Which Direction Should Your Solar Panels Face?

As you can probably guess, solar panels generate more electricity when they are facing directly at the sun. While some utility-scale solar farms have structures that track the movement of the sun, residential and off-grid systems are generally left at the same orientation all year round.

In many cases, you won’t be able to choose which way you mount your panels, as you will be placing solar panels on an existing roof. In this case, it is important to understand how different orientations will affect the output of the panels.

If you have an off-grid or ground-mounted setup, you may be flexible in which way to face your panels. In this case, the ideal direction will depend on where you are located in the world, and what your goals are for your system.

This article will cover both these scenarios.

The orientation of your solar panels can be broken down into two types – Azimuth, and Tilt.

Azimuth

Azimuth refers to the compass direction your solar panels are facing.

In general, facing towards the equator (to the south in the northern hemisphere, and to the north in the southern hemisphere) will produce the most electricity over the course of a day, and should be your default choice where you have that option.

Note that when we say “south” what we are really talking about is geographic south (also called true south), not magnetic south. This means that if you align your panels to the south using a compass you will be slightly off the optimum azimuth.

To calculate geographic south you need to know the magnetic declination at your location which you can find using this website:
https://www.ngdc.noaa.gov/geomag/calculators/magcalc.shtml

This website gives step by step instructions for finding true south:
https://rimstar.org/renewnrg/finding_true_south_pole.htm

If you are installing a ground-mounted system, you are typically able to place the panels facing any direction you like, so you can just choose south (or north in the southern hemisphere). However, if you are placing solar panels on an existing rooftop you will have to work with what you have.

Can I install solar if I don’t have a south-facing roof?

Luckily for homeowners that don’t have south-facing roofs, you can still generate significant amounts of power from west and east-facing solar panels.

As an example, here are some simulated figures for a site in California. The table shows how much energy is produced per kilowatt of solar, per year, at different azimuths. The last column shows the percentage lost compared to 0° azimuth.

As you can see, even when facing directly west (90°), the system will still produce around 83% of a south-facing system.

(These are just some example numbers to give you an idea of how azimuth can affect output. These percentages will vary based on site location, and other factors such as tilt angle)

You need to be sure that you take losses due to azimuth into account when sizing your system. Therefore it is a good idea to use an online solar calculator to help you. Some of the typical hand calculation methods include rules of thumb for losses which assume a 0° azimuth.

Even though south-facing panels will produce the most energy over an entire day, there are some cases where it can be more financially beneficial to install your panels facing more towards the west. For example when your utility uses Time Of Use rates.

Time of use rates

Different utilities have different ways of charging their users for the electricity they use. Some just have a flat rate for every kWh of electricity used, while others use Time Of Use (TOU) rates.

TOU rates are when the utility charges you more for using electricity at peak times, than at off-peak times.

Since peak times are typically in the evening, it can make sense to generate more electricity from your solar panels later in the day, so that you are using less from the grid during these times.

This can be done by rotating your panels to the west, or if you have a rooftop with several different angles, it could mean you are better off placing panels on the west-facing rather than the east-facing sections.

When rotating your panels further to the west, you will generate slightly less electricity over an entire day. But since the value of the electricity you produce is higher, you may save more money, and therefore generate a better return on your investment.

Solar Panel Tilt

The other type of solar panel direction you need to consider is the tilt angle.

Tilt angle refers to the angle from the ground at which the solar panels are tilted, where 0° is lying flat.

During summer, the sun is high up in the sky so a low tilt angle would capture more sunlight. However, in winter, the sun is much lower in the sky so you would capture more sunlight with a higher tilt angle. Therefore the best tilt angle will be somewhere in between.

To generate the most electricity possible over the course of a year, a commonly used rule of thumb is to use the latitude of your location as the tilt angle. So for example, if you are located in Houston, Texas directly at 30° latitude, then you would tilt your panels at 30° for maximum electricity production.

While this method will give you a good starting point, close to the optimum tilt, it can often be improved on. You can usually increase your output slightly by decreasing the tilt to capture more energy during the longer summer days. How much you need to reduce the tilt depends on your location.

While some people use rules of thumb for this, we suggest simply trying a few different tilts close to your latitude angle, in whatever solar calculator you are using, and see which one results in the highest annual output for your location.

The increase in output that you get from this further optimization may be fairly negligible, but in some areas, it can increase output by around 0.5% or so, so it is worth checking.

Keep in mind that your racking installation may only be accurate to within 5° or so anyway, so you don’t need to get too caught up in finding the exact optimum tilt angle to within 1°.

If you are installing a rooftop system you will generally follow the slope of the roof, so you won’t be able to decide what tilt angle to use. Your system may produce a little less electricity than if it was at the optimum tilt, but it is unlikely to mean you can’t install solar at all.

For example, here are some simulated figures for a site in Los Angeles, California. The table shows how much energy is produced per kilowatt of solar, per year, at different tilt angles. The last column shows the percentage lost compared to the optimum tilt angle.

There are a few things to point out here:

• Typical roof slopes in the US are around 20°-35°. Within this range, there is only a very small change in output, less than a third of one percent.
• Even if you have a very flat roof of 10°, you can still produce over 95% of the energy you would at the optimum tilt.
• The optimum tilt here is around 29°or 30°. If you used the latitude (which is 34°) as the tilt, you would produce around 0.24% less than at 29°.

Maximizing output for a particular time of year

The above method tells you how to maximize electricity production over a whole year. But if for some reason you wanted to maximize electricity production during a specific season, then a different tilt angle may be better.

For example, if you have an off-grid cabin that you only visit in summer, you may reduce the tilt of your panels to catch more of the summer sun.

Avoid low tilt angles

Installing solar panels completely flat, or even at very low tilts, should be avoided, as this increases soiling losses.

When solar panels are tilted, the rain can be quite effective at cleaning panels as it hits them and rolls off. If a panel is flat, the water will pool on the surface, and even at low tilts water can collect along the frame. This water evaporates, leaving dirt on the panel and reducing it’s output.

Therefore, near the equator, where the theoretical optimum tilt approaches zero degrees, panels should be installed with at least 5° tilt, and ideally 10°.

For the same reason, if you have a flat roof, you will need to install mounting structures that tilt the panels, rather than laying the panels flat on the roof.

Another situation where low tilt angles should be avoided is in areas that receive a lot of snow. In this case, higher tilts help the panels to shed snow.

RVs/Campers

There is one situation when it is ok to lay your solar panels flat, and that is when they are installed on the roof of an RV or camper. In this case, you generally don’t have any choice, but you also have much easier access to the panels. This means that you can simply clean them regularly, or when you notice a drop in output.

Have any questions or comments? Let us know below!