Notes about buildings with 100% Solar heat

From HUG Wiki

When solar space heating panels are installed, typically they are sized to reduce the heating bill by a relatively small percentage. The first 10 or 20 percent is relatively easy. You just heat the house when the sun shines. As you increase the percentage of fuel replaced by solar, the task gets more involved.

During a Minnesota winter, we are lucky if the sun shines for 5 hours during the day, and we can go many days with virtually no sun at all. That means we need to store heat when the sun does shine. The numbers are brutal. A typical December is both cold and cloudy. If we are to heat with virtually 100% solar, we need to capture 5 days worth of heat in 5 hours, and be able to store it for at least two weeks. This is expensive in two ways;

(1) The solar panels need to be about 24 times larger than the typical installation.

(2) Heat storage involves insulating and thermally connecting to a huge mass.