Cost of saline water well drilling for a single-family house

If you are only allowed to withdraw 30W/m, then the result is the same as if the ground only provides 30W/m. And therefore it is unsuitable. Apart from that, your numbers are outdated, even 2x 80m you no longer get for the price today. I paid that 5 years ago for 1x 130m.

I see it regarding economic efficiency similarly to nordanney. A colleague has a quite identical single-family house (efficiency, size, etc.) but with [Sole-WP]. We need about 3,500 kWh per year for our [Luft-Wasser-Wärmepumpe]. He needs about 1,200 kWh for his [Sole WP]. The difference of 2,300 kWh corresponds to about 700€. He also invested about 25k for the drilling. So quite roughly calculated, the ROI for the drilling would be after 35 years. Now I don’t have on my radar whether the manufacturing/acquisition/maintenance costs are higher or lower for [Sole]. Then, of course, that would also change – positively or negatively. He also told me that the risk for the success of the drilling is borne by the builder. So if the drill bit gets stuck at 70m or so, for example, in granite and it’s not passable, then the project is over.

We need about 3,500 kWh per year for our air-to-water heat pump. He needs about 1,200 kWh for his brine heat pump.

Although this difference should be an outlier. You actually don’t need three times as much for comparable houses. The difference should be a multiple times smaller (more like 20%).

Our neighbor and we have about the same house (if ours is not even bigger) and both have geothermal heat pumps. Our neighbor planned with a plumbing company and got two probes of 90 meters each, with two pipes per probe. (18,000 euros for the drilling) Our company only does heat pumps and made only 1 drilling of 130 meters, with 4 pipes coming out. Price 10,000 euros for the drilling. However, we also only have sandy soil and no sandstone. The question is whether you really need that many kWh for heating? We also have 250 sqm of area heated with 4.5 kWh...