Does Panel Orientation Matter?

Posted by Aman on August 19, 2010 | Comment-bubble
Category: Array Design

Honestly, I am pretty surprised by the lack of information out there about this subject; The majority of information I did find was either misleading or wildly inaccurate.

The short answer to this question is, YES, they do matter. But, how much?

According to this article, titled, "Does Tilt Angle or Orientation of Your Solar Panels Matter?", orientation doesn't matter much at all. The article claims that the Sandia National Laboratories (one of the foremost labs on photovoltaics in the country that considers renewable energy a matter of national security, read: very credible) says "orientation of solar panels has little to no effect on on how much solar energy is converted".

I searched on Sandia's website to try to determine what might have led the author to the conclusion that the "orientation of solar panels has little to no effect on on how much solar energy is converted."

This is what I found:

"A photovoltaic array can be mounted at a fixed angle from the horizontal or on a sun-tracking mechanism. The preferred azimuth (edit: azimuth is another word for orientation) for arrays in the northern hemisphere is true south. The decrease in energy production for off-south arrays roughly follows a cosine function, so if the azimuth of the array is kept to ±20° of true south, annual energy production is not reduced significantly. Some arrays are sited west of south to skew the production toward an afternoon peak load demand. The effect of array tilt angle on annual energy production is shown in Figure 12. For most locations, a tilt angle near the latitude angle will provide the most energy over a full year. Tilt angles of latitude ±15° will skew energy production toward winter or summer, respectively."

While there isn't any commentary in here about how much production is affected based on orientation, it is clear that Sandia believes orientation matters. Even 15° adjustments can help you skew energy production in different seasons if you see fit. The only thing I see that the author might have extrapolated was the part I bolded above, but that only applies to 40 degrees of 360 degrees of possible orientations.
So, how do we answer this question with good, clean data?
I took advantage of the National Renewable Laboratories resource, PVWatts, to determine how much power is produced in Austin, TX at various orientations.

Geography: Austin, TX
Tilt: 30°
Average deration: 77% (deration, aka, the amount of power lost within the system in the DC to AC conversion process, wire losses, head losses, etc.)
System Size: 1 kW
Below, I have included the kWh of power production each month for 5 different orientations, East (90°), Southeast (135°), South (180°, Southwest (225°), West (270°), and North (0°). All of this data has been pulled from PVWatts.

Kwh Production

This is a lot of data to take in. Below, I show how much less energy you would produce in comparison to South-facing panels in July, i.e., a 1kW array facing East would produce -51% less power in January than a 1 kW array facing South in July.Kwh Production Vs South July

This is pretty conclusive evidence, that yes, ORIENTATION MATTERS. Admittedly, orientation barely matters in the summer months because the sun is so high in the sky, bathing all surfaces in light equally, but it does matter in the other ten months. Since solar is still an expensive proposition, it seems like paying attention to design elements such as orientation are crucial when trying to maximize your return on investment and minimize your carbon footprint. I will address how tilt affects power production in a later post.


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