In this article we will discuss solar roofing systems, which integrate roofing materials with solar PV panels or solar thermal systems. Specifically we will cover, metal roofs, PVC flat roofing membranes and asphalt shingles. Although most roof-mounted solar systems are installed on top of an existing roof – be it an asphalt shingles roof or any type of flat roof – these solar systems are not integrated into the roofing material, and therefore are not solar roofs.
Why Are Solar Panels Installed On Roofs?
Most solar systems are installed on a roof of a house or a building. The exception are solar farms or ground-mounted solar installations, but these are rare, and are usually 100% commercial solar systems. There are a number of reasons why most solar systems are installed on roofs. The primary one being limited space – especially in an urban setting, where roofs represent significant unused space. Another reason is that usually roofs are not shaded by trees, nearby buildings, etc – they are the highest point of a building with great sun exposure, which makes them perfect to install solar panels on.
What Is a Roof-integrated Solar Systems?
Solar roofing is a final product, which integrates solar panels with the roofing material suitable for either a sloped or a flat roof. The solar panels used in solar roofing are usually thin-film photovoltaic laminates. Most popular Solar PV laminates commercially used today, are the Unisolar thin-film PV panels.
Unisolar thin-film PV laminates were originally designed to fit into and be integrated with standing seam metal roof panels. Unisolar panels are 15.5 inches wide and fit perfectly into a 16″ standing seam panels, and are attached or laminated with special butyl adhesive that is on the back of each Uni-solar PV panel.
However, unlike with metal roofs, solar integrators were having flat roof leak repair issues with solar systems they installed on flat commercial roofs. After they installed solar mounting racks and attached them to the roof deck, the fasteners would start leaking after a while.
Roofing manufacturers adressed this issue with different versions of flat roofing materials that integrated Unisolar PV panels – one such system is IB Solar Roof. There are many types of both solar metal roofs and solar flat roofs, using solar PV panels from various manufacturers (though as I said, most do use Unisolar PV laminates).
Solar Metal Roofing
The most common type of solar metal roofing is the standing seam metal roof with integrated Unisolar PV laminates. Unisolar PV laminates were initially designed to fit in the pan of standing seam panels, with the connection terminals concealed by the ridge cap. Because the connectors or terminals of these PV panels are not UV stable, they need to be hidden from the sun, while the rest of the panel is of course exposed to the sun to generate solar electricity.
The benefits of standing seam solar metal roofing include fast installation, easy troubleshooting, and lifetime leak free roof performance. Additionally, in the US, you can get the 30% solar tax credit for installing a metal roof, as it is a part of the solar system.
Solar Metal Shingles
Another type of solar metal roofing would be solar metal shingles. The concept is similar to solar standing seam roofing, but since metal shingles are much smaller, the solar PV laminates have to be adjusted to the size of the shingle. Also, all the terminals must be connected during the installation – if you miss just one, the circle will be broken and the solar system will not work. Imagine finding the broken link when you have hundreds if not thousands of metal shingles to take off to find one broken connection!
Price-wise, I think that standing seam solar metal roofing is much more viable, as there is substantially less installation labor involved and much less potential troubleshooting, if something goes wrong. Imagine hiring a solar integrator and a professional metal roofer at $75-100 per hour – each – to find what is wrong with your solar metal shingles roof. Even if everything is peachy, the amount of time that will be used to install solar metal shingles is much more than that of a solar standing seam roof. The total solar system price will be significantly higher just from all that extra labor.
The bottom line is that the choice of solar metal roofing system that you decide to use will be more of a personal preference. Both will work great when professionally installed, and will last a very long time.
Solar Flat Roofing
The main reason why flat roofing materials manufacturers began developing solar flat roofing systems was to A) eliminate roof leaks associated with flat-roof solar installations, and B) sell more flat roofing materials, which is their main business after all.
Solar Flat Roofing is a great concept, but has some limitations. First, the angle on the solar panels is flat, so these panels will not catch as much sunlight as tilted or sloped solar panels. Second, solar flat roofs will be much more effective in warm climates vs. colder northern climates such as New England, as in the winter, flat roofs are completely covered with snow and sunlight does not get through to the solar panels.
That said, the benefits of solar flat roofs far outweigh their drawbacks in colder climates. The solar PV panels that are integrated into the roofing membrane eliminate 99% of roof penetrations, considerably reduce the weight of the solar system and the total solar system price. Not only are the solar panels prices lower for roof-integrated solar systems, you also eliminate the entire rack-mounting system (which costs about $1 per watt of your solar system) – and that is not small beans – you will save about 10-15% off your total solar system cost. Also, since the roof solar system weighs much less than regular solar panels mounted on racks, you also eliminate substantial weight, and your building construction costs will be much less, because you can reduce roof load requirements.
Solar Asphalt Shingles
Solar asphalt shingles are very similar to solar metal shingles described above. The main difference is that they are designed to work with 3-tab or architectural asphalt shingles instead of metal roofing shingles.
Although solar shingles may seem like a great concept, please consider the following factor, which makes them not such a viable option when it comes to solar roofing. Solar shingles, just like metal solar shingles, take a very long time to install, as each shingle must be connected to the rest of the solar system in the series. However, unlike solar metal roofing shingles, there is no room to conceal the terminals under the shingle, so all connections must take place inside the attic space. Holes must be pre-drilled for each shingle, and terminals are fed inside the attic where they are connected.
This slows down the installation process significantly, and usually you cannot finish this in one day. If it starts to rain, your roof is toast. There are too many penetrations under the solar shingles, and it is very easy for water to get in. Of course, there are ways to prevent the roof from leaking even if it rains and the roof is not finished. You can run the last row of shingles and overlap it with roof underlayment, which will prevent the roof leak. Still, this makes the total job that much more complicated and costly.
One more thing to consider is the fact that asphalt shingles only last about 15 years and will have to be replaced down the road, where as a metal roof will last pretty much forever, or at least the lifetime of your house.
Solar Roofing Resources
Solar System Guide – everything you need top know when designing a residential Solar PV system – positioning of your roof toward the sun, shading and angles of your solar panels, choosing the solar panels and inverter, etc.
Metal Roofing Materials – learn about different metal roof types and which metal is better to use – steel, aluminum, copper, zinc, etc., as well as learn more about metal roofing prices.