3D Solar Panel Tilt – Sun Path and Daily Energy

What it shows

A solar panel delivers the most power when sunlight strikes it at right angles. The irradiance on the panel is G = DNI·cos θ plus a little diffuse light, where θ is the angle between the Sun's rays and the panel's normal, and the electrical power is P = η·A·G. The Sun's path is calculated from the latitude, the date and the solar time, and the direct beam weakens when the Sun is low because the light crosses more atmosphere. The daily energy, the area under the power curve, is compared with a household's use and with the best fixed tilt for the year.

How to use

Set Latitude φ and Date, then press Play one day or drag the Sun along its path. Change Tilt β and Panel direction and watch θ, the power and the daily energy. Press Best angle for this day, then choose Energy vs tilt in the Graph menu to compare the best tilt for one day and for the whole year with the latitude. Use Efficiency η, Panel area A and Home use to size a system.

Parameters you can change

• Latitude φ (negative: southern hemisphere) -60–70 °
• Month (the 21st of the month) 1–12
• Solar time 0–24 h
• Panel tilt β 0–90 °
• Panel direction (0° = north, 90° = east, 180° = south) 0–355 °
• Panel efficiency η 5–25 %
• Panel area A 1–40 m²
• Household electricity use per day 1–30 kWh

Questions to explore

1. Why does the panel give the most power when the sunlight hits it at right angles?
2. How does the best fixed tilt for the whole year compare with the latitude of the site?
3. What panel area would a household need in winter compared with summer?