What Affects The Cost of Drilling a Geothermal Borehole?

For those considering investing in some kind of geothermal heating solution, one of the main barriers is often the cost of having a borehole drilled. It can be a substantial investment, but thanks to the cost-saving benefits of heat pumps, it’s one that will typically pay for itself relatively quickly.

How much it actually ends up costing will depend on a range of variables. From depth to site access, these are a few things that can affect how much you need to spend. 

Depth

One of the main factors that will have an impact on borehole drilling costs is borehole depth. Most geothermal boreholes for heat pumps tend to be between around 80-200 metres in depth. 

Deeper boreholes take longer to drill, of course, but also require more loop pipework, more casing, and more grout, all of which will have an impact on the end cost. 

Geology

Another big factor is geology. Softer ground conditions are much easier and faster to drill through, and don’t tend to require much in terms of specialist equipment (aside from a drilling rig). 

Harder rock types can require specialist drill bits, taking much longer to drill through while also resulting in a lot more equipment wear. Your contractor will be able to determine what they’ll be working with based on the results of your geological survey, and use that data to produce your initial quote.

Number of holes required

In most cases, it’s inefficient to bore deeper than around 200 metres. Instead, if more thermal energy is required, more boreholes will usually be added to the project specifications. 

If you’re installing a system to heat a number of commercial properties, then you’ll obviously need a lot more boreholes compared to if you’re just heating a single home. This in turn will push the cost of the project up. 

The planning team will be able to calculate how many boreholes are required relatively easily, based on the results of geological surveys, and the size and thermal ratings of the properties that need to be heated.

Site access

If access to the site in question is particularly tricky, then it’s possible that this might bring the price up as well. Drilling rigs can be pretty big, and getting them anywhere takes a bit of planning, even to locations with good roads and no width restrictions.

If the site you’re interested in developing has narrow access roads, or requires driving over soft terrain such as fields of other soft ground types, it can push project costs up a bit. This will especially be the case if additional pathways or roads have to be installed for the duration of the project. 

Geothermal boreholes unlock access to sustainable, affordable sources of energy, and this will generally pay off in the medium term. Based on the results of some initial surveys, your current heating costs and some rough predictions, you should be able to calculate how long the whole thing will take to pay for itself relatively easily.