The Best Way to Position Solar Panels
Homeowners looking to add solar panels to their houses have much to consider. Some of the decisions include budget, which type of panels to install, and which installers to hire. When it comes to which direction the solar panels should face, it would seem to be an easy decision and not open to debate. After all, it should be easy to measure which direction provides the most sunlight.
Arriving at the correct answer isn't as easy as you might think. For those living in the Northern Hemisphere, conventional wisdom has been to point the solar panels to the south in order to capture the most sunlight and to generate the most energy. According to a 2014 study of 110,000 homes in California equipped with rooftop solar panels, 71% of the solar systems in the state face south. But is this really the best choice?
West May Be Best
While mounting panels to point west would lower overall electricity production, catching the sun in the late afternoon means electricity would be produced at times when it would be more valuable to the grid. This is the time period when residents typically watch TV, turn on lights, and run the dishwasher or other appliances. Consequently, it's the time when electricity prices are higher.
Overall, houses with solar energy systems use about half as much electricity from electric utilities than conventional houses. But beginning around 4 p.m. and throughout the evening, they use more. This actually adds demand during usage time, which is typically at 5 p.m.
By the Numbers
This is what actual usage looks like when you compare west-facing and south-facing panels:
- Starting at 5 p.m., west-facing panels produce 55% of their peak output. A 10-kilowat solar system would produce 5.5 kilowatts.
- During that same time period, south-facing panels produce 1.5 kilowatts, just 15% of peak output.
Why All Solar Panels Don't Face West
Given this information, you may wonder why all solar panels aren't installed facing west. For a start, some homes are oriented north/south, so south is the only way tiles can be installed. Others live in areas where the local electric utility pays a flat rate, rather than having rates based on time of use. Still others use solar power to be off the grid entirely. As an incentive to get homeowners to install west-facing solar panels, the California Energy Commission began paying a bonus of up to $500 for new west-facing installations.
Wait, Not So Fast
In a guest post in the Scientific American blog, Dr. Joshua Rhodes pointed out the Pecan Street report, which served as the source for many articles advising people to point their solar panels facing west instead of south, offered a simplistic solution. His testing process is described below.
Dr. Rhodes' Test
This is the testing method used by Dr. Rhodes and his group, as reported in the journal Solar Energy:
- They built a model of a solar panel and calculated electricity output for every possible placement, including the facing direction and angle of tilt
- They calculated results for more than 1,000 locations in the United States, based on the typical meteorological data for each region.
By factoring in electricity costs in any given location, Rhodes was able to accurately determine the best solar panel placement for each location.
Using Austin, Texas as an example, Dr. Rhodes was able to make these conclusions:
- In the course of a year, the west-facing solar panel array produced about 14% less energy than the south-facing array.
- During summer months, the difference was only 1% less.
- The best placement was approximately halfway between south and west.
The Best Direction
Dr. Rhodes pointed out that ultimately, deciding the best direction for placing panels comes down to incentives, noting that in Texas, homeowners received incentives if the installed panels to face south. In the end, he wrote, the deciding factor will depend on the local solar resources, local prices, and the incentive structure set by the local energy utility.