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Geothermal energy is establishing itself as the leading sustainable climate control solution for single-family homes and residential buildings in southern Europe.
This system, which takes advantage of the stable temperature of the subsoil, offers energy efficiencies of 400-500% and reduces CO₂ emissions by up to 80% compared to conventional systems. In this guide, we analyse the key technical, regulatory and economic aspects for installations in Spain, Portugal and Italy, markets with optimal geological conditions and evolving regulatory frameworks.
Types of geothermal collection: horizontal vs. vertical
Vertical collection
Recommended for limited land areas, it requires drilling to a depth of 50-150 m, where the temperature remains stable between 10-15°C in the Iberian Peninsula and 12-18°C in northern Italy.
- Advantages: Greater efficiency (COP 4.5-5.2), less surface area required, useful life >50 years.
- Cost: £70-120/linear metre in Spain, £85-130/m in Italy, including geotechnical studies.
Example: House in Madrid (120 m²) with 2 boreholes of 100 m: £18,000-21,000
Horizontal collection
Ideal for large plots, with trenches 1.5-2 m deep.
- Efficiency: COP 3.8-4.3, sensitive to seasonal variations.
- Cost: €30-50/m² in Portugal, €40-60/m² in Italian Alpine areas.
Example: House in Porto (200 m²) requires 600 m² of land: €18,000-24,000.
Prerequisites: Geological Studies and Regulations
Mandatory Studies
- Exploratory survey: Determines the thermal conductivity of the soil (€2,500-3,500 in Spain).
- Hydrogeological analysis: Essential in open catchments to assess aquifer flow (required in Lombardy and Veneto, Italy).
- Administrative permits:
- Spain: Responsible Declaration LD24.3 in Alcobendas.
- Portugal: DGEG licence for installations >10 kW.
- Italy: Regional authorisation + landscape impact report in protected areas.
Step-by-step installation process
- System design: Calculation of thermal load (50-70 W/m² in a Mediterranean climate).
- Water collection:
- Vertical: Drilling with polyethylene U-shaped probe (diameter 140-160 mm).
- Horizontal: Trenches with spiral or coil pipes.
- Installation of heat pump: 6-15 kW inverter equipment for homes of 100-300 m².
- Connection to emitters: Prioritise underfloor heating (35-40°C in winter) or low-temperature radiators.
Installation times and legal aspects
Estimated times
| Process | Spain/Portugal | Italy |
|---|---|---|
| Geotechnical study | 2-3 weeks | 3-4 weeks |
| Vertical drilling | 5-7 days | 7-10 days |
| Complete installation | 3-4 weeks | 4-6 weeks |
Cross-border legal framework
- Spain: RD 178/2025 on energy storage applicable to hybrid systems79.
- Portugal: Decree-Law 15/2022 streamlines licences for geothermal energy in existing buildings915.
- Italy: 65% incentives in the ‘Ecobonus’ for renovations with geothermal energy16.
Detailed costs per square metre
Comparative table 2025 (VAT not included)
| Country | Vertical collection | Horizontal collection | With underfloor heating |
|---|---|---|---|
| Spain | 142-178 €/m² | 110-135 €/m² | +28% |
| Portugal | 130-160 €/m² | 95-120 €/m² | +25% |
| Italy | 150-190 €/m² | 115-145 €/m² | +30% |
Practical example:
- House in Lisbon (150 m²):
- Vertical collection + underfloor heating: £20.856
- PT 2025 subsidy: -£5.224
- Payback period: 6.8 years
Practical examples in different types of buildings
1. Renovation of a historic building (Seville, Spain)
- Challenge: Structural limitations for drilling.
- Solution: Horizontal collection in a 400 m² garden + 9 kW heat pump.
- Result: 68% savings on air conditioning (from £2.359/year to £7.584)
2. Alpine Single-Family Home (Trentino, Italy)
- Conditions: Outdoor temperatures down to -15°C.
- System: 3 vertical boreholes of 180 m + underfloor heating.
- Efficiency: COP 4.8 even at -10°C.
3. Housing development in Porto (Portugal)
- Scale: 20 homes with a community geothermal network.
- Technology: Open collection in an aquifer at a constant 12°C.
- Benefits: Shared cost reduced to £7.162 per home.
2025 trends and recommendations
- Hybridisation with photovoltaics: Systems such as Ecoforest Geo+Solar achieve 85% autonomy.
- Active cooling: Reversible heat pumps enable comprehensive climate control.
- IoT monitoring: Real-time performance sensors optimise COP.
For projects in Italy, consider the ‘Superbonus 110%’ for combined energy-efficient installations. In Portugal, the Environmental Fund finances up to 30% of community projects. Geothermal energy is thus positioned as a key investment in the residential energy transition in southern Europe.
