Steam Turbines for Energy Storage

Steam may be a good way to store energy for the cold lunar night in the form of heat. We'll have really good insulation, in the form of regolith, vacuum, and perhaps an infrared-reflecting material. The trick is to put the radiators on the liquid side during the condensation phase, and use them for collecting solar energy during the vaporization phase. The heat stored as steam could also be used directly in keeping the habitat warm at night, in addition to converting it into electricity.

     |||||||||||||||||
     |||||||||||||||||  <-- big dark thing acts as solar radiation
     |||||||||||||||||      collector in day, radiator at night;
     |||||||||||||||||      could be part of liquid vessel structure
     |||||||||||||||||       ::::::::::::::::::::::::::::::::::::::::::::
     |||||||||||||||||     :::::::::::::: ___________________________ :::
      ______||________     ::::_____ ::::/ . . . . . . . . . . . . . \:::
    /                 \   ::::/ . . \ ::| . . . . . . . . . . . . . . |::
   |                   |_____| . . . |__|  . . . gas vessel  . . . .  |::
   |   liquid vessel    _____ turbine __  . . . . . . . . . . . . . . |::
   |~~~~~~~~~~~~~~~~~~~|:::::|  ~ ~  |:::\___________________________/:::
   |~~~~~~~~~~~~~~~~~~~|::::::\_____/ :::::::::::::::::::::::::::::::::::
   |~~~~~~~~~~~~~~~~~~~|::::::::::::::::: regolith insulation :::::::::::
    \_________________/::::::::::::::::::::::::::::::::::::::::::::::::::
   ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
                      daytime flow ------->
                      <------ nighttime flow

The gas vessel would be relatively large since the liquid would be about 300 times more dense than the gas. However, the fact that nearly all the components of this apparatus could be built in situ makes this a very attractive option.

This isn't exactly new technology. For centuries before guys like James Watt discovered how to use the expansive power of steam for practical work, people built engines that used the vacuum drawn by condensing steam.

Of course, H2O may not be the best working fluid for our purposes, but this is the basic idea.

We really won't know if this might work until someone runs the numbers.