A heat pump does not operate in isolation. It forms part of the home’s heating system and, because it runs on electricity, the wider household energy system.
Its electricity can come from the grid, solar panels or a home battery. The heat it produces can warm rooms immediately or be retained temporarily within the building, underfloor heating or a hot-water cylinder.
Smart tariffs and controls can move some electricity consumption into lower-cost periods, while solar panels and batteries can reduce grid imports. But these technologies cannot compensate fully for a poorly designed heating system.
Whole-home optimisation should therefore begin with heat loss, heat-pump sizing, emitters and controls. Solar panels, storage and tariffs can then support an already efficient system.
Heat pumps and home energy at a glance
At a glance
- Efficient heat-pump design comes before tariff optimisation.
- Heating demand is greatest when UK solar generation is usually lowest.
- A battery moves electricity across hours, not seasons.
- The building and hot-water cylinder can store heat.
- The cheapest electricity period may not be when the heat pump is most efficient.
- Short, controlled preheating can move demand, but deep setbacks may be counterproductive.
- Smart-meter data cannot calculate heat-pump efficiency by itself.
- A heat pump, EV and home battery may compete for electrical capacity.
- Battery backup does not automatically mean the heat pump will operate during a power cut.
Where the heat pump sits in the whole-home system
A heat pump uses electricity to move heat from the air, ground or water into the home.
Its electricity may be supplied by solar panels, a home battery or the electricity grid.
That electricity powers:
- The heat-pump compressor
- Fans or source pumps
- Heating circulation pumps
- Controls
- Domestic-hot-water production
- Any auxiliary or backup heating
The useful heat is then delivered through:
- Radiators
- Underfloor heating
- Fan-assisted emitters
- A hot-water cylinder
- Building fabric and thermal mass
- Purpose-designed thermal storage
A simplified energy flow is:
Solar generation + battery discharge + grid import → household electricity and heat-pump electricity → space heating and stored hot water
This relationship connects two systems.
The electrical system determines where the heat pump’s electricity comes from and what it costs. The heating system determines how effectively that electricity is converted into useful heat and delivered to the building.
Both sides need to work properly.
Begin with the heating system
Understand the building's heat loss
Establish how much heat the property loses at design conditions.
Reduce avoidable heat loss where practical
Address the fabric before sizing the equipment.
Size the heat pump at the property's design conditions
Not from floor area or a rule of thumb.
Design the radiators or underfloor heating for a suitable flow temperature
Emitter sizing determines the flow temperature the system can achieve.
Confirm the required water flow and system arrangement
Insufficient flow undermines everything downstream.
Configure weather compensation and controls
So flow temperature tracks outdoor conditions.
Add solar, storage and tariff optimisation
Only once the heating system itself is sound.
Solar panels, batteries and smart tariffs can improve a good heat-pump installation. They cannot completely rescue a poor one.
Common underlying problems include:
- An inaccurate heat-loss calculation
- An oversized or undersized heat pump
- Unnecessarily high heating-water temperatures
- Radiators that require excessive flow temperatures
- Inadequate water flow
- Frequent cycling
- Poorly configured weather compensation
- Uncontrolled immersion or auxiliary heating
- Heating zones that repeatedly interrupt operation
Because everything else follows from it, the heat-loss calculation is worth understanding properly. Our sister site Heat Loss Hub, run by the same team, covers heat-loss surveys, room-by-room calculations and how the result should drive heat-pump sizing, emitter selection and flow temperature.
A cheap tariff reduces the price paid for electricity. It does not reduce the amount of electricity wasted by an inefficient system.
A battery can conceal expensive peak-period consumption by supplying stored electricity, but that does not prove that the heat pump itself is performing well.
Whole-home optimisation should support an efficient heating system, not hide an inefficient one.
Why heat-pump electricity demand changes
A heat pump does not create one fixed daily electrical load.
Its consumption depends on:
- Outdoor temperature
- Building heat loss
- Required indoor temperature
- Heating flow temperature
- Hot-water demand
- Heat-pump efficiency
- Occupancy
- Heating schedules
- Defrost operation
- Auxiliary-heater use
- Wind and exposure
- Solar and internal heat gains
The same home can have very different heat-pump electricity profiles on a mild October day and a cold January morning.
Heat demand and electricity demand are different
Example
Imagine the home needs 30 kWh of useful heat during one day.
