Peak Demand

Peak demand for electricity in the United States typically hits between 4 p.m. and 8 p.m., which doesn’t quite line up with the sun’s schedule. It’s fortunate that the sun is high in the sky during many of the hours when the air conditioning is in demand. But in summer, people tend to need air conditioning during the dinner hour and beyond, when kitchen appliances are whirring, lights are on, and TVs are blaring.
To the rescue comes concentrating solar power (CSP), a technology being tested and deployed by utilities in America’s deserts and southern Spain.
New analysis at the U.S. Department of Energy’s (DOE) National Renewable Energy Laboratory (NREL) has found that CSP, with its greater grid flexibility and ability to store energy for as long as 15 hours, can enhance total solar power generation and actually give photovoltaic (PV) systems a greater presence on the grid.
PV panels convert photons from the sun directly into electrons for electricity — and are grabbing real estate on rooftops across the Americas, Europe, and Asia.
CSP technologies use mirrors to reflect and concentrate sunlight onto receivers that collect the sun’s heat. This thermal energy can then be used to drive a steam turbine that produces electricity for utilities.
Think of power from PV as a roller coaster of highs and lows, and power from CSP, via thermal energy storage, as a gently rolling train.
PV panels and wind turbines contribute electricity to the grid, but without the ability to store that power, they cannot supply the grid after the sun sets, or after the wind dies. Even passing clouds can cause drops in the amount of solar energy that gets on the grid.
Large fossil-fueled and nuclear power plants can’t be quickly stopped or started to accommodate variable energy sources such as solar and wind energy.
CSP can even out these ebbs and flows because it can store power and ramp up output when the amount of direct wind or solar power drops.