Is Solar Energy Inconsistent?
Solar energy refers to radiant light and heat from the sun that is captured and converted into useful forms of energy such as electricity using technologies like solar photovoltaic panels. As defined by Britannica, “Solar energy, radiation from the Sun capable of producing heat, causing chemical reactions, or generating electricity.” (source). Solar energy is considered a renewable and clean source of energy, and its importance in the world’s energy mix is growing rapidly. According to SEIA, “Solar power is energy from the sun that is converted into thermal or electrical energy. Solar energy is the cleanest and most abundant renewable energy source available” (source).
How Solar Energy Works
Solar energy technologies convert sunlight into usable energy in two main ways – through photovoltaic (PV) panels that generate electricity or through concentrating solar power plants that produce heat to drive a steam turbine and generate electricity. Photovoltaic cells are made of semiconducting materials that absorb photons from sunlight and convert them into electricity through the photovoltaic effect. When sunlight hits the PV cell, electrons are knocked loose from their atoms which allows them to flow through the material and produce electricity. This electricity is then fed into the grid through an inverter. Concentrated solar power plants use mirrors to reflect and concentrate sunlight onto receivers that collect and convert it as heat. The heat is then used to drive a steam turbine connected to a generator that produces electricity.
Sources:
https://www.energy.gov/eere/solar/how-does-solar-work
https://www.nationalgrid.com/stories/energy-explained/how-does-solar-power-work
Intermittency of Solar
Solar energy is considered an intermittent energy source because it is not constantly available (Energy Education, n.d.). The amount of sunlight that hits any location on Earth varies throughout the day as the sun rises and sets. It also varies depending on the seasons, with shorter winter days providing less sunlight than longer summer days. Solar energy can be impacted by weather as cloud cover or storms block or reduce the amount of sunlight (Roberts, 2015). This variability means solar power generation fluctuates, producing more energy on sunny days and less on cloudy days.
Solar panels can only generate electricity when the sun is shining on them. The intermittent nature of solar energy presents challenges for integrating solar power into the electric grid, which relies on matching supply with demand (Bonneville Power Administration, n.d.). Unlike traditional power plants which can be ramped up or down as needed, solar energy cannot be dispatched to meet demand. The variability and uncertainty around solar power generation must be balanced through grid management solutions.
Solutions to Intermittency
There are several solutions being developed and implemented to deal with the intermittency of solar energy and integrate it more seamlessly into the electric grid. Key solutions include:
Energy Storage
Energy storage systems like batteries and pumped hydro storage can store solar energy when production is high and discharge when solar production is lower, smoothing out fluctuations. According to the National Renewable Energy Laboratory, adding energy storage to solar projects can reduce the impacts of intermittency and variability by up to 50-60%1.
Grid Improvements
Upgrading transmission infrastructure, increasing grid flexibility through advanced inverters, and improving weather and production forecasting tools can enable grids to better integrate variable sources like solar2. Grid operators can then quickly ramp other sources up or down to complement solar’s daily profile.
Forecasting
Better solar forecasting provides grid operators advance notice of fluctuations in solar output, allowing time to schedule complementary generation. Data from weather forecasts, satellite imaging, and smart sensors make solar forecasting tools increasingly sophisticated and accurate3.
Comparing to Other Sources
Solar energy is often criticized for being intermittent or inconsistent compared to traditional energy sources like coal, natural gas, and nuclear. However, all energy sources have some degree of variability in their output. Other renewable sources like wind and hydropower can also be intermittent.
Wind power depends on having adequate wind speeds to spin the turbine blades and generate electricity. Wind speeds can vary hour to hour and day to day based on weather conditions and location. According to the EIA, the capacity factor for wind farms in the US averages around 35%, meaning they produce about a third of their maximum potential output over a year [1]. The intermittency of wind power can make it challenging to integrate large amounts of wind energy onto the grid.
Hydropower relies on river water flows to spin turbines. These flows can change seasonally depending on rainfall and snowmelt. Multi-year droughts can also reduce hydropower output. The average capacity factor for hydropower in the US is around 40% [2]. Upgrading existing hydropower dams with pumped storage capabilities can help overcome some intermittency issues.
So while solar intermittency presents grid integration challenges, other renewable sources have variability as well. With the right grid flexibility solutions, a diverse mix of renewables can provide reliable clean energy.
