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Hot Water Timers – Should I get one?

7 May 2018

What started off as a novel idea a few years ago has turned into a fairly common add-on for solar customers. The idea is simple enough, if solar only offsets loads on Tariff 11, then why not move my hot water system from off-peak tariff to Tariff 11 and install a timer so that it only operates during solar hours? Sounds simple and should save money right?

Well the short answer is, probably but like many technical things, it isnt quite as simple as that.

First of all, if a timer is all you want to do, then I strongly suggest you install a contactor too. These are like relays and will extend the life of your timer by doing all the heavy switching work. We also use a timer with battery backup as standard so that you dont have to reset it everytime there is a minor outage.

Better still, install a smaller element at the same time and run the timer for longer, this will help to ensure that your hot water heating stays under the solar production more often. Most Hot Water systems have a 3.6kW element, so when the timer switches it on, it will use 3.6kW/hour until either the timer goes off or the thermostat switches it off. A typical 5kW solar system will produce 4.6kW which is only leaving 1000W for other items consuming electricity. And this is assuming that its a good day. With patchy cloud cover, solar production could be below 3.6kW and that means you are buying grid power (at Tariff 11 prices) to heat your water at those times.

Here in this real world example, this clients hot water system is consuming power above the “solar window”




Now with a smaller element, the hot water system is under the solar window.





So while a smaller element is certainly better, its still not the best solution. If its an overcast day, you could once again see the hot water system using grid power as you can see in this next graph.

So what is the best solution? Well, if you are working on a budget, the timer with a smaller element isn’t a bad option but there is a smarter solution. Catch Power is an Australian made energy diverter, which can sense when you solar system is about to export to the grid and diverts that power into the Hot Water system. This system ensures that only surplus solar power is used to heat the water. Once the tank has reached temperature, it will divert the surplus solar back to the grid. Its like a little electronic policeman directing energy flows to where it makes the most of it for you. Climatecare Electrical are proud to be exclusively distributing this amazing product. For more information, check out our Energy Saving Products page.


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