Geothermal heating has been around in some form for a very long time but has received extra attention in recent years due to growing concerns surrounding the climate crisis. So, is geothermal heating bad for the environment?
Geothermal heating isn’t bad for the environment. In fact, as we will explain throughout the article, it is the most environmental friendly way to heat your home. While some types of geothermal heating can produce Greenhouse Gas (GHG) emissions, they are far lower than traditional heating systems.
Now we know that geothermal heating is generally a good idea when it comes to protecting the environment. In this article, we’ll look at all the environmental impacts of geothermal heating and discuss ways to make geothermal even more climate-friendly.
What Is Geothermal Heating?
‘Geo’ means ‘earth’ and ‘thermal’ means ‘heat.’ It really is that simple. Geothermal heating is using the heat that is stored within the earth in order to heat (and cool) your building. Usually, there are a few different ways to harvest and use geothermal energy, but all share the method of extracting heat energy from the earth, then using it for heating.
The Different Types of Geothermal Heating
While all geothermal heat production shares the basic concept of extracting energy from the earth’s heat, the exact method by which it happens can differ. One of the major differences is between open-loop and closed-loop systems. Here is the difference between them:
These are both the most common and most efficient geothermal energy pumps. A closed-loop means that nothing gets used up. A fluid of some sort, usually something along the lines of antifreeze, is heated by the geothermal energy and evaporates, transferring the heat from the earth to the heat pump in your home. The fluid recondenses and returns to its original position. It is a closed-loop system because the fluid never actually leaves the loop.
Open Loop Systems
You may have guessed already, but an open-loop geothermal system is a system in which the fluid used to spin the turbine does not remain within the loop. Usually, these systems pump hot water from the earth directly to the heat pump without using a heat transfer fluid as a middleman. To use this variety of geothermal heating, you need to have access to a substantial body of underground water, which is why this is much less common.
The Environmental Impact of Geothermal Heating
Ok, now that we have gone through the different types of geothermal heating systems, it is time to look at the environmental impact. The first thing to say is that closed-loop systems are always better for the environment since they do not require you to remove water from reservoirs. Even if you reinject the water back into the ground, you will lose some greenhouse gases stored within.
Here are a few of the considerations surrounding the climate impact of geothermal:
You may be wondering how greenhouse gases can be produced by geothermal heating. The answer lies with non-condensable gases (NCGs), which are stored within the geothermal fluid.
These gases do not condensate under the same conditions as water vapor and thus remain in a gaseous state. NCGs are composed of about 95% Carbon Dioxide (CO2), with trace amounts of methane and other gases. They also contain chemicals like hydrogen sulfide.
How to Avoid Releasing NCGs
Closed systems like closed-loop systems are better for the environment because the NCGs do not get a chance to be released into the atmosphere. As described above, in a closed-loop system, the heat transfer fluid never actually comes into contact with the geothermal fluid.
In other words, the heat is transferred, but the geothermal fluid (and NCGs) remain in the same place. Closed-loop systems, then, come pretty close to being carbon-free energy.
How Much CO2 Is Produced by Geothermal Heating?
As you may have guessed at this point, the amount of GHGs released by geothermal heating and electricity production depends largely on what type you are using. However, it also depends on the location since different geothermal reservoirs contain different concentrations of non-condensable gases. However, the greenhouse gases produced by geothermal are significantly lower than even the cleanest fossil fuels.
Estimates vary depending on the sources, but a good rule of thumb is that geothermal energy produces somewhere between 15 and 53 grams CO2e/KWh. Some sources say that the best scenario is 6 grams of CO2 per kilowatt-hour of energy (CO2e/KWh). Other sources say that the worst-case scenario will be if they produce around 750g CO2e/KWh. Both these extremes, however, are extremely unlikely in the real world and most sources won’t even mention them. Again, the emissions largely depend on whether you are using an open or closed-loop system.
