Making the Most of Solar Energy

Experimental facade system by LafargeHolcim and Heliatek has the potential to produce superior energy-generating, energy-saving buildings.

By Shari Held

Solar energy – it’s the most readily available and least expensive source of energy worldwide. In the U.S., homeowners and others who may have scoffed at the idea 20 years ago are now embracing it. By the end of 2018, more than 2 million solar systems are anticipated to be installed in the U.S.1

We’re accustomed to seeing solar panels on rooftops, but in the not too distant future, our buildings could be clad from top to bottom in building-integrated photovoltaic (BIPV) facade systems.

The energy savings could be substantial when you consider that commercial and residential buildings combined used nearly 39% of the United States’ total energy consumption in 2017.2

Development of an innovative, photovoltaic (PV) facade technology is taking shape in Europe. The effort is spearheaded by Paris-based Ductal, a technology of LafargeHolcim Ltd., headquartered in Zurich, Switzerland, and Dresden, Germany-based Heliatek GmbH. The two companies have partnered to produce a PV precast concrete facade system with an energy-generating potential that surpasses traditional rooftop BIPV panels.

“The three parameters that determine when this product will be useful or efficient will be the location, the orientation and the height of the building,” said Carlos Piles, head of Ductal Europe. “The higher the building, the more efficient the panels will become.”

The partners first presented the concept in Paris at Batimat, the international construction/building elements exhibition in November 2017. They completed the first pilot project for the unnamed product in September 2018. The product and the process of creating it are still in the experimental phase.

A productive partnership

LafargeHolcim’s Ductal, an ultra high performance concrete (UHPC), has been in the marketplace for years. Ductal is used for rainscreen cladding solutions, custom-built applications like facades, roofs, sunshading or brise soleil as well as for a building’s structural elements. But, two years ago, the company started thinking about developing an innovative, energy-generating precast building facade featuring its Ductal precast panels. The basic concept was to marry Ductal’s UHPC precast panels with PV technology. This would allow the facade to harvest solar energy on-site that could then be used to heat and cool the building.

“We understood that today, photovoltaic panels were merely being used on the roof,” Piles said. “That is only 20 percent of the building. We felt that using photovoltaic technology in the facade would be much more effective for energy-generation.”

LafargeHolcim had the precast side covered. As luck would have it, BATIMAT, the leading international trade fair for the building industry, brought LafargeHolcim together with Heliatek.

Piles said there were several criteria LafargeHolcim looked for in a partner. First of all, it wanted a partner that was both willing and able to participate for the long term. In addition, the prospective partner had to produce organic PV film because LafargeHolcim was interested in a light weight, thin PV film solution to match the characteristics of its Ductal panels. Ductal UHPC concrete is reinforced with organic fibers rather than bulky rebar. That allows the panels to measure less than 5/8 of an inch.

Heliatek’s HeliaFilm fit the bill, measuring .04 inches thick and weighing just over 0.2 pounds per square foot. The partner’s PV film technology also needed to be upgradable so the aesthetics, such as film colors, could be modified or customized. And, most importantly, the film technology had to be highly efficient when it came to solar energy gain.

“So, within those four parameters, we realized the best partner was Heliatek,” Piles said.

Green and sustainable to the max

It is a big plus when partners share a similar environmentally friendly philosophy.

HeliaFilm is touted as the greenest PV solution worldwide. It contains no heavy metals or toxic materials and uses just 20 grams of carbon dioxide per kilowatt hour produced. It takes only .035 ounces of organic material to produce one square meter of HeliaFilm. The production process consumes very little energy – with a less than three-month energy payback period. The lifetime cycle impact of HeliaFilm is five times less than crystalline PV elements used in traditional cladding systems. In addition, HeliaFilm contains only 1% inorganic material, making it easily disposable.

“What we are trying to do here is reduce energy consumption by producing a concrete-based product that can produce energy for the building.” Piles said. “We chose Heliatek for its sustainable position as well.”

Concrete is known for being one of the most resilient and durable building materials. It can also be manufactured using industrial byproducts and/or some of the most common aggregates and minerals. At the end of its long lifespan, it can be recycled. Piles estimates the Ductal/Heliatek panels will have a lifespan of 50 years or more.

