This is the first post in a series about rooftop solar technology. I was inspired to write this after talking to some members from Hawaii and reading the Tesla SolarCity pricing announcement. The series will cover roofing jargon, costs, underlying technology, legislative policy, regulatory issues and design, so let’s get started.
The growing interest in solar generation in 2016 has been borne out by recent numbers. In May, the UK announced that solar generation has surpassed nuclear and coal generation. Focusing on the US, you can compare state-by-state solar activity using information published by National Renewable Energy Laboratory (NREL) through their Open PV Project. NREL’s SunShot report is an excellent periodical that presents a global perspective. It shows that the US installed the second highest number of solar units in 2016 behind China. This moved the US up to fourth in total installed capacity. Only China, Japan and Germany has more installed solar energy systems. With one more year like 2016, the US will surpass Japan and Germany for installed capacity. Most experts underestimated the performance of US solar in 2016 because of the potential expiration of the Investment Tax Credits (ITC). A future post will be dedicated to legislative and regulatory issues behind solar energy.
Before we can talk more about solar on the rooftop, we should review the rooftop itself. The most common solar setup involves attaching panels to the roof, getting them to point as directly towards the sun as possible, and storing the generated electricity. Some of the more common roofing materials, arranged roughly in cheapest to most expensive order, are:
- Foam, Spray Polyurethane Foam (SPF)
- Basic Asphalt (25 year)
- Architectural Asphalt Shingle (30 year)
- Fiberglass Shingle
- Corrugated Metal Sheet
- Premium Asphalt Shingle (50 year)
- Built Up Roof (BUR) or Tar and Gravel
- Metal Shingle
- Stone Coated Metal Shingle
- Wood Shingle
- Shake Shingle
- Metal Seam
- Copper or Zinc
Not every roof can use these materials. For instance, on flat roofs, you might go with SPF or BUR, but these materials would not be ideal for sloped roofs. You would typically find BUR and SPF on commercial and urban multi-units. All of the others you find on sloped roofs. I have never seen a tar covered sloped roof.
Each method has distinctive installation procedures, and costs vary significantly by geographic location. Chimneys, dormers and other features of the roof design that require fitting of the material to the roof complicate installation and drive up costs. Higher grade shingles cost more (although the difference in cost might not be as high as you think), and even the underlayment varies based on what kinds of shingles are used.
The jargon used by most contractors is unfamiliar to consumers. Consumers think of everything in terms of cost per square foot ($/SQFT). Contractors use the term “squares” for their calculations where one “square” is ten feet by ten feet or 100 SQFT. This simplifies ordering because the materials are organized on pallets, accounts for waste (unused material) and for any mistakes. I had my own roof upgraded nine years ago and I still have a stack of shingles in the shed.
The chart above presents the relative cost differences between different roofing materials. Please use this chart knowing that I have accounted for a typical installation that included removing and disposing of the current roof, all material, labor and incidental costs. There are also regional variations that are difficult to capture, which is another reason these are relative costs. These costs are expressed as “squares”, the common unit that will be used in this series.
The red line on the chart signifies what could be called ultra-high end roofing. This line will become important in later posts, especially when talking about the Tesla SolarCity roofs. Here are a couple of interesting things to notice when looking at total installed cost. From left to right:
- Although the Fiberglass Shingle material cost is less expensive than 30 Year Asphalt, the final installed costs are very close.
- Shake Shingle and Wood Shingles are nearly identical in material cost, but Shake Shingles take more time to install because they are irregularly shaped.
- Copper and Zinc material costs vary all of the time, so they were very difficult to normalize
It is important to consider the entire roof when looking at the economics of solar, especially when considering new approaches such as the Tesla SolarCity roof. You don’t attach anything to a Tesla roof, because the roof is the solar collector. When we get to the economics part of this series, we will evaluate the cost of the roof so that we are comparing apples to apples.
The next post will address the technologies behind solar energy collection. The science has improved greatly over the last couple of years. I found the subject matter interesting, but I am an engineer.