Which Direction Should Solar Panels Face?

3rd Aug 18

Cameron Quin

Written by Cameron Quin

Before installing a solar power system, a very important step is finding the optimal orientation for photovoltaic modules. Consider that the sun’s position in the sky changes during the day due to Earth’s rotation, and its altitude changes depending on the season – the sun is located higher during summer and lower during winter.

Ideally, solar panels should always face the sun, but this requires a special tracking mechanism that increases the cost of the project. Solar trackers can be cost-effective when the available space is limited, but in most cases the best way to increase productivity is simply using a larger solar array. However, regardless of array size, solar panels should be positioned to maximise productivity.

The best orientation for solar panels depends on three main factors: the geographic location of the project, specific site conditions like roof structure and shadows, and the electricity needs of each building.

How Geographic Location Influences Solar Panel Orientation

Depending on where you live, the sun is seen in a different position in the sky. Perhaps you have noticed that the sun is lower in the sky during winter, but the direction in which this behaviour is observed changes based on your location:

  • In Australia and other southern hemisphere continents, the sun can be seen farther to the north during winter.
  • On the other hand, in northern hemisphere countries like the USA, the sun appears to be farther to the south during winter.

From this, we can conclude that most of the annual sunlight comes from the northern portion of the sky in Australia. As a result, solar panels should be tilted towards the north, and productivity is diminished if they face in another direction:

  • South-facing solar panels are the least productive throughout the year.
  • East and west-facing solar panels have intermediate productivity. They are more productive in the morning if they face east, and more productive in the afternoon if they face west.

The direction a solar panel faces only describes its orientation partially. If someone mentions that a solar array faces north, you cannot tell if the modules are tilted slightly or if they are placed completely vertical. To fully describe the orientation of a solar array, a tilt angle must also be provided.

In locations close to the equator, the sun has a high position in the sky during most of the year, and solar panels are installed horizontally, facing up. On the other hand, in locations far to the north or south, a tilt angle is required to maximise incident sunlight.

The NASA Atmospheric Science Data Center has an interesting website where you can input your coordinates to get solar radiation data for your exact location. The database also provides the optimal tilt angle for photovoltaic modules.

Importance of Project Site Conditions

The tilt angle of a solar power system can be optimised easily when the array is mounted on the ground or a flat concrete roof. However, there is less flexibility in tilted roofs such as those commonly used in homes. In these cases, instead of adjusting the tilt angle, solar installers analyse the slope of each roof section to determine the best location for solar panels.

There may be cases where the roof section with the best orientation cannot be used due to other factors. If this happens, solar system designers will normally recommend the second-best option. Some factors that may make a roof section unusable for solar panels are the following:

 

  • Shadowsreduce the output of solar panels drastically, for the simple reason that they reduce the amount of incident sunlight. Also, given that solar panels are wired in string circuits, one shaded panel affects the performance of all others in the circuit. Shadows can be produced by natural features such as trees and hills, or by man-made structures like buildings and unipole signs.
  • Local regulations may limit the use of solar panels in some roof areas. For example, there are councils that don’t allow street-facing solar panels in historic districts. If the best orientation for your solar panels matches the direction  of the street, a project redesign may be required.

 

You should use the roof area that gets the most sunshine to maximise solar system output, assuming local laws and physical obstacles are not a limitation. If you will use a photovoltaic array that uses many roof areas with different orientations, the recommendation is to connect solar panels of the same orientation in the same circuits, in order to maximise performance. When solar panels with different production profiles are wired together, the modules with lower productivity drag down production for the rest.

Matching Solar Generation with Electricity Consumption

Depending on their purpose, buildings have different electricity consumption profiles. For example, a school tends to have its higher consumption during the morning, while a shopping mall will likely have its highest power demand during the afternoon and evening.

Even though south-facing solar arrays are the most productive, other orientations may be more effective in specific projects. For instance, a school could benefit from an east-facing array to maximise energy production in the morning, even if productivity is affected in the afternoon:

  • The electricity generated during the morning is consumed right away, lowering power bills for the school building.
  • On the other hand, the school may be forced to sell most of its afternoon solar generation to the grid, getting only a low feed-in tariff in return.
  • In this case it makes sense to maximise morning generation from the solar array, even at the expense of generation in the afternoon.

Conclusion

The best orientation and tilt angle for your solar power system are determined by its geographic location, but solar designers must also consider the physical conditions of the site and the specific electricity needs of the building.

A commercial solar array is one of the best upgrades available for buildings in Australia, considering the high electricity prices in the country, but the importance of a good design should not be overlooked – inadequate positioning of solar panels can make your array much less productive.

 

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