Solar heating of domestic hot water has traditionally been achieved using ‘Solar Thermal’ technologies (Flat plate panels or evacuated tube collectors). Whilst Solar thermal is more space efficient than Photo-voltaic (PV) in terms of the captured energy per unit area, it typically has high installation costs, is less effective during cold weather or overcast skies, has a shorter life span, and can present several ongoing maintenance challenges and costs (mechanical pumps, antifreeze & corrosion chemicals, leaks, positioning in roof space and routing of pipework etc). Where a larger solar collection area is available (rarely a limitation in the majority of installations), then the use of PV panels now offers a more cost effective, near zero maintenance and better performing ‘solid state’ alternative approach to solar water heating. The rapid and continued decline in PV panel costs has been instrumental in making PV hot water an attractive and economically viable approach. Loadmaster is designed to sit between an array of PV panels and a conventional electric immersion heater and is designed to moderate the load impedance of the heating element to maximise the collection efficiency of PV electrical energy regardless of the sky conditions.