Variable Renewable Energy Examples

Variable renewable energy (VRE) sources are forms of renewable energy that fluctuate naturally and cannot be precisely controlled. The most common types of VRE are solar and wind power. Unlike traditional energy sources like coal, natural gas, nuclear, and hydroelectric power which provide consistent output, VRE sources vary based on environmental conditions like wind speeds and cloud cover.

VRE sources are becoming increasingly important as countries around the world transition to cleaner forms of energy to reduce greenhouse gas emissions and mitigate climate change. According to the World Energy Council, the global share of VRE generation capacity increased from 9% in 2008 to 11% in 2018, and is projected to supply up to 40% of global electricity by 2040.

To maximize the benefits of VRE sources, countries must find solutions to effectively integrate large amounts of variable generation into the electricity grid while maintaining reliability and affordability. This involves developing flexible power systems, improving forecasting capabilities, expanding energy storage, and deploying smart grid technologies.

Solar Power

Solar power is a variable renewable energy resource that harnesses energy from the sun to generate electricity. There are two main technologies used: photovoltaics (PV) and concentrated solar power (CSP).

Photovoltaics convert sunlight directly into electricity using semiconducting materials. PV panels are made up of many individual solar cells and are a common sight on rooftops today. The amount of electricity generated depends on how much sunlight strikes the panels. PV technology is modular and scalable, making it ideal for distributed generation. According to the Solar Energy Industries Association (SEIA), solar accounted for 15.9% of electricity generated by renewable sources in 2022, up from 13.5% in 2021 (source). On average, a residential solar system has the capacity to produce 8,187 kWh annually.

Concentrated solar power (CSP) systems use mirrors to focus sunlight to heat a receiver containing a fluid. The high temperature heat is used to drive a turbine and generator to produce electricity. CSP requires direct solar radiation to operate efficiently and is better suited for large, utility-scale generation. CSP accounted for just 0.4% of US solar electric capacity in 2021. However, the dispatchable nature of CSP with thermal energy storage offers advantages for grid stability.

Wind Power

Wind power harnesses the wind to generate electricity using wind turbines. Wind turbines convert the kinetic energy in wind into mechanical power that runs a generator to produce electricity. Wind power is considered a renewable energy source because wind is continuously replenished by solar heating and the rotation of the earth.

There are two main types of wind power systems: onshore wind farms and offshore wind farms. Onshore wind farms are located on land, often in rural or remote areas. The wind turbines are usually spread out over a large area to maximize energy production. Offshore wind farms are located in bodies of water, usually oceans or large lakes. Offshore wind turbines can harness stronger and more consistent winds compared to onshore, but the initial construction costs are higher.

According to the U.S. Energy Information Administration, wind power supplied over 7% of total U.S. electricity generation in 2019, making it a major renewable energy source. Globally, wind power capacity reached over 650 gigawatts in 2019. The future outlook for wind power remains positive as costs continue to fall and more capacity comes online each year.[Countries at the Forefront of Renewable Energy]

Hydropower

Hydropower is one of the most significant renewable energy sources worldwide. It currently accounts for over 16% of global electricity generation and has the largest installed capacity of all renewables (Matek, n.d.). Hydroelectric dams harness the energy of flowing water to generate electricity. There are two main types of hydropower facilities:

Run-of-river systems divert a portion of a river’s water through a canal or penstock to turn turbines and generate electricity. The water is returned to the river downstream. These systems do not require large reservoirs for water storage.

Reservoir systems utilize dams to impound water in a reservoir. The reservoir water passes through turbines in the dam to generate electricity. Reservoir systems allow for electricity production on demand by controlling water flow. They also enable seasonal storage of water for electricity generation (International Energy Agency, n.d.).

The countries with the most prospective hydropower capacity are China, Brazil, India, Canada, and Colombia [1]. Europe as a whole generates around 20% of its electricity from hydropower, with Norway generating over 95% of its domestic electricity from hydro plants [2]. Overall, hydropower will continue serving as a major source of renewable energy worldwide.

[1] https://www.statista.com/statistics/1414412/global-prospective-hydropower-capacity-by-country/

[2] https://globalenergymonitor.org/projects/global-hydropower-tracker/

Bioenergy

Bioenergy is energy derived from biomass, or organic matter such as plants, agricultural crops and residues, wood, animal manure, and food waste. It can be used to produce power, heat, and transportation fuels like ethanol and biodiesel.

The most common forms of bioenergy include:

• Biomass from plants and trees used to generate electricity or heat.
• Biogas produced from anaerobic digestion of organic matter and used for power generation.
• Biofuels like ethanol and biodiesel made from crops like corn and soybeans for transportation.

According to the International Energy Agency (IEA), bioenergy accounted for around 5% of total global primary energy supply in 2019 [1]. Traditional biomass like fuelwood represents about 60% of total bioenergy use, while modern bioenergy from liquid biofuels, biogas, and biomass power represent the remaining 40%.

The share of biofuels in road transport grew to around 4.1% in 2019, meeting around 3% of global road transport fuel demand. Ethanol production reached around 160 billion litres and biodiesel production around 43 billion litres globally.

Bioenergy offers renewable energy while supporting waste management, agriculture, and forestry sectors. However, its sustainability depends on proper land use practices and advancements in biomass conversion technologies.

