Steam turbines still produce most of the world's power, but supercritical carbon dioxide promises to be much cheaper, and 10% more efficient as a medium than water, using 10X smaller turbines. A US$155-million pilot plant is now complete in San Antonio.

Ribbons were cut at the Supercritical Transformational Electric Power (STEP) pilot plant in Texas on October 27 as it was declared "mechanically complete" by project partners Southwest Research Institute (SwRI), GTI Energy, GE Vernova, and the U.S. Department of Energy.

The device in the image above is the world's first supercritical carbon dioxide turbine. Roughly the size of a desk, is a 10-megawatt turbine capable of powering around 10,000 homes. Ten megawatts is pretty small potatoes in the energy business, but to do it with a turbine this tiny? That could prove to be a revolutionary feat.

Carbon dioxide goes supercritical when the temperature and pressure are above about 31 °C (88 °F) and 74 bar (1,070 psi), respectively. At this point, it stops acting like a gas or a liquid, and instead starts acting something like a gas with the density of a liquid. Past this point, relatively small changes in temperature can cause significant changes in density.

Water can of course go supercritical too – it just takes a lot more energy, requiring a temperature and pressure over 373 °C (703 °F) and 220 bar (3,191 psi).