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Published on November 28th, 2013 | by Guest Contributor


Rooftop Solar Can Meet 58% Of Peak Power Demand

November 28th, 2013 by  

Originally published on Climate Progress.
By Mari Hernandez.


new study by the Pecan Street Research Institute found that residential solar panel systems can cut electricity demand during peak summer hours by 58 percent.

The study used data gathered from Pecan Street’s demonstration project — an innovative living test lab that allows the research institute to provide original research on customer energy use, renewable energy integration and smart grid technology.

By monitoring 50 single-family homes in Austin, Texas with west- and/or south-facing solar panels from June through August this year, the study found that west-facing solar panels produced 49 percent more electricity during summer peak demand hours than south-facing panels, a finding that should make utilities think twice about excluding west-facing solar panel systems from solar rebate programs. According to the study, west-facing rooftop systems cut peak demand 65 percent, while south-facing systems reduced peak demand 54 percent.

Though west-facing systems may be better at cutting summer peak demand and add more value to the grid in certain regions, south-facing systems still have an advantage in total annual energy production — an important distinction mentioned in the report.

The Pecan Street study also looked at how much solar power was being used in the homes versus being returned to the grid. It found that during peak hours, homes used 80 percent of the solar power generated on-site, while just 20 percent was sent back to the grid. Over the course of a full day, 64 percent of the solar power generated on-site was used in the home.

Overall, the study concluded that solar panel systems can be an effective peak demand reduction tool, especially during hot summer months when utilities are trying to keep up with energy consumption.

“These findings suggest that rooftop solar systems can produce large summer peak reductions that benefit utilities and customers alike without requiring customers to change their behavior or sacrifice comfort,” said Pecan Street CEO Brewster McCracken in the report’s press release.

The Pecan Street study makes it clear that utilities have a lot to gain from rooftop solar, which isn’t the prevailing sentiment coming from the utility sector lately. Just last month, Arizona Public Service, the largest utility in Arizona, admitted that it had funded anti-solar ads during its campaign to change the state’s net metering policy.

During peak energy demand in the summer, the cost to provide electricity is extremely high and often unprofitable. By cutting summer peak demand more than 50 percent, solar panel systems offer benefits to the grid that could reduce costs for both utilities and their customers.

Mari Hernandez is a Research Associate on the Energy team at the Center for American Progress.

Image Credit: Shutterstock.

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  • Rockne O’Bannon

    Just have to share this. The news came out about two weeks ago that “westward orientation of panels is the way to go” as it came to be interpreted from this study. Of course, that is not true. It might be best for the utility, but I would never install panels that way, and the utility won’t install that way, you can bet on it. Even in summer, when they will be working hard to meet that peak demand period, westward facing panels will be hot, less efficient… and taking up a lot of resources just to produce power for three or four hours a day.

    Southward orientation. Seemed obvious to me.

    But check this out. I have this neighbor. He is just building his house and lo and behold, he puts up a solar array. Great. And it is huge (for where I live)… about 10 kW. Great. And it probably cost him 40 or 50 thousand dollars (where I live). Great. Must be nice. But it faces WEST. Not southwest. WEST. Actually, a few degrees NORTHWest (I live in the northern hemisphere.).

    Process that for a second. All of that construction cost and prep and materials and inverters and panels… just so the guy can generate a few hours a day. I figure his payback will be about 40 years. And all that electricity he generates? Well, unless he has 6 air conditioners, he is never going to use the peak output. His system is a huge waste of money and is truly a monument to the triumph of “me-too-ism” over reason. I feel sorry for the guy and kind of hope he never figures out what he has done.

    • Bob_Wallace

      Panels facing east or west will produce about 80% as much electricity as south-facing panels. Individuals might choose to mount their panels on east or west slopes due to aesthetic or practical reasons.

      Hiding the panels from the street view might be required in some neighborhoods or people may just not want their panels to show. I know one person who mounted to the east because of afternoon shade from a forest on his west. And I know one person who mounted west because of a mountain to his east that blocks morning sunshine.

      A location with frequent morning fog might be a candidate for west-facing mounting.

      In these cases you would install about 25% more panels to get the desired output.

      As for utility systems, take a look at this graph of electricity prices in Germany on a sunny day. What you see is that solar installed to date has wiped out normal midday peak demand and dropped the price of electricity to the level of late night electricity.

      But there are morning and afternoon peaks when prices are above average. Someone might look at those numbers and see opportunity. Mount some panels so that they would feed in when prices are highest. Produce a bit less, but what you produce would be valuable.

      • Rockne O’Bannon

        Thanks Bob. This tells me all I need to know!

        “Panels facing east or west will produce about 80% as much electricity as south-facing panels”

      • Rockne O’Bannon

        He has it facing a street. There is no morning fog. His roof is maxed out. He did not make a decision on size based on any particular algorithm. He gets a FiT. He is not a utility.

        So none of those points apply.
        And the graph you show has been up on this site for the better part of a year.

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