A solar array's rating turned into a year's energy — with the location named, because the same panels produce more than twice as much in one place as another.
Calculator
Try:
There is no kWp-to-kWh factor, so this asks where the array is. The same panels make more than twice as much in Arizona as in Scotland, and no national figure survives that.
5 kWp in southern england & benelux
4,750 kWh a year
typically 4,250–5,250 kWh depending on orientation, shading and the year · 396 kWh a month on average, and far less than that in winter
The same 5 kWp, everywhere else
Annual output by location, ascending — identical panels throughout
Location
kWh/kWp/yr
This array
Note
Northern Britain & Ireland
700–900
4,000 kWh
Low sun angle and a great deal of cloud. Still viable; the payback arithmetic is simply slower.
Southern England & Benelux
850–1050
4,750 kWh
The figure most UK feasibility studies use before shading and orientation are applied.
Germany & central Europe
900–1150
5,000 kWh
The market that established most of the industry’s conventions, at a fairly modest yield.
US northeast & Pacific northwest
1100–1300
6,000 kWh
Comparable to northern Italy. Cold winters help efficiency and hurt daylight hours.
Northern India
1300–1550
7,250 kWh
High irradiance, but heat and dust both take a slice — soiling losses here are unusually large.
Spain, Italy & southern Europe
1350–1650
7,500 kWh
Roughly half again what the same array would make in Germany.
Australia
1350–1750
7,750 kWh
Among the highest residential yields anywhere, and the reason rooftop uptake is so high.
Southern & western India
1450–1750
8,000 kWh
Very high irradiance. The monsoon months are the constraint rather than the winter.
US southwest
1550–1850
8,500 kWh
Arizona and Nevada. Better than twice the northern-British figure for the same panels.
Top to bottom is a factor of 2.13. The panels are identical in every row; what differs is how much sunlight arrives. This is why a kWp figure alone tells you what the array is and nothing about what it will make.
The 25 °C that never happens
Output at this cell temperature91.3%of the rated figure
Lost to heat8.8%-0.35% per °C above 25
So this array peaks at4.56 kWrather than its 5 kWp label
A panel is rated at a cell temperature of 25 °C in full sun, which is a laboratory condition rather than a weather one — a dark panel in 1000 W/m² of sunlight runs 20 to 35 degrees above the air around it. Heat is a loss: output falls by about a third of a per cent per degree, which is why a cold bright April day can out-produce a hot July one.
What a performance ratio is made of
Six losses whose product is the figure everyone quotes
Loss
Keeps
Costs
Note
Cell temperature
92%
8%
The largest single loss in a hot climate, and the one the rating pretends away.
Soiling and dust
97%
3%
A few per cent where it rains often, far more in a dry dusty climate without cleaning.
DC wiring and mismatch
97%
3%
Cable resistance, plus the fact that a string performs like its weakest module.
Inverter conversion
97%
3%
Modern inverters are efficient, but not at very low input power.
Shading and horizon
97%
3%
A chimney, a tree, or simply the hills. Highly site-specific and often the biggest surprise.
Downtime and degradation
98%
2%
Faults, grid outages, and roughly half a per cent of output lost per year of age.
Performance ratio
79.8%
20.2%
The product, not the sum — which is why it lands near 0.8.
A performance ratio is quoted as a single number between 0.75 and 0.85, and it is always six numbers multiplied. Which one dominates depends entirely on the site: temperature in a hot climate, soiling in a dusty one, shading almost anywhere with a tree. The specific-yield figures in the table above already include a performance ratio of roughly this size, so applying one again would double-count it.
Roof space and panel count
Panel area needed23.8 m²before spacing, walkways or setbacks
Panels at 440 W1211.36 before rounding up
Peak AC outputnot a conversionthe inverter is usually deliberately smaller
The area figure follows directly from the rating: at STC the panel receives 1000 W/m², so a 21% module needs about 4.8 m² per kilowatt-peak. What it does not include is the roof around it — spacing, edge setbacks and access commonly add 20 to 40 per cent on a flat roof, and rather less on a pitched one. Peak AC output is left blank on purpose: inverters are normally undersized against the array by design, and by how much is a decision rather than a conversion.
What this converter covers
Nine regions with published specific-yield ranges, the cell-temperature loss, the six components of a performance ratio, and roof area and panel count.
kWp to annual kWh, by region, as a range rather than a point
The same array in nine locations at once
Cell temperature, and what it costs at −0.35% per °C
The six losses a performance ratio is the product of
Roof area from module efficiency, and panel count from module wattage
No universal factor Nine regions Heat is a loss kWp · kWh · m² · panels
Free, no signup — exact by definition, not an estimate.
Updated 8 September 2026
At a glance
Formula shown
annual kWh = kWp × specific yield for that location, in kWh per kWp per year
Scenario support
5 kWp is 4,750 kWh in southern England and 8,500 kWh in Arizona
Educational estimate
Planning support from the values you enter — not professional advice.
