Geothermal energy has long been viewed as an ideal source of free energy from the Earth. In the Stone Age, geothermal heating was used for bathing in hot springs, and in ancient Rome, it was used for space heating.
Now, it may be poised to revolutionize how the world heats their homes.
In 1904, Prince Piero Ginori Conti of Italy first tested a geothermal electric power generator and then built a small power plant in 1911.
Decades later, in 1960, Pacific Gas and Electric built the first geothermal power plant in the US at The Geysers in California. Today, 22 operational power stations sit on the world’s largest geothermal field with a capacity of 1,517 megawatts and an average production of about 835 megawatts of electricity.
Indeed, naturally occurring heat sources have been easily tapped for geothermal power generation around the world. Iceland gets about 25% of its electricity from its abundant thermal geysers and hot springs.
Types of Geothermal Technologies
For most people, the term “geothermal” simply means harvesting free heat energy from the Earth to heat a home or building.
According to Bryant Jones of Geothermal Rising, a US-based industry trade organization, there are broadly three kinds of geothermal technologies.
The first, he says, is the use of geothermal ground source heat pumps to upgrade low temperatures of around 4–12 °C (39–55°F) using the shallow heat of the Earth. This is often called “geoexchange.”
The second type of use is often referred to as direct use applications in which the heat of the Earth is used in industrial processes and even in district heating systems.
The third application is the use of higher-temperature resources from geysers, hot springs, or deeper thermal reservoirs to generate electricity.
Popular, In-Ground Geoexchange Systems
Geoexchange is the most common type of geothermal project in the world. It involves burying loops of pipes in the ground, horizontally or vertically to harvest low temperatures of between 4°C and 12°C (39°F–55°F). A heat pump is then used to upgrade this to around 50°C (122°F), and it is then used to heat the home or building.
Darren and Darcy Crichton’s accidental journey to their net-zero home in North Edmonton, Alberta, Canada, used a geoexchange system dug right in their front yard. The decision to use geoexchange came in 2021 during an intense heat wave: the in-ground heat pump system provides very energy-efficient air conditioning as well as heat. (See video: https://youtu.be/9CruVmn097w).
There are hundreds of thousands of geoexchange systems installed across North America to heat buildings and even groups of buildings through district heating systems.
Geoexchange is probably the best way to heat a home. Compared to electric heaters—which are considered 100% efficient (in that all the electrical energy is converted to heat)— heat pumps connected to geoexchange systems are up to 400% efficient for heating. (In other words, for every one unit of energy needed to run the heat pump, up to five units of free energy come out of the ground).
These systems are also up to 700% efficient for cooling.
With predictions of rising heat waves … super-energy efficient air conditioning is becoming more important.
With predictions of rising heat waves, thanks to a climate-changing world, super-energy efficient air conditioning is becoming more important. People who have geoexchange systems often talk about their very comfortable homes and low energy bills.
The hitch is that installing a geoexchange system is expensive for a single-family home, costing about $30,000 to $40,000. But the economics really look good when it’s used to heat groups of homes, multifamily buildings, or single-family homes through a district heating system.
Air Source Heat Pumps
Another simpler and inexpensive approach is to use an air source heat pump mounted on the outside of one’s home. It takes heat from the air, no matter what temperature the air is. These systems are much cheaper, but the efficiency goes down with the temperature of the air.
Air source heat pumps must be able to deal with air temperatures ranging from -30°C to +30°C (-22°F to 86°F or higher). This means they will work extra hard when it’s very cold or very hot. Their efficiency can be as high as 300% and as low as 100%, about the same as a space heater.
The big breakthrough in recent years is that air source heat pumps have improved dramatically and are now rated for temperatures as frigid as -35°C (-31°F).
Air source heat pumps are very affordable and a very energy-efficient way to both heat and cool one’s home.
Air source heat pumps are now used around the world. In 2022, more than 400,000 air source heat pumps were installed in the Nordic countries of Norway, Sweden, and Denmark. The reason is simple: Air source heat pumps are very affordable and a very energy-efficient way to both heat and cool one’s home.
Geoexchange District Heating Systems
While air source heat pumps seem to be dominating the single-family home market, geothermal finds its economic sweet spot in almost any buildings that house more than one family.
For example, the Salvation Army has built a 175-unit supportive housing complex in Edmonton, Alberta, Canada. It secured quotes to build net-zero ready using geothermal heating and cooling that were only slightly more costly than conventional code-built quotes. They built super energy-efficient R40 walls and installed a geothermal system for heating and cooling and expect to save $6 million on heating costs in the first 25 years of operation.
In another example in Edmonton, geothermal was used to heat a 15-unit social housing complex and a church, helping the facilities become the first net-zero complex of its kind.
