Efficiency indicates what share of incident sunlight a module converts into electricity. Modern modules are typically around 20 to 23 per cent. Higher efficiency means more output per square metre – important above all when roof space is tight. On large areas it is less decisive than often assumed.
Key points in brief
- Efficiency = the share of sunlight that becomes electricity; the rest is lost as heat.
- Today's modules are mostly around 20 to 23 per cent – clearly more than ten years ago.
- Higher efficiency means more output on the same area, not automatically more yield per franc.
- With a limited roof the value is worth real money, on large roofs it's secondary.
- The efficiency of the system as a whole also depends on the inverter and the conditions.
What exactly does efficiency measure?
In full sunshine a certain amount of energy hits every square metre of roof. Efficiency says what share of it comes out of the module as electrical output. An efficiency of 22 per cent means: a good fifth of the incident light becomes electricity, the rest is lost mostly as heat.
That sounds like little, but is technically remarkable – and the value has risen steadily over the years. Modules installed ten years ago were often clearly lower. Today around 20 to 23 per cent is usual for good modules.
Guide values, as of: July 2026. You'll find the concrete values in the data sheet of the respective module.
Why is higher efficiency useful?
The practical benefit is simple: more efficiency means more output on the same area. Two modules of the same size but different efficiency deliver different amounts of electricity. That becomes decisive wherever roof area is tight.
An example: anyone with room for only twelve modules on a small roof gets noticeably more kilowatts with high-efficiency modules than with average ones. Calculated over 25 years, this difference adds up. That's exactly why high-efficiency modules are the right choice for tight roofs – a connection the article Monocrystalline vs. polycrystalline also takes up.
When is efficiency secondary?
Now the part module advertising rarely emphasises: on a large, unobstructed roof, the efficiency of the individual module is not the decisive criterion. If there is enough area anyway to install the desired output, value for money counts more. A somewhat cheaper module with minimally lower efficiency can then be the more economical choice – you simply put one or two more modules on the roof.
In short: efficiency is a tool, not an end in itself. It solves the problem of tight area. Where that problem doesn't exist, you don't have to buy it dearly.
Module efficiency vs. system efficiency
A widespread misunderstanding: module efficiency is not the yield of the whole system. On the way from module to socket there are further factors:
- The inverter converts the current and has an (very high) efficiency of its own.
- Temperature influences output: modules deliver slightly less in great heat, as the article Heat & output explains.
- Orientation, shading and cabling also play in.
What comes out at the end as annual yield is therefore sensibly measured per installed kilowatt – more on this at Yield per kWp in Switzerland.
Efficiency is the value most liked in sales conversations – because it compares easily and sounds impressive. In the consultation we prefer to turn the question around: how much usable area do you have, and how much output do you want to fit on it? If the roof is big enough, the last half per cent of efficiency hardly matters. If it is tight, the value suddenly becomes important. The area decides, not the brochure.
Frequently asked questions
What efficiency is good today?
Good modules are currently around 20 to 23 per cent (as of: July 2026). Values in this range are standard; clearly higher ones exist but cost a premium that only pays off when area is tight.
Does higher efficiency mean more yield?
More output per area – yes. More yield per franc invested – not necessarily. On large roofs a cheaper module with somewhat lower efficiency can be more economical.
Does a module lose efficiency over time?
Yes, slowly. This so-called degradation is, for modern modules, in the very low range per year; manufacturers guarantee a large part of the initial output even after 25 years. Details: Degradation of solar modules.
Why is no more than around 23 per cent achieved?
Because classic silicon cells have physical limits. Research is under way on higher efficiencies, for example with new cell technologies – but for today's house roofs they are not yet a standard solution.
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Sources: EnergieSchweiz, Swissolar, manufacturer data sheets.
Last updated: 9 July 2026 · Author: ecoEn editorial team
