Solar panels are a great way to generate clean and renewable energy, but they need to be installed at the right angle and direction to maximise their output. In this article, we will explain how the sun’s position changes throughout the day and the year, and how this affects the optimal tilt and orientation of solar panels in the UK. But this is only part of the story.
What does this image show?
The image shows a solar panel angle and performance chart. It illustrates how the tilt angle and the orientation of the solar panel affect its energy output. The chart has the following labels:
- Tilt angle: The angle between the solar panel and the horizontal plane. The optimal tilt angle depends on the latitude and the season of the location.
- Orientation: The direction that the solar panel faces. The optimal orientation is usually south in the northern hemisphere and north in the southern hemisphere, as this maximises the exposure to the sun throughout the day averaged over the year.
- Energy output: The amount of electricity that the solar panel produces. The energy output is measured in kilowatt-hours (kWh) per year. The energy output is higher when the tilt angle and the orientation are closer to the values.
- Optimal values: The tilt angle and the orientation that result in the highest energy output for a given location and season ONLY. The optimal values vary depending on the latitude, the season, and the local weather conditions. The chart shows the optimal values for London, UK as an example.
How does the angle relate to the time of the day?
The angle of the sun relative to the solar panel changes throughout the day, as the sun moves from east to west across the sky. This angle is measured by the azimuth, which is the horizontal angle from the north. The azimuth ranges from 0° (north) to 180° (south) to 360° (north again).
The chart shows that the solar panel produces the most energy when the sun is directly in front of it, which means that the azimuth of the sun matches the orientation of the panel. For example, if the panel is facing south (180°), it will have the highest output when the sun is at its highest point in the sky, around noon. If the panel is facing east (90°), it will have the highest output in the morning, when the sun rises from the east. If the panel is facing west (270°), it will have the highest output in the afternoon, when the sun sets in the west.
The chart also shows that the solar panel produces less energy when the sun is at a large angle from the panel, which means that the azimuth of the sun is far from the orientation of the panel. For example, if the panel is facing south (180°), it will have the lowest output in the morning and evening, when the sun is in the east (90°) or west (270°). If the panel is facing east (90°) or west (270°), it will have the lowest output around noon, when the sun is in the south (180°).
How does the angle change in the summer and winter?
The angle of the sun relative to the solar panel also changes throughout the year, as the earth orbits around the sun and tilts on its axis. The angle is measured by the elevation, which is the vertical angle from the horizon. The elevation ranges from 0° (horizon) to 90° (zenith).
The chart shows that the solar panel produces more energy when the sun is higher in the sky, which means that the elevation of the sun is larger. The sun reaches its highest elevation on the summer solstice (around June 21st), and its lowest elevation on the winter solstice (around December 21st). The sun also reaches different elevations depending on the latitude of the location. The higher the latitude, the lower the elevation of the sun.
The image also shows that the optimal tilt angle of the solar panel changes with the seasons, to match the elevation of the sun. The optimal tilt angle is equal to the latitude plus or minus 15 degrees, depending on the season. For example, in London, UK, the latitude is 51.5°. The optimal tilt angle for summer is 51.5 – 15 = 36.5°, and the optimal tilt angle for winter is 51.5 + 15 = 66.5°. The optimal tilt angle for spring and autumn is the same as the latitude, 51.5°.
How many hours is the 60° ?
The duration of sunlight for each azimuth angle, which is the number of hours that the sun is at that angle during the day. The duration of sunlight depends on the season and the latitude of the location. The longer the day, the more sunlight there is for each angle.
The duration of sunlight varies from 0 to 4 hours, depending on the season and the latitude. For example, in London, UK, the duration of sunlight for the 60° is:
- 0 hours in winter, when the sun never reaches those angles
- 1 hour in spring and autumn, when the sun reaches those angles in the morning and evening
- 2 hours in summer, when the sun reaches those angles earlier and later in the day
- The day total would be 8 Hours between 60° and 60°
Where in the angles would summer be located, explain this?
The chart shows the energy output of the solar panel for different elevation angles, from 0° to 90°. The elevation angle of the sun changes with the seasons, as explained above. The summer is the season when the sun reaches its highest elevation, which means that the solar panel produces more energy for higher elevation angles.
The duration shows that the summer is located in the center part of the chart, where the elevation angles are larger than 45°. For example, in London, UK, the elevation angle of the sun ranges from 15° to 62° in summer, depending on the time of the day year. The solar panel produces the most energy when the sun is at its highest point, around 62°, which is around noon on the summer solstice.