Benefits for all

It’s not just the planet that will benefit from BIPV facade panels. Architects will have another design option to meet the growing demand for residences and buildings that are energy-efficient, low-maintenance, built to last and aesthetically pleasing. Plans are for the panels to be available in a variety of sizes and colors, including yellow, blue, white, black and green. The PV precast facade panels will be produced in standard sizes ranging from .59 in. by 3.9. ft. by 3.9 ft. to .59 in. by 3.9 ft. by 11.8 ft.

“But if an architect wants to have facade panels 30 centimeters wide and 3 meters long (11.8 inches wide and 9.84 feet long), we can deliver it,” said Kathrin Wiertelarz, Ph.D, system application engineer for Heliatek. “That’s no problem. The technology gives us a wide space of possibilities.”

Another plus is the panels can be applied on both new construction and existing buildings as well as residential, commercial and institutional and public buildings.

Construction companies and installers will benefit from the ease of installation. The solar-energy-generation system is built into the precast facade panels, so there are no equipment boxes or wires to install on-site. That means less installation time and no steep learning curve.

“We are not changing the way installers operate today,” Piles said. “It’s a plug-and-play solution, so they can install it the way they would install a rainscreen facade today. They just fit the panels on the horizontal and vertical rails.”

Homeowners and building owners will reap the biggest benefit of all as the facade will literally pay for itself through energy produced. These BIPV facade panels can potentially double the energy-generation levels of roof-based solar systems. BIPV facade panels provide another plus that owners might not think about.

“Horizontal rooftop solar panels have to be cleaned and maintained to achieve 100 percent efficiency,” Piles said. “Since they will be placed in a vertical position, owners won’t need to maintain the Ductal panels.”

Getting down to business: research and development

Heliatek was charged with finding the most efficient way to deliver this new product while containing costs and not slowing down precast production.

According to Wiertelarz, several key challenges had to be overcome. One was to find an adhesive solution that worked with both the UHPC and the HeliaFilm. Another was to determine how to best integrate the HeliaFilm and the Balance-of-Systems (BOS) electrical components such as cables and inverters into the precast manufacturing process. In addition, Heliatek was responsible for devising an experimental lab to produce the prototype and a system for testing the prototype’s overall durability and performance.

“The manufacturing process is very demanding on our sensitive HeliaFilm,” Wiertelarz said. “We had to experiment with different setups to implement this production logic without any loss of the aesthetic value of our film or spending too much time in the production line.”

Another challenge was finding time in LafargeHolcim’s busy production schedule for two experimental, one-week test runs. The first took place in February 2017. The second was conducted in October 2017. After each trial run, LafargeHolcim and Heliatek weighed the pros and cons and tweaked the process.

Field testing

To date, LafargeHolcim has produced nearly 50 square yards of the Ductal/Heliatek facade. Thirty square yards were used for its first pilot project at the LafargeHolcim Research Center in Lyon, France, this September. Next up will be a 239 square yard installation in early 2019, again at the LafargeHolcim Research Center.

“The idea is to start commercializing this product in Europe by summer 2019,” Piles said.

The full production process is straight-forward. The component containing the HeliaFilm and the BOS electrical equipment is placed in the bottom of a steel mold in a horizontal position. A layer of Ductal UHPC is poured over it and allowed to cure. The panels are released from the mold, packaged and shipped.

“We have a specific process that allows complete integration of the organic photovoltaic film with the concrete in one day,” Piles said.

Currently LafargeHolcim and Heliatek are collecting data and measuring and analyzing results. The partners will be looking at a variety of factors, including how durable the panels are and how well they perform under different weather conditions, as well as how efficient the system is at harvesting solar energy. They will also refine some of the connections and the electrical junctions in the box. Meanwhile Heliatek is increasing the capacity of its production line so it can produce approximately 1 million square meters of HeliaFilm by 2020.

“Today the idea is that this product is mainly for the energy gain of the building,” Piles said. “But in the future, it could be connected to a power station or to a power grid. Who knows?”

Shari Held is an Indianapolis, Ind.-based freelance writer who has covered the construction industry for more than 10 years.

Endnotes
1 news.energysage.com/8-facts-solar-energy-2017/
2 www.eia.gov/tools/faqs/faq.php?id=86&t=1