By Dr. Robert Thorson

Alternative energy sources are darlings of the media because each has something novel and potentially important to offer society. They enter our lives like rising film stars, rookie athletes or dark-horse political candidates. Only later does the downside of each hopeful promise become apparent.

Solar voltaic seemed flawless until New Englanders admitted to themselves how gray the skies are during winter, when we need heat the most. Alas, the ambient overcast will only get gloomier as the adjacent North Atlantic warms.

Hydrogen fuel cells also arrived on the scene with a media splash, followed by a flood of government funding. Alas – and as with nuclear fusion – advocates patiently wait and do research while the public looks ahead to something more exciting.

Wind turbines are going up everywhere, despite increased community opposition associated with not-in-my-backyard syndrome. For some, the tall towers with gigantic whirling blades violate the view. For others, it’s the noise. For still others, it’s the long-term ecological consequences of creatures flying into the blades and being killed.

Corn-based ethanol was initially touted to reduce greenhouse gas emissions and foster energy independence. Now, when all the costs are taken into account, we realize liquid corn-based fuels actually release more carbon dioxide pollution than oil.

And now the baton has been passed to advocates of deep geothermal. This includes crestfallen me, who got so excited over the prospect that I wrote a column on it titled “Tapping into Earth’s Power” in February 2007.

Then, in August, a steam-geothermal project in Germany was identified as the likely cause of an earthquake strong enough to shake buildings, create a powerful noise like a sonic boom next door and frighten residents in the small city of Landau in der Pfalz. This story was reported on Sept. 10 by The New York Times.

This seismic event rattled the cages of geothermal advocates in Landau. The initial denial of responsibility by officials of Geox (the company running the plant) made matters worse because it undermined public trust. Geox continues to dispute the seismic-geothermal connection, despite the fact that government seismologists are certain there is one.

Something similar happened in Basel, Switzerland, where officials shut down a deep geothermal plant after it apparently generated earthquakes in 2006 and 2007.

The Landau plant is being allowed to operate while government officials review the events. What a bummer should they decide to close it down. It generates electricity for 6,000 homes with a negligible carbon footprint. An equivalent coal-burning plant would emit about 30,000 tons annually. Given the choice between geothermal and coal, I would prefer the occasional local shock and rattle to an incremental and irreversible global transition.

A deep geothermal project is an artificial geyser brought under human control. In a natural geyser, the cool water from the surface seeps down through fractures where it is heated to high temperatures by hot rock. As the hot water rises, its pressure is lowered, which lowers the boiling point. At some critical depth, the water flashes to steam, propelling the water skyward. This lowers the pressure, which causes more water to boil, which sets off a chain reaction until the geyser blows and is emptied of water. The fractures then refill with cool water, starting the process anew.

With a geothermal project, the release of steam is controlled to make it strong and steady, rather than intermittent and explosive, and is channeled through turbines to generate electricity, as with coal-fired and nuclear power plants.

So what is the geothermal-seismic connection? Practically every solid, including geothermal source rock, when cooled down, contracts. Differential contraction can create stresses large enough to generate small but noisy, rattling earthquakes. Changes in the plumbing system at depth can also initiate earthquakes, as we gave learned from studies of deep-well injection and reservoir-induced seismicity.

Indeed, everything is connected to everything else. And all rising stars have their hidden flaws.