The Clean Energy Regulator rates solar hot water systems and heat pump hot water systems by awarding Small-scale Technology Certificates (STCs) to each available model.
Note that STCs were previously called Renewable Energy Certificates (RECs), and BASIX still uses the term RECs.
BASIX assesses the performance of solar and heat-pump hot water systems based on the number of STCs; the more STCs, the better the system.
For solar (gas or electric boosted) hot water systems, more STCs are generally awarded for larger collector areas, more efficient collectors, and better thermal insulation of the tank and pipes.
For heat pump hot water systems, more STCs are generally awarded for better tank insulation and higher efficiency compressors.
Typically, gas-boosted solar hot water systems will score more STCs than electric-boosted solar systems, which in turn will usually score more than electric heat pump hot water systems.