Designing a Whole-Home Energy System: Generation, Storage, Heat, EV and Control

A whole-home energy system is not one product. It is four things working together: something that generates electricity, something that stores it, something that turns electricity into heat and hot water, and something that decides when each part runs. Most UK homes that go down this route start with solar panels, add a battery, then bring in a heat pump and an electric car, with a controller sequencing the lot. The Climate Change Committee's advisers put a number on the prize: a typical household combining an EV, a heat pump, solar panels and a time-of-use tariff could save around £1,200 a year today, rising to around £1,900 for some rural homes¹.

The combination is no longer exotic. In Energy Systems Catapult's Living Lab, the "full stack" of EV, solar, battery and heat pump was the second most common configuration among the homes taking part, with 208 homes, or 10% of the low-carbon technology homes in the study². That matters for anyone designing a system now, because it means the parts are being made to work together, and the interfaces between them are becoming standard rather than bespoke.

This page sets out how the four parts connect, what each one contributes, where they conflict, and what the finished system still depends on. The honest answer to that last question is: quite a lot. A grid-tied home with solar, storage, a heat pump and an EV is far more self-sufficient than an ordinary house, but it still leans on the network in winter, on a supplier for imports and exports, and increasingly on a manufacturer's software to run it all.

Four components and the strategy binding them

The reason designers talk about a "whole home" system rather than a list of gadgets is that the parts interact. A battery sized without reference to the heat pump will be too small in winter. A heat pump installed without thinking about future solar will miss the chance to run on self-generated power. The Federation of Master Builders describes this as taking a "whole house" approach to a warmer home and lower energy bills with retrofit⁶, and the logic applies equally to electrical design.

A useful first step is a professional assessment. Low Carbon Hub's glossary defines a Whole House Plan as "a professional service that assesses a home's energy-saving potential, helping owners plan and budget for improvements"⁷. The point of planning before buying is sequencing: the order in which parts are added affects the cost of each step, because cabling, inverters and metering put in for one component can be reused for the next.

The four parts and what each contributes:

• Generation: solar PV turns sunlight into electricity for the house, and sets the ceiling on everything downstream⁸.
• Storage: a battery holds surplus generation and cheap off-peak electricity for later use⁹.
• Heat: a heat pump converts electricity into heating, cooling and hot water¹⁰.
• Control: an energy management system monitors and decides when each part runs¹¹.

The scale of the change should not be overstated, either. Electric boilers remain the main method of heating in only 4% of UK homes according to the DESNZ Public Attitudes Tracker for Winter 2025¹², and most homes are still at the start of this journey rather than the end of it. Nesta's work on the next household energy support scheme describes support being built from eight core building blocks¹³, a reminder that policy, not just technology, shapes what households can affordably install.

For energy independence, the four-part architecture is the difference between a home that generates electricity and a home that manages its own energy. Generation alone cuts bills in daylight hours; generation plus storage plus heat plus control shifts the household from a passive consumer to something closer to a small power station that buys and sells at the moments it chooses. The remaining dependence, on the grid, the supplier and the manufacturer's software, is covered later on this page.

Where solar panels fit in as the first step

Solar photovoltaic panels are where nearly every whole-home system begins, because they are the cheapest way to put electricity into the house and the part everything else hangs off. Solar PV "uses energy from the sun to create electricity to run appliances and lighting", in the Planning Portal's plain wording⁸, and Solar Energy UK describes PV systems as "affordable, reliable, low-impact, and popular"¹⁴.

The typical British installation is modest. Ofgem's Feed-in Tariffs annual report for scheme year 13 records that "most of these solar PV installations are domestic roof top installations, and these tend to be in the 0-4kW capacity range"³. That size band is the design assumption behind most of the rest of the system: a 0 to 4 kW array generates enough in summer to charge a car or a battery, and not enough in winter to run a heat pump alone, which is the seasonal mismatch every designer has to plan around.

