Intermittent energy sources

What Are Intermittent Energy Sources?

Intermittent energy sources are forms of renewable energy that are not consistently available due to natural fluctuations in their primary energy input. Unlike traditional, dispatchable power plants that can be turned on or off and ramped up or down as needed, intermittent sources such as solar power and wind power generate electricity only when the sun is shining or the wind is blowing. This characteristic presents unique challenges and opportunities within the broader context of energy markets and utility operations, falling under the financial category of Renewable Energy. Managing the variability of these sources is crucial for maintaining grid reliability and balancing supply and demand within an electrical system.

History and Origin

The concept of integrating intermittent energy sources into widespread electricity grids became significant with the increasing adoption of large-scale wind and solar photovoltaic (PV) installations, particularly from the late 20th century onwards. While wind power has been harnessed for millennia and solar energy has been understood for centuries, their deployment as significant contributors to modern electricity grids is a relatively recent development. Early grid designs were based on the premise of centralized, dispatchable generation, primarily from fossil fuels and hydropower. The variability of wind and solar presented a new operational paradigm.

As concerns about climate change and energy security grew, and as the costs of renewable technologies declined, governments and utilities began to actively promote the investment in these cleaner alternatives. This shift led to a greater understanding of the challenges associated with intermittency, such as the need for forecasting, flexible conventional generation, and the development of energy storage solutions. Regulatory bodies, such as the Federal Energy Regulatory Commission (FERC) in the United States, have implemented reforms to streamline the connection of these variable resources to the grid. For instance, FERC issued Order No. 2023, which aims to improve and speed up the interconnection process for new generation projects, including intermittent renewables⁷.

Key Takeaways

• Intermittent energy sources, like solar and wind, produce electricity only when their natural resources are available.
• Their variability necessitates sophisticated grid management techniques, including accurate forecasting and flexible backup generation.
• Integration challenges primarily revolve around maintaining a constant balance between electricity supply and demand on the grid.
• Technological advancements, such as energy storage and advanced transmission lines, are crucial for increasing the penetration of intermittent renewables.
• Policy and market design play a significant role in incentivizing the deployment and effective integration of these energy sources.

Interpreting Intermittent Energy Sources

Interpreting the role and impact of intermittent energy sources involves understanding their contribution to the overall energy mix and the operational adjustments required for their integration. Unlike baseload power plants that provide a consistent minimum amount of electricity, intermittent sources deliver variable output. This means that a grid with a high penetration of these sources must have mechanisms to compensate for sudden drops or surges in generation.

Grid operators use various tools to manage this variability, including sophisticated forecasting models to predict wind speeds and solar irradiance, and demand-side management programs to adjust electricity consumption in response to availability. The economic interpretation often involves considering the "value defection" or "cannibalization" effect, where increased amounts of solar power, for example, can lower wholesale electricity prices during peak solar production hours, impacting the profitability of other generators. Effective integration requires a flexible grid, often through upgrades to transmission lines and the strategic deployment of energy storage systems.

Hypothetical Example

Consider a hypothetical regional electricity grid that traditionally relies heavily on natural gas power plants. The grid operator, managing the flow of electricity, decides to significantly increase its adoption of intermittent energy sources, adding 1,000 megawatts (MW) of solar power capacity and 1,000 MW of wind power capacity over five years.

On a sunny, windy afternoon, both the solar panels and wind turbines are operating at high capacity, providing a substantial portion of the grid's electricity needs. The demand for electricity is met efficiently, and the operational costs for the natural gas plants are reduced as they ramp down or go offline. However, as the sun sets and the wind dies down, the output from these intermittent sources decreases rapidly. To maintain grid reliability and prevent blackouts, the grid operator must quickly ramp up the natural gas plants or draw power from other interconnected regions. This scenario highlights the need for dynamic system management and underscores the importance of backup capacity or flexible resources like energy storage to ensure continuous supply.

Practical Applications

Intermittent energy sources are practically applied as a fundamental component of global efforts to decarbonize electricity generation. Their integration is central to achieving sustainability goals and reducing reliance on fossil fuels.

• Utility-Scale Generation: Large solar farms and wind farms are built to feed directly into national or regional electricity grids, contributing to the overall generation mix. The International Energy Agency (IEA) projects that renewables will generate almost half of global electricity demand by the end of 2030, with a significant increase in wind and solar capacity⁵, ⁶.
• Distributed Generation: Smaller-scale solar installations on rooftops of homes and businesses (distributed PV) provide localized power, reducing demand on the central grid during daylight hours.
• Grid Modernization: The increasing share of intermittent renewables drives the need for advanced grid infrastructure, including smart grids, enhanced transmission lines, and sophisticated control systems to manage variability and ensure grid reliability. The National Renewable Energy Laboratory (NREL) actively researches and develops solutions for energy-to-grid integration to support this transition⁴.
• Corporate Power Purchase Agreements: Many corporations enter into PPAs to directly source electricity from new wind or solar projects, demonstrating a commitment to sustainability and often benefiting from predictable electricity prices over the long term.
• Investment and Finance: The growth of intermittent energy sources has created new opportunities for capital expenditure in renewable project development, green bonds, and specialized investment funds focused on sustainable infrastructure.

