Heat Pump + Solar PV Self-Consumption UK 2026

The economics of solar PV are dominated by self-consumption ratio:

• Self-consumed kWh value: 25-35p (equivalent to imported electricity you didn't need to buy).
• Exported kWh value: 5-15p (SEG export rate; e.g. Octopus Outgoing 15p, EDF 5p, Eon 4p).
• Spread: 10-30p/kWh per unit you self-consume rather than export.

For a typical 4kWp solar array generating 3,800 kWh/year:

• 100% self-consumed: 3,800 kWh x 30p = GBP 1,140/year value.
• 100% exported: 3,800 kWh x 15p = GBP 570/year value.
• 50% self-consumed / 50% exported: GBP 855/year.

Heat pump load is BIG (4-5,000 kWh/year) - much of it shiftable to daytime. Combined household can typically achieve 50-70% self-consumption vs ~25-30% for solar without heat pump. The marginal value of the heat pump on a solar household is significant.

Simplest approach: configure your heat pump's daily schedule to do as much heating as possible during midday solar peak.

Practical implementation:

• DHW reheat scheduled for 11am-2pm (when solar generation peaks).
• Space heating WC curve adjusted: standard during night-time + early morning; BOOST during 11am-3pm to extend warmth into evening (pre-heat fabric via slightly higher daytime indoor temp ~22C); coast during 4pm-9pm.
• Result: ~30-50% of heat pump electricity sourced from PV in summer; ~10-20% in winter (when generation lower + heat demand higher).

Annual saving (typical 3-bed with 4kWp PV + heat pump):

• ~1,500-2,000 kWh PV self-consumed by heat pump x 30p = GBP 450-600 vs export of same kWh at 15p = GBP 225-300. Net gain GBP 225-300/year.
• Plus existing self-consumption from baseline household load: ~800-1,000 kWh x 30p = GBP 240-300.
• Total saving over standard import: ~GBP 700-900/year.

Zero extra hardware. Works with any heat pump that supports scheduling (all modern UK heat pumps).

A solar diverter (also called PV diverter or immersion controller) sits between your solar inverter + the main electricity meter. It detects when PV is generating MORE than household demand + diverts the excess to the cylinder immersion heater rather than exporting.

Popular models: Marlec iBoost, MyEnergi Eddi, Solis solar smart, Octopus PowerPack integration.

Install cost: GBP 250-500 (unit + installation by electrician).

How it works with heat pump DHW:

• Heat pump heats DHW cylinder primarily via internal coil.
• Cylinder ALSO has immersion heater (standard backup on all hot water cylinders) for legionella cycle + emergency backup.
• Diverter routes excess PV to immersion when generating - cylinder heats from BOTH heat pump (via coil) + immersion (direct electric).
• When cylinder reaches setpoint, diverter switches off; excess PV exports.

Why it's worth adding (alongside heat pump):

• Captures PV generation that would otherwise export at low rate (~15p/kWh).
• Reduces heat pump's DHW reheat duty - heat pump can use that capacity for space heating instead.
• Especially valuable when PV generation exceeds heat pump electrical demand (sunny weekends, midday peaks).

Annual additional saving: typically GBP 100-200 over direct self-consumption alone for a 4kWp PV + heat pump household. ROI 2-3 years on the GBP 250-500 install cost.

Battery storage (Tesla Powerwall, GivEnergy, Solar Edge, BYD) stores excess PV during midday + discharges during evening peak demand.

Install cost: GBP 4,000-8,000 typical for 5-13 kWh battery + installation.

How it works with heat pump:

• Midday: PV charges battery + powers household + heat pump directly.
• Evening: battery discharges through evening peak (4pm-7pm) when grid rates spike to 30-40p/kWh.
• Heat pump runs continuously across the day with optimal source mix.

Annual additional saving: typically GBP 150-300 over diverter alone. ROI 8-12 years - longest payback of the three strategies. Often combined with smart tariff (Octopus Flux) for export bonus during evening peak.

When battery makes sense:

• You have a smart tariff with significant peak premium (Flux 36p peak vs 14p off-peak).
• Your evening + early-morning electricity demand is high enough to fully discharge the battery daily.
• You're planning to keep the property 10+ years (so the payback period fits ownership horizon).

When battery DOESN'T make sense:

• Self-consumption with diverter is already capturing 60%+ of PV generation - marginal value of adding battery is small.
• You're on a non-smart tariff (flat rate eliminates the price-shifting opportunity).
• Payback exceeds your ownership horizon.

For a typical UK 3-bed property with 4kWp south-facing PV + heat pump + 12,000 kWh/year heat demand:

• Standard heat pump install (no PV): ~GBP 1,000-1,400 annual electricity cost.
• + PV with direct self-consumption only: ~GBP 700-1,000 annual cost. Saving GBP 250-400/year.
• + Solar diverter to DHW: ~GBP 550-850 annual cost. Saving GBP 350-550/year vs no PV.
• + Battery storage: ~GBP 400-700 annual cost. Saving GBP 500-800/year vs no PV.

Marginal returns diminish - first GBP saved (direct self-consumption) has highest ROI; last GBP saved (battery) has lowest ROI. For most UK households, the sweet spot is PV + heat pump + diverter (skip the battery unless smart tariff makes it pay).

If you don't have either yet:

• Heat pump first. BUS grant only available for heat pump (GBP 7,500); install drives the rest of the energy strategy. Solar can be added 6-18 months later.
• Solar PV sized for combined load. 4-6 kWp typical for UK 3-bed semi with heat pump (vs 3-4 kWp without). Larger PV captures more midday peak.
• Diverter added at solar install time. Marginal cost ~GBP 250-500 + electrician integration.
• Battery only if smart tariff justifies it. Octopus Flux + battery combo can be excellent; standard tariff + battery rarely pays back.

If you have solar already:

• Heat pump install considers PV as a future free electricity source.
• Configure heat pump schedule for daytime DHW reheat + midday space heating boost.
• Confirm solar diverter compatible with new cylinder install (most are - check before install).