Today there was a nice surprise. Two years ago we got a Solar PV Diverter to heat our hot water with as much solar PV energy as possible. It did cost almost $1,000 (installed) and I wasn't really sure how long it would take to pay off (ROI = return of investment).
Surprise after two years the ROI has been almost reached. Of course that depends on your energy providers tariffs and your hot water usage.
Usually electric hot water is heated at night time with so called "Control Load". This is basically the "base load" of our dirty coal power stations which has no other usage since most of us are asleep and don't use much electricity at night. Therefore it's cheap, currently about $0.176 / kW/h (incl. GST).
A Solar PV Diverter uses only the excess electricity (you would otherwise export to the grid) to heat your hot water. The better diverters do this dynamically on the fly in real-time, in other words: They can exactly divert only the excess electricity without delay to your hot water tank.
In the last two years we used 4.5 MW/h (on average 6.25 kW/h = 2-3 showers per day) to keep the water hot, so we saved 4,500 * $0.176 = $792 or $396 a year.
For the records: We could have saved an additional $112 for the $0.154 Control Load connection feed per day but disconnecting the Control Load would have costed quite a bit and we still use it as backup for those rainy days or weeks.
Most people don't realize that they actually already have a home battery: It's the electric hot water tank. A 400 liter tank stores about 25 kW/h of electric energy!
If you have an electric hot water (tank) system and a Solar PV system, consider a Solar PV Diverter. Within 3 years you can not only reduce your CO2 footprint but also save a lot of money.
And taking a nice extra long hot shower is now even more enjoyable .
In case you build a new home and you are planning to install a solar hot water collector, consider to save that money and install instead a bigger solar PV system with a diverter. Once the water has been heated you can still use the excess electricity for your house, to charge an electric car or to earn money by exporting electricity to the grid.
After all this time, thank you Tommy!