Is a Solar Diverter Worth It in 2026 UK?
In 2026 UK, a solar diverter costs £300–£650 unit + £150–£250 install. Typical savings are £180–£320 per year on hot water, giving a 3–6 year payback for most homes on standard fixed SEG export tariffs. The big question: is your export tariff above or below ~12p/kWh? Below = diverter pays back fast. Above = keep exporting. Here is the full ROI breakdown.
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Solar diverter ROI at a glance — 2026 UK
- myenergi Eddi (premium): £549 + £200 install = £749 total
- Solar iBoost+ (budget): £329 + £180 install = £509 total
- Marlec Solar iBoost (mid): £349 + £180 install = £529 total
- Typical annual saving: £180–£320 (4kWp PV, daily immersion use)
- Payback period: 3–6 years on SEG <12p/kWh; 1–3 years on SEG <6p/kWh
- Lifespan: 10–15 years (Eddi has 3-year warranty)
Worth it if: SEG <12p/kWh, immersion-friendly cylinder, daily hot water demand. Skip if: SEG >15p/kWh or all-heat-pump heating.
The break-even maths in 2026
Solar diverters only make sense when the opportunity cost of diverting beats the export tariff. Here is the simple rule:
Divert if: Gas equivalent cost (~7p/kWh) > SEG export rate. Export if: SEG export rate > gas equivalent cost (~7p/kWh).
For an all-electric home replacing immersion energy (~28p/kWh import), the break-even SEG is much higher (~22p/kWh) — diverting wins for almost any tariff. For a gas-heated home, the immersion only runs when you need it; you are replacing ~7p/kWh gas, so diverting only wins below ~7p/kWh SEG. Most fixed SEG tariffs in 2026 sit at 4.1p (Octopus Outgoing Fix), 5.5p (E.ON Next Export Exclusive), or 12p (British Gas Export & Earn) — meaning most homes win.
Eddi vs Solar iBoost+ vs Marlec — 2026
Three scenarios where a solar diverter is the wrong call
1. High SEG export tariff (>15p/kWh). Octopus Outgoing Agile occasionally pays 25p+/kWh during the summer middle-of-day. If you are on this, export rather than divert.
2. Heat-pump primary heating. A heat pump produces hot water at ~1/3 the energy cost of a resistance immersion. The diverter saving shrinks dramatically.
3. Battery storage already installed. Storing surplus in a battery and self-consuming it later at ~28p/kWh import beats diverting to immersion at ~7p/kWh gas-equivalent — every time.
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Frequently asked questions
Unit £300–£650 plus install £150–£250. Total typical project £450–£900 for a retrofit.
£180–£320/year for a 4kWp system with daily immersion use. Higher with bigger arrays and lower SEG tariffs.
3–6 years for typical homes on SEG <12p/kWh; 1–3 years on SEG <6p/kWh.
Eddi for EV-PV households (£549, 2 outputs, app). iBoost+ for budget (£329, 1 output). Marlec mid-tier with strong UK support.
Less likely worth it — heat pumps already heat water cheaply. Can still pre-heat in hybrid/backup-immersion setups.
Generally no. Export earns more than diverting saves. Diverters win below ~12p/kWh.
Sources used in our 2026 figures
- Ofgem — Smart Export Guarantee (SEG)
- MCS — Microgeneration Certification Scheme
- myenergi — Eddi specifications
- Marlec — Solar iBoost
Methodology: Cost and saving figures use BestBuilders' 2026 regional cost model (national cost guides × regional labour index) plus published SEG tariff data.