For 10 weeks this summer, Ryan Whisnant gets to be the green conscience of SunGard Data Systems Inc.

He'll tell the software company, for example, if it's using too many bulbs to light its offices in Wayne, and if it should keep the temperature higher. SunGard brought in Whisnant, a graduate student at the University of Michigan, to help the company cut its energy use and costs.

"The challenging part is tracking down the numbers," Whisnant said. It took him three weeks to figure out how to read SunGard's byzantine utility bills.

Whisnant, 33, is a Climate Corps fellow for the Environmental Defense Fund (EDF), a nonprofit group that has long advised businesses on things such as how to save energy. The EDF started the fellowship program last year with seven interns, and expanded this summer to 26 and to companies in the East.

Last year's pioneers found ways for the host companies to save a total of $35 million over five years, according to the EDF.

For example, John Joseph, an intern at Intuit Inc., a Mountain View, Calif., software company, determined that it could cut $500,000 annually from its bill with such steps as setting lights in its restrooms to turn off automatically when the rooms weren't in use.

At Cisco Systems Inc., Emily Reyna helped develop plans to make the San Jose, Calif., networking technology company's equipment-testing labs run on about $8 million less per year in electricity costs.

Cisco has another EDF intern this summer to figure out how much funding will be needed to carry out those plans.

"The interns have a broader understanding of green than any of us might, because we're so focused" on running the company's business, said John Hailey, senior manager of sustainable operations at Cisco.

Climate Corps fellows also get people thinking about the environment. Whisnant says some SunGard employees hold up their coffee mugs to show him they're not wasting Styrofoam cups.

Still, placing interns inside companies isn't always easy. When Frank Staats, a vice president at Crescent Real Estate Equities in Houston, sought approval to take on an intern last summer, he met questions about letting an outsider probe company operations.

While the fund and the companies sign confidentiality agreements, Millie Chu Baird, an EDF project manager, said trust played an important role.

Staats eventually won - helped by the fact that EDF used $90,000 of its money to pay all costs for the interns in the program last summer.

Crescent's intern, Tyler Monzel, ended up finding ways to save the company $400,000 annually. After receiving a Master of Business Administration degree in May from Rice University, Monzel is cofounding a consulting firm called NewIntuition to help businesses go green.

SunGard joined the EDF program this summer and said a private consultant might have charged $80,000 for a project such as Whisnant's. The EDF said most of the companies this summer were paying their interns $10,000 each, and the group is funding the rest.

All Climate Corps fellows are M.B.A. students who can make the case that energy conservation makes financial sense. They receive three days of training in San Francisco before they begin their internships, but many come with more experience.

Andrea Sandor, a fellow this summer at the Stop & Shop Supermarket Co. in Quincy, Mass., used to factor in companies' effect on the environment when she evaluated them as a high-yield bond analyst in the 1990s. Most recently, she was an information-technology project manager at UBS AG when the Zurich, Switzerland, financial-services firm considered ways to lower the cost of running its computer systems.

Then she decided to switch into the energy industry and became an M.B.A. student at the Wharton School.

Stop & Shop "is fantastic," Sandor said. "They're concerned for all the right reasons."

Stop & Shop's parent company, Ahold USA, also placed Christopher Anderson at its Giant Food store in Carlisle, Pa. Anticipating his summer work, Anderson chose Ahold's energy-efficiency improvements as his subject when he had to research a company for a Penn State class this spring.