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Base, Intermediate and Peak Load Power Plants

Power Demand_PSU_052021A
[Power Demand - Pennsylvania State University]


- Base Load Power

Base load power refers to the minimum amount of electric power needed to be supplied to the electrical grid at any given time. Day to day trends of power usage need to be met by power plants, however it is not optimal for power plants to produce the maximum needed power at all times. Therefore there are base load power plants like coal-fired power plants which provide the minimum needed electricity, and peak power plants which meet the fluctuating needs. Demand for electricity fluctuates vastly throughout a day, so base load power is not necessarily enough. The grid requires the use of peaking power, which is electricity supplied to match the varying demand in electricity.  

Base load power must be supplied by constant and reliable sources of electricity. They are sometimes dispatchable as well, in order to cover for unreliable intermittent electricity sources. Power plants that provide base load power often run year round - therefore having a high capacity factor - and use non-renewable fuel. Some baseload power plants include coal-fired power plants and nuclear power plants.


- Fuels for The Base Load Power Plants

Base load power sources are the plants that operate continuously to meet the minimum level of power demand 24/7. Base load plants are usually large-scale and are key components of an efficient electric grid. Base load plants produce power at a constant rate and are not designed to respond to peak demands or emergencies. The base load power generation can rely on both renewable or non-renewable resources.

Non-renewable resources (fossil fuels) include: coal, nuclear fuels. Renewable resources include: hydropower, geothermal heat, biomass, biogas, and also a solar thermal resource with associated energy storage.


- Fuels for The Intermediate and Peak Load Power Plants

The base load power plants typically are coal-fueled or nuclear plants due to low-cost fuel and steady state power they can produce. Hydropower and geothermal power can also be used for base load electricity generation if those resources are regionally available. 

The renewable energy systems, such as solar and wind, are most suitable for intermediate load plants. These are intermittent energy sources, with their output and capacity factor depending on weather conditions, daily, and seasonal variations. So, unless there is an effective energy storage system in place, they cannot be relied upon to meet constant electricity supply needs, nor can they be immediately employed to respond to peak demands. However, as intermediate sources, solar and wind systems can be efficient and can help reduce dependence on fossil fuels.

The peak power generation is usually attributed to the systems that can be easily stopped and started. Possibilities are natural gas and oil plants, hydro-facilities. 

From the situation as it is right now, we can see that the niche of base load power is currently occupied by mainly non-renewable energy systems and therefore non-sustainable. But here is a probing question: Can the base load power be entirely provided by renewable energy sources? Or we cannot avoid coal altogether? Apparently, the difficulty with renewables is their intermittence in time and location bias. Comparison of typical capacity factors of various energy systems reflects this difficulty.


- The Time-of-Day Power Demand 

Typically, the power demand varies cyclically from day to day, reaching maximum during day business hours and dropping to minimum during late night and early morning, but never dropping below a certain base. This base load is typically at 30-40% of the maximum load, so the amount of load assigned to base load plants is tuned to that level. The above-base power demand (above the base) is handled by intermediate and peak power plants, which are also included to the grid. The main advantages of the base load power plants are cost efficiency and reliability at the optimal power levels. The main disadvantages are slow response time, lack of fuel flexibility, and low efficiency when operated below full capacity. 


- Nominal Capacity Rating

Base load plants (as well as other energy converting facilities) are characterized by a nominal capacity rating. For example, if a plant rated at 1,000 MW, it means it can generate 1,000 MWh of electricity per hour when working at full capacity. The actual generation can be less, depending on the demand or operating conditions, and can be characterized by the capacity factor (CF):

CF = [actual generated output] / [maximum possible output]

For example, let us calculate the capacity factor for a 1,000 MW base load power plant that generated 512,000 MWh of electricity over the month of January.

In this case, the maximum energy that can be generated by the plant at full capacity over this month can be determined as follows:

E(max) = 1,000 MW x 31 days x 24 hour/day = 744,000 MWh


CF = E(real) / E(max) = 512,000 / 744,000 = 0.69 (69%)

There are a number of reasons why a plant can have lower than 100% capacity factor. Some of them are:

  • lower demand for electricity over certain periods of time;
  • under-capacity operation due to maintenance;
  • equipment failures / interruptions;
  • resource/fuel shortage;
  • equipment upgrade (resulting in high nominal capacity).



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