Output tracks the sun. The technical advice note for solar equipment on residential buildings puts it simply: "Solar PV panels convert the sun's energy into electricity. The greater the intensity and duration of the sunlight, the more electricity is produced"¹⁵. No amount of clever control changes that arithmetic; it only changes how much of the output the household actually uses.

Planning is rarely an obstacle. Solar panels fall within the common projects covered by permitted development rights in most cases, alongside extensions, garage conversions, outbuildings and other renewable energy sources¹⁶, though listed homes and conservation areas face tighter rules. For the system design itself, the array's size sets the ceiling on everything downstream: the battery's useful capacity, the amount of hot water that can be heated for free, and how much EV charging can come from the roof rather than the grid.

Batteries: their role and when they pay off

The battery is the part that converts generation into self-sufficiency. Solar Energy UK's guidance is blunt about the function: "Batteries are a way for homeowners to store excess electricity produced from their solar system"⁹. Without one, a home exports its midday surplus and buys it back, at a higher price, in the evening.

A battery does two jobs, and the second is often the more valuable:

1. It stores excess solar electricity generated during the day⁹.
2. It charges from the grid when the tariff is cheap, then discharges at night or when prices are high¹⁷.

That second job means a battery earns money in winter too, when there is no solar surplus, by arbitrating between cheap overnight rates and expensive evening ones.

The scale of the effect is well documented. The Centre for Sustainable Energy states that "domestic battery systems can store as much electricity as a household typically uses in a day, enabling a PV system to provide up to 70% of a household's annual electricity demand"⁴. That figure is the single best argument for putting storage at the centre of the design rather than treating it as an optional extra.

What a battery saves depends on four things, according to Flexi-Orb's guidance on electrical energy storage: "how much energy you generate, the size of your battery, your energy consumption, and your energy supplier's fees"¹⁸. Batteries also protect themselves: Energy Saving Trust notes that when the battery falls to a set level, "maybe 20% of the total storage capacity, your system will stop taking electricity" from it¹⁷, so the usable capacity is smaller than the nameplate.

Anyone with a home can potentially install a battery system⁹, but the economics depend on matching its size to the array, the heat pump and the car, not on buying the biggest unit available.

Warming the home: pumps, cylinders and hybrid setups

Heat is the largest energy demand in most UK homes, so the heat source is the most consequential design decision in the whole system. A heat pump is the usual answer because it is versatile: CIBSE describes it as "a versatile system capable of providing heating, cooling and hot water for homes, commercial buildings, and industrial applications"¹⁰. It also runs on electricity, which means it can be fed by the solar array, the battery and, in a vehicle-to-home setup, the car.

The heat pump changes the shape of the electrical load. It draws power steadily through the heating season, mostly in winter, exactly when solar output is at its lowest. This is the central tension of whole-home design: the generation and the biggest demand are six months out of phase. A battery sized to cover summer evenings is not the battery that runs a heat pump through a January week, and a design that ignores this will disappoint.

Hot water storage is the quiet hero of the heat side. A cylinder heated by the heat pump, or by surplus solar through a diverter, is a thermal battery: it stores a day's hot water made when electricity was cheap or free. It is cheaper per kWh of storage than a chemical battery, though less flexible, and it is the reason many designers keep or reinstate a cylinder even in homes that had moved to combi boilers.

The financial case for electrifying heat alongside everything else is strong when the parts are combined. The Climate Change Committee's June 2026 statement gives the headline figures: "A typical household could save around £1,200 a year today by combining an EV, a heat pump, solar panels and a time-of-use tariff", and "this rises to around £1,900 for some rural homes"¹. Those savings come from the interaction of the parts, not from any one of them alone: the tariff rewards shifting load, the heat pump and EV provide shiftable load, and the solar and battery supply it.

