Sizing Generation and Storage for a Self-Sufficient Home

Sizing a home energy system is a question about kilowatt hours, not about panels. The starting point is not your roof but your meter: how many kWh of electricity your household consumes in a year, and how that consumption is spread across the day and the seasons. Once you have that number, the array and the battery follow from it, and the whole exercise becomes a matter of matching annual generation to annual consumption, then deciding how much of the gap between a sunny midday and a winter evening you are willing to bridge with storage.

The core measure is what MCS calls self-sufficiency: "The percentage of electricity consumed in the property over a year which is met by either behind the meter solar or electrical energy storage"¹. That definition matters because it is honest about what a grid-connected home can achieve. A house with solar and a battery is not off-grid; it is a house that meets a defined share of its own demand from its own equipment, and the sizing task is to decide what share, at what cost. This page works through the method and the numbers for a typical UK household, using a 5,000 kWh annual demand as the running example, because that is the kind of figure a home with electric heating, a heat pump or an electric car actually sees.

Self-sufficiency measured in kilowatt hours, not in panels

The first mistake in sizing is to start with the product. Panels are sold in kilowatt peak (kWp), batteries in kilowatt hours (kWh), and neither number means anything until it is set against the household's consumption. MCS's self-consumption method defines the terms precisely: self-consumption is "The amount of solar electricity generated by a domestic solar PV system which is subsequently consumed within the property and not exported to the distribution network", and it "can be quoted in kWh or as a percentage of the total PV generation"¹. Self-sufficiency is the related but distinct figure: the share of everything the property consumes over a year that comes from its own solar or storage.

The distinction matters because the two numbers move differently. A household can self-consume a very high percentage of a tiny array, because almost nothing is left over to export, while still importing most of its electricity. Conversely, a large array on a home that is empty all day will export most of its generation and self-consume little. Sizing for self-sufficiency means working from the demand side: the annual kWh figure, the pattern of use across the day, and how much of the generation can be captured rather than exported.

The method also sets sensible bounds. MCS's worked method applies to homes with annual electricity consumption between 1,500 kWh and 6,000 kWh per year, and to solar PV systems generating less than 6,000 kWh per year¹. That covers the overwhelming majority of UK homes, and it frames the running example on this page: a household consuming around 5,000 kWh a year sits near the top of that range, the kind of home where electricity is doing heating or vehicle charging as well as lights and appliances. For the underlying concepts in more depth, see self-consumption and the self-sufficiency ratio.

How much electricity a UK household uses

Every sizing calculation starts with this number, and the honest answer is that households vary enormously. Ofgem classifies the average electricity usage for UK households as 2,500 kWh per year², and the same figure appears in the energy price cap documentation as the typical domestic consumption value for Great Britain⁶. Energy Saving Trust uses the same 2,500 kWh figure as its planning assumption for plug-in solar⁷.

But an average is a poor basis for sizing an individual system. MCS's method spans 1,500 to 6,000 kWh a year precisely because real homes differ by a factor of four¹. A small flat with gas heating and cooking may sit near the bottom of that range. A home with electric central heating will sit higher: Which? notes that a 4 kWp solar system could generate around 3,500 kWh a year, and that figure only covers a meaningful share of demand in homes whose consumption is modest⁸. A household with a heat pump or an electric car can easily consume 5,000 kWh or more, and maker guidance puts the average household at 2,700 to 3,500 kWh annually before such loads are added⁹.

The practical step is therefore to read your own meter and bills rather than use the average. Add up a full year of consumption from statements, including winter, and note whether anything is about to change: a heat pump conversion, an electric vehicle, a working-from-home shift all move the number. The daily pattern matters too, because the shape of use across the day drives battery sizing more than the annual total does. For the national picture on where household energy comes from, see household import dependence.

How many panels you need for 5,000 kWh of annual use

With the consumption figure in hand, the array size follows from a target for annual generation. Maker guidance illustrates the rule: for a home consuming 4,000 kWh per year, the target is 4,800 kWh of annual solar generation, typically requiring a 5 kWp panel array³. The 20% uplift above consumption is deliberate, because no home uses its own generation perfectly and UK generation is uneven across the year. Scaling that logic to a household consuming 5,000 kWh a year points to roughly 5 to 7 kWp, which at typical panel outputs means about 12 to 18 modules.

