The Golden Rule: Chasing the Sun
The principle behind solar panel orientation is simple: get as much exposure to direct sun as possible all year long. The arc of the sun changes with the season and the time of day, so the best position for a given panel is one that gives you the best overall exposure. So, you want to optimize two criteria: azimuth and tilt.
Azimuth: The Compass Bearing
Azimuth refers to the cardinal direction in which the panels are directed, and it has the highest importance on the actual energy production experienced on a daily basis.
The Ideal: True South (in the Northern Hemisphere): True South is the best azimuth direction for solar panels in the Northern Hemisphere. This orientation will maximize direct sunlight to the panels, as the sun moves across the southern sky.
Something Viable: East and West: South is the ideal orientation, but of course that is not always available due to roof design or shading. Panels facing east will produce more energy in the morning, while west-facing panels receive more intense sunlight in the afternoon, which may help offset peak electricity usage and/or receive higher feed-in tariffs during these times in a number of jurisdictions. However, regarding energy production, east and west will typically lose 10-15% energy production versus a south-facing system.
The Poor Choice: North: North-facing roofs, in the Northern Hemisphere, are generally the least desirable roof for residential solar PV systems, given the panels would receive the least amount of direct sunlight.
Tilt Angle: Finding the Right Incline
The tilt angle refers to the elevation of the panels from the horizontal plane. The objective is to position the panels as closely to perpendicular to the rays of the sun as possible throughout most of the year.
A Basic Starting Point: he frequently suggested first approach is to use the tilt angle that equals the latitude of the installation. Thus, if you were at 40 degrees of latitude, you would tilt your panels to about 40 degrees in order to get the average annual solar energy. This tilt angle will orient panels to optimize to a greater degree for the high sun in the summer while balancing the low sun in the winter.
For A More Seasonal Solution: In order to enhance the annual yield, the tilt is often set to be slightly lower than the latitude. If winter performance is prioritized (because the sun is sitting lower), a steeper angle will be used. If summer performance is prioritized, a shallower angle will ultimately perform better. Most fixed residential rooftop systems are installed at a single, optimized tilt angle that provides the best compromise year-round.
The Combined Impact on Power Generation
The relationship between tilt and azimuth determines the efficiency and value proposition of the system. Even a slight variation from the assumed maximum will have a calculable effect. According to the National Renewable Energy Laboratory (NREL), a south-facing array at its optimum tilt is generating 100% of its production potential. In contrast, if you are facing southeast or southwest, you will be 5-8% lower than the baseline, which is the south-facing array. A system oriented due-east or due-west will incur reasonably similar impacts of about 10-15%. If you are northern-facing within the Northern Hemisphere, you will incur loss of more than 30% below the production potential for optimal tilt.
Those losses are not theoretical; they will incur on the realized loss. For example, despite the 15% loss, you will have 15% less electricity to run your appliance, or less electricity in the system that you may be eligible to sell back to the grid, which will increase your payback for that investment.
Beyond the Basics: Advanced Considerations
Local Climate and Weather
Areas that receive heavy morning fog may generate slightly more energy with a west-facing array since the afternoon sun would be clearer. Similarly, places with significant snowfall may find a steeper tilt useful to help snow slide off the solar panels.
Shading
Even the best, theoretically perfect orientation and tilt cannot create energy when there is shading. Any trees, chimneys, or other buildings that shade the solar panels for a portion of the day means that that solar array will not produce any energy during that time period. A professional solar site assessment performed with a tool called a solar pathfinder, or other digital equivalent tool, can help us map out any potential shading throughout the year and adjust the layout of the solar array accordingly.
Electrical Load Profile
If the system is designed for self-consumption, then the orientation of the panel can also be customized to the homeowner's energy use daily. For households that have much of their energy use during the day, a southern facing solar array meets a homeowners need for energy throughout the day, since it is producing energy all day. However, in a household where everyone is not home during the day, then purposefully a west-facing array may generate more electric energy later in the day to capture the homeowner's electrical needs.
To summarize, selecting the installation orientation for a solar array is a complicated undertaking. It involves more than just putting the panels on a roof wherever there is a place to put them. It is an engineering decision that balances the immutable laws of planetary motion with the specific nature of a particular site and the goals for energy use by the owner of the solar array. Getting the orientation correct will be the number one factor to ensuring that your solar investment can achieve the most amount of clean, renewable energy over the life of the solar array.
