# SolarPosition.org

> Free solar position calculator and off-grid solar planner. For any point on Earth it gives the sun's azimuth and elevation, sunrise, sunset, twilight and solar noon, a sun path diagram, the best solar panel tilt (year-round, seasonal and off-grid) and peak sun hours by month. Sun positions use the NREL Solar Position Algorithm (±0.0003°); yields use NASA POWER climate data and a PV model tested against PVGIS (within 3%).

Key facts:
- An off-grid solar array should be tilted for its darkest month, not for the year. Between about 45° and 55° latitude that is roughly 67–76° from horizontal, facing the equator; near 40° it is 50–65°; above 55° it approaches 80–90°.
- Tilting to 70° typically costs 10–15% of the yearly energy at mid-latitudes but gives 15–20% more in December than the year-round optimum.
- One peak sun hour = 1 kWh of sunlight per m². 1 kWp × 4 peak sun hours ≈ 3.2–3.5 kWh after losses.
- Noon sun elevation = 90° − |latitude − declination|; declination ranges ±23.44°.

## Tools
- [Solar Position Calculator – Live Sun Position & Sun Path Map](https://solarposition.org/): Solar position for any place and time on a live map: sun azimuth and elevation, sun path, sunrise, sunset and shadows, plus the best solar panel angle and off-grid sizing.
- [Off-Grid Solar Calculator: Size Panels & Batteries for Winter](https://solarposition.org/off-grid-solar-calculator/): Size an off-grid solar system for your location: array watts, number of panels, battery kWh and Ah, and charge controller current, designed for your darkest month.
- [Solar Panel Angle Calculator: Best Tilt by Location & Latitude](https://solarposition.org/solar-panel-angle-calculator/): Best solar panel tilt angle for your location from real climate data: year-round, summer, winter and off-grid optimum, plus a table of angles by latitude.
- [Peak Sun Hours Calculator: Sun Hours by Month for Any Location](https://solarposition.org/peak-sun-hours/): Peak sun hours for any location, month by month, on a flat and a tilted surface, from NASA POWER climate data. Includes a table for 20 cities.
- [Sun Path Diagram Generator for Any Location and Date](https://solarposition.org/sun-path-diagram/): Draw a polar sun path diagram for any place and date: solstice and equinox paths, hour marks, sunrise and sunset azimuths. Free, printable, accurate to 0.001°.
- [Solar Panel Row Spacing Calculator: Avoid Winter Shading](https://solarposition.org/solar-panel-row-spacing/): Calculate the distance between rows of solar panels so they do not shade each other on the winter solstice, for any tilt, panel length and latitude.
- [Off-Grid Battery Bank Calculator: Capacity in kWh and Ah](https://solarposition.org/battery-bank-calculator/): Calculate off-grid battery capacity from daily use, days of autonomy, depth of discharge, temperature and system voltage, for LiFePO4 and sodium-ion (Na-ion) packs.

## Guides
- [Off-Grid Solar Panel Angle: Why 60–70° Beats the Textbook Tilt](https://solarposition.org/off-grid-solar-panel-angle/): Why off-grid solar panels should be tilted steeper than grid-tied ones: winter yield, snow shedding and albedo, with computed numbers for 14 cities and a tilt calculator.
- [Methodology: How SolarPosition.org Calculates the Sun and Solar Yield](https://solarposition.org/methodology/): The algorithms and data behind SolarPosition.org: NREL SPA, Ineichen clear sky, Hay-Davies transposition, Faiman temperature model, NASA POWER and ICON-EU.

## Learn
- [Learn: Sun Geometry and Off-Grid Solar, Explained](https://solarposition.org/learn/): Short, exact explanations of solar azimuth, elevation, declination, the equation of time, the angle of incidence and the numbers behind off-grid solar.
- [Solar Azimuth Angle: Definition, Formula and Examples](https://solarposition.org/learn/solar-azimuth/): What the solar azimuth angle is, how it is measured, the formula to calculate it and how it changes through the day and the year.
- [Solar Elevation Angle: Formula, Calculator and Examples](https://solarposition.org/learn/solar-elevation-angle/): The solar elevation (altitude) angle explained: formula, noon elevation by latitude, refraction, and what it means for shadows and solar panels.
- [Solar Declination Angle: Formula and Values Through the Year](https://solarposition.org/learn/solar-declination/): The solar declination explained: why it changes, its formula, values for every month and how it sets the sun's noon height at your latitude.
- [Equation of Time: Why Solar Noon Drifts Through the Year](https://solarposition.org/learn/equation-of-time/): Why the sun is up to 16 minutes fast or slow against the clock, how the equation of time is computed and how to find solar noon.
- [Angle of Incidence on Solar Panels: Formula and Cosine Loss](https://solarposition.org/learn/angle-of-incidence/): How the angle between sunlight and a solar panel is calculated, how much energy the cosine loss costs, and how tilt and orientation change it.
- [Solstice and Equinox Dates and Exact Times, 2025–2034](https://solarposition.org/learn/solstices-and-equinoxes/): Exact dates and times (UTC) of every solstice and equinox from 2025 to 2034, computed with the NREL Solar Position Algorithm, and what they mean for the sun.
- [Snow, Albedo and Steep Solar Panels: Free Winter Energy](https://solarposition.org/learn/snow-and-albedo/): How ground reflection (albedo) adds energy to tilted solar panels, why snow makes steep off-grid arrays produce more, and how much to expect.
- [Days of Autonomy: How Much Battery an Off-Grid System Needs](https://solarposition.org/learn/days-of-autonomy/): What days of autonomy mean for off-grid solar, how many you need by climate, and how autonomy trades off against array size.

## Data
- [Sun and solar data for 31,679 places](https://solarposition.org/solar/): one page per town of 15,000+ people in 244 countries — today's sun, sun path, monthly sunrise/sunset, best tilt, off-grid yield at 70°, 48-hour solar forecast in Europe.

Contact: contact@solarposition.org