How long do geothermal boreholes typically last?

Over the past five years or so, there has been an explosion of interest in geothermal energy solutions. While they are highly efficient and easy to run, one of the main points of hesitation is often related to their steep initial investment costs. 

Here, we take a look at what kind of timeframe you can expect that investment to continue to pay out over, but looking at the expected lifespan of a typical geothermal borehole.

The short answer

The borehole should last around 50 years, if everything is installed properly. Whether or not this turns out to be the case will depend on a number of factors, from installation quality to geological shifts.

The importance of longevity

Geothermal boreholes are often great energy investments, but they can also require a substantial amount of capital to get them set up, with the borehole being the most expensive part. 

As a result, it’s natural to wonder how long the system will last for, to try to calculate a timeline over which the system will keep paying for itself. 

Whether you’re a homeowner hoping to save on energy bills over the coming decades, or an investor trying to decide whether a business you’re a stakeholder in is making an appropriate request for additional funds, it helps to have some basic idea as to how these systems work.

It also helps to understand how much of this lifespan is an inevitable design limitation, and how much is within your control. That way, you can ensure that you’re doing all you can to protect your investment.

The borehole itself

The actual borehole is one of the longest lasting parts in a geothermal energy system. The borehole and the loop that’s installed inside it can easily last between 50 and 100 years, over which time you’ll likely go through a number of upgrades in the parts of the system that sit above ground. 

One of the main reasons the borehole can last for so long is the simplicity of the system. The borehole and loop have no moving parts – it’s essentially just a big, strong loop of durable plastic piping that’s buried in the ground. 

Impacting factors

There are a number of different factors that can impact longevity, from ground stability to fluid quality.

Ground stability

One important factor that can have an impact on how long your borehole lasts is the stability of the ground it is drilled into. Harder rocks tend to be a lot more stable than sand or gravel, and areas that have more seismic activity are likely to be less stable still. 

This is something that you can’t really control, as you can’t change the geological configuration beneath your property. What you can do, however, is ensure that you use adequately strong casing and grout materials, to give it a strong chance of surviving geological shifts. 

Water quality

Another factor that can have a big impact on your system is water quality. Geothermal boreholes are supposed to be closed loops, but if any contaminants do manage to get in, then you’ll find that acidic or hard water will likely corrode your pump and pipes faster than regular water. 

This impact is partially inevitable, but you can still take action to limit the negative effects of poor water quality. Regular cleaning and maintenance, along with regular inspections of parts like seals and pumps, can help to ensure that you’re able to take action before things are too late.

Original installation quality

The quality of the original installation job will have a massive impact on how long it lasts. If shortcuts are taken, such as skipping surveys or using cheaper borehole casing materials, then it’s far more likely that the borehole will suffer problems sooner rather than later, if it ends up working at all. 

Paying for an experienced, competent service provider is the only way to go. Otherwise, any small amounts that you manage to save will be more than outweighed by a potentially unsafe, unreliable system.

How to ensure longevity

There are a few things that will need to be taken care of to ensure maximum longevity. 

Installation

For a borehole to last 50 or even 100 years, it has to be designed and installed properly, and be made from the right materials. The well needs to be drilled in a stable location, and the casing needs to be made from the right materials and fixed using the appropriate cements and grouting.

As mentioned above, other factors, such as the water chemistry of the borehole and geological shifts, can also have an impact on the longevity of the system. Some of these risks can be predicted and mitigated; others may be less controllable.

Maintenance

There are also some maintenance-related considerations that can have a positive impact on borehole longevity, and on how long the other parts of the system will last. You will need to use chemicals to remove scale and other mineral buildups, clean pumps, and monitor the chemistry of the borehole. 

Some of these maintenance-related tasks you’ll be able to do yourself. Others, however, may require getting a specialised team in to do more complicated tasks and assessments for you. It’s worth checking with the installation team, so that you can get these regular service checks booked in right away.

Signs that your borehole is failing

All this being said, what does it actually mean for a borehole to fail? There are a number of signs that can be associated with these kinds of issues, including reduced flow rate, a dramatic change in heating quality that can’t be accounted for by filtration issues, or a pump that’s really struggling to circulate fluid despite being in otherwise good condition. 

If you spot any of these issues, it’s worth getting someone round to inspect the borehole more closely. An engineer will be able to determine the cause and suggest an appropriate solution.

If installed and looked after properly, then it’s likely that your geothermal borehole will outlive you. You will need to replace other parts of the system at more regular intervals, but the most expensive part of your investment will remain effective for a long, long time to come.