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How roof angle can affect solar panel performance

There are a lot of factors that can affect the performance of your solar panels and the economic benefits they can generate—things such as where you live and how sunny it is, how much you pay for electricity, which way your house faces—even the pitch of your roof. Variety is the spice of life, but the diversity of our architecture can affect the performance of solar panels. It’s important to understand how those differences in production performance related to the angle of your roof will affect the overall financial performance of your solar power system.

Regardless of roof angle, solar power provides financial returns

Looking at data from six cities- Boston, Los Angeles, New York, Chicago, Philadelphia, and Washington, D.C., we estimated the production levels generated at various tilt angles. We held the azimuth constant at 180° which in layman’s terms means we always assumed that the roof faced directly south. What we found was consistent with our investigations into the effects of other variables: regardless of where you live or what the angle of your roof might be, adopting solar power provides significant financial returns.

The angle or pitch of your solar roof actually has less impact on solar panel performance than the direction it faces. In general, optimal production occurs when solar panels face south at a tilt equal to 30°. But what happens if your roof is flat? Lowering the tilt all the way down to 5° only decreases production by about 10%, regardless of where you live. The difference in production for steeper roofs is barely noticeable. Increasing the tilt from 30° to 40°, for example, results in a negligible decrease of about 1%.

Slope of your solar roof does not decrease financial incentives

Just like other variables that affect production, the financial impact of the slight decreases in productivity related to your solar panel roof’s slope, depends on electricity prices in your specific market. In higher price markets, the economic impact of these reductions can be greater, but the overall savings from systems installed in these markets are greater, too. The net result is still extremely attractive. For instance, if you live in New York where electricity costs more than 18 cents per kWh, decreasing your panels’ tilt to 5° will lower production by a little over 8%. Although this decreases your optimal annual savings by around $120, you will still save about $1,000 per year. Because you live in a high-cost area, your savings over time will be greater, too, as electricity prices continue to rise. In Washington, D.C., the production decrease is a little larger at 10% because it’s further south, but because electricity prices are only around 13 cents per kWh, the economic impact is much less—only about $70 less per year. Annual savings in D.C., despite the 5° tilt, would still be in the range of about $800 per year.

Again, these savings are significant in and of themselves, making solar power systems financially viable alternatives. There are added benefits, however, when property owners can take advantage of federal, state and local programs that offer incentives such as tax breaks, rebates or solar renewable energy credits (SRECs), so sub-optimal conditions can still deliver significant financial returns.

Assessing how the different performance variables will affect your financial outcome can get complicated, but the EnergySage Solar Marketplace will help you to get multiple quotes from qualified installers and then automatically calculate the financial benefits each options provides, making it a lot easier to maximize the returns on your investment.


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