At a COP of 3: 30 kWh ÷ 3 = 10 kWh of electricity.
At a COP of 2: 30 kWh ÷ 2 = 15 kWh of electricity.
The building received the same useful heat, but the less efficient operation required 50% more electricity.
The building needs a certain amount of useful heat. The heat pump must use electricity to produce that heat.
A simplified relationship is:
Electricity required = useful heat required ÷ heat-pump COP
This is why flow temperature, outdoor conditions and system control remain important even when the home has solar panels and a battery.
COP and SCOP
- COP
- Describes the relationship between useful heat output and electricity input over a particular operating period or condition. A COP of 3 means that every 1 kWh of electricity produced approximately 3 kWh of useful heat.
- SCOP
- Describes seasonal performance across changing temperatures and operating conditions.
Neither value is simply a fixed property of the heat-pump unit. Real performance is influenced by the entire system, including:
- Source temperature
- Heating flow temperature
- Hot-water production
- Defrost
- Cycling
- Pumps
- Auxiliary heating
- Controls
- Building demand
Why the coldest days matter
The heat pump faces several challenges at the same time during cold weather:
- The building loses heat more quickly.
- An air source heat pump extracts heat from colder outdoor air.
- The heating system may require a higher flow temperature.
- Defrost operation may become more frequent.
- Solar generation may be low.
- Hot-water and household electricity demand continue.
- The battery may contain less solar energy.
- An EV may also need charging.
These are the conditions against which the complete system should be tested.
An arrangement that appears almost independent of the grid during summer may rely heavily on imported electricity during a cold, cloudy winter week.
The seasonal mismatch between solar and heating
Solar panels and heat pumps can work together, but their strongest seasons do not align.
Solar generation is normally greatest in spring and summer. Space-heating demand is greatest during autumn and winter.
Energy Saving Trust explains that a solar array may generate as much electricity over a year as a heat pump consumes while the household still exports electricity in summer and imports it during winter. Energy Saving Trust heat-pump guidance
Annual totals do not show whether electricity was generated when the heat pump needed it.
Summer operation
During summer:
- Solar generation is relatively high.
- Space-heating demand is low or absent.
- The heat pump may operate mainly for hot water.
- The home battery can fill readily.
- Surplus electricity may be exported.
- Direct solar can make a meaningful contribution to water heating.
The heat pump’s annual electricity consumption may look well matched to solar generation, but much of the summer electricity is available when space heating is unnecessary.
Winter operation
During winter:
- Solar days are shorter.
- Generation is usually lower.
- Space-heating demand rises.
- The heat pump may run for long periods.
- The battery may discharge quickly.
- Grid electricity becomes much more important.
A battery can transfer solar electricity from a winter afternoon into the evening. It cannot carry surplus electricity from July into January.
Spring and autumn
Spring and autumn may provide the strongest overlap between solar generation and useful space-heating demand.
The heat pump still operates, but:
- Outdoor temperature is milder.
- Heating demand is lower.
- Weather compensation can reduce flow temperature.
- Heat-pump efficiency may improve.
- Daylight solar generation remains useful.
These shoulder seasons may produce some of the best opportunities for direct solar-assisted heating.
Can solar panels run a heat pump?
Example
Suppose the solar array is generating 3.5 kW while the home is using 0.8 kW for other purposes and the heat pump is drawing 1.5 kW.
The combined household demand is 0.8 kW + 1.5 kW = 2.3 kW.
The solar panels can cover that demand, leaving approximately 1.2 kW for battery charging or export.
If solar output later falls to 1 kW, the home must obtain the remaining electricity from its battery or the grid.
Solar panels can contribute towards heat-pump operation, but they will not normally power it continuously throughout the year.
Solar electricity can support daytime space heating, domestic-hot-water production, circulation pumps and controls, and other household consumption.
The contribution depends on:
- Solar-array size
- Roof orientation and shading
- Season and weather
- Heat-pump demand
- Time of operation
- Household background demand
- Battery state of charge
- Export and tariff settings
The future Solar Energy Flow Visualiser will demonstrate these changing flows.
