Photovoltaic + heater. Power selection of panels and other components.

Direct PV heating of a 100-liter boiler is possible, but the thread’s consensus is that it is not the cheapest solution; if minimum cost matters, solar thermal collectors are cheaper, while PV only makes sense if you accept higher upfront cost or want a broader system [#16339457][#16338031] For a 100 L horizontal tank, the practical estimate is about 1.2–1.5 kW of PV as a minimum compromise, with around 1.5 kWp often suggested; 0.6 kW is far too little and would need roughly 4 hours at full power to supply the heat [#16338031][#16348108] Use an MPPT/solar regulator that holds the panel operating point instead of simple cascade switching or direct connection to a 230 V heater, because switching heaters caused voltage spikes and poor results in the example build [#16345900][#16346496] Match the panel string voltage to the heater resistance so the heater draws the intended power near MPP; one contributor warns specifically not to run with 230 V at the power point because open-circuit voltage can rise and damage loads [#16345900] A real working setup described in the thread used 12×180 Wp panels (2160 Wp total), about 212 V MPP, a 2500 W MPPT regulator, and a 3 kW heater in a 100 L horizontal boiler, delivering hot water from March to September [#16346496]