Researchers are trying to make mountains of mine tailings more productive and easier on the air we breathe, at the risk of making them more visibly apparent.
An experiment by University of Arizona scientists at Biosphere 2 in Oracle and at the Sierrita Mine west of Green Valley will test the efficacy of converting mounds of waste rock into solar power plants.
UA researchers are testing two membranes and three mounting systems that will encapsulate the fine particles that often blow off tailings dumps, and provide stable platforms for photovoltaic panels that convert sunlight into electricity.
Mining watchdog Roger Featherstone said the approach is a good idea, given two caveats: that it doesn't become "an excuse for not doing total cleanup or an opportunity for more subsidies to these giant mining companies."
"It makes a lot of sense to use mine sites for a number of reasons. The infrastructure is in place, the sites are already trashed. They have roads. They have power lines," said Featherstone, of the Arizona Mining Reform Coalition.
All of those advantages might make it economically feasible to generate solar power on sites that would otherwise not be considered optimal, said Nate Allen, a research scientist at Biosphere 2, where a precipitous slope above the big glass dome is now covered with solar panels in three experimental mountings.
The panels do not point directly south and are not angled at 32 degrees from the horizon - the standard orientation for this latitude. Allen thinks, however, that the unavoidable loss in efficiency will be more than offset by the ease of installation.
Initial indications are that power loss is not that great, said Alex Cronin, a UA associate professor of physics and optical science, whose students have installed sensors on the panels that measure electrical output and temperature, second by second.
The berm of fill material on which the panels are mounted faces 10 degrees west of due south, Cronin said, and the angle is 50 degrees, but the power loss is only about 2 percent.
The bigger problem comes from the ground mounting, Cronin said. In one of the mounting configurations, in which the panels are set in "beds" of fabric-covered dirt, the temperature at the back of the panels is very high, up to 194 degrees Fahrenheit. Heat robs solar panels of efficiency, Cronin said, and the loss for this type of mounting could be up to 30 percent.
The raised panels are not heating as severely, he said.
For Allen, the experiment also presents an avenue for the UA's plan to turn the entire Biosphere site outside Oracle into an experiment in sustainability. Power from the panels will be used at the facility's casitas and conference center.
In addition, rain that falls on the impermeable membrane beneath the panels will be channeled to an underground cistern and used in the facility's cooling towers.
The UA, which took over operation of the privately built experiment in closed living in 2007, is now operating Biosphere 2 as one big laboratory, using its "biomes" of desert, savanna, rain forest and lagoon as research sites. They have the advantage of being much larger than university labs while still giving researchers the ability to control such things as soil content, atmosphere, temperature and humidity.
The solar panels being used were donated by the Tucson arm of Solon Corp., which made them from thin-film solar material made by another Tucson firm, Global Solar Energy.
The membranes used to cover the slope were donated by the manufacturers and installed by a Phoenix firm called Solarmax Arizona, which specializes in using existing coating technology in new ways, said Nathan Barba, co-owner of the company.
The "Solarmax thermal-plastic racking system" is specifically designed for use on degraded sites, he said.
"Mine tailings, abandoned mines and landfills are a prime candidate for this type of product," Barba said. Such sites are already required to install the liners, he said. The addition of racks for solar panels simply adds value to the site without much additional expense.
The U.S. Environmental Protection Agency is encouraging re-use of degraded sites, known as "brownfields." There are 15 million acres of "potentially contaminated properties" in the United States that might be converted to such purposes, according to the EPA's website.
Freeport-McMoRan Copper & Gold, which owns the Sierrita site, is working with electric utilities to investigate the use of inactive mining properties for renewable-energy plants, a company spokes-man said.
"We are currently 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," spokesman Eric E. Kinneberg wrote in an e-mail.
Cronin said data gathered by the UA scientists will aid the decisions of financiers considering such operations in the coming years.
Barba said the Sierrita Mine experimental site could one day lead to a massive deployment of solar panels that he thinks would be a pleasant addition to the western backdrop of Green Valley. "You drive to Sierrita and you just see these gigantic slopes, and our vision is you could truly have a Green Valley, literally, because it's creating green energy."
Featherstone said he's not certain the panels would be a visual improvement, but no worse than what's there now.
"Let's face it," he said. "There's no way in heck that a tailings pile is ever going to look pretty."
DID YOU KNOW
Biosphere 2 is 3.14 acres in area and has 6,500 windows that enclose a volume of 7.2 million cubic feet. It is 91 feet at its highest point.
The Biosphere's human experiments ran from 1991 to 1994, and Columbia University managed the facility from 1996 to 2003. The UA assumed management in 2007.
Source: Arizona Daily Star archives
"It makes a lot of sense to use mine sites for a number of reasons. The infrastructure is in place, the sites are already trashed. They have roads. They have power lines."
Arizona Mining Reform Coalition
How unhealthy is it to breathe mine tailings dust? The UA is finding out.
Contact reporter Tom Beal at email@example.com or 573-4158.