Optimal Solar Panel Angle by Latitude and Season

The best fixed tilt for solar panels is roughly equal to your latitude. A panel in New York at 41°N should sit near 41°; one in Phoenix at 33°N near 33°. The US Department of Energy Federal Energy Management Program puts the optimal tilt at the local latitude, and the PVWatts documentation calls it a common rule of thumb. Across NASA POWER's seven US sites, latitude tilt collects 96.55% to 99.79% of the yearly energy at NASA's modelled optimal tilt, and modelled sky conditions put the optimum lower: NASA POWER's modelled optimal tilt for New York is 31.0°, below the 41° the rule gives. For the seasons, a printed rule of thumb subtracts 15° in summer and adds 15° in winter. The tilt guide at solarpaneltilt.com says books and articles on solar energy often give the advice of latitude plus 15 degrees in winter and minus 15 degrees in summer, and a 2011 conference paper (arXiv 2004.12252) computes seasonal tilts of 16° for summer and 48° for winter at 32.7°N, which is 16.7° below and 15.3° above the latitude (32.7 - 16 = 16.7; 48 - 32.7 = 15.3). Our solar panel angle calculator takes the two offsets as inputs, its summer and winter adjustments, with 15° as the default for each. Check your results against your product data or a licensed professional before acting.

The quick reference below sets a fixed, year-round tilt by latitude. Pick the row closest to your location and tilt your array to roughly that angle. Each tilt is the solar panel angle calculator's Annual result at that latitude; south of the equator the same number of degrees applies, with the panel facing north.

These figures are starting points for a permanent install. The table later in this guide gives summer and winter angles, and the yearly gain from switching between them, at seven NASA POWER sites for arrays you can adjust.

The optimal solar panel angle depends on one number above all others: your latitude. A panel tilted to match your latitude faces the sun more directly across the year, capturing more energy than a flat or arbitrarily angled installation. In NASA POWER's 2001-2020 model for seven US sites, from Miami (25.76°N) to Anchorage (61.22°N), a flat panel collects 5.17% to 15.02% less energy over the year than one at NASA's modelled optimal tilt, and 4.97% to 12.72% less than one tilted at the latitude.

Our solar panel angle calculator takes your latitude, a season (annual, summer, winter or spring-fall) and the summer and winter adjustments, and returns the tilt angle, the direction the panel faces and the season. This guide explains the underlying geometry and helps you decide whether seasonal adjustment, fixed tilt, or tracking makes sense for your situation.

Why Tilt Angle Matters

How much sunlight a panel receives depends on where it is and how it is tilted. NASA POWER's 2001-2020 climatology prints the yearly average for a panel at the latitude tilt in kWh per square metre a day, the same figure as peak sun hours: from 2.923 at Anchorage to 6.4462 at Phoenix across the seven sites captured from NASA POWER. A panel at the wrong angle collects less of it. In Phoenix (33.45°N), NASA prints 6.4462 at the latitude tilt, 6.3674 at latitude minus 15° and 6.1862 at latitude plus 15°: 15° too flat costs 0.0788 a day and 15° too steep 0.2600. Entered as 6.45, 6.37 and 6.19 peak sun hours for a 6 kW system (15 x 400 W panels) with 14% losses, the solar panel output calculator returns 11,006, 10,870 and 10,562 kWh a year: 136 and 444 kWh less than at the latitude tilt (11,006 - 10,870 = 136; 11,006 - 10,562 = 444). In Seattle (47.61°N), NASA prints 3.7838 at the latitude tilt, 3.8914 at latitude minus 15° and 3.487 at latitude plus 15°: there the flatter panel collects 0.1076 more a day, and the steeper one 0.2968 less. Entered as 3.78, 3.89 and 3.49 peak sun hours on the same system, the calculator returns 6,450, 6,638 and 5,955 kWh a year: 188 kWh more and 495 kWh less than at the latitude tilt (6,638 - 6,450 = 188; 6,450 - 5,955 = 495).

If you want to understand how tilt affects your total energy harvest and system economics, our solar panel payback period guide walks through the financial math.

Solar panels produce the most electricity when sunlight hits them at a 90-degree angle (perpendicular to the panel surface). As the angle of incidence moves away from perpendicular, energy capture drops following a cosine relationship. At 30 degrees from perpendicular, the cosine is 0.866, so you lose about 13% of potential output. At 60 degrees, the cosine is 0.5, so you lose 50%.

