How do I find true south for solar panels?

Use a compass and correct for magnetic declination: True South Bearing = 180° − Declination. In New York (−13°W declination), aim your compass to 193°. In Los Angeles (+12°E), aim to 168°. Alternatively, use the shadow method at solar noon — a vertical stick's shadow points true north, and the opposite direction is true south.

What is the magnetic declination for solar panels?

Magnetic declination varies by location: New York is −13° West, Los Angeles is +12° East, London is near 0°, Sydney is +12° East. East declination means true south is west of magnetic south — aim your compass west of 180°. West declination means aim east of 180°.

How much production do I lose for each degree off true south?

Approximately 0.5% annual production loss per degree of azimuth error. At 5° off: 2.5% loss. At 15° off (ignoring Seattle's declination): 7.5% loss. On a 10kW system generating $2,000/year, 15° off costs ~$150/year, or $3,750 over 25 years.

What is the shadow method for finding true south?

At solar noon, plant a perfectly vertical stick in level ground. The shadow the stick casts at that exact moment points true north. The opposite direction (180° from the shadow tip) is true south. Solar noon is when the sun reaches its highest point in the sky — calculable from your longitude and the equation of time.

Should solar panels face true south or magnetic south?

Always true south (in the Northern Hemisphere). The sun follows true celestial paths, not magnetic ones. A compass points to magnetic north, which can be significantly different from true north. Mounting panels at magnetic south instead of true south is a common installation error that permanently reduces output.

Solar True South Finder

Find true south for maximum solar production. Enter your location — get magnetic declination, correct compass bearing, and solar noon for the shadow method.

Location

City?

Date ?

True south bearing for solar panels

Aim 13.0° east of magnetic south (bearing 193.0°)

— True south --- Magnetic south

Location40.71°, -74.00°

Magnetic declination-13.0° (West)

True south bearing (compass)193.0°

HemisphereNorthern — panels face south

Production loss per degree off~0.5%/°

Solar noon (UTC, shadow method)16:54 UTC

Shadow method: At solar noon above, plant a vertical stick in the ground. The shadow will point true north — the opposite direction is true south. No compass or declination calculation needed.

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How to Use This Calculator

Choose your location method

Select a city from the dropdown for instant pre-mapped declination values, or switch to manual coordinates for precise results. For professional installations, always use current NOAA values — magnetic declination changes slowly over time (typically 0.1-0.3° per year) so data more than 5 years old may be out of date.

Read the compass bearing

The result tells you what bearing to dial on your compass to point your panels at true south. The green arrow on the compass diagram shows true south; the red dashed arrow shows where a compass needle actually points to magnetic south. The difference between them is the declination.

Use the shadow method as a no-compass alternative

At solar noon (shown in the results), plant a perfectly vertical stick in the ground. The shadow cast by the stick points precisely true north — the opposite direction is true south. This method requires no compass, no declination table, and no maths. It's accurate to within 1° in most conditions.

The Formula

True South Bearing (compass) = 180° − Magnetic Declination East declination (+): compass bearing < 180° (aim slightly west of magnetic south) West declination (−): compass bearing > 180° (aim slightly east of magnetic south) Example — New York (declination −13°W): Compass bearing = 180° − (−13°) = 193° Aim 13° east of where compass shows south Example — Los Angeles (declination +12°E): Compass bearing = 180° − 12° = 168° Aim 12° west of where compass shows south

The declination formula converts between magnetic bearings (what a compass reads) and true geographic bearings (aligned to the geographic North Pole and true celestial south). Solar panels should always be aimed at true south (Northern Hemisphere) or true north (Southern Hemisphere) — not magnetic south/north.

Example

David — Installing panels in Seattle, WA

David is mounting solar panels on his garage in Seattle. He has a basic compass but knows Seattle has significant magnetic declination. He wants to aim his panels correctly without expensive survey equipment.

LocationSeattle, WA (47.6°N, 122.3°W)

Magnetic declination+15.5° East

Result

Compass bearing for true south164.5°

InstructionAim 15.5° west of magnetic south

Without correction~8% production loss (15.5 × 0.5%)

If David aimed at magnetic south (what his compass shows) instead of true south, his panels would be 15.5° off — losing nearly 8% of annual production. On a 10kW system generating $2,000/year, that's $160/year thrown away. David uses the shadow method at solar noon to double-check and confirms the bearing before finalizing the mount angle.

FAQ

What is magnetic declination and why does it matter for solar? ▼

Magnetic declination is the angle between magnetic north (where a compass points) and true geographic north (the actual North Pole). It varies by location — in Seattle it's +15.5° East; in New York it's -13° West; in London it's near 0°. For solar panels, you want to aim at true south (the sun's path), not magnetic south. Ignoring declination costs 0.5% of annual production per degree of error. In Seattle, a compass-only approach without correction loses ~8% of output.

How do I find my exact magnetic declination? ▼

The most accurate source is the NOAA Magnetic Declination Estimator at ngdc.noaa.gov/geomag/calculators/magcalc.shtml. Enter your coordinates and date for a precise current value. For most solar installations, the city dropdown values in this calculator are accurate within 0.5-1°, which is sufficient since panel mounting tolerances are typically ±2°.

Does magnetic declination change over time? ▼

Yes — magnetic declination changes as Earth's magnetic field shifts. The typical rate is 0.1-0.3° per year, though in some high-declination areas it can change faster. For a 25-year solar installation, this could add up to 2-5° of drift. For most fixed residential installations this doesn't justify remounting panels — the loss is fractional. For new installations, always use the current NOAA value rather than old maps or charts.

Does 1° off from true south really matter? ▼

The rule of thumb is 0.5% production loss per degree off true south. A single degree off costs about 0.5% — on a 10kW system that's 50kWh/year, worth $6-10. That seems trivial, but if you're 15° off due to ignoring declination, you lose 7.5% — $150-200/year on a typical system, or $3,750-5,000 over 25 years. Larger deviations also compound with suboptimal tilt angles. The goal is to get within ±5° of true south; ±2° is excellent.

Should panels face true south or slightly east or west? ▼

True south maximizes annual production — it's the optimal azimuth. However, some installers deliberately aim slightly east (morning peak) or slightly west (afternoon peak) for specific use cases: east-facing systems charge batteries earlier for morning loads; west-facing systems produce more during afternoon peak grid pricing. These are 3-5% compromises for specific benefits. For a general home system on net metering with flat rates, true south is always best.

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