One Winter Day Explains the System Better Than a Wiring Diagram
A home battery works best with a heat pump when the control strategy coordinates three things: when solar electricity is available, when grid electricity is cheapest, and when the house actually needs heat. The battery can shift low-cost or solar energy into expensive periods and provide backup during outages, but reserve SoC, inverter power, heat-pump demand, and available battery kWh determine how much flexibility is really available.
Energy Saving Trust specifically recommends combining heat pumps with solar, batteries and time-of-use tariffs where appropriate, while its 2026 research found that tariff choice can materially change the economics of integrated home-energy systems.
The easiest way to see why is to follow the house for 24 hours.
02:00 — Electricity Is Cheap, but Should the Battery Charge?
Assume a winter time-of-use tariff:
Off-peak: $0.10/kWh
Peak: $0.32/kWh
The battery is at 35% SoC.
Solar production tomorrow is forecast to be poor.
Charging the battery overnight may make sense because that energy can later support the heat pump during the expensive period.
But I would not automatically charge to 100%.
If tomorrow is sunny, filling the battery from the grid overnight could leave no room for midday solar.
The control strategy therefore needs to balance:
tomorrow's solar forecast
expected heating demand
tariff periods
backup reserve
Energy Saving Trust notes that batteries can be charged during low-cost tariff periods and then used to power a heat pump when electricity is more expensive—even without solar PV.
06:30 — The House Wakes Up
Outdoor temperature has fallen.
The heat pump is working harder.
Breakfast appliances start.
Now the battery faces a power problem as well as an energy problem.
Suppose:
Heat pump electrical input: 2.2 kW
Kitchen and household loads: 1.8 kW
Other loads: 0.5 kW
Total:
4.5 kW
A 10 kWh battery may contain plenty of energy, but a 3 kW battery-inverter system cannot independently supply this entire 4.5 kW load.
That is why a Home ESS quotation needs both:
kWh for energy
and
kW for simultaneous power .
A real Energy Saving Trust case study illustrates this constraint: one household's battery inverter was limited to 2.6 kW charge/discharge power , restricting how much battery power could be used by the heat pump despite having battery storage available.
11:30 — Solar Has Two Possible Jobs
Now rooftop PV is producing:
4.2 kW
The house needs:
1.0 kW
The heat pump is averaging:
1.2 kW
Surplus:
4.2 − 1.0 − 1.2 = 2.0 kW
That surplus could:
charge the battery
or
export to the grid .
Which is better depends partly on tariffs.
If exported solar earns nearly as much as electricity costs later, storing every surplus kWh may not make economic sense.
If evening electricity is much more expensive than the export value, retaining solar becomes more attractive.
This is why I would not program a Ruibit/Dawnice Home ESS simply as:
Solar surplus = always charge battery.
The EMS/inverter strategy should understand what the stored electricity is being saved for.
15:00 — The House Itself Becomes Energy Storage
There is another useful tool that does not have a lithium cell inside it.
The building.
If electricity is cheap or solar is abundant before the evening peak, the heat pump may sometimes preheat the home slightly—within the homeowner's comfort preferences—rather than waiting until electricity becomes expensive.
A hot-water cylinder can provide another form of thermal storage.
This does not mean aggressively overheating the house.
Heat pumps generally work efficiently with steady operation and lower flow temperatures rather than repeated high-temperature bursts. Energy Saving Trust recommends longer, steadier operation and appropriate weather compensation for efficient heat-pump use.
The battery and building therefore provide different kinds of flexibility:
Battery → shifts electrical energy
Building/hot-water system → shifts heat demand
A smart control strategy can use both.
17:30 — This Is the Hour the Battery Was Waiting For
Solar generation has collapsed.
The tariff has moved into its expensive period.
The heat pump still needs electricity.
