What Is The Problem With Intermittency And Solar Power?
What is intermittency?
Intermittency refers to the variable or inconsistent power output from renewable energy sources like solar and wind. Unlike traditional baseload power plants that can generate a steady and reliable flow of electricity, renewable sources depend on environmental conditions that fluctuate over time [1].
For example, solar power generation relies on sunshine to produce electricity. The amount of solar irradiation that reaches solar panels varies throughout the day and depends on weather conditions. Solar output drops to zero at night when there is no sunlight. Even during daylight hours, cloud cover can substantially reduce solar electricity production [2].
These variations in renewable generation are described as intermittent. Solar and wind power see significant output ramps up and down on daily and seasonal timescales. This intermittency poses grid integration and balancing challenges compared to more stable baseload generation [3].
[1] https://energyx.com/resources/what-is-intermittency-in-renewable-energy/
[2] https://energyeducation.ca/encyclopedia/Intermittent_electricity
[3] https://www.nature.com/articles/s41598-022-05247-2
Challenges caused by intermittency
The intermittent nature of solar and wind power presents several key challenges for integrating these renewable sources into the electric grid. The major issues caused by intermittency include:
Difficulty balancing supply and demand on the grid – Solar and wind generation varies based on weather conditions and time of day, while demand fluctuates based on consumer usage patterns. The mismatch between renewable supply and electric demand makes it difficult to maintain stability on the grid. Grid operators have to balance these variable resources with other sources that can ramp up or down as needed.
Requirement for backup power sources – To prevent blackouts when solar and wind production drops, backup power supplies are needed to meet demand. This often means relying on fossil fuel sources like natural gas plants that can quickly scale up when renewables fall short. The need for backup generation results in higher costs and undermines some of the environmental benefits.
Increased operating costs – Adapting the grid and power system operations to handle variable renewables requires investments in new technologies and infrastructure. More sophisticated forecasting of renewable generation, enhanced transmission, and advanced grid management capabilities add complexity and costs. The intermittent nature of renewables makes electricity markets more volatile as well.
Solutions for intermittency
There are several potential solutions to the intermittency challenge of solar power, including:
Energy storage systems
Storing excess solar energy when production is high for use when production is low can help smooth out intermittency. Some storage solutions include batteries, pumped hydroelectric storage, compressed air energy storage, flywheels, and hydrogen fuel cells (Scientific American, 2015).
Geographic distribution of solar
Distributing solar generation over large geographic areas can take advantage of diverse weather patterns and smooth out variability. Studies show a “smoothing effect” when solar production from different sites is aggregated (Arka360, 2023).
Advanced forecasting
Improved solar forecasting allows grid operators to better predict fluctuations and schedule other resources accordingly. Forecasting tools utilize historical data, weather modeling, and machine learning algorithms.
Demand response
Shifting electricity demand to match supply through financial incentives and advanced metering can better align demand with intermittent production.
Energy Storage
Energy storage technologies allow excess solar power to be captured and deployed during cloudy periods or at night when the sun is not shining. There are several different types of storage technologies in use or development (https://www.energy.gov/eere/solar/solar-integration-solar-energy-and-storage-basics).
Solar batteries are the most popular storage technology and have become much more affordable in recent years. Lithium-ion batteries in particular are well-suited for home solar storage systems. They have a high efficiency and long lifespan if properly maintained (https://www.altestore.com/blog/2023/01/energy-storage-technologies/). Batteries can provide backup power and maximize solar self-consumption.
Other storage technologies include pumped hydro storage which pumps water uphill into a reservoir when energy supply exceeds demand. The water can then flow back downhill through turbines to generate electricity when needed. Thermal energy storage uses excess heat to warm up materials like molten salt that can retain heat for extended periods. Compressed air energy storage compresses air in underground caverns which can turn turbines to produce electricity on demand.
While costs are coming down, energy storage systems can still add significant upfront costs to a solar installation. The roundtrip efficiency of storing and recovering electricity results in some energy losses. Geography and space constraints also limit some storage options. However, as storage technology continues to improve, it will play a key role in overcoming intermittency and integrating higher levels of solar power onto the grid.
Geographic distribution
Distributing solar generation across larger geographic areas can help smooth output and reduce the impacts of intermittency. This geographic diversification provides redundancy that helps compensate when one area experiences reduced solar output due to cloud cover or other localized conditions. Studies have shown significant smoothing benefits from distributing solar generation across regions like the southwestern United States.