Regional Differences
Solar energy potential varies significantly across different regions and locations. This is due to differences in solar irradiance, the amount of solar radiation that reaches the Earth’s surface. According to data analyzed by Our World in Data, some parts of the world such as Africa, Australia, the Middle East, and parts of Asia have much higher solar resources than other regions like Europe and North America.
For example, across Africa solar potential ranges from 1,500 to 2,500 kilowatt hours per kilowatt peak (kWh/kWp). In comparison, solar potential in Germany is around 900 to 1,250 kWh/kWp. This demonstrates the wide variability in solar resources globally.
Interactive maps provided by the National Renewable Energy Lab (NREL) allow detailed analysis of solar potential for any location in the United States. Similar mapping tools exist for other parts of the world. Understanding the regional differences in solar resources allows proper siting of solar installations to maximize energy generation.
Sources:
Solar energy generation by region
Solar Resource Data, Tools, and Maps
Future Outlook
The future looks bright for solar energy. As technology continues to advance, solar panels are becoming more efficient and costs continue to fall dramatically. According to research from MIT, photovoltaic module costs have declined by 99% since 1977 (https://energy.mit.edu/research/future-solar-energy/). The Department of Energy’s National Renewable Energy Lab (NREL) predicts that by 2050, solar energy could provide up to 40% of the nation’s electricity, compared to just 3% today (https://www.nrel.gov/news/program/2022/building-a-solar-powered-future.html).
One major area of solar technology improvement is increased solar cell efficiency. Typical commercial solar panels on the market today convert 15-20% of sunlight into electricity, but researchers are developing new materials and techniques to push efficiency upwards of 40% or more. As conversion efficiency increases, less surface area is needed to generate the same amount of electricity, reducing system costs.
In addition, new manufacturing processes, economies of scale, and streamlined supply chains are bringing down the hard costs of solar panels and related system components. According to NREL, the cost to install solar has dropped by more than 70% over the last decade, and is projected to fall another 40% by 2050. With solar already cost competitive with fossil fuels in many regions, these continued cost declines will enable mass adoption worldwide.
Policy Support
Government incentives have been crucial for driving growth in solar energy adoption. At the federal level, tax credits like the investment tax credit (ITC) have helped reduce the upfront costs of solar installations (SEIA). The ITC allows commercial, utility, and residential consumers to deduct 26% of the cost of installing a solar energy system from their federal taxes. Many states also offer additional incentives like rebates, grants, and tax exemptions to further lower costs and encourage solar adoption (EPA). In 2021, the Department of Energy announced initiatives to cut solar costs by 60% in the next decade, signaling continued federal support (CSIS).
Environmental Impact
Solar energy has a net positive environmental impact compared to fossil fuels. As reported by the U.S. Department of Energy Solar Energy, Wildlife, and the Environment, solar energy helps reduce greenhouse gas emissions that contribute to climate change. The Environmental Protection Agency found that 1 kilowatt-hour of electricity from photovoltaic solar panels produces 0.07-0.2 pounds of carbon dioxide emissions, compared to 1.7-2 pounds for natural gas and 2.1-3.6 pounds for coal.
However, solar facilities do require significant land use, raising concerns about habitat loss. The Nature Conservancy recommends siting projects to minimize impacts and establishing on-site vegetation and pollinator habitats. Proper solar facility siting, planning and mitigation can reduce land use impacts. According to a 2013 Union of Concerned Scientists report, the land efficiency of PV solar ranges from 3.4-8.9 acres per GWh annually, still less than coal at 12.2 acres/GWh and nuclear at 9.5-11 acres/GWh.
Overall, solar energy generates minimal air and water pollution in comparison to fossil fuels. With responsible siting and wildlife protection plans, solar can provide clean renewable power with manageable land use tradeoffs.
Conclusion
Solar energy will play a critical role in the transition to clean, renewable energy sources. As solar technology continues to improve in efficiency and cost declines, it is positioned to become one of the main sources of electricity generation globally. With supportive policies and further innovation, solar can help nations meet their emissions reduction targets under the Paris Agreement and achieve a decarbonized energy system this century. While solar on its own cannot provide uninterrupted power around the clock, it can be combined with other renewables like wind and storage solutions to provide reliable carbon-free electricity. Overcoming intermittency issues will be key for solar to reach its full potential. With the right strategies and continued investment, solar energy can spearhead the clean energy transition and drive sustainable development worldwide.