A heat-pump home contains several energy stores
| Storage location | What it stores | Principal role |
|---|---|---|
| Home battery | Electricity | Move electricity between solar or tariff periods |
| Building fabric | Heat | Allow limited preheating and coasting |
| Hot-water cylinder | Hot water | Shift domestic-hot-water production |
| Underfloor screed | Heat | Release space heat gradually |
| Purpose-designed thermal store | Heat | Shift heating demand |
| Phase-change heat battery | Heat | Compact thermal storage in suitable applications |
A home battery is only one way to move energy between different times.
Each store has different capacity, power, heat or energy losses, control requirements, response time, installation cost and suitable purpose.
A home-energy strategy should identify what is being stored and why.
Building fabric as thermal storage
Walls, floors, furniture and other materials absorb heat while the home is being warmed.
If the building is heated slightly before an expensive tariff period, the heat pump may be able to reduce its output temporarily while the stored heat maintains comfort.
How long this works depends on:
- Insulation
- Airtightness
- Thermal mass
- Outdoor temperature
- Wind exposure
- Size of the temperature increase
- Occupant comfort
- Heating-emitter output
A well-insulated, thermally stable home may coast for longer than a lightweight or draughty building.
Hot-water storage
A hot-water cylinder stores useful heat for later showers, baths and taps.
This allows water heating to be scheduled around cheap electricity, solar generation, warmer daytime outdoor temperatures and expected household demand.
The stored hot water cannot normally be used for space heating unless the system has been specifically designed to do so.
Underfloor heating and thermal mass
Screeded underfloor heating can retain and release heat gradually.
This can support flexible operation, but it also responds slowly. Excessive preheating may lead to overheating after the tariff period has ended.
The correct schedule depends on the floor construction, insulation, flow temperature and building response.
Buffer vessels are not automatically useful energy storage
A buffer or volumiser may be installed to increase system water volume, reduce cycling, support defrost operation, maintain minimum flow or provide hydraulic separation.
That does not necessarily make it a meaningful store for shifting several hours of heating demand.
A small buffer may contain relatively little useful energy compared with the heat required by the building.
Purpose-designed thermal storage and hydraulically necessary system volume should not be treated as the same thing.
What can a home battery contribute?
A home battery can:
- Store daytime solar for evening heating
- Charge from cheaper grid electricity
- Supply the heat pump during an expensive tariff period
- Reduce peak grid import
- Support hot-water production
- Retain a reserve for essential loads
- Export electricity when permitted and worthwhile
The battery’s most useful role may not be running the heat pump continuously. It might instead cover a particular two- or three-hour tariff peak.
Energy Saving Trust’s technology-and-tariff research found that batteries may become more financially useful in higher-demand homes, including those with heat pumps. Actual results still depend on the property, system performance, tariff and operating strategy. Energy Saving Trust technology research
Battery capacity and battery power
Example
- Battery usable capacity: 10 kWh
- Battery inverter output: 3.6 kW
- Heat-pump electrical demand: 2.5 kW
- Other household demand: 1.8 kW
The home requires 2.5 kW + 1.8 kW = 4.3 kW.
The battery can supply no more than 3.6 kW, so the grid must provide at least the remaining 0.7 kW even though the battery contains sufficient stored energy.
Two ratings must be considered.
Capacity in kWh describes how much electricity the battery can store. Power in kW describes how quickly it can charge or discharge.
The reverse problem can also occur. A high-power inverter cannot continue supplying the home after the stored energy has been depleted.
Size the battery around its intended job
Before choosing a capacity, define what the battery is expected to do.
Possible objectives include:
- Cover the 16:00–19:00 tariff peak
- Carry the home through an expensive evening period
- Store daytime solar for night-time heating
- Prevent expensive hot-water imports
- Supply background heating between cheap periods
- Retain an emergency reserve
- Reduce maximum grid import
- Export during selected periods
A battery intended to cover a short tariff peak may be much smaller than one intended to operate the home and heat pump overnight.
Use the future Home Battery Sizing Calculator to investigate usable capacity and household demand.
Electricity price versus heat-pump efficiency
Example
Period A: cheaper electricity, lower efficiency. Electricity price 12p/kWh, COP 2.4. Cost of useful heat: 12p ÷ 2.4 = 5p/kWh of heat.
Period B: higher electricity price, better efficiency. Electricity price 18p/kWh, COP 4. Cost of useful heat: 18p ÷ 4 = 4.5p/kWh of heat.
Although electricity costs more during Period B, each useful unit of heat is slightly cheaper because the heat pump operates more efficiently.
