How Reliable Is Renewable Energy?

Renewable energy comes from natural sources that are continuously replenished, such as sunlight, wind, rain, tides, waves, and geothermal heat. The five most common renewable energy sources are:

• Solar energy from the sun
• Wind energy
• Hydropower from flowing water
• Geothermal energy from heat inside the earth
• Biomass from plants and organic waste

There is an ongoing debate about whether renewable energy sources are reliable enough to meet energy demands as fossil fuel use is phased out. This article will examine the main question: How reliable is renewable energy? It will provide an overview of each major renewable energy type and discuss factors related to integration, storage, and the future outlook for reliability.

Solar Energy

Solar photovoltaic (PV) systems convert sunlight directly into electricity using semiconducting materials like silicon. Solar panels are made up of many individual PV cells which are wired together to produce DC electricity. This DC power can then be converted to AC power using an inverter for use in homes and businesses.

The amount of electricity generated depends on how much sunlight strikes the solar panels. Capacity factors for solar PV are generally 15-25%, meaning they produce 15-25% of their rated capacity over a year [1]. This is because solar panels only produce power when the sun is shining.

Pros for reliability: Solar PV has no moving parts and degraded slowly over decades. Panels typically come with 20-30 year warranties. Solar energy production can be forecast accurately based on weather data. Rooftop solar provides energy directly at the point of use.

Cons for reliability: Solar output varies throughout the day and seasons. Energy storage or grid backup is needed for times when solar production is low. Solar power is currently more expensive than fossil fuels, though costs have dropped dramatically in recent years.

Wind Energy

Wind turbines convert the kinetic energy in wind into mechanical power that can be harnessed for electricity. The wind turns the blades of the turbine, which spins a shaft connected to a generator to produce electricity.

The reliability of wind power depends on having consistent wind resources. The capacity factor refers to the actual electrical energy output over a period of time compared to the maximum possible output if the turbine operated at full capacity continuously. According to the U.S. Department of Energy, the capacity factor for land-based wind turbines in the U.S. ranges from 25-45% ^[1]. Offshore wind turbines tend to have higher capacity factors of around 37-56% on average ^[2].

The pros of wind energy are that it’s renewable, cost-competitive, and emits no greenhouse gases. The cons are that it depends on having adequate wind, has higher land footprint than other energy sources, and can impact wildlife. However, continued technology improvements for turbine efficiency and reliability are making wind power more viable over time.

Hydropower

Hydropower plants use the energy from flowing water to produce electricity. A dam is typically built to create a reservoir, and water flowing from the reservoir through turbines spins a generator to create electricity. The amount of electricity generated depends on the volume of water flow and the height from which it falls. Hydropower is considered a renewable energy source because it relies on the water cycle – evaporation from oceans causes rainfall inland, which flows back to the ocean via rivers and streams.

The capacity factor of hydropower plants measures the ratio of actual electricity generated compared to maximum possible generation. According to the U.S. Energy Information Administration, the average capacity factor for hydropower plants in the U.S. is around 40% [1]. This is relatively high compared to other renewable sources like wind and solar power. The capacity factor depends on water flow, which can vary seasonally and annually. Multi-year storage reservoirs allow hydropower to smooth out this variability.

A major advantage of hydropower is its ability to quickly adjust electricity generation to meet changing demands. Hydropower plants can go from zero power to full power in just a few minutes. This makes hydropower a reliable source for meeting peak power demands. Hydroelectricity can also help back up intermittent renewable sources like wind and solar. One downside is that droughts can reduce generating capacity if reservoir levels drop too low.

Geothermal

Geothermal power plants use heat from the earth to produce steam to turn turbines and generate electricity. Hot water or steam is accessed by drilling wells into underground reservoirs. At the earth’s crust, temperatures range from 250–700°F, which can be used to generate electricity with binary power plants. These plants transfer heat from geothermal fluids to a secondary “working” fluid with a much lower boiling point than water. The working fluid expands into vapor when exposed to the geothermal fluid’s heat, which causes turbine blades to rotate. The spinning turbine produces electricity.

According to the U.S. Department of Energy, geothermal power plants generally have capacity factors above 90%, meaning they operate at full capacity over 90% of the time. This is significantly higher than other renewable sources like wind and solar power. The consistent heat from the earth’s interior allows geothermal plants to achieve these high capacity factors and provide a reliable, constant supply of renewable energy.

Some key advantages of geothermal energy for reliability:

• Produces steady baseload power not dependent on weather conditions (https://www.enbridge.com/energy-matters/energy-school/geothermal)
• Available 24/7, achieves capacity factors above 90% (https://www.energy.gov/eere/geothermal/geothermal-faqs)
• Sustainable and stable compared to intermittent renewables like wind and solar (https://www.twi-global.com/technical-knowledge/faqs/geothermal-energy/pros-and-cons)

Some disadvantages related to reliability:

• Limited to geographic locations with adequate geothermal resources
• Scaling up new projects can take 3-5 years to bring online
• Older plants can experience temperature declines over decades

Biomass

Biomass power plants work by burning organic material like wood, agricultural waste, garbage, or dedicated energy crops. The heat from the burning biomass turns water into steam, which then spins a turbine to generate electricity. The sustainable crops and waste streams used for biomass means it is considered a renewable energy source.

