Energy Storage

A reader asked a question on compressed air storage the other day, and pointed to a web site that had some information.
http://www.doc.ic.ac.uk/~matti/ise2grp/energystorage_report/node7.html

Energy storage seems to have captured the imagination of the public. Indeed, the wind industry has been caught up in this too. An Irish wind developer invested in a battery system from VRB in Vancouver. An Iowa wind developer is investing in a compressed air storage system.

I think the interest in storage comes from people who want a complete transition of our electricity supply to renewable energy. They know that this can’t happen until storage is available widely, and at low cost. Renewable energy of all types has variable output, depending on the wind, sun, rain, waves, or tides, and so some storage is required to be to 100% renewable.

You will notice that the title of this entry is energy storage. It is not electricity storage. We already store energy in a myriad of ways.

We store heat in hot water tanks. We store cool in office buildings, refrigerators, and freezers. We store potential energy behind a dam. We have industrial processes, such as manufacture of steel or aluminum, that have a vast amount of energy stored in the material transformation. We have batteries, which store energy chemically. And we have the ultimate storage medium – fossil fuels.

The benefit of storage, even without renewable energy, is obvious. In Ontario, for example, we have a peak demand of 27,000 MW, but average demand of 17,500 MW. If we had unlimited storage, and the stored energy was immediately available, we would not need to build 27,000 MW of capacity. We could build only 17,500 MW, and still meet our needs. And that would save $ billion’s in capital construction cost.
We can shift demand to accomplish the same benefit offered by storage. If we can shut off the hot water heaters, the steel mills, the water pumping, the air conditioning, or the heating, even for a short time, we can shift our peak demand to a time when demand is lower. The Smart Meter proposal for Ontario may allow this, although details are still sketchy. The UK used to have surplus power at night. So they offered a very low price. Consumers built heating closets, full of rocks, which they heated at night using resistance electrical heat. The heat was then released during the day. Demand for heat shifted from daytime to night. Shifting demand is an underutilized resource in Ontario.

The biggest conventional source of stored energy is hydro dams. In Ontario, we regularly have about 3000 MW waterpower energy available for use during peak periods. Some places have installed pumped storage, including Niagara Falls, on both sides of the river. Water is pumped at night to a storage reservoir, and released through the generators during the day. Pumped storage has an efficiency of 85-90%, so if you use 100 MWh to pump the water, you will get back 85-90 MWh when you release it.

Compressed air requires large sealed underground reservoirs. These would usually be salt formations, or abandoned natural gas wells, that have demonstrated an ability to store gas for millions of years without leaking. Leaks would hurt your efficiency dramatically. Compressed air is not in widespread use, but might be worthy of more consideration. Ontario has the world’s largest salt mine – we must have some suitable sites.

Battery storage is in widespread use in off grid applications, but is seen as too costly to provide backup for the main electricity grid.

But one of the largest storage mediums we have by far is fossil fuels. If you are producing power from a wind turbine, you don’t have to burn them to make electricity. And that means you can store the fossil fuel for the future. The first use of wind energy should always be to reduce the burning of fossil fuels.

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