How to Install a Solar Panel for the Most Power: Direction, Tilt and Shade

Face the panel toward the equator: south if you live north of it, north if you live south of it. Tilt it up from flat by a little less than your latitude. Then keep all of it out of shade from mid-morning to mid-afternoon. Those three choices decide most of what a panel collects; everything else is worth a few percent.

The three aren’t equal. Shade on a corner of the panel can cost a third of its output. Facing east or west instead of toward the equator costs a fifth to a quarter. A tilt a few degrees off costs almost nothing. The planner below works out the direction and tilt for your location, and the rest of this guide explains where its numbers come from.

Tap the map where the panel will go, or let your browser share your location. The planner shows which way to face the panel, how far to tilt it, and what a magnetic compass reads when it points the right way. Step through the months to see how high the noon sun climbs, how long the day is and where the sun rises and sets; the lines on the map follow along. The recommendations at the bottom change with your latitude.

The all-year tilt is the fit Jacobson and Jadhav published from the best fixed angles in every country. The compass reading comes from the World Magnetic Model, and the rest is the geometry of the sun, worked out for the 15th of the month. Your location is used in your browser and isn’t sent to Watt48.

A panel collects the most when sunlight hits it square on. Light arriving at a slant spreads over more of the panel, so each cell gets less: 30° off square, a panel catches 87% of the direct beam, and 60° off, only half. The guide to solar charging covers the other things that cut a panel’s output.

Where square on points depends on the sun’s path. The sun crosses the sky from east to west and is highest at solar noon, when it stands due south of you in the Northern Hemisphere and due north in the Southern. How high it climbs depends on your latitude and the season. At the March and September equinoxes the noon sun stands at 90° minus your latitude. At midsummer it is 23.4° higher, and at midwinter 23.4° lower, because that is how far the Earth’s axis is tilted.

A panel faces that sun squarely when it is tilted 90° − 27.5° = 62.5° from flat. In June the same sun stands at 74.3°, and the square-on tilt is under 16°. A fixed panel can’t follow that swing, so its best angle for the year is a compromise between the two.

Point the front of the panel toward the equator. In the US, Canada, Europe and most of Asia that means south; in Australia, New Zealand, southern Africa and most of South America, north. Facing the equator puts the panel square to the sun around midday, when the sunlight is strongest.

Direction matters more than tilt, but small errors cost little. In Kansas City, turning the panel 45° away from due south, to face southeast or southwest, costs 6% to 8% of a year’s output. Facing due east or west costs a fifth to a quarter. Facing away from the equator costs about half, and more the steeper the panel.

True north and the compass

The direction to face is true south, or true north below the equator: the line toward the geographic pole, as on a map. A magnetic compass points to the magnetic pole instead, and the angle between the two, called declination, depends on where you are. Magnetic north is about 15° east of true north in Seattle and 14° west of it in Boston, so a compass held on 180° there leaves a panel 15° or 14° off true south.

The planner shows what a compass should read at your spot. Many phone compass apps can show true north instead; look for the setting. Either way, precision isn’t needed: in Kansas City, a panel 15° off due south lost about 1% of a year’s output.

Close to the magnetic poles, in the Canadian Arctic and parts of Antarctica, a compass may be well off or useless. There, line the panel up with the sun at solar noon, when it stands due south, or due north below the equator.

When the best direction isn’t free

On a roof, the roof decides. A slope facing southeast or southwest is nearly as good as one facing south. An east or west slope still collects three-quarters or more at a moderate pitch, and on a flat roof the direction stops mattering. If due south puts the panel in a tree’s afternoon shadow while southeast keeps it clear, take the clear sun: the turn costs well under a tenth, and shade can cost a third or more while it lasts.

For a panel fixed at one angle all year, the best tilt is close to your latitude, and usually a few degrees less. Geometry alone would say equal to the latitude, but two things pull it lower. Clouds scatter light across the whole sky, and a flatter panel sees more of the sky. And summer days are longer, so an angle that favors the high summer sun collects more over a year.

The planner uses the curves Jacobson and Jadhav fitted in 2018 to the best fixed angles for every country in the world. Checked against PVGIS, the European Commission’s solar model built on satellite and weather records, the fitted angle collected 98.9% to 100% of the best possible at all eight places we tried.

The farther from the equator, the more a tilt is worth. Near the equator a flat panel gives up almost nothing; at Kansas City it gives up a sixth, and at Anchorage more than a quarter.

Close enough is fine

Near the best angle, the output barely changes. In Kansas City, 30° and 45° each collected 99% of what the best angle, 37°, did. Use the nearest notch on a bracket, or the pitch of the roof, if it is within about 10° of the planner’s figure. If you get snow, err on the steep side.

