Mono vs Poly Solar Panel Energy Output Calculator

How this calculator works

This calculator works in ranges rather than single figures, because real quotes, yields and tariffs genuinely vary that much. It starts from typical UK price, output and savings ranges drawn from published 2026 industry guides and official scheme documentation, then scales them by the quantities you enter and adjusts them for each choice you make below. The result is a low-to-high band that a realistic outcome is likely to fall within, not a promise of the figure you will achieve.

At the same installed capacity, monocrystalline panels typically out-generate polycrystalline by around 2 to 5 percent over a UK year, mainly because mono cells handle heat and low light slightly better; a kWp is a kWp under test conditions, so the real-world gap is modest. The larger difference is density: mono panels are typically 20 to 23 percent efficient against 15 to 18 for poly, so a given roof holds more mono capacity.

System size

Solar systems are sized in kilowatts peak (kWp), the output of the panels under standard test conditions. A 4 kWp system of around 10 modern panels is the most common choice for a UK three bedroom home, while larger households, or homes with an electric vehicle or heat pump, often go to 6 kWp or more. Bigger systems cost less per kWp because fixed costs such as scaffolding, the inverter and installer overheads are spread across more panels, and the calculator reflects that economy of scale.

Region (solar resource)

The same panels generate more in Cornwall than in Caithness. The industry baseline is around 850 kWh per year for every kWp installed on an unshaded south-facing roof in an average UK location, with southern England running around 5 percent above that and Scotland 10 to 15 percent below. The calculator scales its output and savings figures accordingly.

What else affects the figures

This comparison has largely been settled by the market: by 2026 nearly all mainstream residential panels sold in the UK are monocrystalline, with polycrystalline surviving mainly in budget imports and older stock, so the practical question is usually which mono panel rather than mono versus poly. Poly’s historic advantage was price, and where cheap poly stock appears it can still make sense for large unconstrained roofs such as barns. If you are evaluating an existing poly system, its lower output per kWp is already reflected in these figures; degradation rates are broadly similar between the technologies, at roughly 0.3 to 0.5 percent a year for quality products.

Certification, planning and grid connection

If a calculation here prompts a project, the practical next step is an MCS-certified installer’s survey: MCS installers must provide a location-specific generation estimate using the standard industry methodology, which turns the broad ranges on this page into a figure for your actual roof. Most domestic solar work falls under permitted development, with the usual exceptions for listed buildings, flats and conservation areas, and installations must be notified to the district network operator under the G98 or G99 procedures, which a competent installer handles as part of the job.