A flat panel does not need precise tracking, because the sun moves 15 degrees an hour and a 15 degree aiming error loses only 3.4% of the power, so re-aiming the panel every two hours, pointing it 15 degrees ahead of the sun each time, keeps the average loss near 1.1%. Manual tracking can add about 21% to a fixed panel’s daily energy in the simple geometry here, at the price of someone re-setting the frame about five times a day.
Part of Solar Panel Construction
A hand-turned mount that follows the sun across the sky, the re-aiming interval it needs, and what it gains over a fixed panel.
A Panel Tolerates Far More Error Than A Dish
A concentrating dish loses its focus after a few degrees (Tracking Systems: the sun moves 15° an hour, 0.25° a minute). A flat panel only loses the cosine of its aiming error (Insolation & Angle): at 15° off, cos 15° = 0.966, a loss of 3.4%. So it can be left much longer. Manual Sun Tracking gives the strategy for a dish: point ahead of the sun by half the allowed window so it drifts across the target and out the other side. The same idea works here with a much wider window.
If the panel is aimed ahead of the sun by θ and left until the sun is θ ahead of it, the window is 2θ and the time between adjustments is 2θ ÷ 15° per hour. The average of cos over ±θ is sin θ ÷ θ (θ in radians). With these:
| Window | Interval | Worst-end cos | Average cos | Average loss |
|---|---|---|---|---|
| ±10° | 1.33 h | 0.985 | 0.9949 | 0.5% |
| ±15° | 2.0 h | 0.966 | 0.9886 | 1.1% |
| ±20° | 2.67 h | 0.940 | 0.9798 | 2.0% |
| ±30° | 4.0 h | 0.866 | 0.9549 | 4.5% |
So adjusting every 2 hours holds the average loss near 1%, and every 4 hours near 4.5%.
What Tracking Gains
For a panel facing the noon sun, the beam on it falls with the cosine of the hour angle h as the sun moves. Over a day of useful sun from −60° to +60° (4 hours either side of noon), the fixed panel collects the integral of cos h, which is 2 sin 60° = 1.732, while a tracked panel collects the whole window, 2π ÷ 3 = 2.094. The ratio is 2.094 ÷ 1.732 = 1.21, 21% more. If the useful day were ±90° the ratio would be 1.57, but the low sun at the edges is weakened by the longer air path, so the true gain is somewhere between and should be measured. The estimate ignores diffuse light and the atmosphere.
Compare with adding area: 21% more panel area gives the same gain with no attention each day. Since cells are the scarcest part of the system (Cell Fabrication), a mount that turns by hand may be cheaper than more cells.
What You Need
- A pivot — a pole with a bearing or a pin and plate (Journal Bearings Low-Tech shows a village bearing and its friction)
- A frame carrying the panel with the pivot axis tilted toward the pole at your latitude if you want a true polar axis
- Stops or detents at the positions for each interval
- A shadow pin and a mark board to set the lead
- A clock or a daily routine
Method: Track By Hand
Step 1: Build the pivot so the panel can turn smoothly about an axis that points at the pole (a polar axis, tilted at latitude from horizontal), with the panel’s own tilt fixed or seasonal (Seasonal Angle Adjustment).
Step 2: Mark the positions on a ring or board, one for each re-aim, 30° apart for a 2-hour interval at ±15°.
Step 3: Set the pin. A pin square to the panel casts no shadow when the panel faces the sun; use it to set the position without looking at the sun. Lead the sun by the half-window.
Step 4: Re-aim at the interval, every day. Write the times on a card by the mount.
Step 5: End the day with the panel pointing to where the morning sun will be, so a missed day costs only the difference from a fixed mount.
Worked Example: A Day’s Energy
A fixed 60 W panel at 4 hours of full sun yields 60 × 4 = 240 Wh (hours from the Load Calculation article’s 4–5). A tracked panel at +21% yields 240 × 1.21 = 290 Wh, a gain of 50 Wh a day. With a 2-hour interval a 10-hour working day uses 5 positions: the start setting and four moves. A 4-hour interval uses 3 positions but loses 4.5% on average, 240 × 1.21 × 0.955 = 277 Wh.
Common Mistakes
- Tracking to the minute — the panel does not need it
- Forgetting to reset at night — the first morning is then lost
- Looking at the sun to aim — use the pin’s shadow
- A pivot that jams in wind or cold — keep it clean and free
- A heavy panel on a weak pole — it twists and sags
Safety
A panel on a pivot is live, heavy and can swing in the wind
The panel makes voltage whenever light reaches it, and its cable moves with every turn, so a worn cable can short or expose conductors; use strain relief and a loop, and cover or disconnect before repairing. A panel that can turn catches wind from a different side each hour and can swing into a person beside it. Never look at the sun to aim, keep hands clear of the pivot and stops, and lock the mount in strong wind (Manual Sun Tracking).
What’s Next
- Learn next: Gravity-Driven Clock Tracker — removing the daily chore with a clock drive
- Combine with: Mounting and Orientation — the rest of the mounting rules