The cheapest electricity period does not automatically produce the cheapest useful heat.
A heat pump’s operating cost depends on both the electricity price and the amount of electricity needed.
A useful comparison is:
Cost per kWh of useful heat = electricity price ÷ COP
This does not mean heating should always be delayed until the warmest part of the day. The home needs heat when occupants need comfort, and the system must keep up with building heat loss.
It demonstrates why tariff price should not be considered independently.
A complete comparison may include:
- Electricity price
- Expected COP
- Heat required
- Direct solar contribution
- Battery losses
- Export income forgone
- Comfort
- Preheating losses
- Recovery demand
Flexible heating and preheating
A heat pump can sometimes move part of its electricity use away from an expensive period.
A simple strategy is:
- Increase heat production slightly before the expensive period.
- Store additional heat in the building.
- Reduce heat-pump output temporarily during the peak.
- Resume normal weather-compensated operation afterwards.
Nesta’s HeatFlex research found that controlled preheating could reduce electricity consumption during a later flexibility period while maintaining acceptable comfort in participating homes. Nesta HeatFlex
The amount of useful flexibility differs between properties.
What determines how long a home can coast?
Important factors include:
- Building heat loss
- Insulation
- Airtightness
- Thermal mass
- Outdoor temperature
- Wind
- Emitter capacity
- Normal room temperature
- Occupant comfort
- Length of the expensive period
A short reduction may be almost unnoticeable in one home and uncomfortable in another.
Preheating is not free energy
Preheating may increase indoor temperature, fabric heat loss, total heat delivered, heat-pump output and electricity consumption before the peak.
If the home is heated substantially above its normal setpoint, some additional heat will escape before it is needed.
The aim is not to overheat the property. It is to shift a limited amount of useful heating while preserving comfort.
Avoid aggressive recovery
Important
Switching the heat pump off for a long period may create a large temperature deficit.
The later recovery can require sustained high output, increase flow temperature, reduce efficiency, trigger auxiliary heating, cause comfort problems and move consumption into another expensive period.
A heat pump normally performs best when maintaining conditions steadily at the lowest practical flow temperature.
Flexible operation should gently reduce or shift demand rather than treating the heat pump like a high-temperature boiler.
Weather compensation remains fundamental
Weather compensation adjusts heating-water temperature according to outdoor conditions.
When it is milder outside, the building needs less heat and the system can usually operate at a lower flow temperature. This ordinarily improves heat-pump efficiency.
MCS guidance requires weather compensation to be available on space-heating systems and explains how reducing flow temperature during milder weather improves seasonal operation. MCS Domestic Heat Pump Guide
Smart-tariff control should work with weather compensation rather than repeatedly overriding it.
Hot water as flexible demand
Hot-water production can often be moved more easily than space heating because the cylinder stores the result.
Possible scheduling periods include:
- A cheap tariff window
- A strong solar-generation period
- A warmer part of the day
- Shortly before expected demand
Space-heating and hot-water priority
Many heat pumps temporarily stop space heating while reheating the cylinder.
This means a hot-water schedule can affect room heating.
A poorly chosen schedule could:
- Interrupt space heating during the coldest period
- Create a large recovery load
- Empty the home battery
- Operate during an expensive tariff
- Coincide with EV charging or cooking
The schedule should consider both electricity cost and comfort.
Hot-water temperature and efficiency
Heat pumps generally operate less efficiently when producing higher-temperature water.
The cylinder should be:
- Correctly sized
- Properly insulated
- Set to an appropriate normal temperature
- Scheduled around actual demand
- Configured by a competent installer
Unnecessarily high normal storage temperatures increase electricity consumption.
Sterilisation cycles
Important
Heat-pump hot-water systems normally include a periodic higher-temperature cycle to manage bacterial risk.
Depending on the system, this may use the heat pump, an immersion heater, or a combination of both. The cycle can create a noticeable electricity spike.
Check when it occurs, whether it uses the immersion heater, whether it falls inside a cheap period, whether the battery is expected to supply it, and whether its settings follow the manufacturer's requirements.
Safety functions should not be disabled to save electricity.
Solar diversion and heat-pump water heating
Surplus solar can be directed towards hot water in different ways.
Using the heat pump may produce several units of heat from each unit of electricity, but it may require a minimum operating period and temporarily interrupt space heating.
