The cheapest way to save on electricity

Jack Gilding outlines his hot water system timer that reduces his water heating bills.

There is no doubt that ‘electrify everything’ makes a lot of sense in the long run environmentally and financially. But there are a lot of interacting complexities between solar PV, electric vehicles and associated charging, changing from gas to electric cooking, options for electric water heating, and possibly a home battery. All of these have options and implications for your house wiring and switchboard. Not to mention the capital cost. Because of these interactions, it is best to have a long-term plan that considers all these possible future developments.

I got a bit carried away with looking at the simplest, cheapest solution. If you have a working electric storage hot water system, the cheapest way to save money is to put this on a timer. This applies whether you have solar PV or not, as long as you have an option to move to a time-of-use tariff. It is also relevant if you become eligible for the ‘free power in the middle of the day’ recently announced by Chris Bowen.

Controlling the timing of water heating is the easiest way to reduce the cost of electricity because water heating consumes a large amount of energy and can be done at any time of the day. It is in effect the battery you already own.

There are at least three scenarios in which this makes sense:

• if you have a reasonable size solar PV system, you probably export energy in the middle of the day and buy it back later at a higher price once you use hot water,
• if you are on a time-of-use tariff, you can save money if you avoid heating water when electricity is expensive,
• if you are eligible for the proposed ‘free power in the middle of the day’ this is an ideal time to heat water for later use.

My website (backroad.com.au/energy) explains the various options for adding time control to your hot water service. Even for this simple solution there are at least five different options to consider.

Being a bit of a tinkerer with micro-electronics I got carried away with developing the cheapest, most flexible approach to adding a timer to my hot water circuit. I got an electrician to install a contactor (aka relay) in my switchboard controlling power to the water heater. Using a contactor powered by a 12V supply means you have a range of DIY options for controlling the timing of water heating.

An added bonus of my DIY solution is that, as well as automating cheap water heating, it displays visually when power is cheap. This can be a prompt to manually move other electricity consumption to cheaper times. We do this for our washing machine and clothes dryer.

The colour LCD makes it easy to see what’s going on in the system.

If you are into building stuff yourself, you can buy the components for around $100. Trying to source components as cheaply as possible taught me a lot about the pros and cons of buying components online from China. Some of the components had unexpected complications—the very cheap Arduino Uno clones did not initially work as expected, but some other components were identical to the ones bought in Australia and very much cheaper. Some were not even readily available in Australia.

The software as currently written is based on the Tasmanian time-of-use tariff, but if you have some familiarity with C++ programming you can change both the tariff times and the boost times.

If you don’t want to build this unit yourself it is still worth having an electrician install a 12V driven contactor. You can control this for now with a cheap power point timer and a 12V power pack, and retain flexibility for future upgrades without having to pay an electrician to come back.

By all means investigate the ‘electrify everything’ approach, but don’t ignore the possibility of a much cheaper and easier way of making a start on controlling your electricity use.

Parts list

In addition to the major parts listed above, you will need some miscellaneous components that you may already have. This includes a 12V power supply, LEDs, resistors, wires, and, depending on how you choose to mount the components, sets of mixed 2mm and 3mm spacers, bolts and nuts. Options and prices for these are included in the documentation on github.

1 These are cheapest unit costs and do not account for any supplier bulk purchase requirements or shipping costs. Where I have used local parts for the cheapest build I have included the Australian price in the Cheapest column. You may be able to source these parts more cheaply.

Resources
Jack’s timer instructions and software: github.com/JackGilding/HotTimer
Information on all the options for controlling a hot water system: backroad.com.au/energy