Raise a fixed panel to your latitude plus 15 degrees for winter and lower it to latitude minus 15 degrees for summer, changing it twice a year with a hinge at the base and a prop rod. The carrier claims 15 to 20% more annual energy, but the sun-angle geometry in this wiki gives about 3.5% more noon beam over a year, so treat the adjustment as a cheap small gain and not a large one.
Part of Solar Panel Construction
Changing a solar panel’s tilt between winter and summer, how large the gain is, and how to build the adjuster.
The Noon Sun Moves 46.9° Between Winter And Summer
The sun’s height at noon is 90° minus the absolute value of latitude minus declination, with declination swinging between +23.44° and −23.44° (Seasonal Sun Angle Calculation). A panel faces the noon sun squarely when its tilt from horizontal equals |latitude − declination| (Insolation & Angle). At 45°N that is 45° at the equinoxes, 68.4° at the winter solstice and 21.6° at the summer solstice.
The carrier’s rule of thumb is summer tilt = latitude − 15°, winter tilt = latitude + 15°, with a hinge at the base and a prop rod that make a two-minute adjustment. At 45° that is 30° and 60°. Insolation & Angle works the same case and finds the 60° winter tilt is 8.4° from the ideal 68.4° and costs about 1%. Change the tilt near the equinoxes (about 20 March and 22–23 September in the northern hemisphere, the dates the sun-angle article gives); in the southern hemisphere the seasons and the facing direction are reversed.
The Gain Is Smaller Than The Carrier Says
The loss from a tilt error is 1 − cos(error). At 45°N, fixed at 45°, the error at either solstice is 23.44° and cos 23.44° = 0.918, an 8.3% loss of the noon beam; at the equinoxes the error is zero. Adjusting to 60° and 30° leaves a worst-case error of 8.44° (cos = 0.989, loss 1.1%) at the solstices, but 15° (cos = 0.966, loss 3.4%) at the equinoxes when the change is made. Averaging the noon cosine over the whole year with the declination curve, fixed tilt gives 0.9586 and a twice-a-year change gives 0.9921 (my calculation, using the corpus’s declination formula), a gain of 0.9921 ÷ 0.9586 − 1 = 3.5%. In midwinter alone the gain is 0.9892 ÷ 0.9175 − 1 = 7.8%.
The carrier’s 15–20% is not reproduced by this arithmetic. It may include effects the cosine ignores (low-sun air path, diffuse light), or measure only the winter. It is unverified here, so plan with a few per cent. Near the tropics the rule fails: below 15° latitude, latitude − 15° is negative, and in a summer when the sun is north of overhead at a northern site, the panel should lean the other way. Use |latitude − declination| directly there.
What You Need
- A fixed frame with a hinge at the low edge — Fixed Mount Construction
- A prop rod with notches or holes for the preset tilts
- A protractor or measured template
- A calendar to mark the change dates
Method: Build And Use The Adjuster
Step 1: Compute the two tilts from your latitude (latitude ± 15°), or the exact values for your latitude and the solstice declination if you prefer.
Step 2: Compute the prop positions from the panel length (example below).
Step 3: Hinge the low edge on a strong pin, and make the prop rod with a notch for each tilt.
Step 4: Change the tilt at each equinox, checking the angle with the protractor and the shadow pin (Fixed Mount Construction).
Step 5: Lock the prop so wind cannot knock it out.
Worked Example: Prop Notches For A 0.794 m Panel
With the hinge at the low edge and a vertical prop under the high edge, the prop height is L × sin θ for a panel of length L = 0.794 m (the panel size from Panel Encapsulation and Framing). At 30° the prop is 0.794 × 0.500 = 0.397 m; at 60° it is 0.794 × 0.866 = 0.688 m. The two notches are 0.688 − 0.397 = 0.291 m apart. A prop at an angle (not vertical) is longer by 1 ÷ cos of its lean from vertical.
Common Mistakes
- Changing at the solstices — the two settings swap near the equinoxes, when their ideal tilts cross
- Using latitude ± 15° near the equator — it gives negative tilts
- Hemisphere reversed — in the south, winter tilt is for June
- A loose prop — a gust drops the panel
- Expecting 15–20% — the geometry gives a few per cent
Safety
Lifting a live glass panel to change its angle
A panel is live whenever light reaches it and a string reaches dangerous voltage (three 18 V panels make 54 V, six make 108 V); disconnect or cover the array before you adjust it and treat it as live regardless. A panel being raised can slip or be caught by wind, and the glass can cut or crush a hand under the prop. Adjust in calm weather, use two people on a large panel, and lock the prop before letting go.
What’s Next
- Learn next: Manual Tracking Mount — following the sun through the day
- Combine with: Mounting and Orientation — the orientation rules