The panel count follows from the wattage of the modules. A typical domestic system of 4.5 kWp covers 20 to 30 square metres of roof and uses around 12 panels¹⁰, so a 5 to 7 kWp array means roughly 12 to 18 panels depending on the output of each module. Real installations bear this out: an MCS case study describes a home fitted with six solar panels and a 5 kWh battery¹¹, while a project evaluating solar PV with electric heating in North Devon saw system sizes ranging from 3.89 kW to 5.81 kW¹².

Two cautions apply before settling on a number. First, the target generation must be realistic for your location and roof: a 5 kWp array in northern Scotland on an east-west roof will not produce what the same array produces on a south-facing roof in the south of England. Second, oversizing has diminishing returns once generation regularly exceeds what the household can use or store, because the surplus is exported rather than consumed. The sizing question is covered further in designing a whole-home energy system.

Realistic output from a 5 kWp installation in Britain

The headline numbers for UK domestic generation cluster in a consistent band. The Centre for Alternative Technology states that a well-sited domestic system of about 3.5 kW peak output could produce around 3,000 to 3,500 kWh per year¹³. Which? gives around 3,500 kWh a year for a 4 kWp system, depending on where you are in the country⁸. Scaling from those figures, a 5 kWp system produces roughly 3,750 to 5,500 kWh a year across the typical range of UK locations and roof orientations, with the lower end representing poorer siting and the upper end representing a good south-facing roof in a favourable part of the country.

What drives the spread is a short list of factors: latitude and regional irradiance, roof orientation and tilt, shading, and the efficiency of the installed equipment. The same 5 kWp of panels can produce substantially different annual totals in Cornwall and Caithness. A real household's experience illustrates the usable share: an Energy Saving Trust case study reports that the household's system generates output of which "We manage to use around 3,000kWh"¹⁴, a figure that reflects both generation and the household's ability to consume it.

For the 5,000 kWh household in our running example, this is the sobering part of the calculation. A 5 kWp array generating, say, 4,500 kWh a year does not cover 90% of demand in any usable sense, because the generation is concentrated in spring and summer and in the middle of the day. The annual totals nearly match; the timing does not. That mismatch between annual totals and hourly delivery is the single biggest constraint on household self-sufficiency, and it is covered in detail in the winter gap.

Solar on its own covers only about 30 to 40 per cent of your use

Without storage, most of a home's solar generation arrives when the home needs it least. The evidence is consistent across independent and official sources. Uswitch's guidance states it plainly: "Without a battery, you might only use 30-50% of what you generate", rising to "80% or more" with one⁴. A parliamentary research briefing reports Great British Energy's finding that "adding a battery to a solar installation increases self-consumption from 30 to 40% to 70 to 80%"¹⁵. Maker guidance puts panels-only self-consumption at around 30%⁹.

The MCS worked examples give the most granular picture. In one example, a home occupied all day with 3,879 kWh annual consumption and 4,059 kWh of annual generation self-consumed 29% without storage¹. In another, a home occupied half the day with 5,783 kWh consumption and 2,456 kWh generation self-consumed 39%¹. The pattern is clear: even with someone home during daylight, roughly 60 to 70% of generation is exported because it arrives faster than the household can use it.

The reason is arithmetic rather than technology. A 5 kWp array in June can produce 20 kWh or more in a day, most of it between late morning and mid-afternoon, while a typical household's daytime baseline draw is a fraction of that. Kettles, washing machines and showers come in bursts; the sun does not. The options for closing that gap are storage, load shifting (moving consumption into the sunny hours), or a combination, and the trade-offs between them are set out in how much a battery increases self-consumption and solar diverter vs battery.