Keep at least 10° of tilt anywhere. Rain then runs off and rinses the glass, where a flatter panel holds puddles that dry into dirt. Near the equator, where the best angle is almost flat, 10° costs about 1%.

A mount you can adjust lets the panel follow the sun’s height through the year: steeper in winter, flatter in summer. In Kansas City, changing the angle twice a year, to 15° from April to September and 55° from October to March, collected 4.7% more than the best fixed angle. Changing it every month added 5.9%.

Two things stand out. Summer wants a flatter panel than the noon sun suggests: in June and July the sun rises in the northeast and sets in the northwest, and a flat panel catches the morning and evening light that a south-facing tilt turns its back on. And winter rewards a steep angle, which also sheds snow sooner. The planner’s month view shows the noon sun and the sunrise and sunset directions for any month where you are.

A folding panel on its stand can beat any fixed mount, because you can move it. Most of the gain comes from turning it to face the sun’s direction a few times a day. Jacobson and Jadhav found that a panel turned to follow the sun around the horizon, at a fixed tilt, collects within 1% to 3% of one that tracks the sun exactly, which worldwide averages 17% more than the best fixed angle.

1. In the morning, face the panel toward the sun, roughly where the planner’s sunrise line points, and tilt it steeply, because the morning sun is low.
2. Around midday, turn it toward the equator and set the tilt to the planner’s noon figure for the month.
3. In the afternoon, turn it toward the sunset side and steepen it again as the sun drops.
4. Each time, check the aim: stand a pen upright on the panel. When the pen casts no shadow, the panel faces the sun squarely.

Three moves a day is plenty. Within 25° of square a panel still catches 90% of the direct beam, so an aim that drifts for an hour or two costs little. The hours either side of noon carry most of a day’s energy, so put the panel out by mid-morning.

Turning pays most far from the equator in summer. There the sun rises in the northeast and sets in the northwest (southeast and southwest below the equator), behind a panel that faces the equator, and only a panel you can turn catches that light.

Shade costs more than any angle. A shadow over part of a panel holds back the cells wired to it, so a patch the size of a hand can take a third or more of the output while it lasts. Before you mount anything, watch the spot through a sunny day, and think about the season: the sun is lowest in winter, so shadows are longest then.

The planner’s noon-shadow figure says how far shadows reach when the sun is highest. In Kansas City, a post’s noon shadow in late December is almost twice the post’s height; in June it is about a quarter. So a 6 ft fence 10 ft from a panel shades it at midday in winter but not in summer.

Shadows swing round with the sun, too. In the morning and evening they stretch away from the east and west, so trees and buildings on those sides matter for those hours, and anything tall on the equator side matters all day. Panels in rows shade each other the same way when the sun is low: space the rows by at least the winter noon shadow of the row in front.

A panel loses about 0.3% to 0.5% of its power for every degree Celsius its cells warm above 25 °C (77 °F), so let air reach its back. On a roof, a gap of a few inches under the panel keeps it cooler than one laid on the shingles. On the ground, stand a portable panel on its legs rather than on hot rock, sand or a car roof.

Keep the cable from the panel to the power station short. Use the panel’s own lead where you can, and a short, thick extension where you can’t: a long, thin one wastes power as heat. If you wire panels in series, check their total voltage against the power station’s input limit for the coldest morning you expect, as the charging guide explains.

A tilted panel catches wind like a sail. Weigh down or stake a portable panel’s stand, fold it away before a storm, and on a roof or an RV follow the mount maker’s limits for tilt and wind.

Snow on the glass blocks the light almost completely, and a steeper panel sheds it sooner. Where snow is common, set a fixed panel toward the steep end of its range: in Kansas City, going 8° steeper than the best angle cost under 1% of a year’s output. Clear a buried panel with a soft brush, never a scraper.

Dust, pollen and bird droppings build up fastest on flat panels. At 10° or more, rain does most of the cleaning; in a dry spell, rinse the glass with water and a soft cloth.

Two things people worry about matter less than they think. Cold isn’t a problem: a cold panel is more efficient, so a crisp, clear winter hour can beat a hot summer one. And cloud slows charging without stopping it: under solid overcast a panel still makes about 10% to 25% of its clear-day output.

1. Pick the spot with the least shade from mid-morning to mid-afternoon, allowing for winter’s longer shadows.
2. Face the panel toward the equator, using the planner’s compass reading or a phone compass set to true north.
3. Set the tilt to the planner’s all-year figure, or, for a portable panel, to the month’s noon figure.
4. Keep at least 10° of tilt, and leave air behind the panel.
5. Run the shortest cable you can, check the voltage against the power station’s input, and secure the panel against wind.
6. With a portable panel, turn it to follow the sun two or three times a day.

To see how much a well-placed panel puts back into your power station each day, the calculator sizes the battery and the panels for your own devices.