Geothermal Energy

Geothermal energy is derived from the natural heat of the earth. It can be harnessed in a few different ways. Geothermal power plants use steam or hot water from reservoirs underground to turn turbines and generate electricity. Geothermal heating and cooling systems use underground temperatures to heat and cool buildings directly. Geothermal energy is considered a renewable energy source because the water is replenished by rainfall, and the heat emanates continuously from volcanic activity beneath the earth’s surface.

According to the Geothermal Energy Association, the top countries for geothermal power capacity in recent years have been the United States, Philippines, Indonesia, New Zealand, Mexico, Italy, Iceland, Kenya, and Turkey. The countries with the most geothermal direct use installed capacity include the United States, China, Sweden, Turkey, Japan, and Iceland. Geothermal energy offers a consistent and reliable source of renewable base load power that is not subject to intermittent sunshine or wind conditions. It also provides heating and cooling directly from the earth. With technology improvements, enhanced geothermal systems accessing deeper reservoirs could dramatically increase geothermal power generation worldwide.

Sources:

https://www.infinityturbine.com/search/orc-05/green-machine-series-4000-004.html

http://large.stanford.edu/courses/2016/ph240/barber2/docs/gea-sep12.pdf

Wave & Tidal Power

Ocean waves and tides contain tremendous amounts of energy that can be harnessed to generate electricity. Unlike solar and wind power, wave and tidal energy are predictable and consistent, which makes them attractive options. There are two main approaches to generating power from the ocean:

Wave energy converters capture the energy of surface waves and convert it into electricity. They use technologies like floating structures, oscillating water columns, and submerged turbines. According to Ocean Energy Europe, global wave energy capacity reached just 67 kW in 2022, down from 2.2 MW in 2021. Most demonstration projects are currently located in Europe. Ocean-Energy-Key-Trends-and-Statistics-2022.pdf

Tidal energy utilizes the rise and fall of tidal streams to turn underwater turbines. Tidal barrages also trap water at high tide and release it to turn turbines as the tide ebbs. Global tidal stream capacity was around 524 MW in 2022, with the largest capacities located in South Korea and France. Worldwide capacity of marine energy 2009-2022

While ocean energy holds promise, technology costs need to decrease and reliability increase for it to play a larger role in renewable electricity generation.

Storage

Storage technologies play a crucial role in integrating variable renewable energy sources like solar and wind onto the electric grid. Since the output from solar and wind farms fluctuates based on weather conditions and time of day, storage provides a buffer to smooth out the variability and align generation with electricity demand.

According to Statista, as of 2022 the United States led globally with around 8 gigawatts of installed electrochemical storage capacity, predominantly lithium-ion batteries [1]. Storage enables renewable energy to be dispatched when it is most needed. It also allows renewables to provide ancillary services to the grid such as frequency regulation and spinning reserves. By charging when renewable output is high and discharging when it is low, storage helps mitigate grid instability and prevents over-generation issues.

Looking ahead, Wood Mackenzie forecasts the global energy storage market to expand from 12 gigawatts today to over 60 gigawatts by 2030. With many jurisdictions setting aggressive renewable energy targets, ample storage capacity will be critical to enabling high variable renewable penetration while maintaining reliable grid operation.

Grid Integration

Integrating variable renewable energy sources like solar and wind power to the electric grid can pose challenges due to their intermittent and weather-dependent nature. However, studies by the National Renewable Energy Lab (NREL) have identified solutions to enable high penetrations of renewables on the grid.

One key challenge is dealing with fluctuations in renewable generation throughout the day as cloud cover or wind speeds change. This requires more flexible grid operation and planning reserves to balance supply and demand minute-to-minute. Solutions include improved forecasting of renewable output, market designs that incorporate forecasts, and flexible conventional generation that can ramp up when needed.

High renewable penetrations also lead to oversupply during periods of high generation and low demand. Curtailing or storing excess renewable energy can avoid grid imbalances. Geographic diversity of renewable assets can also smooth out fluctuations in output.

Upgrading transmission infrastructure enables movement of renewable power from source to demand centers. Advanced power electronics help maintain reliability and control power flows as more renewables come online. Improved grid operations, electricity markets, and accurate forecasting also facilitate integration.

Overall, solutions exist to enable very high levels of renewable penetration on power systems. With the right technologies, market frameworks, and grid operations practices, the variability of renewable resources can be managed.

Sources:
https://www.nrel.gov/docs/fy20osti/72143.pdf
https://greeningthegrid.org/Grid-Integration-Toolkit/Topics-And-Resources/grid-integration-studies

Future Outlook

The future prospects for variable renewable energy sources like solar, wind, and hydropower are very positive. According to the International Energy Agency (IEA), global renewable power capacity is expected to grow by 2,400 gigawatts between 2022 and 2027, equal to the entire current power capacity of China (IEA). This rapid growth is being driven by countries seeking to improve energy security and reduce dependence on fossil fuels.

The IEA projects that solar PV additions will continue increasing, reaching over 320 GW per year by 2026. Total solar PV capacity could grow from under 700 GW today to over 4,500 GW by 2030 (IEA). Wind power capacity is also expected to nearly double from around 740 GW today to over 1,400 GW by 2027, despite near-term challenges. Hydropower will continue expanding in emerging economies.

Overall, the share of renewables in global electricity generation could reach over 40% by 2030, up from under 30% today. Continued technology improvements, cost reductions, policy support, and private investment will drive rapid growth in variable renewable energy sources like solar, wind, and hydropower worldwide (IRENA). Their flexibility and sustainability make them well-positioned to meet rising electricity demand.