This is the second post in a series about rooftop solar technology (view the first post here). The first post reviewed roofing costs because they affect the overall solar cost of a home. In 2016, Fortune recognized the trend towards less expensive solar power installations that could drop another 60% in cost from where they are today. Fortune points out that up until the 1990’s much of the cost reductions were due to technology and manufacturing improvements. They believe the future cost drops will be due to non-technical factors such as financing. I believe there are still technology improvements on the way. This post focuses on the variety of panels that are available for installation and the technology they contain.
It is amazing to look back and see how far the solar panel technology has progressed since Edmond Becquerel first observed the ability of light to generate electricity in 1839. Many in our industry worry about what disruptive developments will come from “kids in their garages”, so it is important to remember that Becqueral was only 19 at the time and he was working in his father’s laboratory. I can imagine that laboratories in 1839 are similar to basements, garages or other workspaces today.
Solar cells took over 110 years to become practical and we have Calvin Fuller and Gerald Pearson from Bell Laboratories to thank for their modern form. They were working on the Bell Solar Battery and in 1954 had created a working prototype. Within four years, solar batteries were powering The Navy’s Vanguard space satellite. These cells had an efficiency of around 14%. No meaningful improvement was made in efficiency until the appearance of thin film technology in the 1990’s. The next big jump occurred over the last three years as manufacturing and design improvements pushed efficiency over 20%.
Solar cells are commonly classified by generations:
• First Generation (or Wafer) – Wafer solar cells are created with crystalline silicon (c-Si). They are efficient, but expensive to produce and contain toxic metals like cadmium and lead. Wafer panels are easy to find but are not eco-friendly and easily identified because of their hexagonal shape.
• Second Generation (or Thin Film)– Thin film amorphous silicon (a-Si) is cheaper and cleaner to produce but is less efficient than first generation wafers. Thin film first made its consumer appearance in the 1970’s as the power source for pocket calculators.
• Third Generation (or Organic) – Organic solar cells are still not practical because of their low efficiency. They are cheap to produce but only have 1/3 of the efficiency of Wafer
An exciting development in thin film panels was achieved by Panasonic’s SANYO brand in the 1990’s. They are now producing thin film solar cells with nearly 20% efficiency (in the real world not the lab). Their technology is a real tongue twister, Heterojunction with Intrinsic Thin layer. I prefer the consumer friendly label “HIT”. Panasonic technology is being used in the Tesla Solar Panels scheduled to hit the market in California this year. Tesla will produce the products in both their Fremont, CA and Buffalo, NY plants.
HIT solar panels are examples of thin film technology so a deeper dive is required to understand who why they perform so well. The answer is due to the clever design of the product. They have a sandwiched design that reduces efficiency loss when heated while capturing more sunlight. This approach makes HIT “bifacial” or able to capture direct and reflected sunlight. This approach increases efficiency in the range of 2-3%.
Tesla’s solar roof is not the only product using of bifacial cells; they have been used for some time in space and in multi-positional configurations. A multi-positional configuration could be used to expose two sides of an array at different times of the day. When used in a vertical arrangement, instead of maximizing generation at high noon, two small peaks can be created; one in the morning and one in the afternoon. If the sum is at a low angle, it is possible to increase the angle of a horizontal panel to capture the reflection off of a light colored roof.
The energysage website provides a comparison of solar cell manufacturers. Their Economy, Standard and Premium categories do not match up with the solar cell generations above because energysage is a consumer-friendly guide not a science website. Also on the energysage website, you will find a regional cost comparison information. All of their information is presented using easy to understand graphics.
The next post will address the regulatory and legislative issues technologies associated with solar energy collection. Can government keep up the changes in the technology? Up until now, the answer has been a resounding “Yes”.
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.