Direct Solar Thermal Water Heating

This method uses solar collectors (flat-plate or evacuated-tube) to directly convert solar radiation into heat, which is transferred to water stored in an insulated tank. Circulation is achieved either by natural thermosiphon or by a small pump. Advantages include high conversion efficiency (40–70%), proven technology, and reduced dependency on grid power. Limitations include seasonal variability, need for backup heating, and plumbing complexity.

Direct Electrical Resistance Heating (Utility Grid, AC Power)

Electric geysers/boilers heat water via resistive elements powered by utility AC grid. Advantages include simplicity and reliability. Limitations include high operating cost, inefficiency (COP=1), and strain on utility grids during peak demand.

Direct Electrical Resistance Heating (Home Solar System, AC Power)

In this case, solar PV panels feed into an inverter that powers conventional AC geysers. Advantages include shifting electricity cost from grid to free solar PV and flexibility. Limitations include inefficiency, higher PV capacity requirements, and possible battery dependence (if a timer is not used).

Direct Electrical Resistance Heating (DC Power from PV + MPPT)

PV panels directly power DC resistance elements via an MPPT controller. This design avoids inverter losses, yielding 90–95% efficiency. It is more affordable than AC solar systems but provides hot water mainly during daylight hours, requiring large storage tanks for night use. However, advanced MPPT heater controllers now offer programmable AC input options, enabling supplemental heating from the grid at night and thereby reducing the requirement for oversized storage tanks.

Heat Pumps Powered by the Utility Grid

Heat pumps use grid power to run compressors that extract ambient heat and transfer it to water at a higher temperature. They achieve a Coefficient of Performance (COP) of 3 or more, producing up to 4 kWh of heat per 1 kWh of electricity. This reduces running costs by 40–70% compared to geysers. Suitable for both homes and large institutions, but reliant on grid electricity.

Heat Pumps Powered by a Home Solar System (AC)

Heat pumps powered by PV + inverter combine the efficiency of heat pumps with solar PV. Advantages include very low operating cost and environmental benefits. Limitations include high upfront costs and system complexity.

Heat Pumps Powered by a DC Solar Array

PV panels directly power DC-driven heat pump compressors with MPPT control, eliminating inverter losses. This boosts system efficiency to over 350%. The technology is less common and expensive, but provides the lowest operating costs long-term. Available for homes and large institutions. Advanced models offer programmable AC input options, enabling supplemental power from the grid at night and thereby reducing the requirement for oversized storage tanks.