If you are not getting enough pressure running your domestic hot water thru your solar tank, could you possibly turn that solar tank into a closed loop system and run that hot water into the house and thru a solar hot water heater with heat exchanger inside the tank?
The solar hot water heater could have an electric back up heating element to maintain temp on cloudy days.
or, you could run it thru a similar tank in the house to preheat the water entering your existing hot water heater.
just some thoughts..
You'd of course have to run glycol thru the system to prevent freezing but it beats tearing apart a perfectly good stainless steel tank to insert a coil.
