Ice-Shelf Heat Pipe Power Generator

Water is odd. Seawater freezes at about -2C, and then it floats, which is odd. Water is densest at 4C so in polar regions you have a strange temperature gradient with the cold ice on top, the interface between water and ice at -2C and then a gradual increase with depth to around 2-4C at the very bottom. These are the sorts of conditions below your typical ice sheet, but the temperature gradients get more extreme in the air above. Above the Ross ice sheet surface air temperatures average about -32C and dip to -60C <link> through the winter months. Furthermore the wind speeds are a very healthy average of 10 knots with occasionally brutal 60+ knot periods. The ice shelf thickness over the ocean varies a fair bit but is generally a few meters, very drillable.

Now, using temperature gradients to generate power is baked. There’s one in Japan <link> that operates using the 20-23C difference between surface water and deep oceanic water. That’s 10C worse than my average and 50+C off the best case scenario. The biggest losses derive from the 1000’s of metres of piping to access the cold water at tremendous depths AND the fact that their temperature gradient is upside down, they have to lift all that dense cold water. So let’s beat that system.

Take a large steel tank and insert it below the ice shelf in all that balmy 0C water. Some optimization for surface area and ice shedding will have to be done but that’s what engineers are for. Fill this tank with some ammonia. At 1 atmosphere, this boils at -30C so the sub-shelf water will get a nice vigorous boil going in no time, especially considering the excellent heat properties of water combined with a nice bit of state-change enthalpy. Your boiling ammonia will emit gaseous ammonia, conveniently at the top of the tank, so here you can connect an ammonia turbine, these are baked <link>. While you could just keep pouring ammonia in, that’s a little wasteful, so let’s have a huge air-cooled condenser on top of the shelf. The healthy winds and low winter temperatures should have that ammonia condensed in a jiffy. Conveniently, condensed liquid ammonia will run right back down to the sub-shelf tank all on it’s own. The whole thing can be done with essentially one moving part, the turbine. If the surface winds get above/below -30C then it’s pretty trivial to mess with the pressure of the system to manipulate the condensation point to either keep it running in warmer times or extract more energy from colder winds.

One pitfall is that ice shelves move. So, the clever thing to do here is to build the ice penetrating section very tough, anchor it well and then pump a little of the warm sub-shelf water around the leading edge in a kind of hot-knife manner. Or live with relocating the station every few years.

There, simpler than prior art. More efficient, and it’s extracting thermal energy from arctic region, which should cheer up some people. Just need to work out the grid hook up.