solar diverter for hot water worth it

The arithmetic is straightforward once feed-in tariffs are low. Exporting a unit of energy earns the feed-in rate. Using it to heat water avoids buying a unit later at the retail rate, which is substantially higher. On most current tariffs, self-consumption is worth several times export.

Ways to do it

• A timer on an existing electric storage system, set to heat in the middle of the day rather than overnight. This is the cheapest option and often the best value.
• A dedicated diverter that sends only surplus energy to the element, so it never draws from the grid.
• A heat pump hot water system on a daytime timer, which uses roughly a third of the energy of a resistive element for the same output.

Things to check first

• Whether the system is on a controlled load or off-peak tariff, since moving to daytime heating may mean leaving that tariff and changing the metering.
• Whether the tank is large enough to hold a day's hot water, because the point is to store energy rather than heat on demand.
• Tank insulation and standing losses, which are worse on old units and eat the benefit.