Optimal Tilt for Solar Panels

Question: “What is the optimal angle to install my solar panels at?” This is a common query we get as solar installers, and obviously is one we need to consider when installing solar panels for our clients.

Answer: For most residential customers the optimal tilt is flush-mounted on their existing south-facing roof, what ever pitch that is. For flat-roof (typical of commercial) it is usually 30°, we hope to cover why in another posting. For customers building a new structure or ground-mount racking, the optimal tilt depends on: your latitude, shading, weather, and the type of panels installed. In most cases having solar electric panels in Saskatchewan facing directly south with no shading and tilted between 30° and 60° will be within a few percent of optimal annual output. If that is not specific enough for you to design your own racking, or win the bet you made at the pub last night, here is a table of modeled optimums including the annual energy output for various locations in the province and around the globe.

The following is a snapshot of the table: “Solar Electric (PV) Output at Optimal Array Tilt Angle” which shows modeled optimum tilt and output values for solar PV installs in many Saskatchewan, Canadian and world-wide cities.  You can click on the image to download the full .pdf image, or click here to open the .pdf in a new window.

Discussion: Although it is possible to model optimum solar panel angle or tilt as well as the expected output, these values are only valid for a very specific (if not hypothetical) install, which is subject to “typical” weather conditions and absolutely no panel shading.  In some of our other blog postings, we hope to explore the effect of changing tilt on the expected output of a solar install, some good reasons for using an array tilt angle other than the listed optimum for the majority of our solar installs, and the primary reasons for array output being less than the modeled value.

Source of data: The solar output data presented was generated using the RETScreen software developed for Natural Resources Canada, and available free on the web. RETScreen uses weather and solar irradiation data from a NASA database. Although we find RETScreen to be an extremely valuable tool, it is cumbersome to use, and certainly has its limitations.

Flush roof mounts usually best: For most city residential installs, the best option is to attach the array on a south facing roof. This mounting method generally does not affect the snow or wind loading on your structure, does not introduce any inter-panel shading effects, typically allows snow and debris to readily slide off or be removed from the panels and roof and often provides annual energy output only a few percent less than would be accomplished by racking the panels on top of the roof. In fact, most of the time the extra expense associated with racking the panels is not made up for by any extra output. As a result, the home owner is typically better off to spend any extra money on more flush-mount panels instead of spending it on racking-up a lower number of panels on the same roof.

Shading is more of an issue than panel angle: In virtually all in-city installs we have seen, shading of the solar array has a much larger impact on annual output than the angle of the array itself.

Saskatchewan has a fantastic solar resource: Being lucky enough to be based in Saskatchewan, it is very encouraging to see the extremely high levels of potential solar PV output available to us here. For Solar PV, it is interesting to note that the expected output is not simply a function of hours of sunlight. Specifically cool temperatures and other weather patterns cause the expected annual output from PV systems in Saskatchewan to be significantly higher than virtually all other global locations at the same latitude, and even (surprisingly?) higher than many other cities in the world traditionally associated with sunshine.

What do you think? We encourage you to leave a comment with any general questions, clarifications, etc. or contact us directly to learn more about the optimal install angle for your particular location, or to learn how you can start taking advantage of this amazing energy resource in your own home or business.

4 Responses to Optimal Tilt for Solar Panels

Randy Ingman says:

Hi,
great site!! I interested in the Wood Mountain install for a number of reasons. Firstly it’s South Sask. where Irradiation is high, second it’s installed at optimal tilt. Now I’ve calculated the KWhr/(kW installed) for this site and found about 1260 kWhr/kW installed, assuming 220 W panels. Are they 220 W panels?

    Brent says:

    Hi Randy, thanks for the kind words.

    The Wood Mountain install is 15x180W panels with Enphase microinverters. 2.7kW total install. I see that system produced 4,230 kWh from Jan 29, 2011 to Jan 28, 2012, yielding 1566 kWh/kW over the past year.

    This relatively high realized yield was obtained even with a tree and power pole providing shading on the system during some of the year.

    The Enphase inverters are said to produce 16% more output than standard string tied inverters on average, and can certainly be seen to help when shading exists.

chris reynolds says:

Looking at buying a house and installing pv panels on the roof but I can only put them on the south east side the house is on a 45 angle what kind of losses i’m I looking at I live in Medicine Hat Alberta any advice would help.

    Brent says:

    Hi Chris, that’s a great question. In general, although south-facing is “best” S/E or S/W facing is still really good, and E or W facing are still viable when that’s your only option.

    Again based on RETScreen, and using the same assumptions as were used in the table linked in the article, here are some numbers specific to Medicine hat.
    Optimum tilt for south-facing in Medicine hat is 46° which produces 1732 kWh per year per kW installed.
    45° array facing E or W in Medicine hat will produce 28% less energy per year (1243 kWh/yr)
    If facing E/W RETScreen suggests flat (0° tilt) is the best option providing 1360 kWh/yr. However, dirt and snow build up on a flat panel would likely reduce this theoretical output.

    My feeling is installing panels in the least shaded, most south-facing area available flush mounted on the roof to avoid wind and snow loading issues is typically the best option for in-town installs.

    Note that the 45° West/East facing install in Medicine Hat is still out-producing an “optimal” install in Vancouver, and much of Europe. Most residents of solar happy Berlin should be envious of your options!

    Hopefully that has answered your question?

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