The Future of Replacing Coal and Gas with Renewable Energy

Source: Andrew Messios · AZO CLEANTECH · | July 13, 2021

The problem with many sources of renewable energy - such as the sun, wind and waves - is that their intensity fluctuates. Solar power is unproductive at night or on especially cloudy days, while wind power depends on the speed of the wind, the forecasting of which is difficult.

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For all their faults, coal and gas (as well as some renewable sources, such as hydropower) provide constant and ‘dispatchable’ on-demand energy for the electricity grids they feed. The electricity grids are responsible for balancing energy generation and consumption; if one end of this equation is relatively reliable, predictable and flexible, it makes this challenging task easier.

If we want our power grids to be powered by renewable energy sources instead of fossil fuels while keeping them reliable and flexible, we will need effective forms of grid-scale energy storage. Energy storage systems will hoard excess energy when conditions are optimal, such as when the sun is bright, skies are clear and wind is blowing, and draw on it when conditions are not. They will turn renewable energy sources into reliable and dispatchable energy generation systems.

Compressed Air Energy Storage

One way to store energy is using the elastic potential of compressed air in a system called Compressed Air Energy Storage (CAES). During off-peak periods, low-cost power is used to power motors that compress air and store it in underground caverns, usually disused salt mines, under very high pressures. In peak-load periods, this compressed air is then released and combusted with fuel to force it to expand. This drives a gas turbine to produce electricity.

An estimated 100 million barrels of oil could be saved if current gas turbines in the United States were replaced by CAES plants. Compared with other grid-scale energy storage methods, such as lithium batteries, CAES systems have high power ratings and storage capacity, and long lifetimes.

A History of Compressed Air Energy Storage

CAES is not a new technology. The first CAES plant was built in Huntorf, in the north of Germany, in 1978 to baseload the power of the nearby nuclear station in Unterweser.