphere by the sun, through the use of wind turbines to generate electricity.

Wind turbines work by converting the kinetic energy in wind into mechanical power through their blades, which then spins a generator to create electricity. The amount of energy that can be generated depends on the turbine’s size and the wind’s speed through the rotor. The turbines are mounted on tall towers to take advantage of faster wind speeds at higher altitudes.

There are two main types of wind turbines:

Onshore wind turbines located on land
Offshore wind turbines located in bodies of water

Onshore wind is more mature and widely used today, but offshore wind capacity is expanding rapidly due to stronger and more consistent winds over water. Offshore wind farms are typically built in shallow waters within about 30 miles of shore.

Global wind energy capacity reached over 651 gigawatts in 2018. Wind power meets 14% of electricity demand in the European Union and supplies 6.3% of global electricity. With falling costs and advanced technologies, wind energy capacity is projected to grow substantially in the coming decades.

Hydropower

Hydropower harnesses the energy of flowing water to generate electricity. It uses the force of moving water to spin a turbine connected to a generator. Dams are constructed to create reservoirs and control water flow. As water is released from the reservoir, it flows through a turbine, spinning it, which then activates a generator to produce electricity.

There are several types of hydropower facilities:

Dams – Most common type of hydropower. Stores water in a reservoir and controls its flow.
Pumped storage – Stores energy by pumping water uphill to a reservoir at higher elevation. During peak demand, water is released to generate electricity.

Run-of-river – Channels portion of river through a canal to spin turbine. Does not require dams or reservoirs.
Micro hydropower – Small hydropower systems that typically produce up to 100 kW of power. Often used in rural areas that are not connected to electric grid.

Hydropower is a renewable energy source and offers several benefits. It produces no direct waste or pollution. Dams provide flood control, water supply, and recreation. However, dams and reservoirs also radically alter ecosystems and river flows. They disrupt fish migration and affect water quality and sediment flow downstream. Careful site selection and environmental mitigation measures are necessary.

Geothermal Energy

Geothermal energy utilizes the heat generated and stored inside the earth. The word “geo” means earth, while “thermal” means heat. This heat can be extracted and used to generate electricity or provide heating and cooling.

The earth’s core is extremely hot, reaching temperatures of over 5,000°C. This heat is constantly generated by the slow decay of radioactive particles, such as potassium-40 and thorium-232, in the earth’s core. As depth increases, so does the temperature inside the earth. This geothermal energy heats up underground reservoirs of hot water and steam that can be tapped for energy production.

To generate electricity from geothermal energy, wells are drilled into underground reservoirs to provide a path for steam or hot water to reach the surface. The steam rotates a turbine that activates a generator, which produces electricity. For direct use applications, wells or pumps bring hot water to the surface for purposes like heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes.

Geothermal energy is considered renewable since the water is replenished by rainfall and the heat is continuously produced deep within the earth. The amount of heat available is enormous and will continue for billions of years. With appropriate management, geothermal resources can provide sustainable energy for the long-term.

Bioenergy

Bioenergy is renewable energy derived from organic matter such as plants and animal waste. The most common forms of bioenergy are biofuels used for transportation, biomass burned to generate electricity, and biogas captured from landfills or anaerobic digesters. Bioenergy is considered carbon-neutral because the carbon dioxide released when burned is equal to the amount absorbed during plant growth. However, there are sustainability concerns around bioenergy related to land use changes and lifecycle emissions.

Biofuels like ethanol and biodiesel are made from crops such as corn, sugarcane, and soybeans. They can replace gasoline and diesel in vehicles, but using food crops for fuel has raised concerns about food security. Second generation biofuels made from non-edible plant sources like switchgrass may provide more sustainable options. Biofuels production can also negatively impact land use, biodiversity and water resources if not properly managed.

Biomass power is generated by burning organic matter like wood, agricultural residues, and municipal solid waste. While biomass emits CO2 when burned, it can provide low-carbon energy when sourced sustainably. However, biomass facilities must follow strict air pollution control regulations. The carbon neutrality of biomass depends on factors like regrowth rates and land use changes.

Biogas is produced from the breakdown of organic waste in landfills or anaerobic digesters. This methane-rich gas can be captured and used to generate electricity or heat. Diverting organic waste to produce biogas reduces methane emissions from landfills and provides a renewable energy source. Using manure from farms and food waste from homes or businesses as feedstocks for anaerobic digestion also helps manage waste sustainably.

While bioenergy has many potential benefits, its sustainability depends on proper management of land, water resources and biodiversity. Lifecycle assessments taking into account emissions from both production and use are needed to determine the true climate impact of different bioenergy options. Overall, bioenergy can play an important role in the renewable energy mix when deployed responsibly.

