Reliable power sources in the U.S. and Minnesota: A primer

Continuing pressure on public utilities to stop coal burning is requiring a search for alternative ways to produce large amounts of base load electric power.

Coal burning is the biggest source of atmosphere-warming carbon dioxide, plus it emits pollutants such as arsenic, mercury, soot and sulfur. Xcel Energy has replaced two metro-area coal plants with facilities that burn cleaner natural gas. Coal is also being replaced by nuclear power in China, which has 50 new nuclear reactors in the planning or construction stages. But coal remains the largest worldwide source of the electricity that is essential for modern society.

Conservation will be important, but it cannot solve the entire problem, and there are options for generating clean and reliable sources.

Many people think of wind and solar power as the next-generation power sources. We have observed a large increase in grid-level wind power, which now provides 17 percent of Minnesota electric demand. And coal has declined from 50 percent of U.S. electric fuel in 2005 to 34 percent in 2015.

Intermittent wind and solar require backup, usually from natural-gas power plants. But there is a constant need for stable base load power that runs continuously; a base load that only coal, natural gas or nuclear power can provide.

Natural gas emits significantly less pollution and greenhouse gases than coal, although there is a risk of methane leaks during its production. There is a price risk, as natural gas has sold for three or four times its current price in the recent past.

Power generated from round-the-clock nuclear plants is almost completely free of pollution, but there is a storage challenge for waste nuclear fuel. The $12 billion Yucca Mountain storage facility has the capability to store waste from the 100 U.S. nuclear reactors. The Yucca facility is currently on hold for reasons that the Government Accountability Office has described as political, not technical.

Six new nuclear reactors are under construction in the U.S., all in the Southeast. Other new reactors at 21 sites have recently been proposed for the U.S. These new-generation carbon-free power plants will be necessary if we are to deliver on President Obama's promise to reduce America's greenhouse-gas emissions by 17 percent by 2020.

The journal Science noted in an issue: "The electrical grid demands exquisite balance. At every instant, the supply of electricity throughout the system — thousands of power plants, substations and transmission lines — must equal demand. If not, wires overheat, voltage drops and circuit breakers snap open to protect parts of the grid."

A stable, low-emissions power grid could consist of roughly equal parts base load nuclear, wind and solar renewables, and natural gas that can balance the variable renewables.

To get about a third from each of these sources in the U.S., nuclear would need to increase from its current 20 percent; natural gas already is one-third of our electric supply, and wind and solar would need a major expansion to 33 percent from the current 5 to 6 percent.

The French, with 58 reactors, reprocess their spent nuclear fuel, vitrifying the dangerously radioactive 5 percent in glass cylinders for long-term storage. They recycle the remaining 95 percent into new fuel.

Electric power is the most useful energy source on Earth. Nuclear, wind, solar and natural gas will guarantee its continued dominance in our energy future.