A peak that never happens
A solar panel’s rating is in kilowatt-peak, and the word is doing more work than it looks like.
The rating is measured under Standard Test Conditions: 1000 watts per square metre of irradiance, a defined solar spectrum, and a cell temperature of 25 °C. The first two are a bright clear day. The third is not a weather condition at all.
A dark panel absorbing a kilowatt per square metre runs 20 to 35 degrees above the air around it. To have a 25 °C cell in 1000 W/m² of sunshine you would need an air temperature near freezing — which happens, on cold bright winter days, and is exactly when panels briefly exceed their rating.
So the rating is a comparison label, not a prediction. It lets you compare one panel against another on equal terms, which is what it was designed for. It was never a statement about what the array will do on your roof.
Why there is no factor
The question “how many kWh does 1 kWp make” has no single answer, because the panels are not the variable. The sunlight is.
Annual specific yield, kWh per kWp per year
Location
Typical
A 5 kWp array
Northern Britain & Ireland
800
4,000 kWh
Germany & central Europe
1,000
5,000 kWh
Northern India
1,450
7,250 kWh
Australia
1,550
7,750 kWh
US southwest
1,700
8,500 kWh
Identical panels, and a factor of more than two between the ends. Any converter offering a single number has silently picked one of those rows.
And the location figure is itself a starting point. Orientation matters — an east-west roof in Britain gives up roughly 15 to 20 per cent against due south — and shading matters more, because a partly shaded string can lose far more than the shaded fraction suggests.
Which is why the calculator above reports a range and names the region, and why a real feasibility study runs the actual coordinates, tilt and horizon through a tool like PVGIS rather than multiplying by anything.
Heat is a loss
The most counter-intuitive fact about solar panels is that they work worse when it is hot, and it is not a small effect.
Output falls by roughly 0.35 per cent per degree of cell temperature above the 25 °C rating point. A panel at 50 °C — an ordinary summer afternoon almost anywhere sunny — has lost about 9 per cent before any other loss in the system has had a turn.
The mechanism is in the semiconductor: heat raises the intrinsic carrier concentration, which lowers the cell’s open-circuit voltage. Current rises very slightly, voltage falls considerably more, and the product falls.
Which produces a genuinely surprising result. A cold bright day in April can out-produce a hot hazy day in July at the same latitude, and the panels on a cool, well-ventilated roof outperform identical ones lying flat on a hot one. Mounting that leaves an air gap behind the modules is worth real percentage points.
It also explains why very hot climates do not out-produce merely sunny ones by as much as their irradiance suggests: some of the extra sunlight is spent heating the panels that are collecting it.
A performance ratio is six things
Every solar quotation mentions a performance ratio, usually as a single figure between 0.75 and 0.85, and it is always a product rather than an allowance.
The components, and what each keeps
Loss
Keeps
Where it bites hardest
Cell temperature
92%
Hot climates, flat mounting
Soiling and dust
97%
Dry dusty regions without cleaning
Wiring and mismatch
97%
Long DC runs, mixed module ages
Inverter conversion
97%
Oversized inverters at low light
Shading and horizon
97%
Anywhere with a tree or a chimney
Downtime and ageing
98%
Older systems, unmonitored faults
Multiply those and you get 0.798. Add the losses up instead and you get 0.780 — close enough to look right, and wrong, because losses compound rather than sum. The gap widens as the losses grow, which is exactly when it matters.
Which component dominates is entirely site-specific. In Rajasthan it is soiling and temperature; in a British suburb it is shading; in an ageing commercial array it is usually a faulty string nobody noticed for six months.
One warning about double-counting: the specific-yield figures in the table above already include a performance ratio of roughly this size, because they come from measured systems rather than from panel ratings. Applying a performance ratio to them again would take about 20 per cent off an answer that already had it removed.
Rating, area and panel count
Two further conversions come off the rating cleanly, and one that does not.
Area follows directly, because Standard Test Conditions specify 1000 W/m². A module at 21 per cent efficiency produces 210 W per square metre, so a kilowatt-peak needs about 4.8 m² of panel. At 18 per cent it is 5.6, and at the 15 per cent typical of a decade ago it was 6.7.
What that does not include is the roof around the panels. Edge setbacks, access walkways and inter-row spacing on a flat roof commonly add 20 to 40 per cent to the area actually required, and far more if rows must not shade each other.
Panel count needs the module wattage, and there is no default worth offering: residential modules have gone from about 250 W to 440 W and beyond within a decade, so a panel count quoted without a wattage is nearly meaningless.
Peak AC output is the one that is not a conversion. Inverters are routinely undersized against the array — a DC-to-AC ratio of 1.1 to 1.3 is normal — because the array rarely reaches its rating and a smaller inverter spends more of its life near its efficient operating point. The occasional clipped peak costs less than the larger inverter would. That is a design decision, and this page declines to turn it into a factor.
