Vicaya GlobalCalculator · Solar · output simulator
What will these panels actually make?
Real sun geometry and atmospheric physics for your location — not a datasheet number multiplied by daylight hours. No email, no quote form, and every assumption is on this page.
This estimate assumes nothing shades the roof. Set a shading figure below if that is not true.
4060 kilowatt hours a year, 1015 per kilowatt peak installed. Best month Jul, worst month Dec.
Does the angle of the roof matter?
The angle your panels sit at, measured up from flat.
Flat panels collect less over a year than tilted ones at most latitudes, because the sun is rarely overhead. The best annual angle is roughly your latitude minus fifteen degrees. Most pitched roofs already sit between 30 and 45 degrees, so in practice the roof decides this rather than you.
A steeper angle trades a little annual output for noticeably more in winter. If you are sizing around dark-month performance rather than the yearly total, steeper usually wins.
Does the direction it faces matter?
The compass direction your panels face.
In the northern hemisphere a south-facing array collects the most over a year; in the southern hemisphere it is north. Turning away from that costs output, but far less than most people assume, and a split east-west roof produces a flatter, longer generation day.
East and west facing roofs lose less than people expect — typically ten to twenty percent, depending on latitude and tilt; the probe above gives the figure for this roof. They also spread generation across the morning and evening, which can be worth more than the total suggests if you are home at those times and your exports pay poorly.
How much difference do more panels make?
The total area of the panels themselves, not of your roof.
A typical modern panel is about 1.9 square metres and around 400 watts. Generation scales directly with total area — double the panels, double the output.
Output scales almost exactly with area, so this is the one input with no diminishing return in the physics. The limits are roof space, budget, and what your inverter and your export terms will absorb.
Are expensive panels worth it?
How much of the light landing on a panel becomes electricity, at test conditions.
Budget crystalline panels run around 18 to 20 percent; premium ones reach 21 to 23. The difference decides how much power fits in a given area, not how good the electricity is.
Efficiency only matters when roof space is the binding constraint. If you have room to spare, more cheap panels beat fewer expensive ones for the same money.
How much does shade cost me?
How much of the sky your panels can actually see.
This estimate assumes nothing shades your roof. That is almost never exactly true. A shaded panel still generates — diffuse light reaches it from across the whole sky — but direct sun is what carries most of the output, so losing morning or afternoon sun to an obstruction matters more than the shaded fraction alone suggests.
Shading is the single largest source of error in a rooftop estimate, and the only input here we cannot infer for you. A chimney or a neighbouring tree can cost more than choosing the wrong panels ever would.
Best annual angle here: 23–37° — anything in that range is within 0.5% of the best
That is 4.00 kWp of panels covering about 19 m², working out at 1.90 m² per panel at 21.0% efficiency. What is kWp?
Where the energy goes
Show the loss breakdown as a table
| Stage | Loss | Of the step before |
|---|---|---|
| Nameplate | 4714 | — |
| Reflectance & low light | -151 | 3.2% |
| Temperature | -24 | 0.5% |
| Soiling | -91 | 2.0% |
| DC wiring | -89 | 2.0% |
| Mismatch | -87 | 2.0% |
| Inverter | -171 | 4.0% |
| Downtime | -41 | 1.0% |
| Delivered | 4060 | 86.1% |
Month by month — your solar production
Show these figures as a table
| Month | kWh |
|---|---|
| Jan | 109 |
| Feb | 164 |
| Mar | 327 |
| Apr | 479 |
| May | 519 |
| Jun | 533 |
| Jul | 553 |
| Aug | 480 |
| Sep | 401 |
| Oct | 253 |
| Nov | 151 |
| Dec | 90 |
| Total | 4060 |
Where the sun sits in your sky
This is optional — the figures above do not depend on it. It answers one question the headline numbers answer badly: at this time of year, is the sun actually where my roof is pointing? Move either scrubber and the sentence follows.
Jun, 12:00 solar time: the sun is 62 degrees above the horizon in the south. The panels meet it at 7 degrees off square, collecting 99% of what a panel aimed straight at it would.
Jun, 12:00 solar time: the sun is 62 degrees above the horizon in the south. The panels meet it at 7 degrees off square, collecting 99% of what a panel aimed straight at it would.
