Building-Integrated Photovoltaics: Walls and Roofs that Generate Power and Save Energy

Building-integrated photovoltaics (BIPV) combine function with form, featuring solar panels that generate electricity and blend in with their surroundings. That's not an easy combo, since a solar panel's efficiency and aesthetics are often inversely proportional. In a previous article, we looked through some cutting-edge research on solar windows. Today, let's examine BIPV technology that's commercially available and already generating a buzz.

World's Largest Organic BIPV Installation

Organic photovoltaic (OPV) cells are carbon-based, thin, and manufactured with an environmentally-friendly process. Unfortunately, they also suffer from lower efficiency and less durability compared to their rigid silicon counterparts. As such, they tend to be used mostly in small applications where low weight and high flexibility are the top priorities.

In spite of the trade-offs, researchers and companies have dedicated many hours and dollars to bring OPV into the mainstream. One such firm, Heliatek, just installed a 22.5 kW OPV array onto a school rooftop in La Rochelle, France. The installation - the largest of its kind - was completed in a single day by a mere half-dozen workers. (This page has a video that shows the installation process.)

The solar panels are only 8% efficient - roughly half as efficient as traditional PV - but the easy installation made up for the lower power output. The company declined to reveal the cost of the project, but says that the array will generate about 15% of the school's electricity needs.

Normal PV panels are made of silicon - the same material that's used in the integrated circuits  that allow you to read this article - and as such, their manufacturing process is dirty and energy-intensive. Scientific analyses have shown that the carbon payback period for silicon solar panels is about two years and the energy payback period is around three years. Heliatek's manufacturing process is devoid of toxic materials and uses so little heat that the energy payback period for its OPV modules is only three months.

Here's the part the concerns me: organic solar cells have a short lifespan. Where rigid silicon PV panels typically degrade at less than 1% per year,  OPV panels don't usually last longer than a decade. Heliatek's accelerated testing showed that their OPV panels degrade at just under 10% per 3000 hours at 85^oC .  Heliatek CEO Thibaud Le Séguillon wrote, " The 10% degradation after 3,000 hours at 85C and 85Rh is an accelerated aging done in our lab. This gives us the confidence to warranty the performance of our product for 20 years, i.e. after 20 years we warranty that the product perform at least at 80% of the initial performance (1% degradation per year on average similar to the standard solar panels)."

Since OPV cells tend to perform well in diffuse light, an outside wall, which gets less direct sunlight, would be better suited to OPV than rigid silicon, which prefers direct sunlight. Heliatek also makes semi-transparent OPV cells that can be affixed to windows, producing tinted glass (with a pretty cool look, in my opinion) that generates electricity.

A BIPV Roof with Insulation

Electricity isn't the only form of energy that we use. A good chunk of society's energy consumption is used for heating and cooling. As I write this article, the outdoor temperature in the northern US is hovering around 0F (-18C). Thanks to a well-insulated house, our small wood stove is keeping the interior at a comfortable 75F (24C).

Speaking of insulation, a roofing upstart has created a roof that addresses three issues: wind resistance, insulation, and electricity generation. The company, appropriately named 3 in 1 Roof, engineered a roofing system that can withstand 200 MPH winds (that's higher than a Category 5 hurricane), provide R-16 insulation (equivalent to about 5" of fiberglass batt), and generate electricity on par with the Tesla solar roof. Oh, it looks good, too:

I interviewed Carmen Bellavia, President & CEO of 3 in 1 ROOF Inc, who told me more about his product. Here's the Q&A:

How long has your company been in business? How did you get your start?

• Got my start as a roofing contractor during 1986 in PA and some years later in FL too.

• The design concept (originated in my mind) was to create a tile that didn’t break when walked on.  But the only thing I could think of making the embodiment from was concrete, rendering a 35% heavier and more expensive product.

• In 2009 I began working with SPF roofing systems.

How many engineers worked on the product, and what are their backgrounds/credentials?

• I’ve not counted. Most have came and went, but vendors from companies we promised to buy enormous amounts of raw materials from put their chemical engineers at our disposal. So did a couple of manufacturers we rented floor space and machinery from.  3D engineers were instrumental in creating prototypes and then using those CADs as negatives to create molds that were then modeled into CNC programs. Engineers from Intertek and Underwriters Laboratory have been very instructive as well as.

What type of PV cells are you using? What's their efficiency?

• We can use any cell on the market, standard or color because the product is not pigeon holed nor have we committed exclusivity to anyone.

• I believe efficiency is 21% for black or blue and 18.3% for colored.  But that varies with manufacturer and ratings.
  
  

What material are the roof tiles (substrates) made of?

• Custom blended closed cell 3-lb polyfoam with a proprietary cement based geopolymer 2-part top coating.

How many installations have you completed?

• One (just like Tesla) but it’s been on a home for 2 years while we tweaked the product and enhanced manufacturing capabilities.

I used the cost estimating tool on your website. It told me $30k for a non-solar roof and $44k for a solar roof. I assume that means $44k total, if I went with a solar roof. Is that correct, or is it $44k for the part covered in solar, with $30k for the part not covered in solar?

• You were correct in your first thought 30K + 14k for the solar upgrade total 44k.

How do you determine what part of the roof is covered in PV? Do you conduct a shading analysis?

• No shade analysis.  Because who really orders solar when they know their southern roof is always shaded?  And who orders solar without the installer coming over to look at the structure?

• But, since we reduce BTU consumption before we produce power, we automatically decrease the needed solar array by almost 40%, and our product can be placed virtually at the edges and valleys of the roof (no need for easeway like solar panels because firefighters can walk on top of the solar) allowing for a greater area on the southern side to support solar.

What type of inverters and/or optimizers are you using?

• Microinverters, and they are uniquely installed in what we deem a junction tile, part of our patent.

Your website shows a behind-the-meter energy storage system (ESS). Is that included in every installation, or does it cost extra? If extra, how much?

• Standard Supremacy 1000 is $8,000.00 extra.

What's the capacity (kWh) of the ESS?

• Standard is 5.2 kW of power and about 10 kWh of capacity.

How long is the warranty on the ESS?

• 12- years on the stationary batteries with unlimited cycles, lifetime on the power management system.

Any other technical information you'd like to share?

• Because our roof system allows ZERO thermal gains into the attic, the “Supremacy 1000” is recommended to be placed in the attic.

• At night when the air cools down (upon the first night of installing a 3 IN 1 ROOF), the 160 degree hot air in the attic from that day escapes through the air vents and attic air is cool by first morning after installation.   Here is where it gets interesting, because there is zero heat transferred into the attic, the cool air stays in the attic all day.  In fact, our data shows the attic temp seldom goes above 75 degrees on a 95 degree day.

• Look at Tesla Powerwall; they show it installed in the garage and/or outside by the structure.  That's because most lithium batteries begin to malfunction above 110 degrees.  Therefore, they can’t install it in their attic areas because they have as much, if not more, thermal gains than traditional roofing.

• What’s the difference?  The further away the batteries from the source of power, the more voltage is lost along the lines. In fact once the lines hit 80 feet (24 meters), the voltage drops by 50%.

• By putting those stationary batteries, which perform way better below zero than above 110F, in the attic, the system is practically right under the solar panels.

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Tom's lessons to remember in 2018:

• Windows, rooftops, outside walls - anywhere the sun shines, directly or indirectly, there's power available.

• Inefficiency is acceptable if the price is low enough.

• Reducing consumption is less costly than increasing production, but when both are affordable, do both.

Thanks for reading, and I wish you all a great New Year!

Images courtesy of Heliatek and 3-in-1 Roof, respectively

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