Thursday, September 10, 2015

Install Solar PV Panels - Is East or West Better

Is It Better To Install Solar PV Panels East or West

Solar PV Panels  East or West

Is it Better to Install Solar PV Panels Work Best East Or West In Florida?

Every Day this question seems to arise. Just like the sun that comes up in the east, and sets in the west will happen every day. One of the best ways to help a homeowner feel confident in this answer is to meet with them at their home.

I love meeting with a homeowner early in the mornings to do an onsite evaluation. If there is no shade issues to contend with, the obvious answer is the south side is sunny first thing.

But so is the East side. By 9 AM, any dew left on the south roof can be seen steaming off the shingles. This is the result of cumulative factor of radiant heat present in even in the early hours. But as the day goes on, as the south side stays sunny, the east side starts losing ground around 12 noon to 1pm. It is still light, but the angle of the sun to a directly facing East Roof (90 degrees) is fading quickly.

The suns rays are now straight up, but over the next hour or so, the main difference is in the angle, or pitch of the roof. On a steeply pitched roof, the west side will begin to shade the east side. This is the point that the east side loses its advantage and the west side takes over.

So the question always comes up, Install Solar PV Panels  on the east or west.

Also a factor here is the temperature. During the entire morning, the temp was slowing rising. Since Solar PV Panels work better in cooler temps, the morning sun can produce a slightly better output per hour. 
So now the suns angle is favoring west, but of course the south side is STILL SUNNY. Depending on what season we are in, the west side roof may continue to be productive up until at least 6 pm, maybe a bit longer.

      But here is the reality. During the times of season when the days are longest, we tend to have afternoon cloudiness and rainstorms. This would tend to negate the advantage of the West facing roof on those days. Solar PV needs light intensity, and clouds tend to block more light than heat. 

Dew Collects on Solar Panels
      But in fairness, many mornings in Fla are very dewy (is that a word?) and until the panels would dry off there would certainly be a loss in production as well on the East Side.

This brings up another common question.. How to clean the panels.. Best way is to wait for a dewy morning, and with a high pressure nozzle just hit them from the ground with a blast of water. However, if it is raining at least a few times a                                       a month, this will not be required at all.

        This simple test of how the sun moves on the homeowners roof proves that South facing roofs are best. So, Solar PV electric modules perform best when mounted on the south facing roof in Fla (not taking into account any shading issues). However, what happens if you do not have a south facing roof, or if you south facing roof is not suitable for solar? What if the house is not exactly facing due south? The simplest answer is Most are not.

         Southeast and southwest roofs are the next best options, but east and west facing roofs are not all that bad. Any Degree of South facing improves the results. Just as any degree of North facing reduces the results. In fact, a properly angled  solar array facing east or west will only result in about 5-15% less energy produced here in Florida. But which is better?

        For a definitive answer, most industry pros tend to look to the NREL website, and use the PVWATTS tool. If you want to spend a bunch of time there, then be my guest, but the bottom line is pretty simple.

               South is best. Next is either South East or South West (almost equal), and then directly East comes in b​y only a very small percentage over directly West. Here is the Chart from NREL. For those of you that really only wanted an answer, I am sorry this took so long to make the point. But for the rest that like to know why something is better, I hope this has made some sense.
PVWATTS Comparison East West
The tool that is commonly used to estimate solar electric output is called PVWATTS, which was developed by the U.S. National Renewable Energy Labs (NREL). We can enter a variety of variables to determine how much solar radiation to expect at a given location over the course of an average year. NREL uses historical hourly weather data, array orientation, temperature, and other factors to determine the expected system performance.

    So, the Bottom line is pretty simple, do what you can to get some southern exposure. But if the East roof has a great open space for panels, then use it with confidence. But if shading is a potential issue on one side or the other, then use either East or West that has the best roof surface space without shading. ​

        I hope this helps. It's a rule of thumb guideline that is a great starting point to factor which side to best install solar.  But, remember this... This article is about solar pv, not solar thermal. The difference between light production and heat production is a totally different article.

        But, I can sum that article up here. For any solar thermal, south is best, and then west. Period. The west side is always hotter in the afternoon, so installing solar hot water or solar pool heating will always be better on the South or West Side. Period.

Solar Hot Water Panel Facing West
Solar Thermal Hot Water Collector on South Facing Roof Is Best
Solar PV Electric Panels Facing South

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