Written by Nani Pradeepan, P.Eng.
As the cost of a solar installation come down people are looking for choices for their solar systems. One of the choices people look for is a solar PV system with minimal deviation to the appearance of their house.
Solar roof shingles are one way to turn a traditional shingle roof into an energy producer. Solar roof shingles are a new green roofing product of the past few years. Solar shingles like traditional solar panels use the sun light to create electricity. Each of the solar shingles is comprised of photovoltaic cells and each shingle is a small PV module that has to be connected electrically in series to reach the DC voltage needed by the inverter which converts the DC electricity to commonly used AC electricity.
The typical DC input voltage for inverters is 350 to 500 VDC. That means many shingles need to be wired in series. This requires long strings of module to module connections wires that are all hidden beneath the finished roof and difficult to access.
When one module or its connection fails, all the modules in the string go out just like in Christmas tree lights. A service tech has no easy way of knowing which shingle is defective. A big portion of the roof often needs to be taken apart, and all components tested. Then, if matching replacement solar shingles are available, the array may be able to be reassembled.
PV shingles have been nailed or screwed into place as the PV shingles marketers wanted to entice roofers to be installers. However, roofers do not have the understanding or the necessary training to install solar-electric systems. If there is an electrical arc caused by a faulty shingle-to-shingle connection, it could start a fire in combustible tarpaper and wood roof sheathing.
Solar shingles are less efficient than traditional solar panels meaning need more roof surface than the traditional solar panels. Rated output of solar shingles is about 12 watts per square foot; whereas today’s best crystalline modules offer about 20 watts per square foot. Since solar shingles are installed on the roof deck there is no back-surface convective airflow, the all-black solar shingles run hotter than conventional solar panels, meaning further lower efficiency and possibly shorter product life.
PV shingles have been a transitory product. How long will companies selling this product keep producing them? For example, after five years, Dow ceased manufacturing and distributing solar shingles. There is no long-term experience with solar shingles products and they may or may not last. Will the warranty be supported over twenty five years as with traditional solar panels?
Even if the company and product is still available, will it be in the same form and electrical configuration to allow replacement? With all these uncertainties at present solar shingles are not prudent options for a green roof.
Currently, there’s no mass produced solar PV shingle solution for retrofit. If your house has a black roof, using conventional black-on-black modules installed flush with the roof may offer the best acceptable solution. Standard framed PV modules have been proven, reliable and productive, and we know how to install them well for the long term. For many people, the solution is to accept the beauty of a product that will produce clean electricity reliably for 40+ years.