Biomass power plants can operate at capacity factors of around 80%, higher than other intermittent renewable sources like solar and wind. This means they can generate electricity consistently around the clock. According to the US Energy Information Administration, biomass generated 1.58% of total U.S. electricity in 2020.[1]

A major advantage of biomass is its reliability. Biomass plants can be dispatched on demand, meaning they can increase or decrease output based on needs. They provide steady baseload power. The fuel can be stored on-site, so plants are not dependent on weather conditions like sun or wind. This makes biomass a stable electricity source.

However, biomass does have drawbacks. While the fuel sources are renewable, there can be challenges with sustainable supply chains. Biomass plants also emit air pollution like particulate matter, nitrogen oxides, carbon monoxide, and sulfur dioxide. There are carbon emissions too, though these are considered carbon neutral because replanted crops recapture CO2. Overall biomass offers consistent renewable energy, though supply chains and emissions must be managed.

Energy Storage

Energy storage is a critical component of renewable energy systems that can improve reliability. By storing excess renewable energy for later use, energy storage helps match supply with the times when energy is most needed (MIT 2022).

Energy storage technologies work by converting electricity into a form that can be stored and converted back into electricity when needed. This allows renewable sources like solar and wind to store excess generation and dispatch it even when the sun isn’t shining or wind isn’t blowing (Xcel Energy).

There are several types of energy storage used with renewables:

• Batteries – Lithium-ion batteries are one of the most common, able to charge and discharge electricity efficiently.
• Pumped hydro – Stores energy by pumping water uphill into a reservoir, then releasing it through turbines when electricity is needed.
• Compressed air – Uses excess electricity to compress air in an underground cavern, then expands the air to turn a turbine for power generation.
• Flywheels – Spinning cylinders store rotational kinetic energy for short bursts of electricity.

Overall, pairing energy storage with renewable sources is a key strategy for overcoming intermittency and improving the reliability of clean energy systems.

Grid Integration

Integrating renewable energy sources like solar and wind into the electric grid presents challenges due to their variable and intermittent nature. Unlike traditional generation, output from renewables fluctuates based on weather conditions and time of day.

This variability can make balancing supply and demand more difficult for grid operators. Large amounts of renewables can also lead to oversupply during periods of high generation and low demand. Some key challenges with grid integration include:

• Maintaining stability and reliability as renewables displace conventional generation
• Managing voltage fluctuations from renewables
• Forecasting renewable generation
• Addressing congestion as new generation connects to the grid

There are solutions available to help overcome these integration hurdles. Improved forecasting allows grid operators to better predict renewable output. Flexible resources like battery storage and demand response can help balance supply and demand in real-time. Enhanced coordination between regional grids also enables greater sharing of resources.

Grid operators play a crucial role in renewable integration. By leveraging advanced technologies and optimizing power system operations, they can unlock higher penetrations of clean energy. Careful planning and forward-thinking regulations that account for renewables are also key. With the right strategies, grid operators can maintain reliability and resilience even as more solar, wind and other renewables come online.

Sources:
https://www.utilitydive.com/news/grid-reliability-energy-transition-energy-innovation/688423/
https://www.americanprogress.org/article/renewable-energy-is-the-key-to-building-a-more-resilient-and-reliable-electricity-grid/

Future Outlook

The future looks bright for continued growth in renewable energy. According to the Energy Information Administration, renewable energy deployment is projected to grow by 17% to 42 GW in 2024 and account for almost a quarter of electricity generation (Deloitte). Further improvements in renewable energy technologies like solar panels, wind turbines, and energy storage will enable greater grid integration and reliability.

Policies will play a key role in supporting the continued adoption of renewable energy. Initiatives like renewable portfolio standards, carbon pricing programs, and clean energy tax credits provide long-term certainty for investors and developers. Government funding for research and development can also accelerate innovations to make renewable energy even more efficient, reliable and cost-competitive (American Progress).

With the right policies and sustained technology advances, renewable energy is poised to transform electricity grids around the world. The transition to high shares of renewable energy will increase resilience, mitigate climate change and provide affordable, reliable power for all.

Conclusion

In summary, renewable energy sources such as solar, wind, hydropower, geothermal and biomass have the potential to provide reliable power at scale. However, effectively integrating intermittent renewables into the grid remains an ongoing challenge that requires a balanced approach. Key methods for enabling renewables growth include deploying energy storage to smooth supply, improving grid flexibility through demand response and smart grid technologies, and maintaining backup power from dispatchable sources.

While renewables have clear environmental benefits over fossil fuels, their variability means they cannot entirely displace conventional baseload generation in the near-term. A diverse mix of generation sources and load balancing strategies will be needed during the transition to higher renewable penetration. With continued technology improvements and grid modernization, renewables have the capability to transform electricity supply. But they require investment, planning and innovation to maintain reliability as our clean energy utilization expands.