After applying a release agent and a waterproofing layer to a male mold, a worker encapsulates the liner and steel reinforcing frame in polyurethane spray foam. Completed tanks range in size from 5 by 5 by 4 feet to 8 by 8 by 20 feet.
After applying a release agent and a waterproofing layer to a male mold, a worker encapsulates the liner and steel reinforcing frame in polyurethane spray foam. Completed tanks range in size from 5 by 5 by 4 feet to 8 by 8 by 20 feet.

In theory, liquid-based seasonal heat storage is simple enough: If you have more heat than you can use right away — in the form of warm-season output from solar thermal panels or a biomass boiler that burns a seasonally available fuel — you use it to raise the temperature of a big insulated container of water or some sort of water/antifreeze blend. Then, during the heating season, you tap into that reservoir and circulate the warm fluid to an air handler, conventional radiators, or radiant slab. When spring rolls around, you start recharging the tank with heat for the following season.

But while sunlight is free and water is notably cheap, stockpiling enough hot water to last for an entire heating season is neither. The history of solar heating is full of creative hippie stopgaps — from homemade plywood tanks to above-ground swimming pools and repurposed unused septic tanks — designed to provide adequate storage at a...

or Register to read the full article.