Is there enough space on the plot for geothermal energy drilling?

How Many Boreholes Can Fit on the Plot?

The number of boreholes that can fit on a plot is influenced by the required heat production, which sets a lower limit on the amount of energy that must be obtained from the boreholes. The depth of the borehole directly determines the energy production from a single borehole.

On the other hand, when the depth of the borehole exceeds 400-500 meters, the cost and risks of drilling increase significantly. For this reason, in an optimal situation, the required amount of energy can be produced with multiple boreholes. But how do you know how many boreholes can fit on the plot?

Polygon Data and an Efficient Algorithm to the Rescue

We use geographic polygon data of buildings and plots to map the number and locations of boreholes. Our algorithm places potential borehole locations on the plot in a dense triangular pattern, and through about 200 simulations, we find the combination that maximizes the number of boreholes on the plot.

The constraints for the boreholes require a distance of 15 meters from each other and 7.5 meters from the plot boundary (or the centerline of a nearby road). Additionally, the starting point for drilling a borehole must not be less than 3 meters from the building or 2.5 meters from each other.

A plot of an apartment building in Lauttasaari, Helsinki can accommodate 9 boreholes. Some of the boreholes can be drilled under the building, starting from the free area of the plot, while still meeting the required distance between boreholes underground.

In a 50-apartment building in Helsinki's Lauttasaari with a large 2,400 square meter plot of somewhat complex shape, a simple area estimate suggested that up to 12 boreholes could fit on the plot. However, this gave an overly optimistic picture. Our algorithm found only 9 possible borehole locations on the plot.

From this link, you can fond some inspiration on how the algorithm is implemented under the hood.

Optimizing Borehole Quantity and Depth for Tens of Thousands in Savings

Once the maximum number of boreholes that can fit on the plot is known, our algorithm searches for the most cost-effective number of boreholes and their depths, taking into account the increasing energy production and drilling costs as borehole depth increases. We perform up to thousands of simulations with different borehole depths and numbers to find the cheapest way to produce the required amount of energy.

Placement of boreholes with different numbers of boreholes. In this case, the required energy production could be met with either 5 boreholes at 600 meters or 9 boreholes at 400 meters, but the lowest overall cost was found with a combination of 7 boreholes.

For our example housing company, the sweet spot was found with 7 boreholes at a depth of 475 meters, with drilling costs amounting to around €120,000 (excluding VAT). Compared to, for example, 9 boreholes at 400 meters, the drilling costs are about €15,000 less, as less earthmoving work is required. On the other hand, 5 boreholes at 600 meters would cover the required amount of energy, but drilling to 600 meters significantly increases costs (by about €20,000), making more but shallower boreholes overall cheaper.

The boreholes have been placed on the map based on coordinates calculated using polygons.

Additionally, project costs may include more detailed planning, heat pumps and necessary components, installation work, possible electricity connection upgrades, and VAT.