My vented boiler hot water energy storage system uses a DHW tank and a 140 Litre ‘heat store’ using an un-pressurised copper tank and an energy diverter. This has operated very successfully during the last 9 years and has diverted about 30MWh from my solar panels.
My neighbour now has solar panels and a combi boiler so to do something similar he would need to operate a pressure vessel at mains pressure to provide solar heated water to the boiler.
I was wondering if a non-pressurised approach as shown in the attached diagram would be possible.