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Concentration of CO2 in the Atmosphere

Backing up the Grid – All of It

Pumped storage systems are used to enable baseload power systems to match grid deamnd. Now they can be used to enable renewable power systems to do the same job. The Raccoon Mountain Pumped-Storage Plant is shown. Tennessee Valley Authority image.

George Harvey

It is important to understand that thermal baseload power plants, powered by producing steam, are generally very inflexible and cannot change their output to match demand. Since producing excess power would overload the system and create problems, they are designed only to meet the minimum amount normally needed, the “baseload.” They can run flat out all the time, and any demand greater than what they can provide has to come from some other generating type.

At the same time that the old Vermont Yankee (VY) nuclear plant was being built, to provide an output of about 500 megawatts (MW), the Northfield Mountain Station (NMS) pumped storage system, with a maximum capacity of 1080 MW was also under construction just down the river. NMS was to take up power when demand was low and deliver power to cover demand peaks.

There are not many good sites for pumped storage, so usually peak demand has been covered by special generators that are flexible enough to cover peak loads. They provide a service for which they charge quite a lot of money.

Clearly, baseload power plants need backup because of their inflexibility. That backup has to be available every day on a massive scale.

Some renewable energy generators can power around the clock. Unlike thermal baseload plants, hydropower and geothermal plants can be ramped up and down rather quickly, but like pumped storage, they cannot be built just anywhere.

While it is true that the sun does not always shine, and the wind does not always blow, solar and wind plants have the advantage that they can be “curtailed” to avoid having too much electricity on the grid. They also can produce the least expensive power available to us.

Recently, the cost of power from batteries has been reduced to the point that it is practical for them to take up excess power from solar and wind plants, making curtailment unnecessary. Then they can provide it to the grid as needed. In this way, they can replace existing baseload power plants.

The Hornsdale Power Reserve (HPR), in South Australia, has shown its value backing up all grid generators, not just wind and solar power. When coal plants suddenly go offline, the wholesale price of electricity in that country can legally go to a maximum of over $10 (U.S.) per kilowatt-hour, a price that gets hit occasionally. With the HPR in business providing for unexpected demand spikes, peak prices have dropped over 90%, the state has paid down a third of the battery’s cost in only one year, and the customers have saved a fair amount of money. (See “The World’s Largest Battery System” on page 12.)

A set of recent events in Australia show the value of renewable energy and battery backup for providing energy security. In August, a set of storms took transmission lines down connecting grids in four states, Queensland, New South Wales, Victoria, and South Australia. (These states are huge, by the way. Their total area is about half that of the 48 contiguous states of the U.S.) Power went down in New South Wales and Victoria. South Australia only had momentary flickers because of the Hornsdale Power Reserve, which performed exactly as intended.

Interestingly, Queensland also had only a flicker, despite its lack of a big battery. That was because of widespread use of renewable power. About a third of the homes in that state have rooftop solar power.

What we can see here is that both renewable energy with some battery backup and grid-scale battery systems can provide for unusual demands for electricity that baseload plants cannot. This should probably be no surprise. Baseload power plants were never intended to provide for unusual situations.

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