Solar Panel Tilt Angle Calculator: Best Angle for Solar Panels at My Location

Who Can Use This Solar Panel Tilt Angle Calculator?

Home owners planning a roof or ground array, installers who need a quick check, off-grid cabin owners, RV and boat owners, teachers and students all use it. If you can find your latitude, you can use it. The calculator also helps if you already own panels and want to know how much energy a small change of angle would gain or lose. The PV angle calculator app is also handy in a classroom, because it shows how the sun's path changes the best angle month by month. If you do not know your latitude, find it first with the GPS Coordinates Finder.

Key Features

• A free PV angle calculator app that runs in any browser, with nothing to install.
• Use your current location, search an address, click the map or type latitude and longitude.
• The hemisphere is detected automatically and the panel direction is set to true south or true north.
• Optimal tilt angle for the whole year, for summer and for winter.
• A month-by-month table with day length, noon sun height, the best tilt and the energy at your angle.
• Three sky settings (sunny, average, cloudy) so the answer fits your climate.
• The map has no basemap by default. A bold switch turns on street, satellite or terrain when you need it.
• Download a PDF summary with a letterhead and a maplity.com watermark.
• A table of summer, winter and whole-year angles for 100 famous cities in the USA and Europe.

Why the Angle Matters

Sunlight that hits a panel at a slant spreads over a larger area, so each square centimetre gets less energy. The loss follows the cosine of the angle between the sunlight and a line drawn straight out of the panel. If the sun is 60 degrees away from that line, the panel receives only half of the light it would receive facing the sun directly, because cos 60° = 0.5. The goal of tilting is to keep the sun as close to straight-on as possible, for as many hours and as many months as possible.

How the Sun Moves During the Year

The Earth's axis is tilted by about 23.45 degrees. Because of this, the point on Earth where the sun is directly overhead moves between 23.45°N in June and 23.45°S in December. This angle is called the solar declination. At noon the sun's height above the horizon at latitude φ is:

In New York (latitude 40.7°N) the noon sun reaches about 73 degrees above the horizon in June and only about 26 degrees in December. Days are 14.9 hours long in June and 9.1 hours long in December. Everything about summer and winter angles comes from this swing.

Solar Panel Tilt Angle Formula

These formulas show how to calculate solar panel tilt angle. They are used in installation guides and in this calculator:

Here φ is your latitude in degrees (use the absolute value in the Southern Hemisphere) and β is the tilt from horizontal. The last two rules are for the peak of the season, not for the whole half-year, which is why the half-year angles in the tables below are lower for summer and close to the rule for winter.

How to Calculate Solar Panel Tilt Angle by Hand

1. Find your latitude. For New York it is 40.7° N.
2. Pick the day. On 21 June the declination is +23.45°, at the equinoxes it is 0°, and on 21 December it is -23.45°.
3. Subtract: on 21 June the noon tilt is |40.7 - 23.45| = 17.3°. At the equinoxes it is 40.7°. On 21 December it is |40.7 + 23.45| = 64.2°.
4. For a fixed panel, use the annual rule: 3.7 + 0.69 x 40.7 = 31.8°.
5. Face the panel true south (true north in the Southern Hemisphere).

The hand method points the panel at the noon sun. It ignores morning and evening sun, day length, the atmosphere and clouds. That is why the calculator above uses a radiation model: for New York it gives 32° for the whole year, which is close to the hand result.

Why This Calculator Uses a Radiation Model

The model follows a standard method from solar engineering textbooks. For each month it does five things:

1. It calculates the sunlight above the atmosphere from your latitude and the sun's declination.
2. It reduces that light for the path through the atmosphere. Low winter sun crosses more air, so more light is lost.
3. It applies your sky setting, which represents how often clouds block the sun in your climate.
4. It splits the light into direct sunbeams and diffuse light from the whole sky.
5. It adds up the light that reaches a panel at every tilt from 0 to 90 degrees, then picks the tilt with the highest total for the period.

Diffuse light does not depend much on tilt, and clouds increase its share. So cloudy places get lower optimal angles than sunny places at the same latitude.

