Divert Your Excess Solar

Solar Tariffs cut

When the solar feed in tariff was reduced across Australia, and battery storage not quite economically viable yet, there has been an ever increasing interest in ways to use your produced electricity rather than feeding it back to the grid for only 8c per kWh.


One great was to fix this problem is to divert the solar electricity into your hot water system or underfloor heating. But before we jump into it, let’s do the maths, working with typical peak and off peak tariffs available in Victoria.

Assume we have a 5kW solar system and a 3.6kW element in your hot water system. Just say it heats for 2.5 hours a day then your hot water usage is around 9kWh a day on Victoria’s off peak tariff which is cheaper than your day tariff.

Excess Power Usage 

Most 160lt and above hot water systems are able to comfortably run off peak. The above system would use 9kWh day x 365days = 3,285 kW/year. On the off peak rate of 20 cents your hot water would cost $657 a year. However if you divert all your excess solar power (worth 8c if you exported it) to run you hot water system you could save 12c/kWh or $438 year.

Solar diverter 



A “Solar Diverter” is a smart device that tells the excess solar power to be used by the hot water system instead of feeding back to the grid. The benefit of this method is that it’s totally interactive with solar production and the household load. As the demand from the house and the production from the solar varies, the diverter will automatically adjust so that solar production will be prioritized, first to the house then second to the hot water system or floor heating and at last resort back to the grid. As an additional benefit, (providing you have a tempering valve on your hot water) you can turn your hot water system right up from 60 degrees to 80 degrees, giving you increased energy storage capacity. There are three products on the market that seem to be leading the way, the ImmerSUN, Sunnymate 2.0 and the SolarImmersion IV. Are they worth it?

immersun controller



The “ImmerSun” hot water diverter

The immersSUN diverter an obvious disadvantage of the immerSUN is that it is limited to 3kW larger hot water systems often have 3.6kW elements. They are selling for $924. Or let’s say, $1100 installed.



apollo gem (sunny mate)



The SunnyMate 2.0 inverter

The SunnyMate 2.0 supports dual loads that switches between primary and secondary load and is fully programmable. Units can be banked up together to offer more load and even comes in a 3 phase model offering a 5-year warranty on all Sunnymate models. It diverts power from 100w to 3.6kw load and cost around $1000 installed.




solarimmersion-solar-diverterSolarImmersion 3.8kw Diverter

The SolarImmersion supports dual loads and switches between primary and secondary load. Diverts power from 20w to 3.8kw. The SolarImmersion works on PV systems starting from 500W. There is no upper limit regarding the PV system however, for a large system (PV capacity of more than 4kW), several SolarImmersion units could be attached together to utilize surplus power and comes with a 1 year repair or replacement warranty.






Smart. You will not unnecessarily feed your solar back to the grid for just 8c.
Flexible. You can super heat your water, so it stays hotter for longer.
More suitable for non-routine households, where they are not out of the home just about every day, but still are feeding in power back to the grid.
Will be ideal if the feed-in tariff is reduced further


It’s expensive. (Approx. $1000 installed but return on you money is around 3 years so it’s worth it)


Your hot water can run up to 100 percent off solar, so it will be 100 percent savings if you get a few hours of sun a day  (3650x 12c) = $438 a year ( based on 365 days and at 10% no sun $394.20 a year ).
(AWS conservatively claim a four person family can save nearly $400 a year.) You should, by these figures, pay for the device in under 3 years and go on saving $438 a year.

However, if you use less hot water than 9kWh a day, your payback time will increase proportionally.


Is it worth it?

Installing a load shift timer is a simple and cost-effective way to reduce your power bill assuming you generally do not use a lot of power between 10am and 2pm. As a smarter option is the SunnyMate 2.0, while the outlay is considerable  you can see a return for your investment in under 3 years.


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