The two largest projects - a photovoltaic array on up to 350 acres at the base and a similar-sized array at the city's water recharge site in Avra Valley - would each generate at least 1 megawatt (a million watts) of power initially. In all, the three governments are planning a minimum of 3.1 megawatts of solar generation, which could eventually grow to 10 or more megawatts.
Currently, about 1,500 kilowatts of power (1.5 megawatts) are generated from solar panels in Pima County. Most of the projects would be power-purchase agreements, in which contractors would build and own the systems. They could claim tax and environmental credits and recoup costs with the sale of power to the governmental entity.
"These are really big - some of the largest ones in the country," said Dennis Dickerson, environmental planning coordinator for the Pima Association of Governments. "The good news is people have really realized we're looking at an energy transformation," he said.
Rising energy prices and increased efficiency have combined to make solar-power generation more economical, he said, though the arithmetic still depends on federal tax credits that run out at the end of this year. That's why the UA and one of the city's projects require that installation be completed by the end of the year. Both the city and UA plan expansion of the projects if solar-energy tax credits are extended by Congress.
Governments can't use tax credits, but contractors can claim them and reduce the cost for purchase of the systems or the power they generate. The UA is currently prevented from generating more than 500 kilowatts of power from solar under the terms of its agreement with Tucson Electric Power.
Both sides want to change that agreement, which would need approval from the Arizona Corporation Commission, said Tom Thompson, assistant to UA Senior Vice President Joel Valdez.
"We're all working to change those rules," said TEP spokesman Joe Salkowski. "When those rules were written, the prospect of large-scale photovoltaic generation was not on anybody's radar," he said.
Thompson said the university would prefer to start small anyway.
"The idea is to put on suitable university roofs a small number, to begin with, of photovoltaic generators and see how it goes," he said. A contractor has been selected for the job, Thompson said, but he could not talk about the details of the proposal until a contract is signed.
The university's request for proposals identified 24 sites, including all its parking garages and the Student Union, as potential sites for solar arrays. The city seeks someone to partially power seven city buildings and to provide power for the pumps at its water recharge and storage site in Avra Valley.
The city's request for proposals for the Avra Valley site says it wants to eventually contract for 5 megawatts of power there. The other city project is for seven city buildings, including El Rio and El Pueblo neighborhood centers.
Those photovoltaic arrays will not be power-purchase agreements, said city solar coordinator Bruce Plenk, but would be financed with federal Clean Renewable Energy Bonds. The city has issued a request for qualifications for those projects, estimated to cost $5 million and generate 600 kilowatts of power. D-M is offering up to 350 acres suitable for photovoltaic arrays that will generate, at minimum, one megawatt of power under a power-purchase agreement.