An immersion diverter converts electricity directly into heat. It may absorb small or variable amounts of surplus more easily but produces approximately one unit of heat per unit of electricity.
The better option depends on available surplus, heat-pump operating conditions, cylinder arrangement, tariff, export payment, required water temperature and equipment controls.
Neither approach is universally best.
Heat pumps, batteries and smart tariffs
Several tariff types may suit a heat-pump home.
Flat-rate tariff
The same unit rate applies throughout the day.
It is simple and may suit households with limited ability or interest in shifting demand.
Fixed time-of-use tariff
Electricity has predictable cheap and expensive periods.
This can help schedule battery charging, hot-water production, limited preheating and EV charging.
Dynamic tariff
Prices may change every half hour or another defined interval.
Dynamic tariffs can reward flexible operation but may require more monitoring or automation.
Heat-pump tariff
A technology-specific tariff may offer cheaper periods or special rates for heat-pump operation.
Eligibility and operation vary between suppliers.
Solar-and-battery tariff
These tariffs may coordinate import, battery charging and export. The complete arrangement still needs to suit the heat pump’s demand and comfort requirements.
Compare the complete tariff
Do not compare only the cheapest advertised rate.
Include:
- Peak import rate
- Off-peak import rate
- Duration of cheap periods
- Standing charge
- Export payment
- Battery losses
- Heat-pump demand during expensive periods
- Hot-water scheduling
- EV charging
- Eligibility and equipment compatibility
Apply tariffs to actual or realistically modelled half-hourly demand where possible.
Read Smart Meters & Half-Hourly Electricity Data for guidance on interpreting household electricity profiles.
Adding an EV
A heat pump and EV can both create substantial electrical demand.
They may compete for cheap electricity, time within the tariff window, main-fuse headroom, home-battery energy, solar generation and control priority.
A sensible hierarchy could be:
- Essential heating and hot water
- Minimum EV energy required for the next journey
- Home-battery charging
- Additional EV charging
- Other discretionary loads
This is not a universal order. A household may temporarily prioritise the EV before a long journey or retain more battery energy before severe weather.
Cheap-period competition
Example
- The EV needs four hours of charging.
- The home battery needs three hours.
- The cheap period lasts five hours.
- The heat pump continues operating.
- Hot water also needs reheating.
The EV and battery cannot both complete sequentially within the window. Charging them simultaneously may create too much combined demand.
Possible solutions include:
- Dynamic load management
- Lower EV charging power
- Partial battery charging
- Prioritising the EV’s essential requirement
- Using multiple cheap periods
- Adjusting battery charge according to the solar forecast
- Moving hot-water production
Read Solar + Battery + EV: How They Work Together for a more detailed explanation of charging priorities.
Whole-property electrical capacity
The complete electrical system should be assessed when installing a heat pump, battery or EV charger.
Consider:
- Main fuse rating
- Maximum import capacity
- Heat-pump electrical input
- Compressor starting behaviour
- Auxiliary heater
- Immersion heater
- EV charger
- Battery charging power
- Electric shower
- Cooking equipment
- Solar and battery export
- Consumer-unit capacity
- Single-phase or three-phase supply
A particularly demanding winter period might combine high heat-pump demand, hot-water heating, cooking, EV charging, battery grid charging and a depleted battery.
The installation should be designed for realistic simultaneous demand, not average annual consumption.
Load management can reduce or pause flexible equipment — often EV charging — when essential household demand is high.
Energy Networks Association provides a combined process for connecting heat pumps and EV chargers because their total demand can affect the property and local network connection. ENA connection guidance
Which system is in control?
A whole-home system may contain:
- Heat-pump weather compensation
- Room thermostat
- Heating schedule
- Hot-water schedule
- Battery controller
- Solar inverter
- EV charger
- Electricity supplier
- Third-party energy-management platform
More automation is not automatically better.
Common control conflicts
Poor coordination can result in:
- The battery emptying before the evening heating peak
- The heat pump recovering during the most expensive period
- EV charging using energy reserved for heating
- The immersion heater draining the battery
- Solar being exported while hot water is heated later from the grid
- The battery charging while the heat pump imports expensive electricity
- Preheating creating room-temperature overshoot
- Supplier automation conflicting with household schedules
- Several systems responding to the same tariff signal
Establish a control hierarchy
Document:
- Minimum and maximum comfort temperatures
- Required hot-water availability
- EV departure time and essential charge
- Battery reserve
- Import and export priorities
- The primary controller
- Manual override behaviour
- Response to lost internet connectivity
The core heating system should remain safe and functional if optional tariff or energy-management services stop working.