Limitations and Criticisms

While offering significant environmental benefits, intermittent energy sources pose several limitations and criticisms primarily related to their variable nature and impact on grid operations and market dynamics.

One major criticism is the challenge they present to grid reliability. Since their output cannot be precisely controlled or dispatched to match demand, periods of low wind or solar availability can necessitate reliance on backup power from traditional sources, which often have higher operational costs or carbon emissions. Conversely, periods of high generation when demand is low can lead to curtailment, where available renewable electricity is not utilized due to grid constraints or lack of sufficient demand, effectively wasting potential energy³.

Economically, the zero marginal cost of generation for wind and solar can depress wholesale electricity markets prices during peak production times, making it difficult for dispatchable generators to recover their fixed costs and incentivize new investment in necessary firm capacity. This can lead to what is sometimes referred to as the "missing money" problem, where competitive markets fail to provide adequate revenue signals for capacity needed to ensure supply adequacy². Furthermore, integrating high levels of intermittent generation requires significant upgrades to transmission lines and the implementation of more flexible grid services, which can entail substantial capital expenditure. An academic perspective highlights these challenges, noting that relying on markets for supply portfolios becomes incompatible when significant intermittent generation is present, potentially leading to market failures in delivering adequate capacity¹.

Intermittent Energy Sources vs. Energy Storage

The distinction between intermittent energy sources and energy storage is crucial for understanding modern electricity grids. Intermittent energy sources, such as solar photovoltaic panels and wind turbines, are the generators of electricity whose output depends on naturally occurring and uncontrollable phenomena (sunlight and wind). Their production is not constant and varies throughout the day, season, or even minute by minute.

In contrast, energy storage refers to technologies designed to capture and hold energy for later use. While energy storage systems can be charged by any electricity source, they are particularly vital for mitigating the variability of intermittent renewables. For example, a battery storage system paired with a solar farm can store excess electricity generated during midday sun and release it during the evening peak demand, when solar output has declined. This capability transforms the variable output of intermittent sources into a more dispatchable, reliable power supply, enhancing grid reliability and enabling greater penetration of renewables into the energy mix. Energy storage acts as a buffer, allowing the grid to maintain a continuous balance between supply and demand despite the inherent fluctuations of intermittent generation.

FAQs

What are common examples of intermittent energy sources?

The most common examples of intermittent energy sources are solar power (which depends on sunlight) and wind power (which depends on wind speed and availability). Other forms, like tidal power, also exhibit intermittency due to the predictable but fluctuating nature of tides.

Why are intermittent energy sources challenging for electricity grids?

Intermittent energy sources pose challenges because their output cannot be controlled to match electricity demand. The grid requires a constant balance between supply and demand. When intermittent sources' output suddenly drops (e.g., cloud cover or no wind), other power sources must quickly ramp up to fill the gap, affecting grid reliability. Conversely, excess generation can lead to curtailment if there's not enough demand or storage.

How can the variability of intermittent energy sources be managed?

The variability of intermittent energy sources can be managed through several strategies:

• Energy storage systems: Such as batteries, which store excess electricity for later release.
• Grid modernization: Implementing smart grid technologies and upgrading transmission lines to allow for greater flexibility and power transfer.
• Demand-side management: Encouraging consumers to shift their electricity consumption to periods of high renewable generation.
• Flexible conventional generation: Utilizing natural gas plants or hydropower that can quickly adjust their output.
• Improved forecasting: More accurate predictions of wind and solar output help grid operators plan more effectively.

Do intermittent energy sources affect electricity prices?

Yes, intermittent energy sources can affect electricity markets prices. Because their marginal cost of production is near zero (they don't pay for fuel), a high influx of wind or solar power can drive down wholesale electricity prices during periods of abundant generation. This can be beneficial for consumers but may pose challenges for other power generators trying to recover their capital expenditure and fixed costs.

Are all renewable energy sources intermittent?

No, not all renewable energy sources are intermittent. While solar and wind are intermittent, others like hydropower (from reservoirs), geothermal, and biomass are generally considered dispatchable, meaning their output can be controlled to some extent to meet demand. These sources provide valuable firm capacity and flexibility within a renewable-heavy grid.