Geothermal energy, the idea that we can harness thermal energy radiating out from the earth to power many aspects of our own society. While the idea is not a novel one, it has been used in many different ways throughout human history. But first I should clarify that there are two types of thermal energy that we can refer to with geothermal. The first one is volcanic in origin; where volcanic fluids, such as steam rising from deep within the earth, can be harnessed and used to spin massive turbines that produce electricity. Harnessing these volcanic fluids and gasses however is not an invention of the 20th or 19th century. In fact, humans dating back to the Paleolithic, from around 3.3 MYA to 10,000 years ago at the end of the last ice age have used hot springs for bathing and keeping warm during cold winter months. And in the times of the Romans these hot springs were connected to aqueducts that could transport the hot water to be used for space heating purposes all across Rome. The other form of geothermal refers to the thermal mass the upper 500 feet of the earth’s crust can provide in the form of heating or cooling. This is due in part to ground around the world remaining at a relatively constant temperature of around 60 degrees Fahrenheit regardless of summer highs and winter lows. By using something called ground-source heat pumps fluids, usually water mixed with a bit of antifreeze, can be pumped into wells deep underground where the fluid can either absorb heat from the ground to heat a building or use the ground as a place to dump heat to cool a building in the summer. The technology of ground source heat pumps is a more modern one, but for millennia humans have used the ground to preserve food during long winters and summers, and early humans used caves that stayed at the constant 60 degrees to stay warm in the winter and cool off during the summer.
One of the best examples of geothermal energy that uses volcanic gasses and fluids is the country of Iceland. Iceland is a revolutionary for the fact that 100% of their energy needs come from renewable resources. Of this, nearly 85% comes from renewable energy. 65% of the country’s heating needs are met by using the heat from geothermal wells and around 25% of the country’s electricity is met with electricity produced from geothermal wells. All of this is possible solely due to Iceland’s population size and its location on the continental divide between the North America Plate and the Eurasian Plate. Iceland’s population of around 385,000 people, which is equivalent to the population of people living in the city of St. Paul, makes it the 171st largest country in the world being edged out by the Bahamas with 400,000 people. It is also located on a plate boundary, where two tectonic plates are spreading apart allowing for magma from deep in the earth to flow upwards in vast quantities. In addition to being on a plate boundary there is also something called a mantle hotspot that feeds Iceland’s volcanoes in addition to the tectonic plate boundary. All of this magma heats water trapped below ground until it turns to steam and rises through small cracks before being released on the surface. Wells can be drilled deep into the earth and the steam can be collected under high pressure and used to spin turbines and produce electricity. When steam initially enters these wells it can be in excess of 600 degrees Fahrenheit. And after it has flowed through the system it is still over 200 degrees. At one geothermal power station in Iceland the steam is capable of spinning two 40 MW turbines. For reference, this would be like having 48 of our 2 wind turbines in Morris spinning at their maximum output 24/7/365. And after the steam has spun the turbines it is oftentimes directed into district heating systems that provide heating to many of Iceland’s communities.
A more localized example for ground source geothermal for heating and cooling can be found at the Stevens County Courthouse and at the Morris library. Both of these buildings use ground-source heat-pumps to heat the buildings in the winter and cool the buildings in the summer. While neither system is 100% efficient, both systems negate the need for natural gas heating in the winter. And for cooling in the summer months, dumping heat from the buildings into the ground is significantly more efficient than using traditional air source heat pumps and air conditioners which run condensers to move heat and cool off a building. The system in the Stevens County Courthouse is the newer of the two systems having been recalibrated and updated in 2012. Relying solely on electricity these systems help to decarbonize the thermal loads associated with the building. These thermal loads are some of the most difficult ones to electrify due to the inefficiencies of most technologies. Thus by electrifying these loads, renewable energy can be used to heat and cool buildings instead of relying on fossil fuels. Thanks to recent investment from the federal government, technology that can support electrifying thermal loads is steadily becoming more and more of an option for more people; including everyday citizens. Cold-climate air-source heat-pumps represent a new technology that can help transition residential homes away from heating with natural gas or propane to heating with electricity that allows for more efficient operation and renewable energy ready properties.
This article was originally published in the Stevens County Times
My position with the City of Morris is funded through a grant from the ENRTF. To learn more, head to https://www.legacy.mn.gov/environment-natural-resources-trust-fund