The sun's height in the sky changes with both season and latitude. In summer, the sun rides high; in winter, it stays low. The ideal panel angle compensates for this by tilting the panel to face the sun's average position. At higher latitudes the sun stays lower year-round, so panels need steeper tilts.

For a fixed installation (no seasonal adjustment), the general rule is: tilt angle = latitude. This splits the difference between the high summer sun and the low winter sun. It is not perfect for either season, and NASA POWER's model puts the yearly optimum lower, but across its seven sites a panel at the latitude tilt collects 96.55% to 99.79% of the yearly energy at NASA's modelled optimal tilt.

Worked Example: Denver, 39.74°N

A homeowner in Denver, Colorado installs a 6 kW south-facing array of 15 x 400 W panels. NASA POWER's 2001-2020 model for Denver (39.74°N) prints the yearly average sunlight on four south-facing surfaces in kWh per square metre a day; the three tilted ones are the angle calculator's summer, annual and winter tilts at 39.7°N with its default 15° adjustments. Entered as peak sun hours, rounded to two decimals, with 14% losses, each gives a yearly output in the solar panel output calculator:

Flat (0°): NASA prints 4.9198; the calculator returns 8,395 kWh/year at 4.92. The panel never faces the sun squarely and catches rain, snow and dust.

Latitude minus 15° (24.7°): NASA prints 5.5951, 13.73% more than flat; the calculator returns 9,556 kWh/year at 5.60. A shallower angle, between the 4/12 and 8/12 roof pitches worked out below (18.43° and 33.69°).

Latitude (39.7°): NASA prints 5.6369, 14.58% more than flat; the calculator returns 9,624 kWh/year at 5.64. The most of the four. NASA's modelled annual optimum sits lower, at 34°, with 5.6563, 14.97% more than flat.

Latitude plus 15° (54.7°): NASA prints 5.3818, 9.39% more than flat; the calculator returns 9,180 kWh/year at 5.38. Better than flat but below the latitude tilt over the year: it captures more winter sun at the cost of summer production. It makes sense only if you need the most winter output (an off-grid cabin with winter heating loads).

The gap between flat and the latitude tilt is 1,229 kWh/year (9,624 - 8,395). At an example rate of $0.14 per kWh (an assumption for illustration, not a measured figure), that is about $172 a year (1,229 x $0.14 = $172.06).

Optimal Angles by Latitude and Season

This table gives, for the seven NASA POWER sites, the fixed tilt and the summer and winter tilts the solar panel angle calculator returns at each site's latitude to one decimal, with its default adjustments (summer: latitude minus 15°; winter: latitude plus 15°). All angles are measured from horizontal.

The "Annual Gain from Seasonal Adj." column comes from NASA POWER's 2001-2020 monthly series for each site: two positions a year, latitude minus 15° from April to September and latitude plus 15° from October to March, collect that much more energy over the year than a fixed panel at the latitude tilt, with each month weighted by its days. Setting the tilt to NASA's modelled optimum every month is the upper bound: 4.44% to 9.15% more across the seven sites. The smallest gain is at Miami and the largest at Anchorage, but the gain does not rise in step with latitude: Phoenix gains more than New York.

The seasonal columns follow the printed rule of thumb: set the summer tilt to your latitude minus 15° and the winter tilt to your latitude plus 15°. A solar tilt analysis by Charles Landau refines this for latitudes between 25° and 50°, putting the best year-round fixed tilt at the latitude times 0.76 plus 3.1° (0.76 x 40 + 3.1 = 33.5° at 40°N rather than a flat 40°). The simple tilt-equals-latitude rule is the right starting point: at 40°N the refinement sits 6.5° below it (40 - 33.5 = 6.5), and in NASA POWER's model for Denver (39.74°N), where the modelled optimum is 34°, the latitude tilt still collects 99.66% of the optimum's yearly energy. Local weather, horizon obstructions, and snow also move the ideal angle.

Southern Hemisphere: Same Tilt, Opposite Direction

The latitude rule works the same way south of the equator, with one change: panels face true north instead of true south. At about 34 degrees south, the latitude of Sydney and Cape Town, you enter 34 and the angle calculator's Annual tilt is 34°; at about 44 degrees south, Christchurch's latitude, you enter 44 and it is 44° (the calculator takes the latitude in degrees north). The seasons flip too, so the two-position schedule above swaps its halves: the flatter summer angle (latitude minus 15°) applies from October to March and the steeper winter angle (latitude plus 15°) from April to September. Off-grid sites in Chile, Argentina, and New Zealand follow the same math as their Northern Hemisphere counterparts at the matching latitude. An array that mistakenly faces south below the equator loses yield, as a north-facing roof does in the north.

