One way of looking at sustainable design refers to methods of reducing the environmental impact from the manufacture and use of products. For Jeffrey Brownson, a materials scientist and the faculty advisor for Natural Fusion, Penn State’s entry in the 2009 Solar Decathlon competition, that requires understanding how materials flow through their lifetime, from the moment they are extracted from the ground to the point they are buried in a landfill or recycled. Materials flow is a systems approach to how we use and manage our resources.
"Our two critical resources, I would say, are water and the raw energy we need to do work," says Brownson. "We don’t often think about how to reduce their use in terms of materials science. A lot of materials science has a goal of optimizing a device or finding the highest output potential possible, but when we take a sustainable approach, we look at the opportunity costs of choosing the second best or third best material. If the second best thing is only a 3 percent loss from the best thing, but has huge environmental benefits, for instance in terms of reclamation, shouldn’t that be rolled into the whole design concept from the beginning?"
Indium is a good example of the disconnect between the current approach to materials and a systems approach, which looks at where the material comes from, how it is used, and where it ends up. A large industry is based on indium for use in indium tin oxide, a transparent thin film coating that goes into flat screen TVs, reel-to-reel polymers, and, increasingly, into photovoltaic devices. Yet indium is relatively rare and hard to acquire, being dependent on the mining of zinc for the steel industry. At the same time, the process by which indium tin oxide is applied to a substrate is incredibly inefficient, with 85 percent waste. Finally, there is no recycling program for indium in this country. Indium could be the poster child for unsustainable technology.
"We’ve got this one material identified as the cornerstone of an entire industry, but we could work with alternate materials, such as a fluorine alloyed tin oxide. It has a higher resistivity, but we have a lot of tin and tin is very cheap. Or there are other oxides where we can create a minor alloy with them to make them both translucent and conductive. Will they be as good? No, but we can use them for much longer and we can see ways where we could reuse them for other systems," Brownson insists.
When Brownson is not focusing on photovoltaics, much of his time is spent working with architects and students of design in a process known as integrative design. This process brings designers, scientists, and engineers together at the beginning of a project to build a common language and create a common vision. If the designer can give the materials scientist an idea of what he would like a material or system to do, for instance a wall with a certain thermal efficiency, impermeable to moisture, sound deadening, and three inches thick, then the materials scientist can try to find a solution.
What frequently happens, asserts Brownson, is that the designer will go to the Web and find some material that he thinks may work and try it. What the materials scientist will typically do is develop some new material and go looking for an application. Both would be better off collaborating from the start.
"In my last two years working on the Solar Decathlon house, we’ve come up with answers working with architects that we didn’t ever know existed or were possible," he says.
Two years ago, the Natural Fusion team approached Bayer Material Science, in Pittsburgh, for support, as the only Pennsylvania university participating in the 2009 Solar Decathlon. Bayer management was interested in the team’s ideas about energy efficiency and reducing the embodied energy in the materials they chose for the solar house. Bayer suggested trying their polycarbonate and polyurethane materials, for which they had accumulated reams of information pertaining to life cycle analysis and embodied energy, the total energy input required to produce a material. Two students traveled to Bayer’s spray foam facility in Arizona to test the material for their roof. The rules of the Solar Decathlon require that all the materials and components in the solar house be available commercially. Although the polycarbonate material had never been tried for use in a house, the Bayer scientists were confident it would fit the Natural Fusion team’s requirements.
One of the high points of working with Bayer, according to Brownson, was forging a connection between them and Professional Building Systems of Middleburg, PA, a manufacturer of energy efficient modular homes that is working with the Penn State team on Natural Fusion. It was an opportunity for students and faculty to work professionally with representatives from the materials and building industries from the beginning, and a chance to illustrate the principles of integrative design to the students.
Green Roof Photovoltaics
Many towns and cities have become largely paved and built environments, with storm water drainage problems and heat island effects. Green roofs are a way to cool buildings in summer and absorb large amounts of water during storms, releasing only a portion of the stored water slowly into municipal drainage systems. In Germany, the leader in green roof use, approximately 15 percent of all flat roofs are planted with green material.
