Old news, but I didn’t read it at the time and given I’ve mentioned Geothermal energy in Australia before, I thought I’d link to it anyway. The Economist from nearly a month ago mentions some developments that have been making geothermal power at either extreme (low or high temperature) more usable. The low temperature part I think is particularly interesting.
Not all geothermal activity is hot enough to bring water to the boil. The Chena hot springs, in Alaska, for example, are just right for bathers, at a porridge-like 43°C, but not much use for traditional geothermal power generation. Even within the spa’s wells, the water is only 74°C. Nonetheless, its owners, in conjunction with United Technologies, an engineering conglomerate, have worked out how to generate power from the tepid flow—the coldest ever used in a geothermal plant.
The power station at Chena uses the spring water to heat up R134a, a fluid hitherto employed mainly as a refrigerant. Since R134a has a relatively low boiling point, the water is hot enough to convert it into a gas. This gas is used to drive the turbine just as steam would be. Icy water from a nearby river then cools the gas back to liquid form, to start the cycle again.
The designers of the plant at Chena, however, managed to slash their capital outlay by substituting mass-produced parts from air-conditioners for the bespoke components of most geothermal plants. They reckon their design could be mimicked anywhere there is a difference in temperature of at least 50°C between heating and cooling water. That would apply not only to a huge number of geothermal sites, but also to many oil wells, which often bring up warm water from great depths along with their more valuable output.
The idea that you can use off the shelf construction materials to build cheap “warm” power stations is great. These could be much more widely available than the current deep hot rocks that we are drilling for in Australia is interesting. I’m increasingly convinced that some mix of geothermal is going to be an important part of our greenhouse friendly energy usage in the future along with distributed wind power and perhaps nuclear.
and, at the other end of the scale:
In Iceland, meanwhile, a consortium of utilities is teaming up to do just the opposite: harness steam that is much hotter than the norm. The wells of most geothermal plants are about 2km (a mile-and-a-bit) deep. But the Icelandic outfit hopes to drill to depths of 4km or more, to get closer to the magma that rises towards the surface along local faultlines. In such areas, geologists predict, the steam might be as hot as 600°C.
Tapping this steam would be expensive, since it would require not only extra building materials, but also more durable ones, to cope with the higher pressures and temperatures. But Olafur Flovenz, of Iceland Geosurvey, believes that although the costs might double or triple, the amount of electricity generated could rise by as much as ten times.