Solar Panel Tilt and Azimuth Calculator
What your roof angle and bearing actually cost you — usually far less than people fear — with magnetic declination handled properly.
Every bearing at your latitude
At the ideal tilt, as a percentage of a perfectly oriented array.
Orientation matters far less than people fear
A roof thirty degrees off south costs about three percent of annual output. Even a due east or due west roof keeps around eighty percent. People agonise over a few degrees of azimuth and then put the array under a tree — which costs far more than every orientation decision on this page combined. The reason it is so forgiving is that only the direct beam cares which way you point; the diffuse light arriving from the whole sky largely does not.
- True south is not magnetic south. Declination reaches twenty degrees in parts of the world and a phone compass reads magnetic. Aiming a ground mount by phone without correcting is a larger error than most of the roof angles people worry about. East declination is positive — getting the sign backwards doubles the error rather than removing it.
- Under time-of-use pricing, west can be worth MORE than south despite producing less. A west-facing array shifts output into the late-afternoon peak when the tariff may be two or three times the midday rate. Optimising for kilowatt-hours and optimising for money are different problems, and this page calculates only the first.
- Optimal tilt is shallower than latitude. The naive "tilt equals latitude" rule over-weights winter, when there is little sun to collect anyway. Latitude × 0.76 + 3.1 is the standard fit.
- Adjustable mounts are almost never worth it grid-tied. A few percent a year against a lifetime of climbing up twice. Off-grid, where the worst month decides everything, a winter tilt is a different proposition entirely.
- Steeper sheds snow and rain; shallower collects dust. Neither effect is in these figures, and in a snowy climate the first one outweighs several percentage points of angle.
This is a first-order model — a beam term, a sky-view term and a ground-reflection term. It reproduces published figures to within a few points across the useful range, which is the right accuracy for deciding whether a roof is usable. For a real quote, NREL's PVWatts models the actual sun path at your actual site.
How to use
- Enter your latitude, roof tilt and the bearing the roof faces.
- If the bearing came off a phone compass, add your magnetic declination.
- Read the output as a percentage of a perfectly oriented array.
- Check the table to see how every other bearing would compare.
Frequently asked questions
How much does a non-south roof really cost me?
Much less than most people expect. Thirty degrees off south costs about three percent of annual output, and even a due east or due west roof keeps around eighty percent. The reason is that only the direct beam cares which way a panel points; the diffuse light arriving from the whole sky largely does not, and it is a substantial share of the total. Rejecting a roof for being off-axis is usually the wrong call — the question is whether the economics work at eighty percent.
What tilt should I use?
Roughly latitude times 0.76 plus 3.1 degrees, which is about 33 degrees at latitude 40. That is deliberately shallower than the old "tilt equals latitude" rule, which over-weights winter when there is little sun to collect anyway. In practice the curve is very flat near the top: anything within about ten degrees of optimal is effectively the same array, so an existing roof pitch is almost always fine.
Does magnetic declination matter?
Yes, and it is a bigger error than most of the roof angles people worry about. Declination reaches twenty degrees in parts of the world, and a phone compass reads magnetic rather than true. East declination is positive, so a compass reading of 180 where declination is plus twelve is really pointing 192 true. Getting the sign backwards doubles the error rather than removing it, which is why it is worth checking against a satellite image.
Is a west-facing array really worse?
It produces less energy and can be worth more money. Under time-of-use pricing a west-facing array shifts output into the late-afternoon peak, when the tariff may be two or three times the midday rate. Optimising for kilowatt-hours and optimising for money are genuinely different problems, and a calculator like this one only answers the first. If your utility has steep afternoon pricing, run the numbers on value rather than output.
Are adjustable mounts worth it?
Grid-tied, almost never. The annual gain from swinging between a summer and a winter tilt is a few percent, against a lifetime of climbing onto the roof twice a year and a mount with more parts to fail. Off-grid is a different proposition, because there the worst month decides the whole system size — a winter-biased fixed tilt, or an adjustment made once each autumn, can meaningfully reduce how much array and battery you need.
Should I tilt steeper for snow?
Often yes, and it is not in these figures. A steeper panel sheds snow and rain far better, and in a climate where snow sits for weeks the production lost to a covered array dwarfs the few percentage points a steeper angle costs. Shallower panels also collect more dust and need washing more often in dry regions. Both effects are real and neither is modelled here.
How accurate is this?
It is a first-order model — a direct-beam term, a sky-view term for diffuse light and a ground-reflection term — and it reproduces published figures to within a few percentage points across the useful range. That is the right accuracy for deciding whether a roof is worth using. It does not model shading, which outweighs every orientation decision here combined, or your actual local weather. For a quote, NREL PVWatts traces the real sun path at your real site.
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