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Dear EarthTalk: How are heating, cooling and electricity produced by
geothermal energy? I don’t understand how it works. -- Delano Stewart, Wyandanch, NY
The term “geothermal” is derived from the Greek words for Earth (geo) and heat (therme). In essence geothermal energy is power harnessed from the Earth itself. Heat from the Earth’s core, which averages about 6,650 degrees Fahrenheit, emanates out toward the planet’s surface. Heated springs and geysers up to three miles underground can be accessed by special wells that bring the hot water (or steam from it) up to the surface where it can be used directly for heat or indirectly to generate electricity by powering rotating turbines. Since the water under the Earth’s surface is constantly replenished, and the Earth’s core will continue to generate heat indefinitely, geothermal power is ultimately clean and renewable.
Today there are three main methods for harvesting utility-grade geothermal energy: dry steam, flash steam and binary-cycle. The dry steam process brings steam up directly from below to drive turbines that power electricity generators. Flash steam plants bring the hot water itself up from below; it is then sprayed into a tank to create steam to drive the turbines. These two methods are the most common, generating hundreds of megawatts of electricity across the American West, Europe and elsewhere. But expansion is limited as these plants only work in tectonic regions where it is easier to access ground heated water.
The binary-cycle technology extracts close-to-the surface warm (not necessarily hot) water and combines it with a second (“binary”) fluid, like butane or pentane, which has a low boiling point. This fluid is then pumped through a heat exchanger, where it is vaporized and sent through a turbine before being recycled back into the system. Binary-cycle geothermal plants already pump out dozens of megawatts of electricity in California, Nevada and Hawaii, among other places.
But geothermal isn’t just for utilities. Homeowners looking to go green and lower their utility bills can install a residential system, essentially a scaled-down version of the binary-cycle system. A series of pipes is installed underground. Water circulating in the loop is heated naturally underground and then transferred to a heat exchanger which concentrate the energy and releases it inside the home as heat. In summer and in warmer climates, the process is reversed to fill the home with geothermal-cooled air.
Geothermal has its drawbacks. For homeowners, it may be hard to justify the up-front expense of $7,500 or more to install a system, though the IRS now offers tax credits for 30 percent of the cost. At the utility level, geothermal plants are costly to build and operate. And finding a suitable site requires digging expensive test wells with no guarantee of hitting a productive underground hot spot. Nevertheless, analysts expect utility-grade geothermal capacity to nearly double over the next just six years. The Obama administration has set aside $750 million for geothermal development, and Congress has also been generous, allocating $129 million to the Department of Energy for various geothermal programs.
Geothermal may be in its infancy in the U.S., but it is a big player in Iceland, which derives 26.5 percent of its electricity needs from geothermal, and in New Zealand, which gets 10 percent of its electricity likewise.
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Dear EarthTalk: Apparently boxed wine (instead of bottled) is becoming all the rage for environmental reasons. What are the eco-benefits of boxed wine over
With more and more wineries offering organic varieties to lower their eco-footprint, it’s no surprise that they’re looking at the environmental impacts of their packaging as well. The making of conventional glass bottles (and the corks that cap them) uses significant quantities of natural resources and generates considerable pollution. According to the U.S. Environmental Protection Agency, the process of manufacturing glass not only contributes its share of greenhouse gas emissions but also generates nitrogen oxides, sulfur dioxide and tiny particulates that can damage lung tissue when breathed in.
Beyond manufacturing, the transport of wine in glass bottles across the country and around the world also takes its environmental toll. According to wine writer Tyler Colman, upwards of 90 percent of American wine is produced on the West Coast, but then shipped to the East Coast where the majority of wine consumers live. Trucking all these heavy glass bottles generates a much larger carbon footprint, ounce-for-ounce than the transportation of much lighter boxed wine. Almost half the weight of an ordinary case of wine comes from the bottles; about 95 percent of the weight of a case of boxed wine is the wine itself.
“A standard wine bottle holds 750 milliliters of wine and generates about 5.2 pounds of carbon-dioxide emissions when it travels from a vineyard in California to a store in New York,” reports Colman, who blogs at DrVino.com. “A 3-liter box generates about half the emissions per 750 milliliters.” He concludes that switching to wine in a box “for the 97 percent of wines that are made to be consumed within a year” would reduce greenhouse gas emissions by about two million tons, or the equivalent of removing 400,000 cars from the roads.
According to the Wine Group, the third largest wine company in the world by volume and a big advocate for switching away from glass bottles, there are other advantages to boxed wine (which typically includes a plastic bag within a cardboard box). The vacuum packaging of boxed wines allows the contents to stay fresh for up to six weeks in the fridge once the seal is broken and the first glass has been poured. The Wine Group has launched the “Better Wines Better World” website in an attempt to curry public favor for technologically advanced, environmentally friendly and economically practical boxed wines.
Still, despite the benefits, boxed wine may still be a tough pill to swallow for many wine connoisseurs still bent on tradition. “Even those traditionalists who are coming around to the idea that maybe screw caps are fine for some wines, balk at the idea of a cellar full of cardboard boxes,” says wine writer and vineyard owner Lee Asbell. “It is difficult to imagine how wine service at fine-dining establishments would handle such a change.” For now, boxed wine is still the domain of cheaper brands. But that could all change as more and more wine makers and drinkers take up the mantle of saving the Earth.
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