☀️Solar Position & PV Yield Calculator - Sun Path, Optimal Tilt, Solar Output

How to use Solar Position, Irradiance & PV Yield Calculator

1. 1Choose a city preset or enter latitude, longitude, time zone and altitude, then pick a date
2. 2Drag the time slider or press Play to follow the Sun's elevation, azimuth, path and the shadow length
3. 3On the irradiance tab set the panel tilt and azimuth, and compare horizontal, optimal tilt and dual-axis tracking over the year
4. 4On the PV tab enter system size, losses and the clear-sky fraction to get monthly energy, capacity factor and payback

FAQ

Is the best panel tilt equal to my latitude?

Only roughly. Maximising annual clear-sky irradiance usually gives a tilt a few degrees below the latitude, because summer days are long and the Sun is high, so summer counts for more. Cloudy sites with lots of diffuse light favour an even flatter angle. The monthly optimal-tilt chart shows the winter optimum well above the latitude and the summer one close to flat. A tilt within about 10° of the optimum typically costs only a few percent of annual energy, so roof pitch, row spacing and snow shedding often matter more.

Why do my sunrise and sunset times differ by a minute or two from a weather app?

The tool follows NOAA and uses a zenith angle of 90.833°, which accounts for the Sun's radius and average refraction, as most almanacs do. Small differences usually come from the time zone (standard time is used, daylight saving is not applied), from altitude and the local horizon, and from refraction that changes with temperature and pressure. A 0.1° change in longitude alone shifts the times by about 24 seconds.

How does clear-sky irradiance compare with real irradiance?

A clear-sky model assumes no clouds and only typical scattering and absorption by air, aerosols and water vapour, so it is an upper bound. Real annual totals are usually 40–90% of the clear-sky value: under half in persistently cloudy places and 70–90% in deserts and on high plateaus. The city presets include a rough clear-sky fraction calibrated against measured annual totals, but for real design use hourly data from PVGIS, NASA POWER or a local weather station.

Why does temperature matter for PV output?

Crystalline silicon loses power as the cell heats up, typically 0.3–0.45% per °C. In strong sun the cells run 20–30 °C above the air temperature, so on a 30 °C day at 1000 W/m² they can exceed 60 °C and produce over 10% less than at the 25 °C test condition. The tool estimates cell temperature with the NOCT model and reports the annual temperature loss.

Do higher-efficiency panels produce more energy?

Per kWp, not really: a 1 kWp array of efficient panels and a 1 kWp array of ordinary panels make about the same energy in the same sunshine. Efficiency decides how much area you need, which is why the tool uses it only for the module area. When roof space is the limit, efficient panels let you fit more kWp, and that is what raises the total.