In looking for a location for the storage tank, I realized a tank sized to my solar absorbers will need to be 1000 gallons. I have planned on 500 - 600 gallons, inside the utility room, but 1000 gallons will not fit. The tank size was determined by the rule of thumb of 2.5 gallons per square foot of absorber. This allows a good efficiency of the absorbers, while limiting the risk of overheating. Although there won't be overheating with a drainback system, I do want a tank as big as possible, to have a storage of heat for our numerous cloudy days.
I decided to choose an alternate location for the storage tank: under the deck. There should be plenty of room for a 1000+ gallon tank, and the pipe runs won't be any longer, since the tank will be between the absorber array and the house. The only part of the design that needs change, is the hot water pre-heater. The longer pipe run between the solar tank and the electric hot water tank will decrease the efficiency of the system. So I opted for a heat exchanger, located next to the electric water heater. I haven't decided yet what kind of heat exchanger.
It will be complex and pricey, which is why it will be done in two phases. I may get 4 absorbers instead of just 2 for phase 1, since phase 2 has the 8 absorbers arranged in two banks of 4.
Next will be a bill of material.