About the Solar Panel Simulator
This simulation models the power output of a photovoltaic panel by computing the sun's position throughout the day. It uses the standard declination–hour-angle method, where declination δ = 23.45° × sin(360° × (284 + day) / 365), and solar altitude follows sin(alt) = sin(φ)sin(δ) + cos(φ)cos(δ)cos(h). Direct irradiance on the tilted surface is G₀ × cos(θᵢ), the cosine of the angle of incidence between the sun vector and the panel normal.
The sliders set latitude, day of year, panel tilt and azimuth, cell efficiency η, area and ambient temperature. Output power is P = η × A × Gᵗ × (1 − 0.004 × (Tᶜ − 25)), capturing the thermal derating that real modules suffer when hot. The day curve, sun arc and Auto-Optimise button help you find the tilt that maximises annual yield — the core decision when siting a rooftop or ground-mounted array.
Frequently Asked Questions
What does this simulator actually calculate?
It computes the instantaneous electrical power and the daily energy yield of a flat photovoltaic panel. For every quarter-hour of the day it finds the sun's altitude and azimuth, the irradiance striking the tilted surface, and the resulting output in watts, then sums these to give daily energy in watt-hours.
How is the sun's position found?
It uses the classic declination and hour-angle equations of solar geometry. Declination is approximated as 23.45° times the sine of an angle based on the day of year, and the solar altitude comes from the latitude, declination and hour angle. The hour angle advances 15° per hour about solar noon.
What do the tilt and azimuth controls do?
Tilt is the angle of the panel from horizontal, from 0° (flat) to 90° (vertical). Azimuth is the compass bearing measured from due south, where 0° faces the equator. Together they orient the panel normal, which is compared with the sun vector to find the angle of incidence that scales the captured irradiance.
Why does power drop when the panel gets hot?
Silicon cells lose roughly 0.4% of their output for every degree above 25°C, the standard test temperature. The model estimates cell temperature as ambient plus a rise proportional to irradiance, then applies the factor (1 − 0.004 × (Tᶜ − 25)), so a baking summer roof produces less than its rated peak.
What does the Auto-Optimise button do?
It sweeps the tilt angle from 0° to 90° in 1° steps, integrating the day's irradiance for each, and selects the tilt that maximises energy capture for the current latitude and day. It also resets azimuth to 0° (due south), the optimum for a fixed panel in the northern hemisphere.
What is a good tilt angle for a fixed panel?
As a rule of thumb a year-round fixed tilt roughly equal to the site latitude works well. For summer-biased output you tilt flatter, and for winter you tilt steeper, because the sun rides lower in the sky. The simulator's optimal-tilt readout shows the best single-day value for the chosen date.
How accurate is the irradiance model?
It is a clear-sky, direct-beam approximation. Atmospheric attenuation is modelled with an air-mass term, AM = 1/sin(alt), and a transmittance power law. It ignores diffuse sky radiation, ground-reflected light, clouds, dust and shading, so it illustrates the geometry well but should not replace a full energy-yield study.
Why does the daily curve change shape with the season?
The day of year sets the solar declination, which shifts the sun's whole arc higher or lower and lengthens or shortens the day. Near the summer solstice the sun is high for many hours, giving a broad, tall power curve; in winter the curve is narrow and low, and at extreme latitudes the sun may not rise at all.
What is the angle of incidence and why does it matter?
It is the angle between the incoming sunlight and the line perpendicular to the panel. Only the component of irradiance along that normal is collected, so captured light scales with its cosine. When the sun is square to the panel the angle is 0° and capture is maximal; at grazing angles little energy is gathered.
How can I use this for a real installation?
Set the latitude of your site, sweep the day of year across the seasons, and read off the daily energy and optimal tilt. Adjust efficiency and area to match a real module, then compare orientations to weigh a steeper winter-friendly mount against a flatter summer-friendly one. Treat the numbers as clear-sky upper bounds rather than guaranteed output.