A solar diverter pushes your surplus PV into the immersion instead of exporting it. But since the Clean Export Guarantee, every diverted kWh gives up its export payment — so it only pays if your water heating costs more than the export rate. Put in your numbers and this tool tells the truth either way, including "don't buy one".
Your array size sets how much surplus there is to divert; your export and day rates decide whether diverting beats exporting.
Export rates have drifted down since the CEG's early peaks (~24c) toward roughly 20c in mid-2026. Use the figures on your own bill — they are what makes or breaks the case.
A diverter only saves you the cost of the water heating it replaces. So this is the number that decides everything — the effective cost per kWh of heat that actually reaches the water.
What heats your hot water now?An Eddi runs about €400–450 for the device plus install; a simpler iBoost / Solic-class diverter is roughly €350 installed. Default €550 assumes a fitted Eddi.
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The 0.55 seasonal cap is deliberate honesty: solar surplus is summer-heavy, so a diverter realistically covers just over half your annual hot-water energy — most of April–September, little in November–February.
A diverter salesman won't mention the export payment you give up. You just did the honest sum — if it stacks up for your rates, here's where to look.
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When your panels make more power than the house is using, that surplus normally flows out to the grid. A diverter (a myenergi Eddi, or a simpler iBoost / Solic-class unit) spots that surplus and sends it into your immersion element instead, heating your hot-water cylinder with electricity you'd otherwise export. It modulates in real time so it only ever uses the true surplus — it never pulls paid grid power to heat water.
Before the CEG (roughly pre-2022), exported solar was unpaid — it just spilled to the grid for free — so diverting it into hot water was pure found money, a no-brainer. Now every exported kWh earns you around 20c under the CEG. So a diverted kWh is no longer free: it costs you the ~20c export payment you gave up. Diverting only pays if the water heating it replaces costs more than that. Most online guides still predate the CEG and wrongly call diverters free money — this calculator doesn't.
Probably not, or far less. A battery is second in the pecking order — after the house uses what it needs directly, the battery charges from the surplus, and only what's left over could go to a diverter. The diverter is third in line. With a battery, only about 20% of your generation is still surplus to divert (versus roughly half without one), so there's much less water to heat and the payback stretches out. Self-use first, battery second, diverter a distant third.
No. The SEAI solar PV grant covers the panels and, since it was reworked, battery storage — but not a hot-water diverter. You pay for the diverter in full yourself, which is exactly why the payback sum matters: there's no grant softening the ~€350–550 cost.
No — realistically just over half your yearly hot-water demand, and it's summer-weighted. Solar surplus is abundant from April to September and scarce from November to February, so the diverter does most of its work in the bright half of the year and little in deep winter, exactly when you want hot water most. This tool caps the divertable energy at 55% of annual demand to reflect that honestly. You'll still heat water the normal way through winter.
The myenergi Eddi is the premium option: CT-clamp precision, an app, and tight integration with the wider myenergi ecosystem (the Zappi EV charger, Harvi sensors), which is why it costs more. The iBoost and Solic-class units are simpler and cheaper and do the same core job — divert surplus into the immersion — just with fewer bells and no ecosystem. If your net-value-per-kWh is marginal, the cheaper unit is what shortens the payback; if you already run myenergi kit, the Eddi is the tidy fit.