Solar Panel Tilt Angle Chart by Latitude

This solar panel tilt angle chart shows the optimal angle for panels facing the equator, for an average climate. The last column is the annual rule of thumb from the formula above, so you can compare it with the radiation model. Angles below 10° are shown as 10° so rain can wash the glass. For the Southern Hemisphere use the latitude without its sign, and swap the seasons: summer runs from October to March.

Why Summer Angles Are Low

In summer the noon sun is high in the sky, and days are long. At 40°N the sun rises well to the north-east, about 58 degrees east of north, and sets in the north-west. A steep south-facing panel is nearly edge-on to that early and late sun. A flatter panel catches it. Summer light is also a little more direct, but a large part of it is still diffuse, and diffuse light reaches a flat panel from the whole sky.

What the Numbers Say

For the summer half-year (April to September in the north) the calculator gives 13° at 40° latitude and 22° at 50° latitude. That is roughly one third to one half of the latitude. If you only care about the peak of summer, the best month is June, when the best tilt for New York is about 0°, close to flat. The old rule "latitude minus 15 degrees" is a little steep for the whole half-year, but it is a safe choice for a fixed summer tilt.

Practical Tips for Summer

• Do not go below 10 degrees. Flatter panels keep water and dust on the glass.
• Hot panels make less power. Silicon panels lose about 0.3 to 0.4 percent of power for each degree Celsius above 25°C, so leave a gap behind the panel for air.
• In the Southern Hemisphere the summer angle applies from October to March.
• Near the equator the sun is almost overhead, so a small tilt of 10 to 15 degrees works all year.

Why Winter Angles Are Steep

In winter the noon sun is low. At 40°N on 21 December it stands only about 26 degrees above the horizon. To face that low sun, the panel must be tilted steeply, close to 64 degrees for the noon sun alone. A steep tilt also reduces the light that bounces off the glass at a shallow angle, and it makes dust and water run off. The best angle for solar panels in winter is usually your latitude plus 10 to 15 degrees.

What the Numbers Say

For the winter half-year (October to March in the north) the calculator gives 54° at 40° latitude and 62° at 50° latitude. In December, the darkest month, the best tilt for New York is about 65°. Winter energy is small even at the best angle, so the gain comes from making a low number a little higher.

Snow, Short Days and Off-Grid Systems

• Snow slides off steep panels. Fresh snow on the ground reflects 60 to 90 percent of the light, and steep panels collect much of it.
• Off-grid systems must survive the worst month. If you run a cabin, a boat or a pump from batteries, choose the winter angle, so the darkest month sets your design.
• Grid-tied homes care about yearly energy, so the whole-year angle is usually better.
• Very steep frames face more wind. Follow the mount maker's limits and your local building code.

Choose One Fixed Angle

A fixed panel needs one angle that works in every season. The calculator finds the angle that maximises the total energy over the year. It is lower than your latitude because summer brings more energy than winter. The curve is flat near the top: for New York, a 5 degree error costs only about 0.3 percent and a 10 degree error about 1.1 percent. Pick the closest angle that your roof or frame allows.

Adjust with the Seasons

The table shows what New York gains from changing the tilt during the year, compared with one fixed angle.

Two changes a year capture almost all of the possible gain. Four changes add very little. Monthly changes are only worth the work for a research setup or a tracker.

Which Tilt for Which Goal

Which Direction Should Solar Panels Face?

Face the panels toward the equator: true south in the Northern Hemisphere and true north in the Southern Hemisphere. Use true direction, not a compass reading, because magnetic north differs from true north by up to about 20 degrees depending on where you are. As a rough guide, a direction error of 15 degrees costs 1 to 2 percent of yearly energy, 30 degrees costs 3 to 5 percent and 45 degrees costs 8 to 12 percent. An east or west facing roof loses 15 to 20 percent, but it produces more in the morning or in the evening, which can suit homes that use most power at those times.

Solar Panel Tilt Angle in 50 Cities in the USA

Solar Panel Tilt Angle in 50 Cities in Europe