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Whole-home coordination

Do not make the heat pump chase every watt of surplus solar.

A home with PV, a battery and a heat pump has electrical and thermal storage. The plan should protect safety and comfort first, then weigh efficiency, reserve, forecasts and price.

Editorial owner GridPassport research team Last reviewed Evidence Sources, assumptions and limitations are shown on this page.

Short answer

There is no permanent "battery first" or "heat pump first" rule.

Use surplus PV directly for useful heating when demand exists, the heat pump can run efficiently and the building or tank has safe thermal capacity. Charge the battery when stored electricity will be more valuable later or when reserve is too low.

The decision changes by day. A cold cloudy evening, a clear spring afternoon and an outage-risk morning should not produce the same priority.

Control hierarchy

Optimize only after the hard limits are protected.

  1. 01
    Health and equipment safety

    Manufacturer hygiene logic, anti-scald protection, freeze protection, compressor limits and grid-code controls.

  2. 02
    Comfort and hot-water availability

    Room temperatures, household routines, water demand and recovery time.

  3. 03
    Battery reserve and power limits

    Outage readiness, inverter capacity and the risk of simultaneous high loads.

  4. 04
    Heat-pump efficiency

    Outdoor conditions, flow temperature, short cycling and useful thermal capacity.

  5. 05
    Solar, tariffs and export value

    The financial timing decision after the physical constraints are satisfied.

Two stores

Electrical storage and thermal storage have different losses.

A battery can return electricity to many loads, but charging and discharging loses energy and adds battery throughput. A building, buffer or hot-water cylinder can hold useful heat, but higher temperatures can reduce heat-pump efficiency and increase standing losses.

In one 12-month Fraunhofer field study, raising thermal setpoints to use more PV was associated with a 4.0% reduction in space-heating seasonal performance and a 5.7% reduction for domestic hot water. Those figures describe one installation, not a universal penalty.

The right comparison is therefore not "free solar versus battery". It is the value of useful heat now versus the future value of stored electricity, with both loss paths included.

Decision matrix

Different conditions create different priorities.

ConditionsLikely priorityChecks before acting
Clear, cold dayPre-heat usefully during sustained PV while preserving evening battery reserve.Comfort range, heat-pump run time, forecast duration and evening demand.
Clear shoulder-season dayAvoid overheating; battery or export may be more useful than extra heat.Actual heat demand, tank capacity, export value and battery room.
Cloudy, expensive evening aheadProtect battery and meet heating need at the most efficient available time.Load forecast, reserve, cheap import window and outdoor temperature.
Export-limited solar peakUse a supported sustained heat-pump window if useful thermal capacity exists.Minimum run time, device interface, temperature limits and expected surplus duration.

Control interface

Ask the heat pump. Do not remove its power.

SG Ready is one supported route on compatible heat pumps. It uses defined input states that can request or force certain behavior. The exact response still depends on the model and installer settings.

A HEMS should not imitate control by repeatedly cutting mains power. The heat pump needs its own controller active for compressor protection, circulation, freeze protection, timing and fault handling.

Compatibility must be tested for the exact model and function. The HEMS compatibility checklist shows what that evidence should contain.

Commissioning

Verify the whole loop, not only the command.

  • Device responseDid the heat pump enter the expected supported state and complete a sensible run?
  • Comfort and hygieneWere room, hot-water and manufacturer safety requirements preserved?
  • COP or SPFDid higher targets reduce heat-pump efficiency more than expected?
  • Battery impactHow did reserve, throughput and later imports change?
  • Whole-home costUse actual import, export and tariff intervals rather than solar self-consumption alone.
  • FallbackDoes the heat pump return to normal manufacturer control when HEMS data or communication fails?

The conclusion is deliberately conditional: coordinate both stores around the household plan; do not assign one device permanent priority.

FAQ

Coordination questions.

Should surplus solar charge the battery or run the heat pump first?

There is no universal priority. The better action depends on heat demand, expected solar, battery reserve, tariff, export value, heat-pump efficiency and how much thermal storage is safely available.

Is direct solar use by a heat pump always most efficient?

It avoids battery conversion losses, but raising water or room temperature can reduce heat-pump efficiency and increase heat losses. The temperature target and timing still need limits.

Can a HEMS switch a heat pump off at the mains?

That is generally not a sound control strategy. Use a manufacturer-supported input or API and leave the heat pump powered so its own safety, compressor and freeze-protection logic remains active.

Does SG Ready provide full heat-pump control?

No. It provides defined operating states, but exact behavior depends on the heat-pump model and settings. It is not automatically a two-way telemetry and control interface.

Can energy automation change a hot-water hygiene programme?

Safety requirements come first. Automation should not disable or weaken the manufacturer-defined hygiene programme. Any supported timing change must preserve completion and follow manufacturer and installer instructions.

Sources

Heat-pump and control references.