What factors determine when to activate peaking units in power grids?

Factors Determining When to Start Grid Peaking Units

The timing for starting grid peaking units is primarily determined by multiple factors to ensure the stable operation and efficient use of resources in the power system. Below are the main factors that influence when to start peaking units:

1. Load Demand Variations

• Peak Load Periods: During times when grid load reaches or approaches its peak (such as during working hours or summer air conditioning usage peaks), additional generation capacity is needed to meet demand. At such times, peaking units may be started.

• Off-Peak Load Periods: During nighttime or other periods of low electricity demand, the grid may need to reduce generation to avoid waste. Peaking units can quickly adjust their output or even shut down to accommodate load variations.

2. Intermittency of Renewable Energy

• Fluctuations in Wind and Solar Power: As renewable energy sources like wind and solar increase their share in the grid, their intermittency and unpredictability pose challenges to grid stability. When wind speeds or sunlight are insufficient, peaking units can quickly supplement the missing generation.

• Weather Forecasts: Accurate weather forecasts help dispatch centers anticipate renewable energy generation, allowing them to decide when to start peaking units.

3. Electricity Market Prices

• Price Fluctuations: In electricity markets, prices fluctuate based on supply and demand. When prices are high (usually due to excess demand), starting peaking units can be more economically beneficial.

• Marginal Costs: The marginal cost (i.e., the cost to produce one additional unit of electricity) of peaking units is typically higher, so they are only started when market prices are sufficiently high.

4. System Reliability Requirements

• Reserve Capacity: To ensure system reliability, a certain amount of reserve capacity must be maintained. If conventional generating units fail or require maintenance, peaking units can serve as backup power and quickly come online.

• Frequency and Voltage Control: The stability of grid frequency and voltage is crucial for normal power system operation. Peaking units can rapidly respond to changes in frequency and voltage, maintaining grid stability.

5. Environmental and Policy Factors

• Emission Limits: Some regions have strict limits on carbon emissions and other pollutants, which affects the choice and use of peaking units. For example, natural gas peaking units are generally more environmentally friendly than coal units and thus are more favored in areas with stringent environmental requirements.

• Policy Support: Governments may introduce policies encouraging the use of flexible peaking power sources or provide subsidies for unstable renewable energy, which also influences the decision to start peaking units.

6. Technical Characteristics

• Startup Speed: Different types of peaking units have varying startup speeds. For instance, gas turbines can start within minutes, while hydroelectric units can also respond quickly, but coal units take longer to start. Therefore, the choice of peaking unit depends on the grid's required response speed to load changes.

• Ramp Rate: The ramp rate (i.e., the ability to increase power output per unit time) of peaking units is another critical factor in determining their suitability for rapid response to load fluctuations.

7. Availability of Energy Storage Systems

Battery Energy Storage Systems: In recent years, battery energy storage systems (such as lithium-ion batteries) have become an important means of peaking. When energy storage systems have sufficient capacity, the need to start peaking units may decrease. Conversely, when energy storage systems are low on charge, the frequency of starting peaking units may increase.

8. Seasonal Factors

Seasonal Load Variations: Load demands vary significantly across different seasons. For example, increased air conditioning usage in summer and heating needs in winter both lead to load fluctuations, affecting the decision to start peaking units.

9. Grid Infrastructure Status

• Transmission Line Capacity: If transmission line capacity is limited and cannot deliver power from distant sources to load centers, peaking units can be started locally to alleviate transmission bottlenecks.

• Substation and Distribution Facility Conditions: If certain substations or distribution facilities are undergoing maintenance or upgrades, peaking units can temporarily fill the power supply gap.

Summary

The decision to start peaking units is a complex process involving multiple factors such as load demand, renewable energy fluctuations, market prices, system reliability, environmental policies, and technical characteristics. Power system dispatch centers typically consider these factors comprehensively and use advanced monitoring and control systems to dynamically adjust the operation of peaking units, ensuring the safety, reliability, and economic operation of the grid.