NYT : Ice To Store Power

Tuesday, July 17, 2007

No matter how much scientists and engineers lower the cost of electricity produced from sunlight — or from the wind, the other widely available renewable source — the energy’s value is less than electricity made from coal or natural gas, because it is less reliable and, in utility lingo, not “dispatchable,” meaning a customer cannot order it turned on or off at will.  And neither resource is a good match to handle the load of a typical grid.  Wind tends to be strongest at night and in the winter, while peak load is usually on summer afternoons.  Solar production is strongest in the afternoon but ends long before the peak does, since high temperatures persist when the sun is very low in the sky or below the horizon.  Storage technologies are emerging, though none are in common use and all have disadvantages.

One method is batteries. They may use technology similar to car batteries, using chemicals that react either to absorb electrons or give them off.  But these batteries are set up differently, with vastly larger quantities of those chemicals.  VRB Power Systems, of Vancouver, B.C., sells “flow batteries,” with tanks to hold hundreds of gallons of the chemicals, called electrolytes.  The company has sold one installation at a solar power farm in Germany, and has announced sales to Australia.  The battery system costs $500 to $600 to store a kilowatt-hour, the quantity of electricity that sells for an average of 10.5 cents in the United States.  And the system has a “round-trip efficiency” of 65 to 75%, meaning that it loses 25 to 35% of the electricity put into it.  At a solar thermal installation, that has the potential to raise the price per kilowatt-hour, already a multiple of the market price, by another 50% or more…..

Another form of energy storage is ice, typically a 500-gallon block in the basement of a large building with a big cooling load.  The idea, said Frank R. Ramirez, the chief executive of a company called Ice Energy, is that all air conditioners gather heat from within a building and dump it outside, but that moving it outside gets progressively harder as the outdoor temperature rises.  His company installs the ice storage system and runs it at night, when electricity is cheap and when making ice is easy, because the outdoor temperature is lower.  Then during the day, the compressor in the building air conditioning system rejects its heat to the cold block, instead of to hot air, sharply lowering the electric demand on hot afternoons.  Unlike the battery, ice storage can break even, or better, Mr. Ramirez said.  For every kilowatt-hour put in at night, the system will return a kilowatt-hour of savings the next day, assuming the nighttime temperature is at least 17 degrees cooler than the daytime.  In many places, though, the daily temperature swing is larger; if the swing is 35 degrees, which is common in some climates, then three-quarters of a kilowatt-hour deposited will yield a full kilowatt-hour the next day.  Ice Energy markets the system in California, where electricity generated at night creates fewer smog-forming pollutants than electricity made during the day.  But if the system saves electricity, it also saves greenhouse gases, he said, and it reduces peak-hour load on transmission and distribution systems.  “What we don’t do is store electrons,” he said.  His system sells for $166 a kilowatt-hour, less than a third of the battery system…..In California, the Ice Energy system runs on natural gas, and some of the nighttime production is more efficient than daytime production.  In many parts of the country, wind is strongest at night, and could be used for storage, experts say.

Reference : http://www.nytimes.com/2007/07/16/business/16storage.html

2 Responses to “NYT : Ice To Store Power”


  1. Interesting piece. What always makes my blood boil (to temperatures well in excess of all global warming forecasts) is sentences like: ” … electricity that sells for an average of 10.5 cents in the United States” when the *real* cost is MANY, MANY times this. Fossil fuel energy is heavily subsidised around the world. I also wonder if people will still make “market price” comparisons when there is no market anymore because climate change means the economy has ceased to function. Go and buy your farm in the outskirts of Delhi, put 10-12 solar panels on your south-facing roof, and you’ll be getting a uninterrupted supply of electricity. It will be effectively ‘free’ after about 10 years, and then you can sell it to the grid after that.

  2. MMM Says:

    Right on, Dr. Angry Green Dude – couldn’t agree with you more. The rules of the game are defined, however, by the heavily entrenched incumbents (coal burning fools) and, like it or not, green types will have to play by them. I did love the ingenious use of ice to trap energy though. After all, battery banks – the conventional instruments used for the purpose – are not very environmentally friendly at all…Enthusiastic thumbs up to the Delhi idea…


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