The main heat losses in DHW are always, [no matter what system you select], in that little piece of pipe between the heater and the faucet. Every time you draw hot water, that length cannot be used and the heat is lost...
A conventional modern foam lagged storage cylinder, properly sized for family needs, has very low heat losses because the surface area is low compared to the volume stored. Surely the additional costs of new panels and wiring able to carry over 120 Amps will never get recouped?