A primary controller may optimise the system automatically, but the homeowner should still understand the underlying priorities.
Monitoring cost and performance
A household may have a low electricity bill because the heat pump is efficient, solar supplies part of its demand, the battery avoids expensive periods, the tariff provides cheaper electricity, or the home requires relatively little heat.
These are different outcomes.
| Measurement | What it reveals |
|---|---|
| Smart-meter import | Electricity bought from the grid |
| Smart-meter export | Electricity sent to the grid |
| Solar-inverter data | Solar generation |
| Battery data | Charging, discharge and state of charge |
| Dedicated heat-pump electricity meter | Heat-pump electrical input |
| Heat meter | Useful heat delivered |
| Indoor-temperature data | Comfort |
| Outdoor temperature | Operating conditions |
| Flow and return temperatures | Heating-system operation |
| Tariff data | Cost by time period |
A low bill does not prove that the heat pump is efficient. A high COP does not guarantee the lowest possible bill if the electricity tariff is unsuitable.
Calculating heat-pump performance
To calculate COP over a period, you need useful heat delivered and electricity consumed by the heat-pump system.
The calculation is:
COP = useful heat output ÷ electricity input
Whole-house smart-meter data includes lighting, cooking, appliances, EV charging and other loads. It cannot isolate heat-pump performance accurately.
Dedicated electricity and heat measurement provide a much stronger assessment.
Four whole-home operating scenarios
Mild sunny day
Conditions: modest space-heating demand, lower weather-compensated flow temperature, good heat-pump efficiency, useful solar generation.
Possible flow:
- Solar supplies household demand and the heat pump.
- The heat pump provides low-temperature space heating.
- Hot water is heated during daylight.
- Surplus charges the battery.
- Remaining electricity is exported.
- The battery supplies evening demand.
This may be one of the most favourable conditions for the combined system.
Cold sunny day
Conditions: high heating demand, useful but limited solar generation, lower heat-pump efficiency than on a mild day.
Possible flow:
- The grid and battery support the heat pump before sunrise.
- Solar reduces grid import during daylight.
- The battery receives surplus only if generation exceeds demand.
- Hot water is scheduled around the best available period.
- Battery reserve is managed for the evening peak.
Solar contributes but does not independently run the home.
Cold cloudy day
Conditions: high heating demand, little solar generation, long heat-pump operating periods, greater chance of defrost.
Possible flow:
- The grid supplies most of the day’s energy.
- The battery covers selected expensive periods.
- Hot-water and EV schedules are coordinated.
- Load management protects the household connection.
- The battery may empty earlier than forecast.
This scenario tests whether the tariff and battery strategy remain useful during the conditions that matter most.
Flexible tariff day
Conditions: a defined expensive period, suitable building thermal storage, home battery available, hot-water cylinder available.
Possible flow:
- The battery charges during a cheap period.
- Hot water is prepared.
- The building is preheated slightly.
- Heat-pump output reduces during the expensive period.
- The battery supplies remaining household demand.
- Normal weather-compensated heating resumes gently.
The objective is to reduce expensive grid import without creating discomfort or an inefficient recovery.
Will the battery run the heat pump during a power cut?
Important
Only if the complete installation has been designed for it.
Battery backup requires islanding capability, compatible inverter and switchgear, sufficient backup output, appropriate circuits, available stored energy, correct protection, a heat pump suitable for the backup supply, and management of immersion and auxiliary loads.
Some battery systems support only selected essential circuits such as lighting, refrigeration and communications. The heat pump may not be included.
Even if the inverter can supply the heat pump's normal demand, simultaneous defrost, immersion heating or other household loads may exceed its backup output.
Solar panels may or may not continue operating and recharge the battery during an outage. This depends on the system architecture.
Do not assume that installing a battery automatically provides heating resilience.
Common whole-home mistakes
- Using solar and batteries to disguise poor heat-pump design
- Optimisation begins with heat loss, emitters, flow temperature and controls.
- Comparing annual solar generation with annual heating demand
- Matching annual kWh does not mean the solar electricity is available when the heat pump needs it.
