Solar Slopes Seek Sustainability at Biosphere 2

Hillside solar project at the facility near Oracle could lead to new renewable energy sources that could cut carbon emissions.
May 26, 2010
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(Click to enlarge) The glassed-in Biosphere 2 structure near Oracle encloses 3.14 acres.
(Click to enlarge) The glassed-in Biosphere 2 structure near Oracle encloses 3.14 acres.
(Click to enlarge) Nate Allen, sustainability coordinator at Biosphere 2, explains a demonstration site at Biosphere 2 showing how solar panels can be effectively mounted on steep slopes like mine tailings.
(Click to enlarge) Nate Allen, sustainability coordinator at Biosphere 2, explains a demonstration site at Biosphere 2 showing how solar panels can be effectively mounted on steep slopes like mine tailings.

The hilly terrain surrounding Biosphere 2 has led to efforts to mount solar panels on steep slopes in research that could pave the way for large-scale deployment of solar devices on mine tailings, landfills and other sites.

A test bed of photovoltaic solar panels perched on an abrupt hillside adjacent to Biosphere 2 is testing ways to install solar panels on unstable hillsides, said Nate Allen, sustainability coordinator.

Most existing solar fields currently providing sustainable energy are located on flat terrain, but a lack of such flat terrain at the Biosphere 2 campus led researchers to consider a new approach.

"It's actually a challenge to figure out where we can put large amounts of solar out here. Currently one of the biggest limitations on doing large scale solar deployment is grade," Allen said. "Most systems out there that are a megawatt or more in size can't be put on a grade steeper than 2 percent. We now have a solar array installed on a 50-percent slope."

About the same time Biosphere 2 scientists were looking at ways to make solar work on hilly terrain, an Arizona mining company called looking to develop creative ways of using mine tailings, Allen said.

Mine tailings, the waste product left after extracting valuable metals from the source material, create huge piles often covering tens of thousands of acres.  Mining companies devote vast resources in mitigating dust and rainwater runoff pollution. Some sites cover the tailings with a membrane topped with soil and try to revegetate the tailings mounds, he said.

"We talked about doing a number of different options. We were immediately interested in how to install solar panels on it, and then we realized that there are all these hurdles to doing solar panels," he said. These hurdles included the fine consistency of tailings, which would not provide a stable , and the need for sealing the tailings as a pollution remediation strategy, he said.

Working with Solarmax Arizona, Biosphere 2 researchers adhered solar panels to the material used to cover the tailings mounts, Allen said. Three different mounting options are now being tested at Biosphere 2, he said, including welding the panels directly to the membrane.

The project has expanded beyond the Biosphere test bed.

"We have a test plot at the Sierrita mine. Freeport-McMoRan has been really generous to give us space to test things out," Allen said. "We're also in discussions with a coal mine in West Virginia about doing a demo out there."

 "Freeport-McMoRan is pleased to be working with the University of Arizona to test the technical and economic feasibility of solar energy generation on panels placed on a tailings impoundment at our Sierrita operations in Green Valley," a spokesman for Freeport-McMoRan Copper & Gold said. "With projects such as this, we are taking steps to expand the role of alternative energy sources through initiatives at our mining operations and local communities, actively pursuing the development, implementation and transfer of cleaner, more efficient, cost-effective technologies such as solar energy generation."

Research has shown that placing solar panels far from horizontal, or pointing in directions other than due south, can still offer an efficient solar field.

"Panel angle has not been shown to be as significant a factor on performance as previously thought. There is a big difference between 30 degrees and flat, but there is not a big difference between 30 degrees and 15 degrees or 45 degrees," Allen said. "So we are taking advantage of that. Especially when you get the scale of a mine's tailings, where you are talking about 60,000 acres, on that scale of a solar field, it doesn't make any difference at all if the panels are 30 degrees or not."

Biosphere's hillside solar array provides power to guest casitas where visiting researchers stay. Four inverters turn the panels' current from DC to AC for use in the casitas. Power output is closely monitored as well as how many pounds of carbon dioxide are being saved by using the renewable energy source, Allen said.

The project uses solar panels built and donated by Solon Corp.'s Tucson manufacturing facility, Allen said.

Installing solar fields on mine tailings could go a long way to implement renewable energy sources and cut carbon emissions, Allen said.

"There are 6 million acres under mining in the United States right now. A large part of that is mine tailings. If you can devise a system where you can put solar on land that is already been wasted, and do it is a way where it contributes to the future environmental quality around those mine tailings, there is a lot of good reasons to put solar on mines," Allen said. "There is huge, huge potential for doing solar on tailings. It's a great opportunity for us to do large scale deployment of renewable energy sources on land that has already been used rather than tiling under virgin desert."