Geothermal may beat batteries for energy storage
Many of the greenhouse Youtube channels I watch do a smaller DIY version of this.  They have either dark barrels of water in the greenhouse with the windows facing south to the sun, or a thin metal wall filled with clay and pipes acting as a sun-heat-battery.  They pump the water through the barrels or clay battery into pipes that are under ground to store the heat.  In winter time they extract the heat from the ground keeping the greenhouse warm using a combination of solar and commercial power for the pumps.  Heat is also extracted from compost bins at each end of the greenhouse.   This works well in extremely cold climates in Canada and Alaska.  A few of these folks do all of this without using any electricity at all and somehow manage to get water moving through the pipes using heat convection alone.<p>I've been thinking about doing something like this but connecting it to pipes under the foundation of my home so I can get rid of the wallboard heaters or just leave them off.  Electricity is the only commercial utility near me.