The United States boasts a diverse electricity generation mix, incorporating various energy sources that produce electricity at different points throughout the day.
Maintaining a balance between electricity generation and demand is crucial for the stability of the power grid. This balance results in cyclic patterns in daily and weekly electricity generation.
The graphic below illustrates the hourly fluctuations in U.S. electricity generation over the course of one week. This data is derived from the U.S. Energy Information Administration (EIA) and offers insight into the dynamic nature of electricity production and consumption in the country.
It’s essential to differentiate between the three primary types of power plants in the U.S. electricity generation mix:
- Base Load Plants: These power plants generally operate at or close to their maximum capacity and are designed to fulfill the base load, which is the minimum level of electricity needed at all times. Common base load sources include coal-fired and nuclear power plants. In regions with access to such resources, geothermal and hydropower plants can also serve as base load providers.
- Peak Load or Peaking Power Plants: Peak load or peaking power plants are typically dispatchable and can be rapidly brought online when electricity demand surges. These plants often run at their maximum capacity for only a few hours each day during periods of high demand. Examples of peak load plants include gas-fired power plants and pumped-storage hydropower facilities.
- Intermediate Load Plants: Intermediate load plants bridge the gap between base load and peak load demand. They are used during transitional hours when electricity requirements are neither at their lowest nor highest. Sources suitable for intermediate load generation include intermittent renewable sources like wind and solar (when not coupled with battery storage), as well as other energy sources.
Zooming In: The U.S. Hourly Electricity Mix
Taking a closer look, the table below offers a snapshot of the average hourly electricity generation by source during the week spanning from March 7 to March 14, 2023, in the Eastern Time Zone.
It’s important to bear in mind that while this data reflects a standard week of electricity generation, these patterns can shift with the changing seasons. For instance, in June, electricity demand typically reaches its zenith around 5 PM, when solar generation remains robust, which differs from the situation in March.
With that context, the table below provides an overview of average hourly electricity generation by source for the week of March 7–March 14, 2023, in the Eastern Time Zone.
It’s worth noting that while this is representative of a typical week of electricity generation, these patterns can change with seasons. For example, in the month of June, electricity demand usually peaks around 5 PM, when solar generation is still high, unlike in March.
Natural gas is the largest source of electricity in the country, and gas-fired power plants consistently generate around 176,000 megawatt-hours (MWh) of electricity per hour during the week we’re discussing. The flexibility of natural gas is evident in the chart, as its electricity generation decreases during the early morning hours and rises during business hours.
In contrast, nuclear power generation remains stable throughout the week, consistently providing between 80,000 and 85,000 MWh per hour. Nuclear plants are designed to operate for extended periods (typically 1.5 to 2 years) before needing refueling, and they require less maintenance, making them a dependable source of baseload energy.
However, wind and solar power exhibit significant fluctuations during the week. For instance, in the period from March 7 to March 14, wind power generation varied between 26,875 and 77,185 MWh per hour, depending on wind speeds. Solar power had even more pronounced extremes, often dropping to zero or even producing a net-negative output at night, while surging to over 40,000 MWh during the afternoon.
Integrating wind and solar energy into the electricity grid can be challenging for grid operators because these sources are variable and dependent on location. Grid operators rely on forecasts to ensure a balance between electricity supply and demand. So, how can we address these challenges and ensure a stable and reliable energy supply?
Solving the Renewable Intermittency Challenge
As more renewable capacity is deployed, here are three ways to make the transition smoother.
Managing the variability and intermittency of wind and solar power generation is indeed a challenge for grid operators. Here are some strategies and technologies that can help address these issues:
- Energy Storage: Implementing energy storage systems, such as batteries, can store excess electricity generated during periods of high wind or sunshine and release it when generation is low. This helps smooth out the intermittent nature of renewables and ensures a more consistent power supply to the grid.
- Advanced Forecasting: Improved weather forecasting and predictive analytics can provide more accurate forecasts for renewable energy generation. Grid operators can use these forecasts to anticipate fluctuations and adjust their energy dispatch accordingly.
- Demand Response: Encouraging demand response programs allows grid operators to modify electricity consumption patterns to match renewable generation peaks. Incentives can be provided to consumers to reduce or shift their electricity usage to times when renewable generation is high.
- Grid Enhancements: Upgrading and modernizing the grid infrastructure with smart grid technologies can enhance grid flexibility and responsiveness. This includes better monitoring, control systems, and grid automation.
- Hybrid Systems: Combining different renewable sources (e.g., wind and solar) in a single location or using hybrid systems that incorporate renewables with other technologies (e.g., natural gas) can help ensure a more reliable and stable energy supply.
- Interconnection and Grid Expansion: Expanding the electricity grid and interconnecting it with neighboring regions or countries can provide access to a wider range of renewable resources. This allows for the sharing of energy resources and can mitigate the impact of local variability.
- Diverse Energy Mix: Maintaining a diverse energy mix that includes a combination of renewables, nuclear, natural gas, and other energy sources can help balance supply and demand more effectively. This reduces reliance on a single energy source and provides greater energy security.
- Policy and Regulation: Establishing supportive policies and regulations, such as feed-in tariffs, tax incentives, and renewable portfolio standards, can incentivize renewable energy development and integration.
- Grid-Forming Inverters: The use of advanced inverters that can “form” the grid, rather than just “following” it, can provide grid stability and enable greater penetration of renewables.
- Microgrids: Implementing microgrid systems in specific regions or communities can create localized energy resilience by combining renewable energy, storage, and demand management.
- Research and Development: Continued research into energy storage technologies, grid management systems, and renewable energy technologies can lead to innovations that improve grid reliability and renewable energy integration.
Solving the challenges posed by variable renewables requires a combination of these strategies, tailored to the specific characteristics and needs of the local grid and energy resources. Collaboration among energy stakeholders, including governments, utilities, and technology providers, is essential to ensure a smooth transition to a more renewable and sustainable energy future.
