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Student Guide: Cal Poly solar class took a vote on SLO's all-electric building code—and got a different result 

It's not every day that a college classroom is asked to pick a side on local government policy.

But in March, Cal Poly students in a popular solar energy course, Solar Photovoltaic System Engineering, were tasked with doing just that.

Cal Poly electrical engineering professor Art MacCarley got the idea for an outside-the-box assignment after he read a newspaper article on the city of San Luis Obispo's then-proposed building code that would discourage natural gas in new development. The city's goal? To lower carbon-dioxide (CO2) emissions by transitioning to all-electric buildings.

To MacCarley, who's spent his career studying and teaching renewable energy science, the policy was eyebrow-raising—and made for great classroom material.

"I thought, what better forum to analyze it in the most neutral way than in my own class, which is very hands-on," MacCarley told New Times. "We learn everything about electric power generation from solar ... and, in the field, design and build complete solar installations. It's the 'learn by doing' theme of Cal Poly."

For the assignment, MacCarley asked his students to become city policymakers: "Either support or oppose this ordinance, solely on the basis of total CO2 emissions from energy source to end-use," the directions read.

Students broke into groups, crunched the numbers using neutral data sources, like the Department of Energy, and ultimately cast votes for or against an all-electric building code in a mock city council hearing.

"The issue here is whether or not this ordinance will accomplish its stated objectives," MacCarley explained.

While SLO's actual elected leaders voted on Sept. 3 to adopt the new code, MacCarley's class in the spring came to a different decision.

Among the 17 student groups that analyzed the policy (which MacCarley acknowledged was in a conceptual form at the time), the opinion was unanimous.

"There wasn't a single one that would defend the ordinance," MacCarley said. "I was shocked when I couldn't get anyone to argue the other side."

When looking at the switch from mixed-fuel to all-electric buildings, MacCarley and his students concluded that CO2 emissions would actually increase under the policy. That conclusion, he said, was based upon the current energy mix in California. Since natural gas power plants are still a major supplier of energy in the state, the electricity demand created by making buildings all-electric would ultimately lead to more greenhouse gas emissions than what's saved by removing natural gas in buildings, the class found.

Natural gas power plants not only create greenhouse gases, MacCarley said, but they're inefficient: about 64 percent of natural-gas-made power is lost across the distribution system. So while an all-electric code might make sense when the state is closer to reaching a 100 percent renewable energy portfolio, it doesn't right now, he argued.

"For now and the near future, it doesn't add up," MacCarley said. "The CO2 generated with electric power generation and distribution using natural gas is going to be greater ... than if you took that natural gas, delivered it directly to the house, and, even with a fairly inefficient appliance, say a gas stove, burned it directly."

The findings in MacCarley's class run contrary to the data that led the SLO City Council to adopt the new building code. According to a city staff report, by 2035, the code is expected to reduce community CO2 emissions by 7,800 metric tons per year.

City officials—not just in SLO but in cities across the state—leaned on a 2019 California Energy Codes and Standards study to recommend the changes. Prepared by PG&E, the study is the touchstone for cities that want to adopt local building codes that go above and beyond the state's codes in terms of energy efficiency.

That study states that an all-electric building, on a square-foot basis, creates fewer CO2 emissions than a mixed-fuel building. And as California's grid gets cleaner over time, CO2 emissions from electric buildings will only continue going down, SLO Sustainability Manager Chris Read told New Times.

Additionally, SLO will become a member of Monterey Bay Community Power in 2020—which means residents' ratepayer dollars will be used to purchase carbon-free energy. So, on paper, the city's all-electric buildings will be responsible for no CO2 emissions.

But skeptics like MacCarley note that all buildings are dependent on the state's grid—no matter who's buying SLO's power from whom.

"If indeed all of our power in this area is coming from renewable sources, their argument is valid," he said. "But I find that argument specious. ... [Our electricity] is mixed up in the soup."

While his Cal Poly class and the city disagree on the numbers, MacCarley said he also has concerns about the vulnerabilities of the electrical infrastructure. With poorly maintained power lines starting wildfires, regional power shut-offs possibly looming on the horizon, and more and more electric cars in need of charging overnight, he wonders if the grid is ready to handle a shift to all-electric homes, too.

"The ramifications of that are not even known yet," he said.

While MacCarley's students may have expected to support a city policy pitched as part of the solution to climate change, he said their resounding opposition in the assignment was somewhat of a surprise to all.

"The result was maybe a bit of an epiphany for the students involved," he said. Δ

Assistant Editor Peter Johnson can be reached at


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