Solar diverters for hot water in Perth: making the most of excess midday solar

Most Perth solar households export excess midday generation to the grid at 2c/kWh DEBS (or up to 7.135c under legacy REBS). That exported energy is worth very little — but you're heating your hot water with grid electricity at 33.26c/kWh when the sun is shining.

A solar diverter solves this mismatch. It monitors your solar generation and household consumption, detects when there's surplus solar, and diverts that excess to your electric hot water element at variable power — heating water for free instead of exporting for 2c.

How solar diverters work

A solar diverter installs at your switchboard alongside your hot water element. It continuously monitors the grid connection point:

• If solar generation > household consumption: surplus is being exported
• The diverter detects this surplus and throttles power to the hot water element accordingly
• As household loads change (a kettle turns on, the diverter reduces element power), the diverter adjusts in real time to always be using only the surplus, not importing additional grid power

This is different from a simple timer:

• A timer might switch the element on at noon regardless — but if there's cloud cover, you'd import from the grid.
• A diverter only activates when there's genuine surplus, avoiding grid import.

Products available in Perth

Catch Power (Green):

• Australian-made solar diverter
• Works with any single-phase resistive element (250W–3600W)
• Continuous monitoring via current transformer on the grid connection
• Can be paired with Catch Power's app for monitoring
• Price: approximately $450–$650 installed

MyEnergi Eddi:

• UK-designed, available in Australia
• Supports two hot water zones (can also divert to a second element or towel rail)
• Zappi EV charger integrates with the same ecosystem
• Price: approximately $600–$900 installed

Solar Analytics + hot water control: Some solar monitoring systems (Solar Analytics platform) can also control a hot water element through a relay — less sophisticated than a purpose-built diverter but uses existing monitoring hardware.

Alternative: Catch Power (Relay): A simpler relay version that switches the element fully ON when surplus exceeds a set threshold (e.g. 1kW surplus) and fully OFF when it drops below. Less precise than the proportional control but lower cost (~$200–$350 installed).

How much can a solar diverter save in Perth?

Scenario: 6.6kW system, north-facing, no battery

Annual solar generation: approximately 9,500 kWh
Self-consumption (household uses directly): approximately 3,500 kWh
Net export: approximately 6,000 kWh/year

Without a diverter, the hot water element (3.6kW, 1.5 hours/day = 5.4 kWh/day = 1,971 kWh/year) is typically on a timer running overnight at off-peak. Under A1, that's 1,971 × $0.3326 = $655/year for hot water.

With a diverter, the element runs on surplus solar during midday hours. Perth's sunny months (September–April) provide reliable surplus. Winter generates less but the diverter still captures surplus when available.

Realistic annual diversion: approximately 1,400–1,700 kWh/year (not all 1,971 kWh will be divertable — some days will have cloud, system factors)

Annual saving: 1,500 kWh × ($0.3326 − $0.02 DEBS) = 1,500 × $0.3126 = approximately $469/year

At an installed cost of $500, payback is approximately 12–15 months.

Diverter vs battery: which first?

If you're choosing between a solar diverter and a home battery as your next investment:

| | Solar diverter | Home battery (10kWh) | |---|---|---| | Installed cost | $450–$900 | $12,000–$17,000 | | Payback (typical) | 1–2 years | 6–12 years | | What it does | Heats hot water for free | Stores solar for evening peak avoidance | | WA rebate | No | Yes ($1,300) | | Works without battery | Yes | N/A |

For most Perth households, a solar diverter is the better first step if you have a resistive electric hot water system. The payback is far quicker than a battery. A battery may be the right next investment once the diverter is in place.

What hot water systems work with a diverter

Works:

• Electric storage hot water system with a resistive element (252L, 315L — most Perth standard electric hot water)
• Any wattage element: diverter matches power output to available surplus

Does not work (or works differently):

• Gas hot water: no electrical element to divert to
• Heat pump hot water: some diverters can control a heat pump via relay, but it's more complex (heat pumps have compressors that prefer to run at constant power, not throttled)
• Solar thermal hot water (separate roof collectors): these have their own solar heat source and don't use electricity for heating (grid element is backup only)

The Midday Saver interaction

Under Midday Saver, the 9am–3pm window costs 8.85c/kWh. If the diverter is running on surplus solar (exported energy that would otherwise earn 2c DEBS), the net saving from diversion is:

• Without Midday Saver: 33.26c avoided − 2c lost export = 31.26c/kWh saved
• With Midday Saver (9am–3pm, all surplus solar): 8.85c avoided − 2c lost export = 6.85c/kWh saved

The diverter saving is significantly lower on Midday Saver during the super off-peak hours, because grid electricity during those hours is only 8.85c. The diverter saves most on A1 tariff or during Midday Saver peak hours (3pm–9pm, where it saves 55.33c − 2c = 53.33c/kWh for any evening solar surplus).

Conclusion: for Midday Saver households, the diverter remains a good investment but the payback is longer than for A1 households (the cheap midday electricity reduces the value of the diverted energy).

Diverter product prices are indicative for Perth mid-2026. Savings calculations assume A1 tariff at 33.26c/kWh effective 1 July 2026.