Start here8 min readLast reviewed 20 August 2026

How many solar panels do I need?

See how electricity demand, usable roof space and panel wattage shape a sensible system.

Panel count is the result of a design, not a number that can be chosen from house type alone. A useful starting point combines household demand, future changes, usable roof geometry, local generation modelling and the exact wattage of the proposed panels.

House type is not enough

Two similar houses can use very different amounts of electricity and have different roof sections, orientation, shading and future plans. A sizing conversation should begin with annual demand and when electricity is used, then test what can be installed safely on the usable roof.

Start with current and future demand

Use recent electricity data where available and identify major expected changes such as an EV, heat pump, electric hot water, home working or an extension. Future demand is still uncertain, so show it as a separate scenario rather than quietly adding it to the current case.

System size and panel count are related but different

System size is usually described in kWp. Panel count depends on that target, the exact wattage of each panel and the layout that fits. Higher-wattage panels may reduce the number needed for the same kWp, but dimensions, electrical design, warranty and cost still need to be checked.

Only usable roof area counts

A roof plan should account for dimensions, orientation, inclination, shading, obstructions, access, edge clearances and any sections excluded after structural or condition checks. An online estimate can provide a starting range but cannot replace a measured layout and appropriate assessment.

Annual production does not need to equal annual demand

Matching two annual totals can hide the hourly and seasonal mismatch between generation and use. A larger array may increase both household use and export, subject to roof, electrical and network constraints. The right trade-off depends on objectives, tariffs and the evidence used for expected energy flows.

Orientation, shading and location affect the forecast

Generation models use location and system inputs such as orientation, inclination and losses. Shading can be more complex than a single label because it changes by time and season. Ask which tool or method produced the forecast and which roof sections and losses were included.

EVs and heat pumps deserve separate scenarios

An EV or heat pump can materially change electricity demand, but the timing may not match solar generation. Record the expected annual and time-of-use change separately, then compare current and future scenarios. Do not assume every additional kWh can be supplied directly by solar.

The installer still completes the final design

The final panel count should follow a survey, measured roof layout, structural and electrical checks, exact equipment selection and any applicable distribution-network process. Ask the installer to explain why the proposed size suits the home and what would make that design change.

Key takeaways

Do not size a solar system from house type alone.
Separate current demand from future EV, heat-pump or lifestyle scenarios.
Panel count follows from kWp, exact panel wattage and a measured layout.
Check the location, roof, shading and loss inputs behind the generation forecast.
Treat Solar Check as an indicative starting range, not a final design.

This guide is for general information only. It is not a substitute for a survey of your home or professional advice. Solar Help Centre does not install solar equipment or produce the final design for your home.

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