Carlisle SynTec, a roofing materials manufacturer with experience in green roof technologies based in Carlisle, PA, worked with Natural Fusion to develop an innovative system that combines green roof technology with solar energy in a system the Penn State team calls GRiPV, for Green Roof Integrated Photovoltaics. German research had previously shown that green roofs will cool solar panels, and when they are cool the panels work more efficiently, better even than with normal air convection cooling.
Carlisle SynTec had connections to a California company called Solyndra that manufactures an unusual cylindrical photovoltaic in which a CIGS-type thin film is wrapped in a spiral around tubes that capture reflected light from every angle. CIGS are made of a composite layer of copper, indium, gallium, and selenium that is only a couple of micrometers thick. The Solyndra technology is purported to turn 12 to 14 percent of captured sunlight into energy when placed above a reflecting surface.
"The two companies took our rather complicated design and collapsed it into something simple," Brownson recalls with delight. "Their cylindrical design takes care of the problem of having to tilt the solar panels toward the sun. Now you have photovoltaics integrated with a green and living roof, being cooled at the same time as capturing rain water. It will be a great test case for a variety of materials when it goes up on the National Mall in October."
The Penn State Solar Decathlon house will have a number of innovations, in addition to the roof insulation and solar technology. The south façade of the 800-square-foot house is designed for passive heating with a large amount of glass that will allow light in to heat up a water-filled bladder system in the floor that is similar to the Camelbak hydration system for runners and cyclists. This is a new design the team is working on with Bayer that will be commercially available by the time the house is finished.
They will also be using an energy recovery ventilator, a system that uses the cross flow of air to recover the heat or cold rather than dumping it outside. The system they are using is provided by a Penn State alumnus and includes a number of his proprietary technologies. "It works incredibly well," Brownson says.
To the Solar Decathlon team, Natural Fusion means fusing several new technologies in modular systems that can be taken apart. Also it means fusing interior and exterior space, nature and the manmade environment, so that an occupant is as engaged with the space outside as with the interior space. Although the various parts of the house are as carefully engineered as a high powered racecar, all of the systems can be scaled down to the needs of a modern modular home.
"Pennsylvania has a lot of modular building companies, and many of them want to upgrade. So we want to be able to provide them with this kind of technology," Brownson concludes.
Brownson on Solar Cell Technology
- The biggest growth in photovoltaics is in grid connected PV. Using the electric grid there is no need for batteries, so PV systems are cheaper. With a power purchase agreement, companies are able to get a fixed price for electricity, providing for stability. Some companies may not own the PV systems on their roof, but instead lease them and receive energy credits. Grid connected PV is best for providing a buffer against brown outs and offsetting peak loads during the day when electricity tends to be most expensive.
- Thin films are the direction PV is heading. Currently, 90 percent of all photovoltaics is made from single crystal silicon, which is cut from large crystals that are slow and expensive to grow. Thin films allow us to reduce the amount of material, and the material does not have to be as pure.
- Solar efficiency is a poor yardstick when it comes to judging types of PV technology. The best silicon solar cell systems actually in use have a top efficiency of about 22 percent. The best thin films are 12-15 percent. The real question is, can you produce it cheaply and quickly, in a large scale like for instance the glass industry?
- The U.S. has the experts in thin film solar technology. We are good at this. We are selling thin film solar cells produced in the U.S. to other countries, because we don?t incentivize photovoltaics.
- The biggest thin film producer is First Solar in Tempe, AZ, which produces a cadmium telluride PV, much of which is sold to Germany and Japan. First Solar takes a cradle to cradle approach. They guarantee that when the module has ended its 25-year lifecycle, they will collect the module and recycle the materials.
- Thin films will dramatically grow their share of the market in the next ten years and the U.S. can play a major role. There is still a stark contrast between what is being done in Europe and what is not being done in the U.S. in regard to PV. We have all the skills, but they are in silos. We need to start the engines going again to develop our own PV industry.
"Penn State has almost all the components necessary to be a premier photovoltaics research facility. Do we have the ability to focus and promote photovoltaics? We'll see."