Choosing a battery: 10 kWh suits a 5 kWp array, 6 to 13.5 kWh in practice

Battery sizing follows from the daily pattern rather than the annual total. The question is how many kWh the household needs to carry from the generation hours into the evening and overnight, plus a margin for days when generation is poor. Real UK installations give a clear picture of the range: the North Devon project evaluating solar PV with electric heating installed systems from 3.89 kW to 5.81 kW "with batteries between 6kWh and 13.5kWh in capacity"¹². Maker guidance describes a typical configuration as "3kW to 5kW photovoltaic panels paired with 5kWh to 18kWh" of batteries⁹.

For a 5 kWp array, a battery around 10 kWh is the pairing that appears in national data. Uswitch reported during the June 2026 heatwave that British homes with solar were reaping substantial savings, with a self-consumption rate of "70% with 10kWh battery" according to its data¹⁶. That 70% figure sits comfortably inside the range the official briefing gives for solar-plus-storage, 70 to 80%¹⁵, and below the 80% to 90% that maker guidance reports for a 4 kWp solar plus 5 kWh battery on a time-of-use tariff³.

The sizing logic, in order:

1. Take your average daily consumption, worked out from your annual kWh figure².
2. Estimate the share used in the evening and overnight, when the array is not generating.
3. Add capacity to cover that overnight demand, plus a margin for consecutive dull days.
4. Check the result against the array: a battery much larger than the array can fill on a typical day adds cost without adding usable energy.

Two limits are worth stating firmly. A battery sized for one evening is not sized for a winter week of low generation; days of autonomy against the worst month is a different and much more expensive calculation, and it is the one that matters if the aim is genuine off-grid operation, as covered in going off-grid and off-grid in winter. And batteries age: independent guidance notes that battery systems "typically start from around £4,000 and last about ten years"¹⁷, so the storage layer of a self-sufficiency plan has a shorter life than the panels it serves.

Roof space, system losses and the safety margin

Roof area sets a hard physical limit on array size. The official and independent figures line up well: Hammersmith and Fulham Council states that a 3.5 kWp system typically covers between 10 to 20 square metres of roof surface¹⁸, while Energy Saving Trust gives 20 to 30 square metres for a 4.5 kWp system using around 12 panels¹⁰. Which? says the average system of around 4 kWp requires at least 20 square metres of roof space¹⁹, and maker guidance puts a 4 kWp system using modern 400W+ panels at roughly 15 to 20 square metres of unshaded, structural roof³. A 5 to 7 kWp array therefore needs somewhere above 20 square metres, and orientation and shading need checking before the space is counted as usable.

The relationship between roof area and capacity is also visible from the planning side. A Northern Ireland building regulations discussion document notes that "a house with a roof plan area of more than 59m2 would be typically expected to have an array larger than 3.68kWp" where an export-capable connection is provided²⁰. That gives a rough rule of thumb for what a given roof can host, and it underlines that most UK roofs can physically accommodate the 5 to 7 kWp a high-consuming household would want.

Output erodes between the nameplate figure and the meter, through shading, orientation, soiling, inverter and wiring losses, and cold-weather performance. This is why the sizing method builds in a buffer, targeting generation above consumption rather than matching it exactly³. It is also why the same 5 kWp array produces 3,750 kWh on one roof and 5,500 kWh on another: the losses are not a fixed percentage but a function of siting. Bromley Council's guidance simply notes that most homes "have sufficient space" for a solar installation²¹, but sufficient space is not the same as ideal space, and the difference shows up in the annual generation figure.

Typical results from solar panels with a battery

Worked examples give a better feel for achievable numbers than any rule of thumb. The MCS self-consumption guide models a home occupied all day with a 7.5 kWh usable battery, and finds self-consumption with storage of 69%, equivalent to 2,801 kWh of the 4,059 kWh generated²². The Centre for Sustainable Energy describes a household with 3.5 kW of solar and a 6 kWh battery that "might now be able to use 70% of the solar generated energy"²³. Maker guidance reports 65 to 75% self-consumption for 6 kWp plus 10 kWh battery installations in the East Midlands⁹.

