More than 20 percent of the energy needs of Arizona State University's main campus eventually could be met by one of the largest rooftop solar-power plants in the U.S.

The university announced an agreement Tuesday under which three companies would install, at their expense, solar electricity-generating equipment that would provide 2 megawatts of generating capacity by the end of the year. The equipment would be on rooftop space at Arizona State's main campus in Tempe.

The largest rooftop installations so far belong to Google, which has a 1.6-megawatt facility on the roof of its Mountain View, Calif., headquarters; and drugmaker Schering-Plough, which last month announced plans for a 1.7-megawatt rooftop system at its Summit, N.J., campus, according to the American Solar Energy Society.

Long-term plans call for up to 7 megawatts of solar-generating capacity to be built at Arizona State in Tempe, with additional solar installations at its campuses in other locations.

The rooftop facilities, however, are dwarfed by proposed ground installations, such as a 280-megawatt solar plant planned by Arizona Public Service Co. near Gila Bend.

Honeywell Building Solutions, Independent Energy Group and SolEquity will build the Arizona State systems. Honeywell Building Systems is a unit of technology and manufacturing company Honeywell International. SolEquity is a new venture backed by Arizona Technology Enterprises, a subsidiary of the Arizona State University Foundation. Independent Energy Group is an investment group.