So my idea of pushing CSST into the tank as a HX did not pan out. I just could not get a seal around the outside of the CSST coming out of the tank.
This type of module could be added to any tank, or connect it to an electric WH of your choice. A timer on the electric tank would allow solar to prioritize, elements kick in at 3:00.
This is a air tank from Harbor Freight, HX off e-bay, misc parts all came up to around 500.
I'm waiting for a few fittings and Webstone purge ball valves to allow flushing the HX.
The panel is an old door off a refrigerator, 1-1/2" of foam insulation, aluminum wrap.
Pumps could be changed as need. The HX above the db tank allows most energy to be purged and put into DHW without leaving a hot db tank at days end. I think it will drawback through the plate hx fine?