Solar panels, while they mitigate the effects of global warming by replacing fossil fuels, can add heat in the locations where they are installed, reports a team of University of Arizona researchers.

At first blush, the experimental results, published Thursday in Nature Science Reports, seem to contradict computer simulations that said solar photovoltaic arrays, by intercepting some of the sun’s warming rays and converting them into electricity, would have a cooling effect.

The UA researchers measured the heat-island effect of a solar array at the UA Tech Park at Rita Road and Interstate 10. They found that its overnight temperatures were about five to seven degrees (Fahrenheit) warmer than a nearby plot of undisturbed desert.

Additional experiments are being conducted to determine the potential effect of the measured heating on nearby communities and the overall environment.

Preliminary results suggest that off-site impacts are negligible, said Greg Barron-Gafford, assistant director of the UA School of Geography and Development and lead author of the report.

“It’s a minimal thing and relatively contained,” he said.

Temperature readings from an ongoing study at an even larger array in Marana suggest that the increased temperatures dissipate quickly and can’t be measured 100 feet away, he said. “Heat rises.”

Results from the team of current and former UA researchers, which included Alex Cronin, Rebecca Minor, Nathan Allen, Adria Brooks and Mitchell Pavao-Zuckerman, are not inconsistent with published computer simulations, said a Colorado atmospheric scientist.

Aixue Hu, research scientist at the National Center for Atmospheric Research, published conclusions from a computer model last year in Nature Climate Change.

Hu found that installations of vast arrays of panels in desert areas would produce a cooling effect of about 3.5 degrees Fahrenheit.

Contacted by phone Thursday, Hu said his study was predicated on highly efficient PV panels that would convert 30 percent of the sun’s energy into electricity. The panels in the UA study had an efficiency of about 20 percent. Hu said his model might produce some slight heating at that efficiency.

Barron-Gafford said he suspects the heating at the UA Tech Park site results from its lack of vegetation. “I’m a plant guy and plants are little evaporative coolers,” he said.

Leaving natural vegetation in place, or planting grasses that would thrive in the partial shade of the arrays, could mitigate temperatures. That approach is currently being tested on a solar array at Biosphere 2, he said.

When it comes to solar power, the cooler the better, he said. Photovoltaic panels lose efficiency at higher temperatures.

Barron-Gafford said the study was “an interesting challenge” for a team of scientists who support solar energy, some of whom have solar panels on their own homes.

“But are there unintended consequences? How do you approach a question you might not want the answer to?”

Contact reporter Tom Beal at tbeal@tucson.com or 573-4158. Follow on Facebook or @bealagram on Twitter.