The Supercritical Carbon Dioxide Generator

Many electrical technologies – coal, oil, fission, fusion – really just produce heat that is used to boil water, which is then used to drive steam turbines. It is the spinning blades of the turbine that actually generate the electricity. This is a great technology, and we have gotten really good at building steam turbines after 200 years of practice.

But that doesn't make it the best technology for converting heat into electricity.

This brings us to the a new(ish) technology that may turn out to be much more efficient: the supercritical CO2 generator. These are similar to steam turbines but instead of water they use supercritical CO2. "Supercritical" means that the carbon dioxide is heated and compressed (84C, 74 atmospheres) until it turns into a "supercritical" state, sort of a very dense gas that behaves like a liquid. This dense fluid can spin turine blades more efficiently than steam, and it does not lose energy to the phase transition (liquid to gas) that uses up a lot of energy in a steam engine. Because the CO2 is so much denser, these turbines can be much, much smaller than those using steam:

The 10 MW US$155-million Supercritical Transformational Electric Power (STEP) pilot plant was completed in 2023 in San Antonio. It is the size of a desk and can power around 10,000 homes. [top photo]

The US Department of Energy has been funding research in this area for decades. The biggest problem they found was that supercritical CO2 corrodes steel, so that however efficiently it generated power, the system could not be made reliable or stable. Then a decade or so ago Sandia National Laboratory discovered that certain kinds of nickel steel were not degraded by supercritical CO2, and this launched a worldwide spate of experiments and innovations. Recently commercial generators have gone online in both the US and China, with claims that they are up to 50 percent more efficient that steam turbines.

This is the Chinese entry, a recently announced 30 MW system in a steel plant, which is using waste heat to generate power for the grid.

Technological doomsterism is silly. We can generate all the energy we need, without CO2 emissions, whever we decide to do so.

(16-minute video, short article, wikipedia)