Solar PV Calculator: What Could Your Roof Generate?
A calculator is a useful starting point, but a credible result needs roof direction, pitch, shading, usable dimensions and local solar data — not simply a postcode and panel count.
A better estimate starts with better property information.
Usable roof area
Chimneys, roof windows, ridges, edges and access zones reduce the number of modules that can actually be fitted.
Direction and pitch
South is not mandatory. East and west arrays can perform well and spread output more evenly through the day.
Shading
Trees, neighbouring roofs, chimneys and aerials can affect individual modules and the inverter design.
System losses
Temperature, cables, inverter conversion, dirt, mismatch and downtime mean annual AC energy is not simply panel wattage multiplied by sunshine hours.
Power rating and annual energy are different.
A 5kWp array is the combined laboratory-rated peak power of its modules. Annual generation is measured in kilowatt-hours and varies with the location and roof.
For example, ten 500W panels equal 5.0kWp, while twelve 450W panels equal 5.4kWp. The larger array will not necessarily deliver the best household value if much of its output is unused or the roof has different shading.
Calculator FAQ
Can a calculator promise savings?
No. Savings also depend on electricity use, tariff, export rate, battery behaviour and future energy prices.
Should I enter panel wattage or array size?
Use the exact input requested. Array size in kWp is panel wattage multiplied by panel quantity and divided by 1,000.
Why can two 5kWp systems generate differently?
Orientation, pitch, shade, local weather, inverter design and downtime can all differ.
Start with a proper solar assessment.
Tell Mr Solar about your property, electricity use and future plans. We will recommend a system around the building and the way you actually use energy.