Works out the array a home needs — capacity, panels, battery and what it saves — from a postcode, a roof direction and a year of electricity use.
Most of the form is filled in already with figures that give a sensible answer. Adjust what you know and press the button.
Work out the solar PV system a UK home needs: the capacity in kWp, the number of panels, the battery to go with it, and what it would do to the electricity bill.
This runs the MCS arithmetic backwards. The other solar calculators here each answer one question about a system somebody has already specified. This one starts from what a household uses and arrives at the system that covers it, which is the question a householder actually has.
The chain is short and every link is published. Annual consumption sets the generation the array has to make. The MCS irradiance dataset behind MIS 3002 says what one kWp makes on that roof, which gives a capacity. Capacity divided by panel size gives a panel count, rounded up, because panels come whole. The MGD 003 tables then say how much of that generation the household will use and how much it will export.
Only the postcode and the roof direction are required. Direction is a compass point, not an angle: 'S', 'SE', 'SW', 'E', 'W', 'NE', 'NW' or 'N'. Give the annual consumption from a bill if it is known, since the 3,500 kWh default is only the British average. Shading can be described in words instead of measured, and a roof area caps the panel count where the roof is the constraint.
No cost is assumed. Installed prices vary far too much between houses to guess at, so a payback figure appears only when a cost from a real quotation is supplied.
Use this to size a system or to sanity-check a quotation. Use 'solar_pv_output' instead when the capacity is already known and the question is only what it will generate.
The same calculation answers on
POST /api/v1/calculators/solar-pv-system-size
and as the MCP tool solar_pv_system_size.
How to call them.
It also runs from a plain link, with the JSON fields as query parameters: GET /api/v1/calculators/solar-pv-system-size?postcode=BS1+5TR&direction=SW&annualConsumptionKwh=3600&occupancy=in_half_the_day&shading=light&includeBattery=true&electricityPricePerKwh=0.27&exportPricePerKwh=0.15. This page takes its own form fields in the address in the same way, so an answer can be linked to.
From 27 October 2026 you can borrow at low or no interest to pay for a heat pump, solar panels and other clean energy upgrades, with nothing to pay upfront. The article explains what you can borrow, how the loans compare with ordinary credit and what to check before you apply.
Energy prices only go up, the argument runs, so panels and a heat pump protect you against inflation. This article checks that against what electricity, gas and savings accounts did from 2016 to 2025, for one solar roof and one heat pump.
Less needs doing than for a heat pump, and one thing people expect to have to do turns out not to matter at all. What is worth checking before you get anyone out.
What a solar system is worth depends far more on how much of its output the house uses than on how much it generates. The Microgeneration Certification Scheme (MCS) publishes tables for working that out, and this is how to read them for your household.
Panels get a little better every year, which makes waiting sound sensible. What a year's delay costs, worked through with real numbers.
What a roof will realistically generate, why the direction matters less than you think, and why the same panels are worth more to some households than others.
Short answers on what a roof will generate, whether direction and shading matter, what happens to the electricity you do not use, and what the panels need.
A quotation should show its working. What ought to be in one, what the gaps usually mean, and the handful of numbers that matter more than the price.
Three numbers on your bill do all the work, and finding them takes about five minutes. They are also the numbers every calculator here asks for.
Every solar quotation under the Microgeneration Certification Scheme (MCS) contains a figure for annual generation, and every one of them is arrived at the same way. This guide sets out the method and the data behind it, and how to check the figure on a quotation.
The MCS method is fixed, so two correct estimates for the same roof should agree. When they do not, the difference is nearly always in one of five inputs.