How Many Solar Panels Do I Need?
Author: Steve Fairless
Originally Published: 14th December 2023 · Updated: 3rd September 2026
The right number of solar panels is not determined by bedroom count or a national “average home”. We size from actual electricity consumption, roof-specific annual yield, usable roof area, future loads and what the customer wants the system to achieve. Ofgem's new 2026 medium single-rate electricity TDCV is 2,500 kWh/year, but that is a communication benchmark - not a substitute for your bills.
At Sustainable Energy Engineering, we calculate how many kWp the property can usefully support and then convert that capacity into a practical module count using the exact panel proposed. With current 500 W modules, ten panels make a 5.0 kWp array; that does not mean every 2,500 kWh household should install ten panels.
This guide explains the sizing process, including future EV or heat-pump demand, batteries, export, roof orientation and why deliberately producing more than historic annual consumption can sometimes be sensible.
Our solar PV for home designs start with household data and the roof, while battery storage is sized as a separate energy-shifting decision rather than used to guess the panel count.
Updated: 3rd September 2026
How Many Solar Panels Do You Need? The Short Answer
- Start with your own annual and time-of-day electricity use. A recent bill or smart-meter data is more useful than the number of people in the house.
- Use Ofgem's 2,500 kWh medium single-rate TDCV only as context. The final 2026 values took effect on 1 July 2026 and also include 1,600 kWh low and 3,800 kWh high reference levels.
- Convert the required system capacity into a module count using the actual panel. Ten 500 W panels = 5.0 kWp.
- Model the roof yield. A 5 kWp array does not produce the same annual kWh on every UK roof.
- Include realistic future loads. EV charging, a heat pump or increased home working can justify capacity above current historic use.
Why the old “average household uses 3,800 kWh” rule is no longer a good starting point
Ofgem reviewed Typical Domestic Consumption Values in 2026 and implemented new values from 1 July. For standard single-rate electricity, the low, medium and high reference levels are 1,600, 2,500 and 3,800 kWh/year. The old 3,800 kWh figure should therefore not be presented as the current medium or “average” household benchmark.
Ofgem 2026 single-rate electricity reference values
| Usage level | 2026 TDCV |
|---|---|
| Low | 1,600 kWh/year |
| Medium | 2,500 kWh/year |
| High | 3,800 kWh/year |
These are industry communication benchmarks. We size a customer's solar from their real consumption and plans, not from the TDCV label.
Start with the electricity the property actually uses
Annual kWh tells us the scale of demand, but half-hourly or time-of-day data tells us when that demand occurs. A household using 3,000 kWh mostly in evenings has a different self-consumption profile from a 3,000 kWh home with daytime working, immersion heating or EV charging.
Then model what each kWp of solar should produce on the roof
The amount of annual energy produced by each installed kWp depends on location, orientation, pitch, shading and system losses. PVGIS provides a useful independent way to model the performance of a chosen location/configuration. We compare that with the roof design rather than using one UK-wide “kWh per panel” number.
Panel wattage converts system size into panel count
Current module power is substantially higher than in many older guides. AIKO's current residential range includes a 500 W module. With that product, eight panels equal 4.0 kWp, ten equal 5.0 kWp and twelve equal 6.0 kWp. Another module may have a different rating, so the number of panels is a consequence of the selected kWp and product - not the first design decision.
| Panel count at 500 W each | Array size |
|---|---|
| 6 panels | 3.0 kWp |
| 8 panels | 4.0 kWp |
| 10 panels | 5.0 kWp |
| 12 panels | 6.0 kWp |
| 14 panels | 7.0 kWp |
Should annual solar generation equal annual consumption?
Not necessarily. Matching two annual totals hides timing. A system can generate 3,000 kWh/year while still importing heavily on winter evenings and exporting on sunny summer afternoons. Conversely, a customer may deliberately install more annual generation than current consumption because they plan an EV, heat pump or battery.
What changes if you plan to buy an EV?
An EV can add a large flexible electrical load, but only the portion charged during solar generation or via stored energy can directly improve PV self-consumption. We ask expected annual mileage, charging location and likely charging schedule rather than adding an arbitrary “two extra panels for an EV”.
What changes if you plan a heat pump?
A heat pump can increase annual electricity use, particularly in winter when solar generation is lower. It may justify a larger array, but annual matching should not imply winter self-sufficiency. The monthly generation and heating-demand profiles need to be understood separately.
Does a battery mean you need more panels?
A battery does not create solar energy. It changes when generated energy can be used. A larger array can create more surplus to charge a battery, but a large battery paired with a small shaded array may spend much of the year undercharged. We size capacity and storage together while keeping their roles distinct.
Roof space can set the upper limit
Sometimes the customer's ideal energy model suggests more capacity than the roof can support. In that case we optimise the usable roof: higher-efficiency modules, the best roof planes, sensible shade decisions and a suitable inverter/MPPT arrangement. The answer may be “install the best 4.5 kWp the roof allows” rather than force a theoretical 6 kWp target.
Network connection can affect the inverter strategy
The DNO connection route is based on the generating equipment and connection configuration, not simply the DC sum of panels. More modules do not always mean a proportionally larger AC export. We account for G98/G99 requirements, inverter capacity, battery power and any export limitation before finalising the design.
Why we do not size from bedrooms
Two four-bedroom homes can have completely different electricity consumption. One may use gas heating, work away from home and have no EV; the other may have an EV, heat pump, home office and electric cooking. Bedroom count is useful for estate agents, not for engineering a PV array.
A practical sizing workflow
- Collect actual data: annual kWh, tariff and ideally half-hourly smart-meter usage.
- Add credible future demand: EV, heat pump, extension or home working where genuinely planned.
- Map the roof: usable dimensions, orientation, pitch, shading and structure.
- Model annual/monthly solar yield: use the proposed kWp and real site.
- Choose module/inverter architecture: convert kWp into a buildable panel and string layout.
- Model self-use, storage and export: check that extra capacity delivers useful value.
We size for the customer the property is becoming
A PV system can remain on a roof for decades. If an EV or heat pump is genuinely planned, ignoring it because it was not on last year's bill can be as misleading as assuming a future load that may never happen. We document both current and planned demand so the recommendation is transparent.
What we recommend
Do not ask an installer for “the standard number of panels for a three-bedroom house”. Give them your actual kWh use and future plans, then ask for the proposed kWp, expected annual generation and module count. A strong answer will explain why those figures fit both the roof and the way you use electricity.
Want the Panel Count Calculated From Your Own Usage?
Send us your annual electricity use and we can assess the roof, expected generation, future loads and whether battery storage changes the best design.
Request a tailored quote from Sustainable Energy Engineering.
