The shortest useful explanation
Dedicated PV modules can supply a matched electric heating element through purpose-designed controls. The element heats a storage medium—water in the PVDHW system—while a heat exchanger keeps potable water separate from the storage volume.
Energy conversion, step by step
- Solar irradiance reaches the modules.
PV cells produce DC power that varies with sunlight and temperature.
- Controls connect an appropriate load.
The electrical design must manage variable voltage and current, disconnects, temperature limits, faults, and applicable code requirements.
- The element produces resistance heat.
Nearly all electricity entering a simple resistance element becomes heat at the element, although system-level solar capture and losses still matter.
- The tank stores thermal energy.
More water and better insulation increase storage duration, while standing losses and required temperature determine useful capacity.
- Domestic water receives the heat.
The Sisyan system used a stainless-steel heat exchanger immersed in the storage tank.
Why use a large tank?
Sun and hot-water demand rarely match minute by minute. Thermal mass moves energy through time without electrochemical batteries. A documented single-family configuration used about 1.1 cubic meters, but tank sizing must be engineered for the actual load, climate, temperature range, and backup strategy.
What happens without enough sun?
A practical domestic system needs a safe way to meet temperature and hygiene requirements through poor weather and seasonal changes. That may mean auxiliary electric or fuel heat, grid-connected PV, a heat pump, a smaller dedicated solar contribution, or another engineered configuration.