If we can dream it, we can do it.
Wrong, according to Arizona State University physics professor Peter Rez.
As Rez's new book, The Simple Physics of Energy Use, explains, too much solar or wind power in the electrical grid would actually increase the carbon emissions that advocates of clean-energy goals want to reduce.
Rez has little patience for policy-makers who fail to account for mathematical realities. Last month, the professor fired off a letter to Arizona Corporation Commissioner Andy Tobin after Tobin released an "Energy Modernization Plan," which proposed that the state move toward a radical new plan to generate 80 percent of the state's electricity from clean energy sources, including nuclear, by 2050.
A new Arizona ballot initiative has the same problem, Rez said Tuesday.
The Clean Air for a Healthy Arizona constitutional amendment planned for November's ballot, backed by California billionaire Tom Steyer, would force the state's utilities to generate 50 percent of their electricity from non-nuclear clean energy sources by 2030. The mandate would be achieved primarily from solar power, since Arizona has relatively low wind resources.
The overarching goal of these proposals is to reduce carbon emissions that lead to global warming. But today's technology places physical limits on what's possible, Rez said.
Solar and windmills are intermittent electrical sources — that is, sometimes they're on, sometimes they're off, depending on the sun or the wind. Since Americans demand full power 24 hours a day, something has to fill in the gaps at night, when clouds pass in front of the sun, or when the wind stops blowing. And the gaps in electricity output must be filled almost immediately.
The most efficient thing that can be turned on and within a few minutes be cranking out scads of electricity is a combustion gas turbine. But using a combustion gas turbine pumps out lots of greenhouse gas. Turn on these powerful gas engines too much, and the benefits of solar and wind get erased.
As Rez points out on pages 107 through 109 of his book, this effect means that if a generation system using this method of solar plus combustion turbines replaced a coal plant, carbon emissions would go down. But if the solar system replaces nuclear power, emissions would rise.
Using the system to replace natural gas power plants, which emit about half the greenhouse gas of coal plants, will work to reduce emissions up to a point. According to Rez, an electrical grid replacing natural gas plants with the solar-plus-turbine method could use solar to generate a maximum of up to 39 percent of the grid's peak power in the summer, and 15 percent in the winter.
Passing a law, then, that essentially mandates using solar for nearly half the state's electrical generation could mean the law would actually boost the amount of greenhouse gas in the atmosphere, under Rez's analysis.
"This goal is totally divorced from physics reality," Rez said.
The experience in Germany, which has the highest solar adoption in the world, is telling, he said. Despite billions invested and an electrical system that mandates heavy solar (and wind) use, per capita carbon emissions in Germany haven't gone down in recent years, and even increased for a couple of years this decade.
Rez's figures assume a lack of storage for generated solar electricity, which for the most part is the current reality. If only Arizona had a giant battery that could take in solar power during the day, then discharge it at night or when it was cloudy, there would be no need for the combustion turbine, and emissions would be minimal. (Some carbon emissions would still be created by the manufacture of the battery and solar power equipment.)
Unfortunately, Rez said, the 50-megawatt capacity of the battery "isn't a lot — it's pathetically low." The battery would provide about two to three hours of electricity for the equivalent of two ASU Tempe campuses, he said.
A megawatt is 1 million watts, or the amount of power needed to turn on 10,000 100-watt light bulbs.
A battery big enough to allow the whole state to be powered by solar panels for part of the day and the battery for the rest of the time would need to have 150 billion watt-hours of storage, Rez calculates. That's about 1,000 times as powerful as the APS battery.
Rez made headlines in 2010 with his warnings about the X-ray body scanners previously used by the Transportation Security Administration. He said they could dose people with too much radiation. Following the warnings by Rez and other experts, plus complaints by the public that the scanners created images that were too intrusive, the TSA removed the X-ray body scanners in 2013 and now use only millimeter-wave technology.
While Rez's numbers show renewable energy won't work to curb carbon emissions under current power generation schemes, using more solar and less coal and natural gas for electricity might benefit air quality in specific locations. Residents who live near coal plants would have better air (and maybe no jobs, but that's another story).
Metro Phoenix would see much less benefit in air quality, though, because most of its electricity comes from generation sources that are many miles from urban areas. Figures from the Maricopa Association of Governments shows that wood burning in metro Phoenix produces nearly eight times the carbon monoxide of all of the Valley's natural gas plants combined. Vehicles, by comparison, produce more than 150 times as much carbon monoxide annually in Phoenix as the city's dozen or so natural gas plants.
Rez doesn't completely write off renewable energy, noting that it can have practical applications. Windmills, in particular, make sense in places where the wind blows hard and regularly, his book says. Rez likes nuclear as the best carbon-free option.
In the book's last chapter, "What Should Be Done," Rez describes how a city the size of Phoenix could use solar and hydropower to provide all electricity. In theory, by tapping an elevated reservoir, solar power could pump water to the top of the reservoir in the day, and hydroelectric power could be derived from the water falling back down at night, his book says.
Yet that could only be done in a few places in the world where a large, elevated reservoir happens to be next to a large city. How large a reservoir would be needed to provide all of the electricity for the city of Phoenix with a solar-and-hydro plan? About the size of two Bartlett Lake's, (each with about three square miles of surface area), in Rez's estimate.
"Total decarbonization is not possible," Rez writes in the conclusion of his book. "Ultimately, the best that can be done is to eliminate coal-fired electrical energy generation, and to cut back on everyone's traveling around and consumption of materials."