Suppose the house now draws:
Heat pump: 2.0 kW
Other loads: 0.8 kW
Total:
2.8 kW
If the battery supplies 2.8 kW for three hours:
2.8 × 3 = 8.4 kWh
A nominal 10 kWh battery may or may not provide that full amount as usable AC energy after considering its usable SoC window, conversion losses, and reserve setting.
So I would model the evening load profile , not simply say:
10 kWh battery = three hours of heat-pump backup.
Energy Saving Trust's 2026 modelling across more than one million scenarios found that households combining heat pumps, solar and batteries can make greater use of low-cost electricity, but savings vary substantially with tariff, heat-pump performance, household demand and system configuration.
21:00 — Stop Discharging or Keep Saving Money?
Battery SoC has reached:
30%
The peak tariff continues for another hour.
Should the system keep discharging?
That depends on what the homeowner values.
If the objective is maximum tariff savings, the battery may continue toward its normal minimum SoC.
If the homeowner wants outage protection, the system may preserve:
20–30% backup reserve
or another selected value.
That reserved energy has an opportunity cost.
A battery cannot simultaneously use its final kWh to avoid expensive grid electricity and keep that same kWh untouched for a future outage.
This trade-off should be explained when quoting backup capability.
23:15 — Then the Grid Fails
Now the system design becomes visible.
The battery may have 3 kWh remaining.
What happens next depends on:
whether backup/EPS operation is supported
which circuits are protected
battery discharge power
heat-pump startup requirement
remaining usable energy
and whether PV can operate during the outage.
DOE identifies backup power, solar-energy shifting and time-of-use management as reasons homeowners may consider battery storage.
But "battery backup" does not automatically mean:
whole-home heat-pump backup for the entire outage .
For a Ruibit/Dawnice Home ESS proposal, I would define the protected loads and reserve strategy explicitly.
What I Would Ask Before Quoting the System
I need only a short dataset:
| Input | What It Decides |
|---|---|
| Heat-pump electrical profile | Daily heating demand |
| Startup/peak power | Inverter requirement |
| Half-hourly home load | Simultaneous household demand |
| PV generation | Solar charging opportunity |
| Tariff periods | Economic dispatch |
| Battery usable kWh | Energy shifting/runtime |
| Battery/inverter kW | Maximum supported load |
| Backup reserve | Energy unavailable for daily optimization |
Then I would simulate several winter days rather than one annual average.
A cold cloudy Tuesday can reveal much more than annual electricity consumption.
For a Home ESS distributor, that also changes the quotation. Instead of selling:
10 kWh battery + inverter
the proposal becomes:
battery capacity + inverter power + heat-pump compatibility + solar integration + tariff strategy + backup scope .
That is the system the homeowner is actually buying.
A battery does not make a heat pump cheaper simply because the two Products are installed in the same house.
The value appears when solar production, cheap grid electricity, heating demand, battery SoC and backup reserve are coordinated as one energy system.
FAQs
1. Can a home battery run a heat pump?
Yes, if the battery discharge power and inverter output are sufficient for the heat pump and other simultaneous household loads . Battery kWh determines available energy, while kW determines how much power can be supplied at one time.
2. How can a home battery reduce heat pump electricity costs?
The battery can store surplus solar energy or electricity purchased during low-cost time-of-use periods and discharge later when the heat pump is operating during more expensive tariff periods.
3. Should a home battery charge from the grid overnight when using a heat pump?
It can make sense when overnight electricity is inexpensive and high heating demand is expected the next day. However, the control strategy should also consider solar forecasts, expected heating demand, tariff periods, and available battery capacity for daytime solar .
4. How does backup reserve affect heat pump operation?
Keeping part of the battery at a minimum reserve SoC provides energy for potential outages, but that energy cannot simultaneously be used for daily tariff savings. The reserve level should reflect the homeowner's preferred balance between backup resilience and energy-cost optimization .
5. What information is needed to size a home battery for a heat pump?
Use the heat pump load profile and startup power, household interval consumption, PV generation, electricity tariff, usable battery kWh, battery/inverter kW, required backup loads, and reserve SoC .