The pattern across these examples is consistent: once a battery of roughly 5 to 10 kWh is in place, self-consumption lands in the 65 to 90% band, with the upper end associated with time-of-use tariffs and deliberate load shifting. Case studies from MCS installations show smaller systems in the wild too: one home was fitted with six solar panels and a 5 kWh battery alongside a heat pump¹¹, another with a 5 kWh battery storage system²⁴. At the national scale, UK homes have 6.6 GW of solar power installed²⁵, and Uswitch reported in May 2026 that three million households plan to get solar panels in the next five years²⁵.

What these examples do not show is full annual self-sufficiency. Even at 90% self-consumption of generation, the household still imports in winter, on dull days, and overnight once the battery is empty. The gap between "uses most of its own generation" and "covers most of its own demand" is the difference between the two definitions in the first section, and it is why the honest framing of a grid-connected solar and battery home is a high self-sufficiency percentage, not independence. More real-world numbers are collected in UK homes that cut their imports.

Prices and the payback debates explained

The installed cost of a typical system is now well documented. Uswitch states that solar panel prices "currently range from around £4,600 to £8,000" depending on panel quality and system size⁴. Energy Saving Trust gives a typical figure: domestic systems are generally around 4.5 kWp and "cost around £7,600"¹⁰. Battery storage adds "around £5,000 to £8,000"¹⁰, and industry guidance puts the average battery cost at around £4,500 on top of an existing solar system²⁶. Which? lists combined solar and battery packages from £7,518²⁷. These are installed prices quoted by installers; no single published price covers every home.

On payback, the independent estimates cluster tightly and the maker estimates run faster. Which?'s comparison of rooftop and plug-in systems puts rooftop payback at 10.9 to 12.2 years⁵, repeated in its plug-in solar review²⁸, and its myth-busting guide says a typical rooftop system takes "between 10-13 years" to pay for itself through bill savings²⁹. Hammersmith and Fulham Council says solar panels "usually pay for themselves in 10-12 years"¹⁸, and Home Energy Scotland gives around 8 to 12 years depending on maintenance³⁰. Maker guidance is more optimistic: 5 to 7 years for larger 6 to 8 kWp systems with a south-facing roof, full battery and smart tariff; 7 to 9 years for a standard 4 to 5 kWp setup with a 5 to 10 kWh battery; over 10 years for shaded, north-facing or undersized systems⁹. A full solar, EV and battery setup is estimated at seven to 12 years³¹.

The disagreement is not mysterious. The faster estimates assume higher self-consumption, smart tariffs that reward shifting load, and larger systems whose savings scale faster than their costs. The independent figures assume more typical behaviour. The saving itself is real either way: adding a £2,500 battery can increase annual savings to £932, according to industry guidance²⁶. Plug-in solar, legal across Great Britain since 27 August 2026, offers a much cheaper entry point with payback of five to ten years³² or two to three years for a two-panel 800W set³³, but at 400 kWh a year it covers only about 15% of a typical household's demand³⁴, so it is a supplement rather than a sizing solution. The full cost picture, including financing, is in what energy independence costs.

How much independence the right system size gives you

A correctly sized solar and battery system buys a household a great deal: 70 to 90% self-consumption of its own generation, a large reduction in imported electricity across the year, and a meaningful buffer against price volatility. It does not buy disconnection. The system still depends on the grid for winter imports, on a supplier for those imports and for any export payments, on the manufacturer for the battery's expected ten-year life¹⁷, and increasingly on software and apps for the load shifting that makes the numbers work, a dependence examined in local control versus the manufacturer's cloud.

The sizing method on this page, working from measured consumption to a generation target to a storage capacity, is the right order of operations because it keeps the honest arithmetic in view. A 5,000 kWh household with a 5 to 7 kWp array and a 10 kWh battery can expect to meet a substantial share of its annual demand from its own roof, with self-consumption in the 65 to 90% band that the worked examples show. What it cannot expect is to close the winter gap without either a much larger store, a different generation source, or a change in how the home uses energy, options explored in can a UK home be fully self-sufficient.

The measure to track is the one MCS defines: the percentage of consumption met by your own solar and storage over a year¹. Sizing the system to raise that percentage as far as the roof, the budget and the household's pattern of use allow is the aim, and the remaining percentage is the dependence that remains.