TCS Daily


More Equal Than Others

By Herbert Inhaber - May 13, 2003 12:00 AM

It is difficult to pick up a magazine or check out a website dealing with energy or electricity without finding an uncritical article extolling the merits of renewable energy. But, as George Orwell would have put it if he had lived long enough, not all kilowatt-hours (kWh) are created equal. Some are more equal than others.

For the record, a kilowatt-hour of electricity is consumed if a 100-watt light bulb burns for ten hours. It will cost eight to nine cents on average in this country.

How could one unit of electricity be more valuable than another? After all, in physics they are equal. But some renewables are highly variable in their output. If the sun doesn't shine and the wind doesn't blow, consumers still want the lights to go on when they flip the switch.

I was reminded of this when reading a discussion of financial risks of renewables. The author said that solar and wind had a "strike value" of zero. That is, for the next hour of a solar collector or windmill, there is no exact way of predicting how much energy will be produced.

Now this is a bit of an exaggeration. If the sun is shining at 8 a.m. in the Mojave Desert, it is reasonable to assume that it will be shining at 9 a.m. But in Boston, New York, Chicago and other places, you cannot make that assumption.

How do the electrical engineers handle this extreme variability? After all, they are accustomed to conventional sources of electricity, such as coal, gas or nuclear. These produce the same amount of electricity hour after hour. Electricity companies deal with the ever-changing renewable output by "spinning reserve." That is, they keep regular turbines, powered by coal, gas or nuclear, spinning to take up the slack when the wind suddenly dies down.

So when a "green" utility says in its annual report that they generated so many millions of kilowatt-hours of solar and wind energy, they do not tell you that they had to burn so many extra tons of coal or cubic feet of gas to appear green to their stockholders.

There's a further complication. Electrical grids are based on the assumption of stability, that is, no changes. Of course, a conventional plant can be taken off line for repairs or other reasons. Electrical engineers have procedures to make sure the entire grid doesn't go haywire when this happens.

But the nature of solar and wind introduces natural instability. While engineers debate the exact figure, it is likely that a grid with more than about 10% solar and wind would likely crash too often for decent reliability. This is why Denmark, touted by greens as the promised land of wind energy, probably will not get much beyond that 10% of its electricity supplied by wind at present.

What about storing electricity for the times when Mother Nature doesn't cooperate? There are ways of storing electricity, but none of them is cheap. That massive battery in your car might store about a dime's or a quarter's worth of electricity. About the only way to store electricity on a large scale is pumped storage, in which water is pumped up to the top of a mountain when electricity is not needed, and descends into turbines when the electricity is wanted.

But pumped storage is rare, and depends on having mountains nearby. Near where I live in Las Vegas, a utility proposed pumped storage for a proposed solar plant. Angry environmentalists jumped all over it, even though it would have made the solar plant much more commercially viable. The entire project is in limbo.

Anyone who has traveled through the West has seen the remnants of a once-thriving windmill industry. At one time, hundreds of thousands of these windmills dotted the nation, without any government subsidies or programs or rules to require them. Farmers used them because they were based on storage. They did not generate electricity, some moon-eyed environmentalists believe. Rather, they pumped water for farm animals and people. The entire concept was based on storage of the produce - water.

Although windmills to produce electricity have been around for decades, few if any farmers bought them. Although they weren't engineers, they knew the difference between storing water and electricity.

Some other renewables also don't need spinning reserves, so they may be suitable for a modern energy system. For example, methane is generated from garbage dumps. In some places, pipes can be installed to collect the methane, the same as natural gas. Although the rate of collection can be highly variable, the gas can be stored in tanks, and fed into the regular gas system when enough is collected. In this case, the variability of renewables will not make the energy system less reliable.

The same applies to geothermal resources, which produce a fairly constant source of heat. Incidentally, although geothermal is often regarded as renewable - Senator Reid of my home state has fought for years to get it the same tax breaks as other renewables - it isn't. It is just a big source of heat. When it is exhausted, like a coal mine can be depleted - that is the end of that geothermal resource. So much for truth in labeling.

Renewables vary considerably in their energy output. In certain circumstances, this variability is not a problem, the case of Western windmills and methane from landfills. But most of the renewables we read about are too variable to make more than a small contribution to our energy needs.
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