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Solar Thermal Storage
Over the course of the heating season, there will be enough solar heat energy to provide the comfort we want (see Energy Analysis). The problem is the sun provides this energy intermittently. The challenge is to store the energy as it comes so it will be available when and where we want it. The space for and cost of storage, especially water storage, makes this problem more challenging.
My solution is to utilize three types of heat storage, each with its advantages and costs:
The intermediate goal is to maximize the collection and storage of solar heat and then manage the use of that stored heat to meet my main goal of keeping the Active Area comfortable, with as little wood stove use as possible, and the bathrooms warm for daily showers.
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Especially Water Storage
Conceptually, a massive, well insulated water storage tank in the basement could be charged throughout the summer and fall, and then, through the winter would provide the supplemental heat needed. Advantages of this approach are that you maximize the number of BTUs collected per collector (only half the collectors would be needed), it is much easier to collect heat in the summer, and the heat needed in the winter is available when needed – no real timing issues. The disadvantages are cost and space. Say you “just” need to store half of the seasonal BTUs needed (the other half comes from the sun during the winter). For a house like mine, you would need to store about 12 mmBTUs, which with a 30 degree delta T (water stored at 110+ degrees) would require about 40,000 gallons of water. Such a tank would take up 5,343 cubic feet (about 20’x 33’x 8’). Not discourage yet? Such a stainless steel tank would probably cost between $80,000 and $100,000, without insulation or peripherals! So, conceptually massive water storage is a great idea, but practically we really need to work with the solar resources we have during the winter.
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