Fixed Tilt vs. Seasonal Adjustment vs. Tracking

Three mounting strategies exist, each with different cost-benefit profiles.

Fixed tilt at latitude has no moving parts, no maintenance and no adjusting hardware to buy. You give up the gain from seasonal adjustment, which in NASA POWER's monthly series at the seven sites is 3.37% to 5.16% of the year's energy at a fixed latitude tilt, but avoid the complexity and labor of climbing on the roof twice a year. For a grid-connected home, fixed tilt is often the right choice: the payback on the extra effort of seasonal adjustment rarely justifies it when electricity is cheap and plentiful from the grid.

Seasonal adjustment (changing the tilt a few times a year) makes sense for ground-mounted systems with easy access to the mounting hardware, especially for off-grid systems where every kilowatt-hour counts. Adjusting between summer and winter angles adds 3.37% to 5.16% over the year in NASA POWER's series at the seven sites (two positions: latitude minus 15° from April to September, latitude plus 15° from October to March). On a 10 kW system of 25 x 400 W panels at Kansas City's 5.18 peak sun hours (NLR's PVWatts annual print at tilt 39, roof mount, rounded to two decimals) and 14% losses, the solar panel output calculator returns 14,732 kWh a year, so 3.37% to 5.16% is about 496-760 kWh/year (14,732 x 3.37% = 496; 14,732 x 5.16% = 760), or about $74-$114 at an example rate of $0.15 per kWh, an assumption for illustration, not a measured figure (14,732 x 3.37% x $0.15 = $74; 14,732 x 5.16% x $0.15 = $114). This matters more for off-grid systems where every kWh counts and winter production is the bottleneck. Use the solar panel size calculator to find the right array size for your seasonal production needs.

Single-axis trackers follow the sun from east to west throughout the day and collect more than a fixed tilt; we hold no measured figure for the gain at a given site. Dual-axis trackers also follow the sun's seasonal height. A study by Morcos, cited in the arXiv paper above, found that changing the panels' azimuth and tilt daily to the optimum in Egypt gave 29.2% more annual solar radiation than a fixed panel tilted at the latitude. Trackers add cost and have moving parts that require maintenance. They pay off mainly on large ground-mount installations or high-value-per-kWh applications (off-grid, commercial, agriculture). For a residential rooftop, weigh the tracker's cost against the value of the extra production; we hold no measured figure for either.

Practical Installation Considerations

Your roof pitch might already be close enough. A roof pitch converts to an angle by arctan(rise / run): a 4/12 pitch is 18.43° and an 8/12 pitch is 33.69°. Near 35°N, a south-facing roof pitched at 30° sits 1.5° below NASA POWER's modelled optimal tilt for Albuquerque (35.08°N), 31.5°, and in NASA's model there even a panel 15° flatter than the latitude collects only 1.19% less energy over the year than one at the latitude tilt. Spending extra on tilt-adjusting mounts for that is rarely worth the cost.

Orientation matters as much as tilt. A south-facing panel at a suboptimal tilt produces more than a perfectly tilted east or west-facing panel. If your best roof face points east or west, expect less yearly production than from a south face at any tilt; we hold no measured figure for how much at your site. Our solar output calculator takes panel wattage, peak sun hours, system losses and the number of panels and returns daily, monthly and yearly output; orientation and tilt enter it only through the peak sun hours you enter.

Snow shedding favors steeper tilts. In snowy climates, steeper panels shed snow more readily. Flatter installations accumulate snow that blocks production until it melts. As our solar panel output guide explains, even partial obstruction cuts production disproportionately due to how cells are wired in series. If you are in a region with heavy winter snow, biasing the tilt a few degrees steeper than the annual optimum can improve net winter production even though the angle is not geometrically ideal.

Wind loading increases with tilt. Steeper panels catch more wind. Building codes and structural engineering requirements may limit tilt angles based on your local wind zone, especially for ground mounts and flat-roof ballasted systems. Check local building requirements before designing a steep-tilt installation. The solar time calculator takes clock time, longitude, standard meridian and day of year and returns the Solar Time (apparent solar time), solar noon in clock time, the EoT Offset (the equation of time, in minutes) and the Lon Correction (the longitude correction, in minutes).