Solar hot water diverter or a battery for your surplus solar? Often the diverter goes in first — but only if the fit is right.

A solar hot water diverter is a small device that watches for surplus rooftop solar you're about to export to the grid and instead sends it to your hot water tank's electric heating element. It chops the AC waveform to fine-tune the power, so it uses only your excess rather than drawing from the grid. Some units can also run pool or spa resistive elements. The idea is simple: instead of exporting midday solar for a near-zero feed-in tariff, you store that energy as hot water, which is one of the largest single energy loads in an Australian home. It only works with a conventional electric-element tank.

No. A diverter only works with a conventional electric hot water system that has a resistive heating element. It does not work with a heat pump hot water system, which uses a compressor rather than an element, and it does not work with gas hot water at all, because there is no electric element to send solar to. This is the single most important compatibility check before you consider one, and it's the main thing dishonest sales patter gets wrong. If you have gas or a heat pump, a diverter is not an option for you, and your surplus-solar decision has to be approached differently.

Yes, substantially. Worked examples put a diverter at roughly $990 for a Catch Power unit up to about $1,500 fully installed in a Perth example, which is many times cheaper than a home battery that typically runs to five figures. Treat those diverter figures as illustrative order-of-magnitude numbers rather than a fixed price, and confirm current costs at quote time. The lower cost is a big part of why, for pure self-consumption, a diverter can store surplus solar far more cheaply than a battery. But cheaper hardware doesn't automatically mean a better return for your household, which depends on your hot water use and feed-in tariff.

No. A diverter stores your surplus solar only as hot water. It provides no electricity backup during a blackout and cannot power evening household loads such as lights, appliances or EV charging. Only a home battery can do those things, and even then only if backup is specifically specced and wired in at installation. This is the core capability trade-off between the two options: a diverter is a cheap way to use surplus solar for one specific job, water heating, while a battery is a far more expensive device that can return energy as electricity later. If keeping the lights on in an outage is part of your reason, a diverter will not meet that need.

There is no single universal figure, and that's the honest answer. The value of each kilowatt-hour a diverter sends to your tank equals the cost of the grid electricity it displaces minus the feed-in tariff you would otherwise have earned by exporting it. So the lower your feed-in tariff, the more a diverter is worth. Where feed-in tariffs are high relative to heating electricity rates, a modelled analysis showed a diverter can actually lose money, with negative returns in some cities. Whether it pays is highly dependent on your household's hot water use and surplus solar. Ask an installer to model it against your actual tariff and usage rather than trusting a headline saving.

For many homes with a conventional electric hot water tank, a diverter is the smarter first step: it costs a fraction of a battery and targets one of the home's biggest loads, so for pure self-consumption it can give a better financial return than a battery in favourable circumstances. But the verdict is conditional. If you want evening power or blackout backup, a diverter cannot provide either and a battery is the honest choice despite its cost. A common sequence is to fit a diverter now for the cheap self-consumption win, then add a battery later if your needs and the numbers justify it. Have your specific home modelled before deciding.