A solar diverter is only worth it if your export rate is lower than the effective cost of heating water your existing way. That's the whole decision. A lot of published advice on this gets it wrong — either because it's still based on the old Feed-in Tariff (closed to new applicants since 2019, and worked completely differently from today's export tariffs), or because it states a single example rate as if it applies universally. It doesn't. Check your own numbers before buying one.
Why old advice about diverters is often wrong now
Under the Feed-in Tariff, most households were paid for an assumed 50% export regardless of what they actually exported — so using every spare watt at home via a diverter genuinely was free money, since your export payment didn't change either way. That logic doesn't apply anymore. Today's export tariffs (Smart Export Guarantee-style arrangements) pay you for what you actually export, metered. If your export rate is decent, diverting solar away from export costs you real income — the opposite of the old advice.
Some content still online hasn't been updated for this change. If a guide talks about "the feed-in tariff" as a reason to install a diverter, it's describing a scheme that's closed and a set of economics that no longer apply to you.
The actual comparison
Compare two numbers:
- Your export rate (what you're paid per kWh sent to the grid)
- The effective cost of heating water your existing way — most commonly gas, adjusted for boiler efficiency (roughly divide the headline gas rate by ~0.85, since not all the fuel's energy becomes usable heat)
If your export rate is higher, exporting wins — buying a diverter would cost you money, not save it, even though it feels like you're "wasting" solar.
If the effective gas-heating cost is higher, a diverter genuinely saves money — and the saving compounds every sunny day, since it's not a one-off decision but a permanent installation.
What it actually costs
Typical installed cost sits around £320–£700, most commonly £450–£550. Where it's worth it, payback is often in the 3–6 year range — but that range only applies when the underlying rate comparison actually favours diverting. A cheap, fast-payback diverter installed on the wrong side of that comparison still loses money; the low install cost doesn't rescue a bad rate comparison.
Who it doesn't suit at all
- Combi boiler homes with no hot water cylinder — a diverter needs a tank to divert into; there's nothing to fit it to without one.
- Anyone whose export rate already beats their gas-heating cost — the comparison above settles this either way.
Having a home battery doesn't settle it either. Solar charging a battery is only worth your off-peak rate — that's what the battery would otherwise charge at overnight — and on time-of-use tariffs that often loses to export. So a battery doesn't automatically make a diverter redundant, or the better destination for spare solar: run each option against your export rate on its own. If a heat pump heats your water, the same applies — a diverter then replaces the heat pump's cost of heating that water, not gas, so compare that against export.
Not sure which side of this comparison your own home falls on? Our free calculator runs your actual export rate against your actual gas cost — see our full method for every diversion decision for how this generalises to battery and EV charging too.