Happy Solstice

happy-solticeThe long days of summer are here and solar production is at its peak for Cincinnati. We have plenty of sunshine here in the summer, but many people ask us if we get enough sun during the rest of the year to make solar projects feasible? The answer is, absolutely!  With thousands of solar power systems installed in southwest Ohio, there is no doubt solar works here.  The table below shows the percent of our annual sunshine we receive each month of the year.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total
5% 6% 8% 10% 11% 11% 11% 11% 10% 8% 5% 4% 100%

Obviously our best sun conditions occur from March thru October, but even those cloudy months of winter provide some good solar days.

The sun’s angle above the horizon peaks on June 20, the summer solstice, and reaches its minimum angle on December 20, the winter solstice.

How does this play into the best orientation of solar panels?  Ideally when the sun is perpendicular to the surface of solar panels, the panels receive optimum sun and thus produce optimum power.  So to maximize production at the summer solstice, we tilt our solar panels at 26 degrees so the panel is at a right angle to the sun (26 + 74 = 90 degrees).  This would make production optimum for one day of the year, and suboptimum for the rest of the year.

But solar is forgiving and solar power systems which don’t have optimal siting still produce lots of solar power! There is a large “solar sweet spot” such that, even if the tilt and orientation of the panels towards south is not perfect, we take a relatively small performance hit.

What happens in practice is typically one of three things:

  1. We mount the solar panels flush with the roof of the home.
  2. We mount the solar panels on a fixed tilt mounting system on the ground.
  3. We mount the solar panels on a variable tilt mounting system.

In the end, if the modules do not face true south and are not tilted at just the right angle, solar still works and we still produce power.

Let’s discuss the three options above.

Option 1

We mount the solar panels flush with the roof of the home. This configuration provides the best aesthetics and lowest installed cost for most residential systems.  Typical roof angles are 18 – 45 degrees in the Cincinnati area, the most common being 18 – 26.6.  The systems perform well and the neighbors don’t think a space ship has landed on your roof.

Option 2

We mount the solar panels on a fixed tilt mounting system on the ground. This approach is often taken when there is available ground real estate and building roof structure or orientation is not conducive to a solar installation.  Here is a  solar carport constructed for a client in Cincinnati. The home has a large south facing roof, but it is encumbered by a large dormer and two large chimneys.  The carport array tilts at 15 degrees as a trade off to maximize solar production and minimize wind loading on the structure.  The array is producing 100% of the electrical needs of the home. At this  local farm we had plenty of real estate and freedom to line up the array to face true south with a tilt of 30 degrees (optimum for Cincinnati).  In general, ground mounted structures will be more expensive than roof mounted systems due to the cost of building the mounting system.

Option 3

We mount the solar panels on a variable tilt mounting system. This allows the tilt angle of the modules to be adjusted (typically monthly) to follow the sun’s seasonal elevation changes.  This approach adds some cost due to the increased complexity of the structure, but the benefits are many. It is easy to mow and trim around the structure, solar production is maximized, and less real estate is needed for the array. SunRock Solar installed a  seasonally adjustable pole mounted array in Reading, Ohio. This site is interesting as it has some late afternoon shade so the array was oriented to face slightly south east rather than true south.  This actually improved the system performance by approximately 5% over a true south facing array.

To wrap up, there are many factors which contribute to the performance and aesthetics of solar power systems.  Each situation is different. By taking the time to analyze and discuss options with its customers, SunRock Solar can deliver a power system which melds aesthetic and performance expectations, with the reality of site conditions. Solar works well in Cincinnati!