Ivanpah tower

Solar Thermal Electricity Generation

After spending a near cloudless weekend on the Buffalo National River, my thoughts turned the considerable power of heat from the sun. When concentrated the sun’s heat can be used to do work, specifically generate electricity.

A new facility has begun operation near the Nevada border in the California desert. Ivanpah, CA in the Mojave desert is home to a solar thermal power plant covering a little over five square miles. The plant produces enough energy to power 140,000 homes (377 megaWatts.)

The plant consists of three towers each surrounded by thousands of mirrors.

Ivanpah plant

Ivanpah plant

Computers control where the mirrors are pointed such that they are always pointed at the top of the tower. There boiler tubes convert water to steam to at very high temperature and pressure. This is used to turn turbines for the generation of electricity. It works just like a conventional coal or nuclear power plant, but without the carbon emissions or radioactive waste. Clean sustainable energy.

Solar thermal power technology is not really all that new. A solar thermal power system was demonstrated at the the 1878 World’s Fair in Paris. A 20 square meter parabolic reflector, basically a light concentrating mirror, was used to make steam to run a printing press. Other solar thermal plants employing power towers have been built but the Ivanpah plant is by far the world’s largest and most efficient.

It is very efficient in multiple ways. Solar photovoltaic plants, usually seen on rooftops, are also configured in large numbers in fields to produce power for the grid and operate at about 15 per cent efficiency. The Ivanpah facility captures upwards of 20 per cent or more of the sun’s energy.

A unique feature of this solar thermal plant compared to other sustainable but intermittent power sources such as wind and solar PV is the ability to generate power around the clock. Some of the day time heat energy from the plant can be stored in special insulated reservoirs containing molten salt solutions. At night, generators can be run off of steam produced by water circulated through the heat storage reservoirs.

Another important variable in any thermal power plant is water use. This is especially important in the desert. When water is heated to make steam, it can only be used to do work if and when it is cooled back to water. Cooling the steam can use lots and lots of water. That’s why you see thermal plants like coal or nuclear fired plants located near large bodies of water – rivers, lakes, even sea coasts. The Ivanpah plant uses an air cooled system to condense the steam so it is particularly frugal when it comes to water use.

To complete the discussion I should mention downsides, two come to mind. First is land use, solar thermal plants of this type require relatively large areas in sunny climates. Luckily we have much desert land that with proper oversight to protect natural habitat can provide a significant amount of electricity production.

Finally there is the issue of bird kills. Some species of birds, especially fly catchers are being killed by flying into the heated air near the towers. Estimates are that about 30,000 birds are killed per year. That may sound like a lot but compare that with the number of birds killed annually by collisions with man made objects. A billion, yes that is a billion with a capital B, birds die from running into windows, and towers and what not.

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