- Expecting a battery to move summer energy into winter
- Domestic batteries normally shift electricity within a day or between tariff periods.
- Checking battery capacity but not inverter power
- The battery may contain enough energy but be unable to supply the complete household load.
- Selecting heating times from electricity price alone
- Heat-pump efficiency, solar generation, comfort and recovery demand also matter.
- Turning the heat pump off for long peak periods
- Deep temperature setbacks can create inefficient recovery and discomfort.
- Preheating with excessive flow temperature
- The purpose is gentle demand shifting, not rapid boiler-style heating.
- Ignoring hot-water and sterilisation cycles
- These can create significant electricity demand at unintended times.
- Letting the immersion heater drain the battery
- A high-power resistive load can rapidly consume stored electricity.
- Charging the EV and battery without checking household demand
- The combined load may exceed the available connection capacity.
- Running several conflicting controllers
- Decide which platform has primary responsibility.
- Measuring cost without measuring performance
- Low electricity cost and high heat-pump efficiency are related but separate objectives.
- Assuming the battery automatically provides backup
- Power-cut operation requires a purpose-designed system.
Whole-home planning checklist
Before coordinating the system, establish:
- Room-by-room heat loss
- Heat-pump size and output at design conditions
- Required heating flow temperature
- Expected annual electricity demand
- Expected cold-day electricity demand
- Hot-water requirement
- Solar-array size and monthly generation
- Battery usable capacity
- Battery charge and discharge power
- Half-hourly household electricity profile
- EV charging requirement
- Import and export tariff structure
- Main fuse and connection capacity
- Comfort and hot-water priorities
- Primary control system
- Monitoring equipment
- Backup requirements
- Planned future technologies
Frequently asked questions
Can solar panels fully power a heat pump?
Solar can make a useful contribution, particularly during daylight and milder seasons. It will not normally supply all heat-pump electricity through winter, at night or during prolonged cloudy weather.
How much can a battery reduce heat-pump running costs?
It depends on the battery capacity and power, heat-pump demand, tariff, solar generation and timing of consumption. A battery may be most useful for covering an expensive tariff period rather than running the heat pump all day.
Should a heat pump run during cheap tariff periods?
Sometimes. Cheap periods can be useful for limited preheating, hot water and battery charging. The decision should also consider heat-pump efficiency, outdoor temperature, comfort and later recovery demand.
Is preheating with a heat pump efficient?
Controlled preheating can move demand away from an expensive period. Excessive preheating may increase heat loss and total consumption, so the temperature increase and duration should remain modest.
Can a hot-water cylinder store cheap or solar energy?
Yes. The heat pump can heat water during a cheap or solar-rich period for use later. The cylinder must be correctly sized and properly insulated.
Can a battery and heat pump operate together during winter?
Yes, but winter heating demand may empty the battery quickly. The battery’s capacity, inverter power and charging opportunities should be checked against realistic cold-weather demand.
Will a heat pump, EV and battery overload the electricity supply?
They can create substantial combined demand when charging or operating simultaneously. Appropriate design and dynamic load management can keep total import within the permitted limit.
Can a home battery run the heat pump during a power cut?
Only when the battery, inverter, isolation equipment, circuits and heat pump have been designed for backup operation. Standard battery installation does not guarantee it.
Bringing heat and electricity together
A heat pump should first be designed as an efficient heating system and then integrated into the wider flow of electricity through the home.
Solar panels can contribute towards daytime heating and hot water. A battery can shift electricity between tariff periods. The building and cylinder can retain heat. Smart controls can reduce demand during selected periods.
But optimisation must continue to protect:
- Indoor comfort
- Hot-water availability
- Low flow temperatures
- Stable heat-pump operation
- Required EV charging
- Household electrical limits
- Safe fallback operation
The best whole-home system does not simply consume electricity at the cheapest advertised time. It produces the required heat efficiently, obtains electricity at sensible times and coordinates every major load around the needs of the household.
Continue exploring
Sources and further reading
- Energy Saving Trust: Heat-pump questions answered
- Energy Saving Trust: Low-carbon technology and tariff combinations
- Energy Saving Trust: Efficient heat-pump operation
- MCS: Domestic Heat Pump Guide
- Nesta: HeatFlex UK
- UK Government: Smart and Flexible Heat Pumps
- Energy Networks Association: EV charge point and heat-pump connection process