There is widespread confusion between the terminology of geothermal energy and ground source heat pumps, also known by their acronym, GSHPs.
This confusion is understandable when we consider that the two terms are used almost interchangeably, particularly in North America. There is also a true similarity between the two energy solutions in that both harness heat from the ground.
Nonetheless, these are two vastly different processes, and, as we will see, only one of them is really viable for heating an individual home.
This article will explain the differences between geothermal energy and ground source heat pumps, and will also go over how they each work. You’ll also learn about alternative heating options to geothermal energy and GSHPs.
What is Geothermal Energy?
Geothermal energy is produced by tapping into the heat at the core of the earth, which can reach temperatures of up to 6000ºC. In order to reach this heat (between 500 and 2,500 metres underground in the UK, for example), a deep borehole is drilled and filled with water.
The water inside the borehole is then naturally heated by the hot rock. The hot water produces vapour that can be used to drive turbines and create electricity.
In countries with more tectonic activity, the heat from the earth’s core naturally emerges close to the surface of the earth. An example of this is in the form of geysers or hot springs in Iceland or New Zealand.
For these countries, extracting and using geothermal energy is less complex and more cost-effective, as shallower drilling will reach the natural heat source. Scientists estimate that this powerful source of renewable energy will be available for another 4–5 billion years.
What is a Ground Source Heat Pump (GSHP)?
Rather than extracting heat from the earth’s core, a ground source heat pump (or GSHP) uses the heat that is stored in the soil or water under Earth’s surface level, at a maximum depth of 200 metres.
This heat is created when the sun warms the earth, particularly during the hotter seasons, and it is still stored consistently during the colder seasons.
In fact, roughly 15 metres below ground, the earth sustains a consistent temperature all year round, which is “approximately equal to the mean annual air temperature (8–11ºC in the UK)” according to the British Geological Survey.
Ground source heat pumps are different from geothermal energy, as geothermal energy uses the heat generated from the core of the earth. Ground source heat pumps, however, use the sun’s energy, which is stored in the ground as heat.
So, how exactly do ground source heat pumps work?
Using a system of antifreeze fluid-filled pipes buried underground, a ground source heat pump can extract this heat from the earth, pass it through a heat exchanger, and circulate it within a property to provide its occupants with year-round heating and hot water.
Ground Source vs. Geothermal
If you’re fortunate enough to live in Iceland, more than 90% of all housing is powered by geothermal district heating schemes.
Typically, however, geothermal energy is harnessed by large plants and isn’t done for individual properties or small communities.
For those of us who live in more tectonically stable regions, geothermal energy is not feasible and only accessed through a huge, and costly, drilling operation.
A ground source heat pump is almost always a more realistic option for enjoying a sustainable domestic heating system. Although GSHPs require a relatively large investment to install, in the long-term they have the potential to save lots of money per year on energy bills.
Furthermore, as the popularity of ground source heat pumps continues to rise, we will see a reduction in the cost of manufacturing and other upfront costs. The market is booming, and this will help the end customer.
It’s worth bearing in mind, however, that if you’re looking for a truly green energy source, a GSHP does require a small amount of electricity to function. Choosing a renewable energy supplier for that electricity or installing your own solar PV panels will help ensure that your GSHP system is carbon-neutral.
GSHP vs Geothermal: Why does terminology matter, and why is it important?
One of the biggest barriers to renewable energy uptake is awareness and understanding. With so much information flying around from different industry stakeholders, the landscape is complex and confusing.
As a homeowner or small business owner, it’s difficult to navigate all the official and unofficial blogs, news sites, videos, and podcasts. There is good information out there, but it’s a noisy place.
Therefore, it is important for people to get clear information. If somebody is keen to switch to a renewable source of heating for their property, they might search for “geothermal energy” and learn that it’s not suitable. This might prevent, or delay, further research and damage the potential for switching to a ground source heat pump – which is a more feasible option.
We can’t prevent the emergence of different terminologies around the world, but we can be aware of them. We can add caveats and explanations, as well as cautionary notes. It’s important for all experts to consider this in their content, and when talking to consumers.
Alternative heating options
A ground source heat pump is a solid choice, but not always suitable for every property. You need plenty of outdoor space in a garden to install the ground loops or boreholes, and unfortunately not everybody has enough space to do so.
But, you should rest assured, as there are still plenty of renewable heat options.
Air Source Heat Pump
Firstly, an air source heat pump is worth exploring. These look similar to classic air conditioning units and sit on the outer wall of a property.
Air source heat pumps (ASHPs) are similar to GSHPs, but they use latent heat from the outside air rather from underground. They can work year-round, even during the cooler months when the weather is more volatile.
Biomass boilers are another feasible option. Instead of burning gas, biomass boilers burn wood logs or pellets which are made from other wood waste. This fuel is often cheaper than fossil fuels for boilers, and much less fluctuating in price, thanks to the option of sourcing locally.
Solar Thermal Panels
Another alternative heating system is solar thermal panels. These can sometimes be limited in effectiveness, and might need support from a secondary heating source.
Solar thermal panels are best suited to heating hot water, rather than powering the warmth for a whole home.
Geothermal energy and ground source heat pumps are radically different approaches to utilising the earth’s natural heat reserves.
Unless you live in a region with high tectonic activity, geothermal energy can only be extracted by drilling hundreds, or even thousands, of metres deep into the earth. The expense and complexity of this process means that it is only viable for large-scale geothermal schemes.
In contrast, a GSHP system can be established on a much smaller scale, for a more modest budget, and is suitable for heating a single dwelling, or a small community of properties. When combined with a renewable energy source for the electric pump, a GSHP can be an effective and affordable solution to comfortably heat your home whilst drastically reducing carbon emissions.
About the Author: Marcus Franck
Marcus Franck is the Co-founder and Marketing Director at Smart Renewable Heat, a UK heat pump installer. He is a regular writer, having contributed to renewable energy websites and leading international media outlets. He is passionate about the decarbonisation of heat, and works to promote the benefits of renewable technologies.