The 2 Types of Solar Hot Water
Last Updated: 13th Apr 2026
There are 2 very different types of solar hot water systems to choose from:
Solar Thermal Hot Water
This uses a solar collector on your roof that absorbs the sun’s rays and transfers the heat from them directly to water, which is pumped through the collectors.
The water heats up as the sun hits it. When the sun isn’t shining, you obviously can’t heat the water with solar energy, so you need to have a backup fuel source, usually gas or electricity. Of course, to avoid using this electricity or gas, you store the hot water in a well insulated tank.
Generally, these systems can provide from 50 to 100% of your home’s hot water – depending on where you live and how efficient your solar hot water panels are.
In Hobart, you’ll get about 50% of your water heated by the sun. In Darwin, you may get 100%.
Here’s a typical collector based system that uses a ‘flat panel’ style collector. This one has its hot water tank integrated with the panels:
Heat Pump Systems
A heat pump works by moving heat from outside air into its hot water storage tank. While it may seem strange, a good heat pump can still extract heat from outside air that is below freezing. Because they don’t directly use electricity to generate heat, they are usually at least 3 times as energy efficient as a conventional electric hot water system.
While this may not seem like solar hot water, as there are no collectors, it is — in a roundabout way. This is because 99.96% of the heat in the air originally came from the sun, while only 0.04% is from underground primordial heat and radioactive decay. Heat pump hot water can also be made 100% solar powered by running it off rooftop solar. This means both the electrical energy it uses and the thermal energy it takes from the air will come from the sun.
Here is a typical heat pump system – you can see the similarities to an air conditioner!
And if aesthetics are important to you, don’t worry, you can get really sexy looking ones (to an engineer like me anyway!) with the heat pump integrated into the cylinder, so it is almost invisible.
Which Is Best?
Many years ago, a solar thermal hot system could be an effective way to reduce electricity bills. However, because electricity generating rooftop solar has fallen dramatically in price, and heat pump hot water has both fallen in price (after adjusting for inflation) and has improved in reliability, heat pump hot water is now far more cost effective. These days, we only recommend solar thermal hot water if there are special circumstances. But simply liking it is definitely one of those circumstances.
If you’re after details, check out our guide to heat pump hot water.