Wave and Tidal Energy

Wave and tidal energy represent two of the most promising renewable energy technologies that utilize the natural power of water. Both are in relatively early stages of commercial development but hold enormous potential to provide clean, renewable electricity.

Wave energy works by capturing the energy of ocean surface waves and converting it into electricity. Typically, this involves using floating or submerged devices that move up and down as waves pass. This motion powers an electricity generator.

There are three main types of wave energy converters:

Point absorbers that float on the surface and capture energy in all directions
Attenuators that are oriented parallel to the direction of wave propagation
Terminators that are perpendicular to the direction of wave propagation

Tidal energy utilizes the rise and fall of tides to generate electricity. Tidal barrages are essentially dams built across inlets that trap water at high tide. When the tide goes out, the water flows through turbines to generate electricity. Tidal stream generators work more like underwater wind turbines, capturing energy from tidal currents.

Wave and tidal energy are still developing and face challenges around device durability, grid integration, and environmental impacts. However, costs are falling as technology improves. According to the U.S. Department of Energy, the worldwide wave energy resource is estimated at about 300 gigawatts and tidal resources exceed 100 gigawatts.

Hydrogen

Hydrogen is a versatile energy carrier that can be used as a transportation fuel and for energy storage. When hydrogen is produced using renewable energy sources, it serves as a clean and sustainable energy option.

Hydrogen is most commonly produced through electrolysis, where electricity is used to split water molecules into hydrogen and oxygen. Other production methods include reforming natural gas, gasification of coal, or extraction from fossil fuels. The source of electricity or feedstock determines how clean the resulting hydrogen is.

As an energy storage medium, excess renewable electricity can be used via electrolysis to produce hydrogen. This hydrogen can then be stored and later converted back into electricity in a fuel cell when renewable resources are unavailable. Hydrogen provides a solution for storing intermittent renewable energy.

Hydrogen fuel cells can also be used to power electric vehicles. Fuel cell vehicles convert stored hydrogen into electricity that runs an electric motor. The only byproduct from the fuel cell is water, making hydrogen a zero-emissions transportation fuel. Hydrogen fueling stations are expanding in several regions to support fuel cell vehicle growth.

Storage

The growth of renewable energy sources like solar and wind is dependent on developing adequate and affordable electricity storage. Storage helps overcome the intermittent nature of sun and wind by capturing excess energy when available and discharging when needed. Effective storage is key for the large-scale deployment of renewables.

There are several storage technologies under development today:

Pumped hydro storage – Stores energy by pumping water uphill into a reservoir when electricity supply exceeds demand. The water can then be released to generate power at times of peak demand.

Compressed air energy storage – Uses excess electricity to compress air in large underground caverns. The pressurized air is heated and expanded through a turbine when electricity is needed.
Batteries – Store energy chemically for later use. Lithium-ion batteries are becoming popular but remain expensive. Other battery types like lead-acid and flow batteries are also used.
Hydrogen – Can act as an energy carrier and storage medium. Excess electricity is used to produce hydrogen through electrolysis. The hydrogen can then be stored and used later to generate electricity.

Thermal storage – Captures excess heat or cold to help balance energy supply and demand between day and night.

Many of these technologies are still evolving with efforts focused on improving performance and reducing costs. But storage will be pivotal in increasing the contribution of renewables to electricity supply.

Growth of Renewables

Renewable energy capacity has seen rapid growth over the past decade. In 2021, total global renewable energy capacity reached over 3,000 gigawatts (GW), up over 8% from 2020. The majority of this growth came from solar and wind power. Solar power capacity increased 22% in 2021 to over 1,000 GW globally. Wind power increased 12% to reach over 837 GW. Together, solar and wind power now make up over 10% of global electricity generation.

By region, Asia Pacific leads in total installed renewable capacity, followed by Europe and North America. China has the most renewable energy capacity of any country, with over 1,000 GW. The United States comes in second with over 380 GW. India, Brazil, and Germany round out the top 5 countries for total installed renewable capacity.

Looking ahead, renewables are projected to continue their strong growth. The International Energy Agency (IEA) forecasts renewable capacity will increase over 60% to 2026 under current government policies and targets. With more ambitious commitments, renewables could reach 4,800 GW globally by 2026. Key drivers supporting this growth include cost declines, technological advances, policy support, and increased investment.

Many countries have implemented policies to accelerate the transition to renewable energy. Over 130 countries have net-zero emissions targets, with goals to dramatically scale up renewables. Major markets like the European Union, the U.S., India and others have implemented incentive programs, mandates, and regulations to phase out fossil fuel use in favor of carbon-free energy sources. If these policies are successfully implemented, renewables have the potential to supply over 90% of global electricity by 2050, playing a central role in mitigating climate change.