[osolemio]

I was not intending to arrive at a precise formula of how to calculate produced or anticipated energy. This was mainly about the fact that it is not straightforward to compare different heat sources like electric, combustion and solar.

As I mentioned earlier, the main problem with solar is to

1) Get a temperature which is high enough to meet demand (or lower the required temperature of the demand, to the solar temperature available)

2) Store solar heat either seasonal, weekly or daily

During all my research, thinking and experience so far, I have come to the conclusion that one of the vital points of solar heating (space heating in particular) is to maximize the difference between temperature available and temperature required.

To mitigate this challenge, it is vital to make a heat system with as large a surface as possible. Imagine if you could heat all floors in the house, and even all walls. In this case, even by the worst of winters, you just need to heat these floors and walls to 80 F or less. And the heat would be much more comfortable than a house with alternating cold windows, hot radiators and the resultant drafts and difference in radiated heat.

It is like a business and the bottom line. You can improve by increasing the sales, lowering the cost or a combination of the two.

To "increase the sales" is using a heat pump to transform the temperature available to a higher level, but there is a cost. This "cost" could be seen as "advertisement" in the business parallel.

To "reduce the cost" is in this case to lower the required temperature of the heating system. Although not exactly the same, the principle is the same. Because we use the simple method of combining two masses of heat (solar heating liquid, mixed with heating system liquid, in a heat exchanger). The temperatures of these two will merge, for the purpose of heating the house. But without a heat pump, there can be no heat transfer unless the produced temperature is higher than the required one.

To have a lower required temperature of a space heating system with a large surface not only increases the efficiency and extent to which you can extract heat from the solar panel. It also means that storing heat can be done at a lower temperature. The lower the difference between the heat storage, and the surrounding temperature, the less the loss.

In my system, the seasonal heat storage is high volume, low temperature, placed below the house. Insulated on the sides, the top is the house, and the bottom will eventually saturate over the years until it stabilizes somewhat. (providing ground water is not too close to the ground).

Whatever heat loss is upwards, goes into the floor of the ground floor. And whatever heat loss there are to the other sides, is not really that great a loss. Remember, this heat is excess summer heat, which is close to free and could not otherwise have been used. The energy it takes to pump it into, and out of the ground, is so minor it is easily made up by photo-voltaics.

As the final backup, one can add on a heat pump to make hot water for taps and shower out of the heat storage temparature, and to get the last bit out of the heat storage in late winter and early spring. Since the heat increase here is quite minor, this heat pump would run at a quite high CoP, especially compared to a heat pump trying to make hot water out of freezing air!

As for the calculation of how much heat is actually produced it is quite easy. All it requires is one flow meter, two temperature probes and a meter. The meter needs to be calibrated for the liquid used, like in the case where glycol or other anti-freeze liquid is used. If the meter has a logging function, one can compare the heat produces against other factors, like outside air temperature, available sun, time of year and so on.

I will take measurements in my system at the relevant places, and log these data for later analysis, to prove how much heat it is possible for me to extract and store from this system. And I will hold future energy bills toward historic ones, and compare energy production and usage from before and after the installation of this system. As electricity and heating rates increase over the year, I will keep producing my own heat, and the same close-to-nothing rate. All I need to pay is interest on loans, and minor occasional maintenance.

Finally, I will sum up all the expenses, and all the savings, and I will include all the added benefits as "savings". It would not be fair to expect the energy bill savings to entirely sponsor all the improvements done to the house while doing this project.