Related calculators
Other energy, power and electrical tools:
EnergyJoules, kilojoules, calories, food Calories, kWh, BTU and therms — with the two calories listed apart, since one is a thousand of the other.
PowerWatts, kilowatts, horsepower and BTU per hour — with mechanical and metric horsepower listed apart, since they differ by 1.4% under one word.
Gas m³ to kWhMeter readings to billed energy for UK, EU, US and Indian networks — with the calorific value as an input, because no factor connects volume to energy on its own.
kVA to kWApparent, real and reactive power with the line current for single and three-phase supplies — power factor required, because kVA and kW are different quantities.
Battery CapacitymAh to watt-hours at any cell voltage, the airline 100 Wh limit, and how many charges a power bank really gives.
IlluminanceLux, foot-candles, lumens, candela and nits — asking for the area, the beam angle or the surface, because three of those pairs have no answer without one.
The first is the modelling tool that actually produces location-specific yields and is what a real feasibility study uses; the second sets out the loss categories a performance ratio is assembled from; the third defines the test conditions the rating is measured at; and the fourth is where the performance-ratio band comes from.
PVGIS — Photovoltaic Geographical Information SystemEuropean Commission Joint Research Centre · verified 2026-09-08 · Location-specific annual specific yield in kWh per kWp for European, African and Asian sites, including the effects of orientation, tilt and local irradiance that make a single national figure inadequate
Solar Energy Technologies OfficeUS Department of Energy · verified 2026-09-08 · The system loss categories applied in US photovoltaic performance modelling — soiling, shading, mismatch, wiring, connections, inverter efficiency and availability — which are the components combined into a performance ratio here
IEC standards for photovoltaic modulesInternational Electrotechnical Commission · verified 2026-09-08 · IEC 61215 and IEC 61853, which define Standard Test Conditions of 1000 W/m² irradiance, 25 °C cell temperature and AM1.5 spectrum, and the energy-rating measurements that exist because those conditions do not represent operation
IEA Photovoltaic Power Systems ProgrammeInternational Energy Agency PVPS · verified 2026-09-08 · International reporting of performance ratios and specific yields for operating systems, which is the basis for the 0.75 to 0.85 band quoted on this page
Conversion note
The specific yields here are representative regional figures for a well-oriented, unshaded array, and they are not a site assessment. Real output depends on latitude, tilt, azimuth, the local horizon, nearby trees and buildings, module and inverter selection, and the weather of the particular year — and any of those can move the answer by tens of per cent. A roof facing away from the equator, or shaded for part of the day, will not reach these figures. Use a location-specific tool such as PVGIS or PVWatts with your own coordinates and roof geometry, and a quotation from an installer who has visited, before committing money to any of it. Nothing here estimates savings, payback, export tariffs or self-consumption, all of which depend on your tariff structure and on when you use electricity rather than on how much the array makes. Panel and inverter specifications, degradation rates and warranty terms come from the manufacturer's datasheet.
Published the kWp to kWh Converter: a solar array's peak rating turned into annual energy for nine regions, with each figure given as a published range rather than a point.
Refuses to produce an energy figure without a location, because there is no kWp-to-kWh factor: specific yield runs from about 800 kWh per kWp in northern Britain to 1700 in the American southwest, a factor of more than two for identical panels.
Explains what a kilowatt-PEAK is: the output at 1000 W per square metre with a CELL temperature of 25 degrees, which is a laboratory condition rather than a weather one, since a dark panel in full sun runs 20 to 35 degrees above the air around it.
States that heat is a LOSS. Output falls by about 0.35 per cent per degree of cell temperature above the rating point, so a 50-degree cell has lost about 9 per cent before anything else in the system has had a turn -- which is why a cold bright April day can out-produce a hot July one.
Decomposes the performance ratio into the six losses it is the product of -- temperature, soiling, wiring and mismatch, inverter, shading, and downtime -- and shows that multiplying them gives 0.798 while adding them gives 0.780, because losses compound rather than sum.
Warns against double-counting: the specific-yield figures already include a performance ratio, since they come from measured systems rather than from panel ratings.
Converts a rating to roof area from the module efficiency, since Standard Test Conditions fix the irradiance at 1000 W per square metre, and to a panel count only when given a module wattage -- which has roughly doubled in a decade and is not a constant.
Declines to give a peak AC figure, because inverters are deliberately undersized against the array and by how much is a design decision rather than a conversion.
Verified by 112 automated cases, asserting that a missing specific yield returns null and that no export offers a location-free annual figure, that the sunniest listed location beats the dullest by more than double, that the temperature factor is exactly one at 25 degrees and falls monotonically above it, and that the performance ratio equals the product of its components.
Add this calculator to your site
Responsive embed — and private: nothing your visitors type leaves their browser.