Mount solar panels facing the equator, true south in the northern hemisphere and true north in the southern, tilted up from horizontal by about your latitude for year-round use, and keep them clear of shade. Small aiming errors cost little, since the power lost follows the cosine of the error, but shade and a compass error of 20 degrees cost real energy, so find true south from the sun and not from a magnetic compass.
Part of Solar Panel Construction
Where and how to point solar panels so they collect the most energy, with the aiming error, tilt and shading rules.
A Panel Keeps The Cosine Of Its Aiming Error
A surface square to the sun receives the full beam, about 1,000 W/m² at a clear noon. Tilted away from the sun by an angle θ, it receives that times cos θ (Insolation & Angle). So small errors are cheap and large ones are not:
| Aiming error | cos θ | Loss |
|---|---|---|
| 5° | 0.996 | 0.4% |
| 10° | 0.985 | 1.5% |
| 15° | 0.966 | 3.4% |
| 20° | 0.940 | 6.0% |
| 30° | 0.866 | 13.4% |
The sun’s noon height is 90° minus your latitude at the equinoxes, and the tilt that faces the noon sun squarely is the angle between latitude and the sun’s declination, which swings between +23.44° and −23.44° over the year. A fixed tilt equal to latitude is the sound compromise (Insolation & Angle). The carrier’s table gives tilt = latitude: 20° at 20°, 35° at 35°, 45° at 45° and 55° at 55°.
Finding True South Matters More Than Fine Tilt
A magnetic compass points to magnetic north, which can differ from true north by 5° to 20° or more (Finding True South). From the table, a 20° error costs 6% of the noon beam. Find true south with a vertical stick and its shadow (Shadow Stick, Finding True South), then check the compass against it. The same sun geometry is worked in Seasonal Sun Angle Calculation.
Shade is worse. A winter-noon shadow is 2.0 times an object’s height at 40°N and nearly 3 times at 48°N, and a tree that is harmless in June can shade a panel from November (Sun Exposure & Shadows). Because panels in a string share current, shade on part of one hurts the whole string (Bypass Diodes).
What You Need
- A shadow stick and a straight edge — for true south
- A protractor or an angle template — for tilt
- A site clear of shade from the equator side, checked in winter if possible
- A frame — Fixed Mount Construction
Method: Choose And Aim
Step 1: Pick the spot with no trees, buildings or hills to the equator side. Check where shadows fall at the winter-noon sun height.
Step 2: Find true south with the shadow stick.
Step 3: Set the tilt to your latitude (or the seasonal values in Seasonal Angle Adjustment).
Step 4: Fix the frame, check it again at noon next day.
Step 5: Re-check the shade each season.
Worked Example: What Aim Is Worth
A 60 W panel at 4–5 peak sun hours (the Load Calculation article’s figure for temperate climates) gives 60 × 4 = 240 Wh to 60 × 5 = 300 Wh a day. Aimed 15° off, it gives 0.966 × 240 = 232 to 0.966 × 300 = 290 Wh, a loss of 8 to 10 Wh. Aimed 20° off from trusting a compass: 0.940 × 240 = 226 to 0.940 × 300 = 282 Wh, a loss of 14 to 18 Wh. A single shaded cell can cut the whole string’s output to zero (the bypass-diode article gives the voltage), which is more than any of these.
Common Mistakes
- Using a magnetic compass for south — up to 20° or more out
- Facing the wrong way in the southern hemisphere — face true north
- Mounting in the shade of a winter-bare tree — winter shadows are the longest
- Tilting for summer and expecting winter output — the winter sun is low
Safety
Mounting means working at height with live panels and heavy glass
A panel is live whenever light reaches it, rain included; a string of panels reaches dangerous voltage (three 18 V panels make 54 V, six make 108 V), so cover panels or leave them disconnected at the array while you mount them, and treat them as live regardless. Panels with glass are heavy and cut when dropped; use two people and avoid working on a roof or pole in wind (Glass Recovery).
What’s Next
- Learn next: Fixed Mount Construction — building the frame
- Combine with: Manual Tracking Mount — following the sun through the day