Geothermal is an Earth-Friendly Option
By Dave McCarthy
As we move into a post-fossil fuel economy, we often think mostly in terms of renewable energy technologies such as wind and solar. But the Earth herself is an amazing and mostly untapped energy resource.
“Geothermal” is the general term for systems that make use of the Earth’s energy. About one percent of the world’s electricity is generated by plants that make use of high temperatures from deep in the Earth. There are almost 100 geothermal plants in the US, mostly in the west, and the Philippines generates some 17 percent of its electric grid power in this way.
This article, though, is about another, much more widely available geothermal resource, one that is literally in our own backyards. Geothermal heat pump technology takes advantage of the fact that, at a fairly shallow depth, the Earth’s year-round temperature remains constantly in the range of 50 to 60 degrees (in our Hudson Valley region it is around 50 to 52 degrees). Also known as a “ground source” heat pump, this type of system is a localized method of energy production. It does its work on-site, pretty much anywhere.
How does it work? If you put an ice-cube in a drink, warmth from the liquid is absorbed by the ice in the process of melting, and the drink cools down. This illustrates the most basic process involved: heat exchange. From there it’s a fairly short jump intuitively to see that when it’s 90 degrees outdoors, and the Earth 10 feet below the surface is at 50 degrees, it’s possible to run a system of pipes through the cool ground and let it absorb heat from above. This heat exchange process takes place in steps: from the air, to a fluid (usually water), and back to the air. Notice that we’re not getting energy from the earth here. We’re putting unwanted heat into the ground.
It’s not quite as intuitively obvious why, if it is 30 degrees outside in the winter, and the earth is still at 50, that we could warm our house to 70. For that we need to understand a heat pump. Charles Lazin has installed over 100 geothermal systems.
“A heat pump is an energy concentrator, working like a magnifying glass,” Lazin says. “It takes a low-grade heat source and focuses it, so to speak, into a higher temperature. A heat pump works through a cycle of compression and decompression, much like an air conditioner in reverse. The heat pump, and the pumps that cycle the fluid through the ground, are powered by electricity, but the overall energy use is far less than conventional furnace and A/C systems — 30 to 70 percent less.”
Studying geothermal systems is a great way to see how the local relates to the global. Let’s talk about carbon footprint: if you were to generate the electric energy on-site to power a geothermal system (using, say, wind and photovoltaic sources) the operation of your heating and cooling system could have near zero carbon footprint (of course, the manufacture and transportation of any sort of equipment has its own carbon footprint). Nevertheless, integrated renewable energy systems — which can also include the direct capture of solar energy as heat — present remarkable possibilities for a post-fossil fuel future.
What is more common with geothermal systems is to power the whole thing through grid-sourced electric power. This is where the process becomes interesting and instructive when it comes to carbon footprint. In countries like the United States and China, which rely very heavily on coal-fired electric plants, the carbon footprint of an electric-powered geothermal home heating system could still generate roughly the same, or even a bit more, carbon emissions than one using natural gas. Of course, the homeowner is still saving very substantially on operating costs in this scenario. This is interesting even though there are very few ecologically conscious people today who view natural gas through the rose-colored glasses of its earlier reputation as a clean, efficient, and relatively low-carbon fuel. The emerging, ugly truth about hydro-fracking (a highly controversial form of natural gas drilling) has changed all that. Still, there are a couple of lessons in this: first of all, analyzing something according to one factor alone will never give you a full picture. If you just look at it from the point of view of cost — or, for that matter, of carbon emissions — you’re going to miss things, in this case very serious ecological consequences.
One very positive option in using grid power for a geothermal heat pump is to purchase wind energy from your utility. Though it is a bit more expensive, by increasing demand for wind power at the grid level, you are encouraging the development of this renewable source.
Here are some practical points on geothermal heat pump systems, courtesy of Charles Lazin (his website, altren.net is a rich source for further information). The average payback time for the investment required to install such a system is surprisingly short: three to five years. There are substantial tax credits and benefits available, including a 30 percent federal income tax credit on the complete system, plus there are often state rebates and utility company incentives available.
A system can be installed relatively quickly. The energy exchange loop can be installed horizontally at around five to six feet beneath the ground, or it can be installed vertically. There are also open loops using ground water, and systems that work in a pond. The average installation time is one to three weeks.
Aside from the cost saving, we can individually gain by installing renewable energy systems; anything we can do to decentralize and “de-fossilize” energy production has tremendous benefits at the level of the human whole. System by system, backyard by backyard, we can democratize energy production and greatly reduce our climate-change impact.
The challenge of this movement is that it depends on the individual. One by one, we can get educated and motivated, and feel a sense of empowerment and inspiration around the very practical idea of harvesting our own renewable energy from the local environment.