Geothermal vs Geothermal - Episode 97

We sometimes use certain terms in the energy transition interchangeably - chief among them is "geothermal". In this episode, Paul discusses some of the different types of emerging technologies that get tagged with this moniker - and why and how these different systems have different use cases and applications. No, no one is suggesting drilling a hole to the earth's core in order to heat your building ... yet!

For further research:

"Geothermal Energy vs. Ground Source Heat Pumps: What’s the Difference?" - GetGreenNow

"Explainer: This is how geothermal energy works" - World Economic Forum

"The geothermal innovation powering Google’s data centres" - Seequent

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Transcript

This is Eight Minutes – a podcast helping you understand the energy and climate challenge in just a few minutes – I’m your host, Paul Schuster.

The earth could be an amazing resource in our transition to clean energy. And there are multiple ways that innovative companies are looking to harness the ground beneath our feet for both heating as well as in generating power. 

We’re sometimes lazy and use geothermal energy as a catch-all for any of this type of new technology, but – really – the technologies we use for earth based energy ARE very different, with different applications and different challenges. So, today, let’s look at the differences between geothermal … and geothermal. 

Eight Minutes – it’s how long it takes the sun’s rays to hit earth – or about the length of time it takes you to bob for one of those darn apples at the county fair. Just give up and let your kid do it in, like … twenty seconds already!

Let’s get it on!

The energy transition can get confusing. There’s lots of new technologies, new business models, regulations, investment types. And – we don’t do ourselves many favors when we start to use some of there terms interchangeably.

One area where we could probably use a bit more diligence? In talking about the awesome potential of earth based energy.

There are basically two types of ground based energy systems that look to play big roles in the clean energy transition – geothermal energy and then ground source heat pumps. 

While similar in that each technology uses the natural heat of the earth to extract energy – these two technologies remain very different in both size and application.

For instance, geothermal technologies attempt to harness the heat that is present within the earth, itself. These systems will drill hundreds, if not thousands, of feet into the ground, accessing underground reservoirs of water that have been superheated by the earth’s core.

That water is normally trapped beneath the surface, but these geothermal bore holes act as something of a release valve, allowing the pressurized water to race to the surface, carrying all of that stored up heat with it. 

While underground, the water is under intense pressure and actually heats up ABOVE its normal boiling point. Water down there can be significantly higher than 100 degrees Celsius, just because of how pressurized it all is. But once that water comes up to the surface, it loses pressure and begins to boil – turning into steam.

That steam is then harnessed to either turn a turbine and generate power- or is used for large, city-wide district heating situations where pipes distribute the steam for space heating applications.

This type of geothermal is big. Utility scale. Big investment, big energy output, big opportunities.

Because *this* form of renewable energy isn’t as intermittent as a wind farm or a solar facility. Geothermal units produce power on a consistent, day-long, year-round basis. They operate far more like a coal or nuclear plant – which is important.

But, geothermal systems do have some drawbacks. First, there’s the cost – because drilling that far into the earth can get pricey. Especially if the underground water reservoir is thousands of feet below the surface.

Which means that geothermal systems have only really made economic sense in geographic areas where the tectonic activity is high – and we can access the earth’s heat closer to the surface. That’s why big volcanic areas such as Iceland and New Zealand have such advanced geothermal capabilities.

That’s not to say, though, that geothermal is limited to just a few geographic locations. Innovative companies like FERVO are taking the underlying technologies and improving upon them to make geothermal energy available anywhere in the world.

In Fervo’s case, their systems utilize a horizontal drilling capability that enhances the amount of energy that they are able to harness per bore hole. Essentially, they drill a single hole at the earth’s surface and – once the reservoir has been tapped below ground, are able to drill multiple horizontal holes off of that initial point. Doing so reduces the cost – and makes geothermal a lot more attractive in less – lava spewing-esque areas!

But THIS type of geothermal technology isn’t the only way to harness earth power. The other technology that we use is ground source heat pumps.

Now – “geothermal” is often used interchangeably with ground source heat pumps, hence the confusion, but I’m going to stick to the heat pump term. Because this is, fundamentally, a different technology than what I had discussed before.

For one thing, ground source heat pumps only need a few dozen feet of vertical drilling to be effective. See the heat pumps operate similarly as to every other heat pump technology on the market – air sourced, water sourced. Instead of drawing superheated water from the earth, the heat pumps use a closed loop system that cycles a refrigerant through pipes buried underground.

You only need to go a few dozen feet down to get to a point where the ground is pretty much always at the same temperature. And it doesn’t even really need to be a very high temperature. The refrigerant used in the heat pumps boils at a temp below zero, so even just a mildly warm ground will heat that fluid up to boiling, turn it into a gas and then the pipes bring that gas back up to the surface where it can be compressed and the heat removed for use.

That’s the general application of all heat pump systems – but here air source pumps have to work harder (or lighter) depending on the temperature of the day or season, ground source pumps have a consistent, even heat to always work from.

See how they’re different than geothermal units? They use their own fluid rather than extracting it from the ground – and the vertical drilling is only a few feet down.

Which also makes ground source heat pumps far more useful for smaller applications – such as a single home or commercial building. GeoTHERMAL units basically extract enough energy for a small city but heat pumps can be individually sized to a household. They’re also very versatile in being able to be installed just about anywhere.

There is one other kind of earth based energy system that I should probably touch on as well. And that is Thermal Energy Networks, a topic I covered in an earlier episode during an interview with Matt Rusteika of Building Decarbonization Coalition. TENs are networked sets of underground pipes and heat pumps that capture excess heat (or cooling) from buildings and reuses that thermal energy for use in other nearby buildings. Now – technically, the HEAT doesn’t really come from the earth in a Thermal Energy Network – but the earth DOES provide a thermal insulator for the water flowing through a TENs system. In fact, deep boreholes can be used to store heated water and then, during the winter, that heat can be used more effectively. That – kinda counts in my book!

TENs are still new, still getting traction. But the technologies of geothermal and ground source heat pumps are more advanced and developed. They are different, with different use cases, but each has a role to play in the emerging clean energy system.

I’m Paul Schuster – and this has been your eight minutes.