Your electric car as a power store: V2G and V2H

An electric car parked on the drive is the largest battery most households will ever own, and the design question is whether the system is allowed to use it. Energy Saving Trust's best practice guide captures the opportunity: "Having electric vehicles as battery storage will allow us to better manage the UK's energy", and EV batteries "could be one of the best ways of storing excess renewable energy"²⁰.

Vehicle-to-grid, or V2G, is the two-way version. Energy Networks Association explains that "V2G is a technology that allows electric vehicles to not only draw power from the grid to charge their batteries but also to send electricity back to the grid when needed, generating cash for the EV owner"²¹. The legislation underpinning it is already in place: the 2024 regulations add "electrical batteries that store electricity generated by certain ESMs and from the National Grid (the grid)"²² to the framework of permitted storage.

A close cousin, vehicle-to-home, keeps the energy in the house. "V2H utilises the energy to power a home rather than being delivered back to the grid"²¹, which makes the car a backup power source as well as a sink for surplus solar. The Climate Change Committee's monitoring framework notes that "at household-level, further innovation in home battery technology, vehicle-to-everything (V2X), and solar can provide households with additional backup options during power outages"²³.

The technology is arriving rather than arrived. Toyota has announced that its charging ecosystem expansion "will allow EVs to not only draw energy from the grid but also return it when needed"²⁴, with vehicle-to-grid integration planned as a more advanced solution as its energy collaborations expand. For a household designing now, the practical step is to specify cabling and a charger position that could take a bidirectional unit later, even if the first charger is a one-way smart one.

The price of vehicle-to-grid and its returns

The money in V2G comes in two streams: what the household earns, and what the country saves. On the household side, estimates vary and should be treated as just that:

The figures differ, and none is a guarantee. Actual earnings depend on the tariff, the charger and how much the car is plugged in.

On the system side, the numbers are larger. The V2GB study found that "V2G operation could generate a net saving of between £40M-90M/annum, depending on limits to V2G energy throughput" by 2030²⁵, and Energy Systems Catapult's report found V2G "could save additional £40-90M annually in GB by 2030" on top of smart charging savings, while helping to avoid "£200m of cumulative distribution network investment by 2030"²⁶. Cenex estimates V2G "could defer network upgrades of £5bn, or £180 per household"⁵.

Hardware cost is the barrier today. Cenex predicted V2G hardware prices would fall below the £3,000 to £5,000 range by 2025, and "predicts V2G charger cost to fall to £1000 by 2030"⁵. Battery wear, the worry most owners raise first, cuts the other way: "capacity fade can be reduced by 9.1% over a year through battery management", which "could extend useable battery life by 10%, giving an annual depreciation saving of £230"⁵. There is also a carbon dividend: storing generation from a 4 kWp domestic solar PV system in an EV battery over a weekend with 6 hours of sun per day can save over 600 kgCO₂e per year, and reduced renewable curtailment nationally could amount to 6 MtCO₂e per year⁵.

What an energy management system really handles

Every part described so far works on its own. What makes them a system is the controller. SolarEdge's guidance defines it plainly: "An Energy Management System (EMS) is a technology that helps homeowners monitor, control, and optimize their use of energy"¹¹. In a home with storage, "the EMS controls how and when energy is stored", saving excess solar power for use at night or on cloudy days¹¹.

The controller's job is sequencing. It decides whether the next kilowatt-hour of solar goes to the house, the battery, the hot water cylinder or the car; whether to buy from the grid now or wait for the cheap window; and when to discharge the battery into the evening peak. The Centre for Sustainable Energy notes that home energy management systems can integrate "EV chargers, heat pumps and PV diverters"⁴, which is precisely the list of controllable loads a whole-home design creates.

Brand mixing is usually workable but not always. "Some of these systems may require a particular inverter while others can be universally retrofitted"⁴, and many EMS solutions are compatible with solar panels from different brands "as long as the system components, like inverters and optimizers, are supported by the EMS"¹¹. The practical lesson for a designer is to choose the inverter and controller with an eye on compatibility, because the panels are the easiest part to mix.