Geothermal has been used in district heating systems in the US starting as early as 1892. A system in Boise, Idaho, heats more than 80 buildings for about the cost of natural gas heating. There are about 20 such systems in the US and others in Paris, Munich, and other places around the world.
Geothermal district heating makes emissions-free heating affordable and reliable, and it's one of the few proven ways of decarbonizing building heating.
Geothermal district heating makes emissions-free heating affordable and reliable, and it's one of the few proven ways of decarbonizing building heating. “We're starting to see companies being founded that are wanting to partner with municipalities to create those district heating systems,” says Bryant Jones of Geothermal Rising.
In Europe, about a dozen countries have already or are in the process of banning fossil fuel heating systems. Air source heat pumps sales have skyrocketed, and many are looking at geothermal district heating as well.
Geothermal Energy
In 1911, Italian Prince Conti built the first geothermal power plant at the massive Larderello steam field where temperatures of 202°C (396°F) were found close to the surface. The second geothermal plant followed decades later, in 1958 in New Zealand. Two years later, Pacific Gas and Electric built the first plant in the US at The Geysers in California.
The Geysers development expanded to a complex of 22 operational power plants capable of producing 1,517 megawatts, making it the largest in the world today.
As of December 2022, there is 14,877 megawatts of geothermal electricity capacity around the world, which is still a nearly invisible blip in charts showing global electricity production.
Most of the geothermal energy plants rely on naturally occurring geysers, hot springs, or liquid-dominated reservoirs that are relatively close to the surface in large, easy-to-find resources.
Most of the geothermal energy plants rely on naturally occurring geysers, hot springs, or liquid-dominated reservoirs that are relatively close to the surface in large, easy-to-find resources such as The Geysers in California.
Less commonly, deeper reservoirs are found from which brine liquid is harvested and recirculated.
In recent years, enhanced geothermal systems are using hydraulic fracturing where they inject water to expand fissures in the rock to enhance the flow and improve productivity.
Most of these methods require prospecting to find a viable resource, which is easier if there are geysers or hot springs (think of Iceland or California) and harder in other cases.
Cracking the Geothermal Nut
In recent years, companies began using closed-loop systems and the natural propensity of the Earth to warm about 30°C (86°F) for every kilometer (0.6 miles) one goes beneath the surface.
The idea is to drill down 4–7 km (2.5–4.3 miles) and then horizontally another 4 km (2.5 miles) and install a dozen or more loops of pipe at this depth. This is done using horizontal drilling and magnetic ranging, a technology used to connect pipes deep under the Earth developed by the oil industry.
If this sounds familiar, it should. This very closely mimics the geoexchange systems that use closed loops but at shallow depths in the Earth.
EAVOR, a company out of Calgary, Alberta, thinks they have perfected the process of using closed loops deep into the Earth. After building a pilot project in Alberta that has operated for five years with very reliable production, they are now building a full-scale plant in Geretsried, Germany.
EAVOR’s geothermal project will produce 64 megawatts of heat, enough to heat 120,000 homes in a district heating system. It will also produce 8 megawatts of electricity, enough to power 8,000 homes.
This idea has already attracted interest on both sides of the Atlantic Ocean. “We have follow-on projects in Germany that are other heat projects. We have another project in the design phase in the Netherlands. And we have a portfolio here in North America that we're working through,” says Jeanine Vany, a geoscientists at EAVOR.
Geothermal Breakthrough?
The big advantage of this closed-loop technology is that no one has to search for an elusive thermal reservoir; they are simply using the Earth’s natural levels of heat that occur almost everywhere on the planet.
Jones believes geothermal is about to become a mainstream technology for providing a low-carbon source of baseload electricity and heat.
And indeed, with record installations of solar and wind power around the world, there is a lot of demand for baseload electricity that does not produce emissions—and geothermal just might be the missing link.
“Geothermal is a bipartisan technology. Republicans like it, Democrats like it, conservatives, and liberals like that geothermal is a clean renewable energy. It has the lowest environmental footprint of all energy technologies,” says Jones.
*David Dodge is an environmental journalist, photojournalist, and the host and producer of GreenEnergyFutures.ca, a series of micro-documentaries on clean energy, transportation, and buildings. He’s worked for newspapers and published magazines and produced more than 350 award-winning EcoFile radio programs on sustainability for CKUA Radio.
Additional Sources:
Heat Pumps 101: Jean-Marie of NAIT Polytechnique explains how a heat pump works and where one can use them: https://youtu.be/IyV452N9GAQ
Geothermal 101: Devon Winczura of Envirotech Geothermal explains how geoexchange systems work in northern climates and how to heat a home with 400% efficiency: https://youtu.be/5gmFk_TgLrw
留言