Road to Renewable

A physicist plots a plausible course for an all-renewable energy supply, encountering an occasional headwind along the way.

Energy Revolution: The Physics and the Promise of Efficient Technology. Mara Prentiss. 352 pages. Belknap/Harvard University Press.

By Old Dane, Creative Commons.
By Old Dane, Creative Commons.

This ambitious book sets out the underlying physics of converting the U.S. energy supply to 100 percent renewable energy sources. The topic is timely and deserves much discussion as policymakers grapple with Environmental Protection Agency regulations on power plants’ carbon dioxide emissions and the availability of competitively priced wind and solar energy.

Large-scale wind farms have been part of the electric grid since the 1980s. Solar energy has begun supplying significant power in only this decade. Practical experience has addressed many questions and myths about variable energy production from wind and solar, although that engineering knowledge is not widely recognized in nontechnical communities. This book brings the reader just inside the door to a place where practical answers can be found.

In addressing the feasibility of a 100 percent renewable energy supply, author Mara Prentiss provides some helpful introductions to basic questions of how much energy the country consumes and how to distinguish productive energy generated from the fuel going into engines and power plants from energy inputs that are lost as wasted heat. With that information, the book easily handles calculating total rainfall, sunshine and wind resources in the United States and compares these numbers. The math adds up, and the author describes how it’s feasible for the nation to replace its present energy supplies with solar or wind power but not with hydroelectric power.

Two things obscure this good news.

As the author eventually points out, there are some practical engineering problems in a solar-only or wind-only approach. For solar, the obvious obstacle is sunset. A solar-only strategy, for example, would require adequate electricity storage for long winter nights.

On practical points like this, Prentiss—a Harvard University physics professor—could be more clear about the book’s intention and message. She suggests such things as combining wind and solar in power pools and connecting dispersed generation facilities around the country but doesn’t distinguish between theory and practice.

In fact, practical experience demonstrates that diversifying the location of wind farms and the mix between solar and wind energy production can help in planning and operating regional power systems. Connecting neighboring regions with transmission lines to improve reliability and smooth variations, a practice initiated nearly a century ago, also helps manage high levels of renewable energy. But in the electric utility industry, political and institutional obstacles can inhibit implementing these lessons. For example, the debate in California over the expected energy surplus from solar panels at midday during the cooler spring season is colored—and perhaps dominated—by the state’s history of using the existing interstate transmission system for imports only.

The author includes the myth of Sisyphus and an example of a sailboat owner making fresh water but dismisses the economics of home-based solar panels.

A reader who wants to delve deeper into the central themes of running the nation on 100 percent renewable energy can find a body of work by regional grid operators and the Utility Variable-Generation Integration Group, an organization (now self-funding) the U.S. Department of Energy started 25 years ago. Its website offers a number of analyses for comparison with the book’s authoritative-sounding statements, such as “Correlation between wind farm locations begins to decrease when turbine separations exceed 600 miles.” Presently, Iowa has more than 3,000 wind turbines, which generate more than 25 percent of the state’s electricity. These turbines are within 250 miles of another 2,000 wind turbines in western Minnesota.

This brings out my second advisory about this book: The author has ventured beyond an emphasis on physics fundamentals and tried to provide observations about economics, or worse, the state of technological deployment, that don’t really reflect current conditions.

On the book’s central question, adoption and reliance on renewable energy, the author mixes careful analysis with cursory descriptions and poorly selected illustrations and digressions. She includes the myth of Sisyphus and an example of a sailboat owner making fresh water but dismisses the economics of home-based solar panels. This could obscure the reality of 2014, when some 400 residences per day got solar panels. (For an update on solar deployments, see here.)

Prentiss holds hope for a transition to renewable energy but too often suggests it will depend on new solutions that already are in place. Many of these are technological, such as “revolutionary” long-distance electricity transmission and “computer power increases to allow plants to operate at maximum capacity where most efficient.” Readers should know we have these already. The regional power grid operators recognized the economies of pooling diverse generation and using detailed algorithms to identify the lowest cost marginal units, within constraints of the transmission system. These tools, adopted over decades, are useful for integrating the high levels of renewable energy we see today, both in the United States and in Europe.

Perhaps even more important, Prentiss laments that there can be room for renewable energy investment only through increased electricity use, perhaps from electric cars. Meanwhile, the regulatory and economic reality is way beyond that point, yet this is where her discussion ends. In the real world, aging fossil- and nuclear- fueled power plants are retiring, and there is a pronounced shift to renewable energy. Long-delayed federal toxic emissions regulations are helping, but historians will credit state mandates for bringing renewable energy into the electricity supply mainstream.

In the current context of low-priced fossil fuels but rising costs from climate change, there is no more urgent technological question than the one Prentiss has raised. This energy transition, however, is too important to leave to the technologists.

Michael B. Jacobs is senior energy analyst at the Union of Concerned Scientists, where he leads efforts to shape federal and regional electricity markets, regulation and policies that encourage the expansion of renewable energy resources and the reduction of unsustainable generation. He has worked as the markets and policy director at several renewable energy and energy storage companies and at the American Wind Energy Association and previously served as the National Renewable Energy Laboratory’s liaison to the Federal Energy Regulatory Commission.


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