One install we have been working on is for the Hartford Emergency Services Building (Police and Fire) on the VA Cutoff road in White River Junction, VT. This project calls for 13kW solar array on its flat roof, which was recently resurfaced with a white membrane material. Since it was a new roof with a warranty, we had the roofing company do training, inspections and repairs for us in order for them to uphold the warranty.
With these membrane roofs, it is especially important to avoid penetrations if at all possible. So a ballasted, or weighted, solar panel mount can be a good choice. We reviewed a couple of different systems out there and decided to go with a relatively new product by ECOlibrium, which is called the ECOFoot. It is made in the USA from recycled plastic.
But, after an analysis of how much solar energy we might lose due to snow remaining on the panels for many days in the winter, this building should still be able to reduce its electric bill by about 13,000kWh per year.
We do get a lot of snow in this area, but it occurs at the same time of year when we aren’t getting a lot of hours of sun… so the snow cuts out some potential energy, but probably less than 15% of the year round total. We get so many more hours of sun in the summer, that we can produce almost 85% of the annual total during the other three seasons. Shading between 8am and 4pm in the summer months reducing energy production much more dramatically than snow that we get in the winter.
To use these ECOfoot mounts you need to add a slip sheet or buffering material between the footing and the roof material. In our case we used a sheet of the same roofing material. You need to work carefully on the roof, removing sand or stones from all surfaces to avoid gouges or weaknesses to the material that will cause a leak. From a structural perspective, since these footings are so light, the total weight we added to the roof amounted to less than 7 psf (pounds per square foot).
Be sure to order and pay for the professional engineer design for your system, especially when working on a municipal or commercial building. This design takes into account the wind loads, snow loads, and shape of the building to determine the amount of ballast and or clamping between modules that might be needed. ECOlibrium was able to provide this service and worked with us directly to answer questions and solve issues that came up along the way.
Just a note on summer and winter electrical usage: Our utility providers in NH and VT (and many other states) offer a “net metering” capability that means they will provide credits in the summer for any extra energy produced by your solar PV system, and those credits can be used during the evenings or in the winter when there is much less sun. This crediting occurs over the course of a calendar year. If your solar PV system makes more energy than your building uses at the end of the year, then you will be donating those credits back to the utility. This may change in the future, but that’s the situation for NH and VT today.
In the next blog I will post pictures from this install and the public url for monitoring the Hartford solar PV system. There should be a press release and ribbon cutting ceremony in the next few weeks as well!