Making a Case for Flywheel Energy Storage

Oklahoma, United States [Renewable Energy World North America Magazine]

“Electricity is the ultimate in a perishable commodity. If it is not used or transformed as it is generated it will be lost. So the systems that supply electricity have been designed with flexibility in mind so that supply may be made to closely match whatever the demand happens to be.

Consumers take this balance for granted but our local electric company closely studies historical demand, accounting for the change in seasons, changes during the day, weather forecasts and even whether there is a baseball game at the stadium. When utilities turn to their supply side they may have hundreds of generator sets all varying in kilowatt rating size, cost efficiency and on/off flexibility. The electric company has taken its best bet as to which of the large inflexible turbines to have powered on. They would like to maximize the use of these turbines as they are generally the most efficient turbines to run and cleanest turbines for the environment. Due to the need to be able to follow demand they also need to have in the mix a spectrum of smaller turbines that may be turned on and off easily. this is the most expensive electricity and these are also the dirtiest turbines.

The electric company is more likely to own the larger capital intensive gensets and issue supply contracts with independent power producers for the smaller turbines (where there are deregulated markets). The contract prices are usually priced based on the kilowatts that can be provided and the speed at which they may be turned on or off. This spectrum of adjustability is referred to as “load following” on the broad scale and “frequency regulation” on the fine scale.

The need for frequency regulation is the main reason that power generators have to match supply to demand. It would sometimes be easier simply to create more electricity than is being demanded. But this is more dangerous than not supplying enough electricity. When there is more supply of electricity than is demanded the frequency of the alternating current goes above 60 Hz and when the supply is exceeded by demand the frequency drops below 60 Hz. (In Europe and other parts of the world this standard is 50 Hz.) Electric companies are mandated by federal laws to maintain 60 Hz on the grid. The bigger the disparity above or below 60 Hz the larger the fines that may be imposed on them.

Power companies are used to having a deterministic supply side. If they tell a supplier to fire up a turbine that is rated for 30 MW they can count on having 30 MW delivered within the contracted time with near certainty. With wind and solar energy, however, we are now asking the power company to deal with intermittency on their supply side and not just on their demand side. Although renewable energy sources (not counting hydroelectricity) account for less than 2 percent of the total energy generated in the United States, the popular press and politicians are talking about having 20 percent of our electricity generated by renewables within 10 years. Common sense suggests that load following and frequency regulation will become more difficult and expensive with this increase in supply side variability…”

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