The Difference Between Power Generation Capacity and Energy

As a power plant professionals you are probably very aware of the difference between capacity and energy. That said the PowerPlantPro staff receives many questions related to capacity and energy. Let's review.

Electric system operators and munis such as CAISO, PJM, NYISO, NEEPOOL, BPA, WAPA, NCPA and others handle much of the US electric system. The system operators ensure regional grid reliability and over  200+ investor owned utilites, 2,000+ munis and 800+ rural coops.

As a system operator, it must ensure that electricty is available 8,760 hrs/ year whether in the middle of the night with low electric loads on hot summer days when all components of the electric system is being utilized. The difference between the load (electric usage) and generation resources is the reserve margin.

In North America, base loaded power generation is provided by coal, nuclear, hydo-electric and some natural gas fired combined cycle plants. There are some base loaded cogeneration (QF) plants as well as select renewables such as biomass and alternative fueled projects. These technologies provide much of the kwh's (or energy) used each year.

System operators utilize different technologies to meet the need for kwh (energy) along with other important services such as voltage support, black start etc. This is complicated by as available energy from wind and solar.

Typical capacity technologies include:

1) Gas Turbine Peakers- natural gas

2) Geothermal

3) Boiler - natural gas

4) Boiler- Oil (where air permit allows)

Capacity is generally dispatched through a stack analysis where a load duration curve (LDC) versus cost is created. This curve varies from region to region. The result is a price duration curve.

This is a basic review. There are detailed analysis of capacity for your regional system operator on their respective websites.