Solar Panel Calculator
How many solar panels can you fit on your roof? Enter your available roof area and the direction it faces — our calculator estimates the number of panels, system size in kWp, annual energy generation and CO₂ savings.
How our solar panel calculator works
The calculator uses standard UK yield figures to estimate how much electricity your solar array will generate. We assume modern 450 W panels, each covering approximately 2 m². A usable roof factor of 80% accounts for access gaps, spacing, and setbacks — you can't cover every square metre of a roof with panels.
The system size in kWp (kilowatt peak) is calculated from the number of panels, then multiplied by the annual yield factor for your roof orientation to give estimated annual generation in kWh. South-facing roofs in the UK typically yield around 1,000 kWh per kWp per year, while east and west-facing roofs yield around 850 kWh per kWp.
What affects solar panel output
Roof orientation is the biggest single factor — south-facing roofs generate the most electricity in the UK. But several other elements influence real-world output:
- Roof pitch (angle) — 30–40° is optimal for south-facing roofs in the UK; steeper or shallower angles reduce yield slightly.
- Shading — trees, chimneys, neighbouring buildings and roof vents can all reduce output, especially if they shade panels during peak sunlight hours.
- Panel efficiency — modern panels range from around 400 W to 460 W per panel; higher efficiency means more power from the same area.
- Inverter choice — string inverters, power optimisers and micro-inverters each handle shading and panel mismatch differently.
- Local weather — the East Midlands receives around 1,000–1,100 peak sun hours per year, making it a viable region for solar generation.
Understanding kWp, kWh and solar yield
kWp (kilowatt peak) is the maximum power output of your solar panel system under ideal conditions — essentially the "size" of your system. A typical residential system is 3–4 kWp, while commercial systems can range from 10 kWp to several hundred kWp.
kWh (kilowatt hours) is the actual energy generated over time. Yield is the amount of energy generated per kWp of installed capacity — in the UK this ranges from around 600 kWh/kWp (north-facing) to 1,000 kWh/kWp (south-facing) per year.
A typical 4 kWp south-facing system in the East Midlands generates approximately 4,000 kWh per year — enough to cover a significant portion of an average home or small business's electricity needs, and potentially worth hundreds of pounds in savings and Smart Export Guarantee (SEG) payments.
Turn your roof into a power station
Our MCS-certified team designs and installs solar PV systems across the East Midlands — for commercial buildings, factories, farms, churches, village halls and heritage properties. We handle the full project from initial design and structural assessment through to G99 grid connection applications and final commissioning.