Comparison of Carbon Emissions With Fossil Fuel Heating
The heating system with the highest carbon emissions is coal-fired boilers. No surprise there. But how does geothermal heating compare to other systems? Well, really, it depends on a huge number of factors. Deep geothermal heaters in Scotland, for example, emit 93% fewer GHG emissions than gas-fired boilers. On average, the figure seems to be that there is about an 88% reduction of GHGs compared to natural gas boilers.
US estimates put the GHG emissions of geothermal heating at 10-38g CO2/kWh. Compare that to 414g CO2/Kwh for hard coal. In other words, coal produces as much as 41.4 times more carbon per unit of electricity than geothermal heating. For oil, the figure is about 314g CO2/Kwh, or as much as 31.4 times more CO2 than geothermal.
It is clear to see from this preliminary look that geothermal heating is significantly better for the climate than any fossil fuel system.
Comparison of Carbon With Other Renewable Heating
But how does it compare to other renewable energy sources? Let’s find out.
Biomass, in addition to problems with deforestation, produces about 230g CO2/kWh of energy, or about ten times the emissions of the average geothermal heating system.
Heating using electricity generated through nuclear plants and marine hydropower have similar carbon emissions to geothermal, but with more adverse environmental impacts.
The carbon footprint of solar power is around 6g CO2/Kwh, and for wind power, it is about 4g CO2/kWh. However, this does not quite tell the whole story since converting that electricity to heat energy can be inefficient, and you end up losing energy in the process. The main takeaway should be that, when it comes to heating, geothermal has perhaps the lowest impact of all on the environment.
If you would like to learn a bit more about the different ways to heat your home with renewable sources, have a look at our article “Heating your Home with Renewable Energy“.
As well as GHGs, it is important to know whether a particulate matter is released into the atmosphere since this can have a serious effect on human health. The main emission from open-loop systems is hydrogen sulfide, which turns to sulfur dioxide in the atmosphere. As well as causing heart and lung disease, sulfur dioxide causes acid rain.
However, it is worth noting that open-loop geothermal pumps produce around 30 times less sulfur dioxide than coal plants.
There is no denying that geothermal heating is much more environmentally friendly than traditional heating methods like coal or gas-fired boilers. While there are some GHG emissions from geothermal energy, they are much lower than for fossil fuels.
What’s more, the more recent versions of geothermal heat pumps have hugely minimized the GHG emissions, largely by switching to closed-loop systems, in which the non-condensable gases in the geothermal fluid are not exposed to the atmosphere.
We hope this has helped to convince you that geothermal is a great way to heat your home.
- Alistair T.McCay, Michael E.J.Feliks, Jennifer J.Roberts: Life cycle assessment of the carbon intensity of deep geothermal heat systems: A case study from Scotland
- Balanced Energy Network: Carbonwatch Calculator for GSHP Heating
- Carbon Independent: Emissions from home energy use
- European Geothermal Congress: CO2 Emissions from Geothermal Power Plants: Evaluation of Technical Solutions for CO2 Reinjection
- ESMAP: Greenhouse Gases From Geothermal Power Production
- Conserve Energy Future: Types of Geothermal Energy Pump Systems
- Executive Cooling and Heating: 4 Types of Geothermal Heat Pumps
- Forest Research: Carbon emissions of different fuels
- Geothermal Communities: Environmental Impacts of Geothermal Energy
- Geothermal Genius: Are You in the Loop? Open vs. Closed Loop Systems in Geothermal
- Green Match: Advantages and Disadvantages of Geothermal Energy
- Houses of Parliament: Carbon Footprint of Electricity Generation
- Office of Scientific and Technical Information: Geothermal Electrical Production CO2 Emissions Study
- National Geographic: Geothermal Energy
- Nordic Heating & Cooling: How a Heat Pump Works
- Power Technology: What Is Geothermal Energy and Where is It Used in the World?
- Union of Concerned Scientists: Environmental Impacts of Geothermal Energy
- World Bank (ESMAP): Greenhouse Gases From Geothermal Power Production
- Intech Open: Geothermal Energy as an Alternative to Reduce Atmospheric Emissions and Provide Green Energy