This page explains options for saving money on hot water heating in Tasmanian residential properties. It assumes you purchase electricity from Aurora (or another retailer) on a residential time-of-use tariff and have an electric storage hot water cylinder. This fact sheet includes information on making best use of solar if you have, or are planning to get, solar PV. However it is relevant even if you do not have solar.
To understand about tariffs see our fact sheet on Tasmanian residential tariffs.
To understand options for hot water, see Hot water options.
This article describes options for the cheapest way to save money with an existing electric hot water system. There is a strong case for electrifying all your appliances at once, particularly if you are purchasing an electric vehicle and/or a home battery. In this case you will probably want a ‘home energy management system’ which is beyond the scope of this article. There are many competing options, typically provided by the suppliers of home battery systems.
The challenge with this is that you tend to be locked into a particular supplier’s ‘ecosystem’ of equipment, or you need to spend a lot of time and effort integrating different components.
All the options described here require a licenced electrician to install some equipment in your switchboard. This is definitely something you should not try yourself, it is illegal and highly dangerous.
If you are planning to get solar installed it makes sense to decide on one of the options below and get it installed at the same time. Some of these options require a 230 V supply. If you are getting a new or upgraded switchboard talk to your electrician about include a 230 V outlet in the switchboard.
The simplest, cheapest solution is to install a timer in the switchboard and allow this to directly control the power to the hot water service.
The disadvantage of this solution is that to change the timer you will need to access the switchboard. You should ensure that the timer is rated to handle at least the power requirement of the hot water service.
An additional problem is that even if the unit is rated to control the load (eg this just adequate 16A analogue switch), if the timer fails, you will need an electrician to replace it.
Your electrician will advise on a timer that they think is up to the job.
A contactor (or relay) allows a lower power or voltage to control a larger power or voltage. If pursuing this option you will need to decide whether the contactor is driven by a 12 V or a 230 V supply. 230 V contactors are more common and are required for the Catch Solar Relay (see below). A 12 V supply input means once it is installed it can be controlled from a low voltage circuit and you can make changes without requiring an electrician.
We use the Finder 22 Series Modular Contactor. This will control a 25 Amp load (a typical hot water service is 15 Amps, ie 3600 Watts). An additional advantage is that this contactor has a switch which allows the controlled circuit to be on, off, or controlled by the 12V input.
You could combine the Finder contactor with a 12 V power supply and a simple programmable powerpoint timer. This requires enough room in the switchboard for a power point, timer and 12 V power supply. The advantage compared with a simple timer in the switchboard is that you can add an external controller later.
This is the approach used with our HotTimer controller. This is a DIY product.
Before getting the electrician to install the contactor in your switchboard you will need to decide where the 12 V input cable leads. If you plan to use an external controller (such as our HotTimer) the cable will need to be terminated where you want the external controller. This should be a position where you can readily see the display and use the controls. The location will also need ready access to a powerpoint for the 230 to 12 V power supply.
Green Catch is a solar diverter and is designed to operate with solar panels. It measures the surplus solar and provides only that amount of power to the hot water system. As a result it works only with simple resistive loads (like a conventional storage hot water system), it is not suitable for use with a heatpump hot water system. This is the only solution that provides exact solar surplus to the hot water system. For example if you have 2 kW of surplus solar at a given moment, then 2 kW of power is provided to the hot water system (even if it is rated at 3.6 kW). This maximises self-consumption of solar energy. All other solutions switch the hot water on or off. So if power is supplied to a 3.6 kW water heater and there is only 2 kW of surplus solar, then 1.6 kW of power will be bought from the grid.
This product (formerly known as Catch Solar Relay) provides sophisticated control of loads but requires a contactor as well as the Catch Control unit. It works best with a resistive hot water service but can also control a heat pump if the heat pump has an interface for an external control.
Purchase of Catch Control includes the Monocle app which provides various options for load control as well as free access to Solar Analytics monitoring.
The Catch Solar Relay has additional features that are useful if you have an electric vehicle and/or a home battery.
Option | Pros | Cons |
|---|---|---|
Timer in switchboard | Cheapest solution Set and forget | Have to access switchboard to alter times. Contacts might fail |
Contactor is switchboard with timer and 12V power supply | Allows for future upgrades | Might not be room is switchboard for everything |
Contactor in switchboard with external control | Most versatile | Requires 12V cable from switchboard to external location Requires external controller (eg our HotTimer). Not a commercial product. |
Green Catch solar diverter | Maximises use of surplus solar | Only works with resistive load (ie not heat pumps) |
Catch Solar Relay | Best option if you have EV charging and/or a home battery Works with some heat pumps Provides free real-time monitoring plus load control | Most expensive option Requires contactor in switchboard with a 230 V coil |