Where in the angles would winter be located, explain this?
The energy output of the solar panel for different elevation angles, from 0° to 90°. The elevation angle of the sun changes with the seasons, as explained above. The winter is the season when the sun reaches its lowest elevation, which means that the solar panel produces less energy for lower elevation angles.
The chart shows that the winter is located in the lower part of the chart, where the elevation angles are smaller than 45°. For example, in London, UK, the elevation angle of the sun ranges from 7° to 15° in winter, depending on the time of the day. The solar panel produces the least energy when the sun is at its lowest point, around 7°, which is around noon on the winter solstice.
We hope this article has helped you understand how the sun hours and seasons affect the optimal angle and direction of solar panels in the UK. By following these guidelines, you can ensure that your solar panels capture the most sunlight and generate the most energy throughout the year.
Another post; 2024 Solar down turn The suns on the down turn — RenewSolar
What is the Actual Time during the day?
While the tilt is important the panels angle to the sun will change over the day, the image shows that the production is relative to the panel angle to the sun. For example the time between south ( shown as 0°) Would yield power between 30°-35° this amounts to 2.33 hours either side of noon. 60° and 0° Would account for 4 hours
What is the radiance of the sun at a given time?
The sun’s radiance is the amount of solar energy that reaches a given area per unit time. It depends on several factors, such as the distance from the sun, the angle of incidence, the atmospheric conditions, and the time of the day and year.
If there were no clouds in the sky, the sun’s radiance would be higher in the morning and lower at noon, because the sun’s angle changes throughout the day. The sun’s angle is the angle between the sun and the horizon, and it affects how much of the sun’s rays are absorbed or scattered by the atmosphere. The higher the sun’s angle, the more direct and intense the sunlight is. The lower the sun’s angle, the more diffuse and weak the sunlight is.
For example, in Basingstoke, UK, the sun’s angle ranges from 6° to 29° in the morning, and from 29° to 15° at noon, on February 26, 2024. This means that the sun’s radiance is higher in the morning than at noon, because the sun’s angle is increasing in the morning and decreasing at noon. The sun’s radiance is also lower in the winter than in the summer, because the sun’s angle is lower in the winter than in the summer.
The sun’s radiance is lower in the winter because the sun is lower in the sky, and the sunlight is less direct and more spread out over a larger area (diffusion). This is due to the tilt of the earth’s axis, which causes the sun’s angle to change with the seasons1.
The diffusion coefficient
The diffusion coefficient of the sun is a measure of how much the sunlight is scattered by the atmosphere. It depends on the wavelength of the light, the air density, the humidity, and the presence of aerosols and clouds.
Based on clear skies, the diffusion coefficient of the sun is higher in the winter than in the summer, because the sun is lower in the sky and the sunlight travels through more air. The diffusion coefficient also varies with the latitude and the time of the day.
According to one study, the average diffusion coefficient of the sun in the UK for clear skies is about 0.06 in the summer and 0.12 in the winter, at noon. This means that the sunlight is more diffuse and less direct in the winter than in the summer resulting in lower yields of solar power.
The UK’s sun radiance is the amount of solar energy that reaches a square meter of surface per hour, measured in kilowatts (kW). It varies by month, season, and location, depending on the sun’s angle and the cloud cover. According to one source1, the average sun radiance for the UK by month is:
| Month | Sun Radiance (kW/m2) |
|---|---|
| Jan | 0.52 |
| Feb | 0.77 |
| Mar | 1.15 |
| Apr | 1.51 |
| May | 1.67 |
| Jun | 1.63 |
| Jul | 1.55 |
| Aug | 1.38 |
| Sep | 1.07 |
| Oct | 0.76 |
| Nov | 0.51 |
| Dec | 0.37 |
Using this chart and your solar panels datasheet (or sticker on the back) The STC data on which they are tested is 1kWm2, there will be lots of argument’s that the UK never sees 1kWm2, but here is the data which we’ve known about for years.
Further reading: How to Position Your Solar Panels for Maximum Energy Output — RenewSolar
Maximise Solar for a battery — RenewSolar
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[…] Solar sun hours:Sun hours are a bit different to daylight hours and im sure you have seen a solar curve but we would be looking at around 4 hours of sun in a day, this varies from summer to winter, so the charge time will vary over the year and the battery and solar can buffer each other, this is a must for loads when a cloud passes. you can read more on sun hours here […]