For example, research examining output from 15 large utility-scale solar plants in California and Nevada found that geographic dispersion smoothed 60-80% of hourly PV output variability. This smoothing effect results from weather events typically impacting more localized areas, so distant regions can balance out short-term drops in solar production.1
However, taking full advantage of geographic distribution requires substantial transmission infrastructure investments. Transmitting solar power from sunnier regions with excess capacity to other areas helps provide consistent nationwide solar output. But this depends on major high-voltage transmission projects to move renewable energy long distances.
Advanced forecasting
Advanced forecasting techniques can help grid operators manage the variability and uncertainty of solar power generation over shorter time horizons. Short-term solar forecasting provides predictions from minutes to days ahead to support grid planning and operations.
There are different modeling and prediction techniques used for short-term solar forecasting. These include numerical weather prediction models, satellite/sky imaging, statistical models based on historical data, and hybrid approaches that combine multiple techniques. Machine learning is also being applied to further improve solar forecasting accuracy.
Despite advances, solar forecasting still has limitations in accuracy. Predictions become less reliable at longer time horizons. Forecasting errors are also larger for localized, small-scale systems compared to regional utility-scale solar farms. However, forecasting accuracy continues to improve with higher resolution data and new techniques. Overall, advanced solar forecasting provides critical information to help grid operators adapt to increasing solar intermittency.
Sources:
https://www.sciencedirect.com/science/article/pii/B9780128129593000034
https://www.nature.com/articles/s41467-020-18602-6
Demand response
One method to address the intermittency of solar power is through demand response. Demand response aims to shift electricity use to better match the variable output of renewable generation like solar [1]. This is done through strategies like smart appliances, time-of-use pricing, and other incentives that encourage users to reduce energy consumption during periods of peak renewable generation and increase it during periods of lower output.
Some of the demand response methods used for solar intermittency include [2]:
- Smart thermostats that preheat or precool buildings ahead of solar ramp-downs.
- Electric vehicle charging that aligns with renewable availability.
- Time-of-use electricity pricing that encourages usage when solar output is high.
While demand response shows promise for integrating intermittent renewables, there are challenges in shifting user behavior and consumption patterns. Consumers may resist changes to habits or routines. There are also limits to how much electricity use can be shifted from peak to off-peak times.
Case Studies
There are several real-world examples of solutions being implemented to address the intermittency challenges of solar power:
In California, the Beacon Solar Project combines a 250 MW solar PV plant with a 20 MW lithium-ion battery storage system. This allows excess solar energy to be stored and dispatched when needed, smoothing out supply. The project began operating in 2014 and provides power to Los Angeles (https://blogs.scientificamerican.com/plugged-in/renewable-energy-intermittency-explained-challenges-solutions-and-opportunities/).
The Kauai Island Utility Cooperative in Hawaii has integrated over 60% renewable energy through a combination of solar, hydroelectric, and battery storage. This isolated island grid uses weather forecasting, demand response, pumped hydro storage, and utility-scale batteries to manage intermittent resources (https://www.quora.com/What-are-some-ways-to-solve-intermittency-issues-with-renewable-energy-like-wind-and-solar-power-on-a-large-scale).
In South Australia, the 129 MWh Hornsdale Power Reserve uses Tesla batteries to store excess renewable energy and provide grid services. This has reduced intermittency and stabilized the network at lower costs compared to conventional generation.
Future outlook
The future looks bright for overcoming intermittency issues with solar power. Studies project that storage costs will continue to decline thanks to improving battery technology and economies of scale. Forecasting accuracy is also expected to improve with larger datasets from solar installations and advancements in meteorology and AI. New technologies like printable solar and solar window coatings could greatly expand solar generation. Despite the challenges of intermittency, solar power is projected to grow substantially. The International Energy Agency predicts solar will provide 16% of global electricity by 2050, a fourfold increase over 2019 levels.
Conclusions
In summary, while intermittency poses challenges for solar power, there are solutions available to integrate higher levels of solar onto the grid. Energy storage, geographic distribution, advanced forecasting, and demand response can help mitigate solar’s variability and uncertainty. There is no single perfect solution, rather the best approach is likely utilizing a diverse mix of solutions tailored to specific circumstances.
As solar expands its role in renewable energy generation, it will be critical to continue diversifying the toolkit of solutions to smooth out its intermittent nature. Innovation in storage technologies, forecasting techniques, and grid management will enable higher solar grid penetration.
Despite its intermittency, solar power will remain a key technology in the transition to renewable energy. Cost reductions and efficiency improvements will continue to make solar competitive. With proper planning and grid integration methods, solar can provide a major share of electricity generation in a clean and sustainable manner.
