Optimum Tilt of Solar Panels

Optimum Tilt of Solar Panels for Osoyoos, BC, Canada.

To get the most from solar panels, you need to point them in the direction
that captures the most sun. This page is optimized for Osoyoos, BC, Canada, Latitude 49°N, using formulas and text found at: www.solarpaneltilt.com/optsolar.html

This advice applies to any type of panel that gets energy from the sun;
photovoltaic, solar hot water, etc. We assume that the panel is fixed, or
has a tilt that can be adjusted seasonally. (Panels that track the movement
of the sun throughout the day can receive 10% (in winter) to 40% (in summer)
more energy than fixed panels.) This page doesn’t discuss these so called ‘Trackers’. The current thinking is that with the continuing fall in prices for PV panels, it is easier to add more fixed PV panels rather than to build a tracker at considerable expense and, as with all mechanical systems, to then maintain it.

Solar panels should always face ‘true south’ here in the northern hemisphere. If you are using a compass to orient your panels, you need to correct for the difference, which varies from place to place. More on the subject can be found at “magnetic declination” at Wikipedia, you can try http://www.magnetic-declination.com/ to find the correction for your location. This also changes with time since the magnetic core of the planet is slowly moving!

The next question is, at what angle from horizontal
should the panels be tilted? Books and articles on solar energy often give
the advice that the tilt should be equal to your latitude, plus 15 degrees
in winter, or minus 15 degrees in summer. It turns out that you can do better
than this – about 4% better.

Fixed or Adjustable?

It is simplest to mount your solar panels at a fixed tilt and just leave them there. But because the sun is higher in the summer and lower in the winter, you can capture more energy during the whole year by adjusting the tilt of the panels according to the season. The following table shows the effect of adjusting the angle, using a system at 40° latitude as an example. (The comparison would be a little different for different latitudes.) Each option is compared with the energy received by the best possible ‘Dual Axis‘ tracker that always keeps the panel pointed directly at the sun.

Fixed Adj. 2 seasons Adj. 4 seasons 2-axis tracker
% of optimum 71.1% 75.2% 75.7% 100%

In short, adjusting the tilt twice a year gives you a meaningful boost in energy. Adjusting four times a year produces only a little more, but could be important if you need to optimize production in spring and fall. You can jump to the section on the best fixed tilt angle, or skip to the sections on two-season or four-season adjusting.

The graph below shows the effect of adjusting the tilt. The turquoise line shows the amount of solar energy you would get each day if the panel is fixed at the full year angle. The red line shows how much you would get by adjusting
the tilt four times a year as described below. For comparison, the green
line shows the energy you would get from two-axis tracking, which always
points the panel directly at the sun. (The violet line
is the solar energy per day if the panel is fixed
at the winter angle, discussed below.) These figures are calculated for 40°
latitude.
ideal solar calcs graph

Fixed Tilt

If your solar panels will have a fixed tilt angle, and you want to get the most energy over the whole year, then this section is for you. A fixed angle is convenient, but note that there are some disadvantages. As mentioned above, you’ll get less power than if you adjusted the angle. Also, if you live where there is snow, adjusting the panels to a steeper angle in winter makes it more likely that they will shed snow. A panel covered in snow produces little or no power!

For latitudes between 25° and 50°, use the latitude, times 0.76, plus 3.1 degrees.Taking Osoyoos as 49°N, this would be:
40.34 degrees from the Horizontal.

Adjusting the tilt twice a year

Formulas used: The best tilt angle for:

  • Summer take the latitude, multiply by 0.93, minus 21 degrees.
  • Winter take the latitude, multiply by 0.875, plus 19.2 degrees.

The best dates on which to adjust and the angle from horizontal:

Adjust to summer angle of 24.57° on March 3rd
Adjust to winter angle of 62.075° on September 12th

Adjusting the tilt four times a year

This would be the situation if you are connected to the grid and can use or sell all the power you produce.

Formulas used: The best tilt angle for:

  • Summer take the latitude, multiply by 0.92, and subtract 24.3 degrees.
  • Spring and Autumn, take the latitude, multiply by 0.98, and subtract 2.3 degrees.
  • Winter, take the latitude, multiply by 0.89, and add 24 degrees.

The best dates on which to adjust and the angle from horizontal:

Adjust to summer angle of 20.78°on April 18th
Adjust to autumn angle of 45.72°on August 24th
Adjust to winter angle of 19.61°on October 7th
Adjust to spring angle of 45.72°on March 5th

Summary for Osoyoos:

  • Fixed all year

    • 40.34°
  • Changed twice a year

    • Summer: 24.57°
    • Winter: 62.075°
  • Changed four times a year

    • Summer: 20.78°
    • Winter: 19.61°
    • Autumn: 45.72°
    • Spring: 45.72°