Graphic for Solar and Wind Article

Using Google’s Project Sunroof, available space for solar panels can be calculated. This graphic illustrates one scenario of how Purdue’s campus, which is about 2,468 acres, could fit 210 acres of panels.

Solar panels on the roof of the Elliott Hall of Music, covering the tops of parking garages or on scaffolds above parking lots around campus — could solar energy feasibly power campus?

Purdue currently uses an estimated 300 million kilowatt-hours per year, enough to power more than 27,000 average American homes. Three hundred million kWh translates into an average of 821,917.80 kWh a day.

This estimate for Purdue’s electricity usage is based on 2009-10 data and direction from Larry Nies, a professor of civil and environmental and ecological engineering. Despite several attempts, Purdue did not respond to questions requesting more recent data.

Although the calculations below are simplified calculations that do not account for solar intensity variability between seasons or for the variability of renewable sources from day to day, they serve as an interesting illustration. A future scenario for renewables would likely depend not solely on either solar or wind, but a combination of the two, which was not calculated.

Current technology

Purdue’s campus is currently powered by Wade Utility Plant, a combined heat-and-power plant with three natural gas boilers and one coal boiler, as well as energy bought off the grid.

“We used to have four coal boilers and we went from coal to natural gas,” said Xavier Rivera, director of energy and utilities at Wade. “That’s what we have done in the past few years.”

This change allowed the plant to cut greenhouse-gas emissions by a little more than 40%, Rivera said. He also said that Wade has placed a lot of emphasis on efficiency.

“I’m a big believer where if you reduce the load from an efficiency point of view then you don’t ... have to burn more, so it’s better as a steward of energy to eliminate waste and improve efficiency,” Rivera said. “So then, by the sheer merits of the engineering and the efficiency, you reduce emissions.”

As a combined heat-and-power plant, Wade provides heating and cooling to the buildings on campus, as well as generating 50% of the electricity used on campus.

On cold days, steam heated in the boilers at Wade is pumped throughout campus to provide heating. On hot days, steam runs a chiller system that cools water that is pumped through pipes to provide campus with air conditioning.

The Wade Utility Plant operates at 81% efficiency, Rivera said. The national average for power plants is 33%, according to the Environmental Protection Agency’s website. But Rivera said those at Wade are always on the lookout for ways to make the plant more efficient, such as investing in a heat-recovery steam generator system that would allow the plant to reach 91% efficiency.

“They’ve been running the most efficient power plant in the state of Indiana for decades,” Nies said. “I still think that Purdue should have a more aggressive plan to transition to renewable energy.”

Nies said achieving carbon neutrality is possible for Purdue.

“It starts with a commitment,” he said. “We have technology that will allow us to make progress, there’s no question about that.”

Purdue’s Office of Sustainability is scheduled to release a University Sustainability plan on Earth Day 2020. The last such report was released in 2010, containing a pledge to generate 10% of electricity with renewable energy by 2025.

“It would be interesting to see if (the new plan) is actually a quantitative commitment or if it’s just vague platitudes about believing in sustainability,” Nies said.

Purdue could probably be powered by about 210 acres of solar panels or 33 wind turbines, according to The Exponent's calculations.

Obstacles for renewables require technological innovation

In recent years, the prices of solar and wind have plummeted. According to Lazard’s Levelized Cost of Energy Analysis from 2018, the levelized costs of energy for both utility-scale solar and wind are at or below the marginal cost of coal and natural gas. As prices for these technologies fall, financial limitations become less insurmountable obstacles.

Even so, the simplified renewable energy scenario produced here ignores several challenges of powering campus using only renewable energy.

The first is that the heating and cooling on campus is powered by steam, creating a need for a non-carbon-emitting method of producing steam.

Nies pointed to a recent breakthrough by clean-energy company Heliogen. The company recently achieved temperatures of over 1,000 degrees Celsius with their commercial concentrated solar system.

Concentrated solar power uses mirrors to focus rays of light into a single location, generating extremely high temperatures, according to a Heliogen press release.

“I mean, the ability to make steel and glass and aluminum without having to burn coal is a transformative step,” Nies said. “If you can make steel out of concentrated solar power, you can sure as heck make steam.”

In this way, concentrated solar power is one example of promising technology that could transform how Purdue produces steam to heat and cool buildings.

A second problem with renewable energy is variability: the classic problem of solar panels not working when the sun is not shining and wind turbines not working when the wind is not blowing. According to a report by the National Renewable Energy Laboratory, solar intensity varies greatly in Indiana. In June, solar intensity is about 2 kWh per square meter per day more than the annual daily average, and in December, it’s about 2 kWh per square meter per day lower than the annual average.

“Storage is really one of the existing challenges for the intermittency of solar and wind, for sure,” Nies said. “I just think you have to be progressive and a little daring and have a little foresight.”

By upgrading the grid to a “smart grid” — a grid that uses digital communication technology — energy demand would be able to be managed more precisely. This would open up the possibility of using parked electric vehicles as power storage capacity for the grid.

“One way that we can manage the storage issue is by using (electric vehicles), because most of the time a car is just sitting there and not being used, and electric vehicles have pretty big batteries,” Nies said. “If you have a few thousand cars plugged into the grid — I mean, they could provide some storage, and they can provide some capacity — but that takes a smart grid to run that.”

Nies said electric vehicle owners could be compensated for their contribution to a more stable grid. Based on rough calculation, 4,100 electric vehicles would be needed to provide storage for half of the daily demand of Purdue’s campus.

Purdue is a relatively isolated, small-grid system, Nies said, with potential to be a living laboratory that can experiment with smart grid technology.

“There have been many opportunities to get funding from the Department of Energy to be a testbed for smart grid technology,” he said. “And, to my knowledge, Purdue hasn’t won any of those contracts.”

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