Show the sun's position through the day as a table
| Hour | Height | Bearing | Panel response |
|---|---|---|---|
| 04:00 | 1° | 53° north-east | 0% |
| 06:00 | 18° | 75° east | 11% |
| 08:00 | 36° | 98° east | 55% |
| 10:00 | 53° | 130° south-east | 88% |
| 12:00 | 62° | 180° south | 99% |
| 14:00 | 53° | 230° south-west | 88% |
| 16:00 | 36° | 262° west | 55% |
| 18:00 | 18° | 285° west | 11% |
| 20:00 | 1° | 307° north-west | 0% |
What do these units mean?
What do kWp and kWh mean?
- kWh — kilowatt-hour
- A unit of energy, and the thing your electricity bill charges you for. A 1,000-watt heater running for one hour uses one kWh. A typical home uses somewhere between 2,000 and 10,000 kWh a year depending on where it is and how it heats.
- kWp — kilowatt-peak
- A unit of capacity — how big the solar array is, not how much it makes. It is the output the panels would produce under standard test conditions: bright, cold and perfectly aimed. Real roofs rarely see those conditions, which is why a 4 kWp array does not generate 4 kW for most of the day. One modern panel is roughly 0.4 kWp, so 4 kWp is about ten panels.
- Putting them together
- kWp is the size of the system; kWh is what it produces over time. The ratio between them — kWh generated per kWp installed, per year — is the honest way to compare locations, because it strips out how big the system happens to be. It runs from roughly 700 in cloudy high latitudes to over 1,800 in sunny deserts.
What this assumed
| Assumption | Value | Why |
|---|---|---|
| Temporal resolution | 8760 intervals | Hourly across a full year |
| Module temperature coefficient | -0.38%/°C | Panels lose output when hot |
| Nominal operating cell temp | 45°C | Standard rating condition |
| Soiling | 2% | Dust and dirt, annual average |
| DC wiring | 2% | Resistive loss before the inverter |
| Module mismatch | 2% | Panels never perform identically |
| Inverter efficiency | 96% | Weighted, not peak |
| Downtime | 1% | Faults and maintenance |
| Ground reflectance | 0.20 | Light bouncing up off the ground |
| Snow | Not modelled | Declared rather than silently ignored |
How much to trust this
This model is compared against PVGIS, the European Commission’s reference tool, across 144 fixtures spanning eight sites on five continents. The measured deviation is published rather than summarised: see the methodology page for the figures by climate, latitude and orientation, including where the model is known to run high.
Agreement with a reference model means this implementation reproduces an independent one of the same physics. It is not proof that either matches a real roof, and this page does not claim that.
Frequently asked questions
How much electricity does a solar panel produce per day?
It depends on the panel’s rating AND your location’s sun, not the watts alone. A panel only makes its rated output under 1,000 W/m² — roughly clear midday sun — so it runs at full strength for only a few hours. This calculator walks a full year of sun geometry and atmosphere to give the real kWh per day, month and year, instead of multiplying nameplate watts by daylight hours.
Use it to estimate solar panel output for your location: the expected kWh per day, per month and per year for the panels you enter.
Why is my solar output lower than the panel’s rated watts?
Rated watts are a lab figure at 1,000 W/m² and 25 °C. In the real world the sun is weaker most of the day, panels run hotter than 25 °C — which cuts output — and inverter, wiring and soiling losses take a further share. This tool models all of it, so its figure is what you would actually meter, not the datasheet number.
How many kWh does a solar system produce a year?
It swings with latitude, tilt, orientation and climate, so there is no single number that holds everywhere — a cloudy maritime site and a sunny desert one differ by more than half. Rather than quote an average, this calculator computes the annual and monthly kWh for your own location and array.
Is a solar output calculator the same as a solar power output calculator?
On this page, yes. Output is reported as energy — kilowatt-hours over a day, a month and a year — because that is what a meter records and a bill charges for. The panel’s rated watts are power, an instantaneous figure the array only reaches under test conditions; the kWh here is what those watts become once the sun’s path, the temperature and the losses on the way to the meter are applied.
Does the calculator use my real location’s weather?
Yes — it runs the sun’s path and atmospheric physics for the coordinates you enter, validated against PVGIS, so the output reflects your actual climate rather than a national average.