The regulatory position is still settling. In its response to the DESNZ consultation on the Smart Secure Electricity Systems programme load control licence, Energy Systems Catapult argued that "Government should clarify how Home Energy Management Systems (HEMS) and optimisation services are treated where they may initiate or schedule control actions"²⁷. Until that clarity arrives, a household's controller sits in a grey zone between a private convenience and a grid service, which matters if the system starts responding to signals from outside the home.

Staying connected: why going off-grid rarely wins

It is technically possible to design a home with no grid connection, and for a few homes it is the right answer. Welsh Government guidance on behind-the-meter energy systems states that "while not mandatory, a grid connection enhances the value of BTM systems by enabling the export of surplus electricity"²⁸. Export income, and the ability to import through the winter gap, are what the connection buys.

For homes with no mains supply but access to a suitable watercourse, "a good hydro system can generate a steady, more reliable electricity supply than other renewable technologies at a lower cost"²⁹. Hydro is the exception rather than the rule: it is the one home generation technology whose output in winter, when it is needed, is strong rather than weak. For everyone else, going off-grid means buying enough battery to bridge the darkest weeks, which is far more expensive than the connection charge it avoids.

Staying connected also lets the home help the wider system. When homes generate and store their own electricity, "the grid needs to generate less electricity from fossil-fuelled generators, because enough renewable energy is generated to cover more homes for longer throughout the day"³⁰. The grid's job is governed by demand and availability³⁰, and a million homes with batteries and EVs smooth both.

Keeping it running: upkeep, software and information

A whole-home system is mostly software, and software needs looking after. The official home energy information, advice and guidance landscape is itself substantial: Energy Systems Catapult completed the report that maps what advice households can get³². At the sharp end, building automation and control systems are defined in legislation by their capability for "continuously monitoring, logging, analysing and allowing for adjusting energy use"³³, which is a fair description of what a home EMS does every day.

Day-to-day, the work is light but real. Local advice programmes, such as the grants and funding offer in Tameside, include giving households "day to day energy efficiency hints and tips and make sure your heating controller is working correctly"³⁴. The controller is the one component whose failure is felt everywhere at once, because heating, hot water, battery charging and EV charging all route through it.

Two dependencies deserve plain words:

• The manufacturer's cloud. An EMS that depends on a company's servers depends on that company staying in business and keeping the service running.
• The household's data. A system that monitors everything in the house generates a detailed record of the household's life, and who owns and can export that record is a question worth asking before buying.

On the practical side, most EMS systems with app support "allow for the management of multiple properties" from one account, depending on the app's capabilities¹¹, which suits households with more than one home to run.

The design's benefits and its limits

The honest summary of a whole-home energy system is that it buys control and cuts imports, but it does not buy total independence. The National Energy Efficiency Data-Framework exists to "assess the impact of installing home efficiency measures such as loft insulation on household energy consumption"³⁵, and the evidence base it builds is a reminder that fabric comes first: no amount of generation and storage compensates for a house that leaks heat.

The financial picture also needs context. The Consumer Council's Home Energy Index tracks energy prices as a composite, and its coverage of the Energy Price Guarantee period, which "artificially lowered gas and electricity prices from 1 November 2022 until 30 June 2023"³⁶, shows how much of what a household pays is policy rather than physics. Savings of £1,200 a year from a combined system¹ are real but sit inside a market whose prices move for reasons outside the home's control.

What the design genuinely buys is resilience and optionality. A home with generation, storage, heat and control can ride through price spikes, keep hot water and some power through outages with the right backup configuration²³, and add V2G when the hardware and tariffs mature. What it does not buy is escape from winter: the seasonal gap between summer generation and winter demand remains, and the grid connection remains the bridge across it. For most homes, that is not a failure of the design but its most sensible feature.