Closed-Loop Geothermal Systems: The Companies Building the Next Generation of Underground Energy Image : The Eavor Technologies Geothermal Project Closed-loop geothermal systems represent one of the most promising frontiers in renewable energy, offering continuous, baseload power without the environmental concerns associated with conventional geothermal development. Unlike traditional open-loop systems that require hydraulic fracturing and consume large volumes of water, closed-loop geothermal circulates a working fluid through sealed underground pipes, extracting heat from hot rock formations while maintaining a self-contained system that eliminates fluid loss, induced seismicity, and reservoir depletion risks.This technology has attracted significant investment and technical innovation from a diverse array of companies spanning startups, established energy firms, and drilling specialists, each pursuing distinct approaches to unlock the vast thermal energy stored beneath the Eart...
Geothermal milestone at Geiselbullach: 10 MW of heat confirmed after successful second deep well test
On 15 August 2026 the Geiselbullach geothermal project reached a pivotal technical milestone: performance testing of the second deep production well completed successfully, delivering a sustained flow of 90 liters per second of thermal water at 79–80 °C. These measured parameters translate into roughly 10 MW of usable thermal power for district heating, enough to replace a portion of heat currently supplied by the municipal waste-to-energy plant (AHKW) and to create headroom for expanding the regional district heating network. The result confirms the project’s technical assumptions and moves the scheme into system-integration and commissioning activities ahead of planned commercial deliveries for the 2027 heating season.
This article explains the test results and their significance, outlines the technical and operational consequences, and places the Geiselbullach development in the broader context of municipal energy transition, heat decarbonization and geothermal deployment strategies.
What the test proved: flow, temperature, and thermal output
Performance tests of deep geothermal wells are the most direct measure of how much useful heat a project can deliver. The Geiselbullach second production bore reached a stable extraction rate of 90 L/s at a temperature band of 79–80 °C. Converted into thermal power under standard assumptions for district heating integration and accounting for realistic temperature drops across heat exchangers, this production equates to approximately 10 MW of thermal energy continuously available for the local network.
Why those numbers matter:
- Flow rate (90 L/s): determines the mass of hot water available for heat transfer. Higher flow increases the thermal energy that can be extracted without lowering the reservoir temperature quickly.
- Temperature (79–80 °C): sets the achievable supply temperature to the district heating grid and influences network layout, heat-exchange sizing and return temperatures.
- Combined output (~10 MW): provides a practical metric for planners and financiers to estimate avoided fossil fuel use, CO2 reductions, and revenue under tariff structures.
Taken together, the data validate the project baseline used in feasibility studies and financial models, reducing development and performance risk for the owners and local stakeholders.
Technical context: wells, integration and redundancy
Geothermal district heating projects typically rely on at least two deep wells—one production and one reinjection—to maintain reservoir pressure, manage thermal breakthrough, and sustain long-term output. The Geiselbullach project has completed two deep boreholes whose results align with the technical assumptions made during design.
Key technical points:
- Well pairing and reservoir management: Confirmed production capacity supports the planned production–reinjection scheme. Stable flow and temperature improve confidence that reinjected cooler water can be managed without rapid temperature decline at the production well.
- Use of existing plant infrastructure: Integrating geothermal heat at the Geiselbullach power station site allows reuse of mechanical, electrical and grid connection assets. This reduces capex and shortens the time from well completion to commercial operation.
- Pumping and station works: With drilling finished and the rig dismantled, the project has moved to installing downhole pumps and constructing the district heat transfer station. Correct pump sizing, hydraulic balancing and heat-exchanger design will be critical to convert wellhead flow into grid-ready thermal energy while minimizing parasitic electricity consumption.
Integration into a mixed-source heat plant also provides operational flexibility. During peak winter demand or planned maintenance, the existing waste-to-energy and other combustion plants can backfill shortages. Conversely, when geothermal heat is available, fuel consumption and emissions from conventional units fall.
Economic and operational implications
A confirmed 10 MW of geothermal heat has several economic implications for the municipality, plant operator Amperland Thermalwärme GmbH, GfA and the host counties.
Direct financial impacts:
- Fuel and operating cost reduction: Substituting geothermal for fossil or waste-derived heat lowers variable fuel expenditure and reduces exposure to fuel-price volatility.
- Avoided carbon cost and emissions: Replacing fossil heat saves CO2 emissions, potentially creating value under carbon pricing systems or through local climate accounting.
- Added capacity: The geothermal source increases available heat capacity, enabling network growth and new customer connections without immediate capital investment in additional combustion capacity.
Project economics hinge on upfront capital and ongoing O&M. Reusing site infrastructure at Geiselbullach reduces capex relative to greenfield geothermal sites. Pump electricity consumption and well maintenance determine ongoing operational costs; designing for high efficiency and serviceability will keep levelized heat costs competitive.
Risk reductions from the recent test:
- Technical risk: Confirmed reservoir productivity reduces a major development risk that typically affects bankability and loan pricing.
- Schedule risk: Completing drilling and moving to mechanical installation shortens the critical-path activities before commercial heat delivery.
- Stakeholder confidence: Successful testing strengthens the case for offtake agreements, municipal financing decisions and community acceptance.
System benefits: flexibility, security, and decarbonization
Beyond direct economics, geothermal adds several systemic benefits to the regional heating system.
Supply security and diversity
- Geothermal provides a controllable, baseload-capable heat source that is not dependent on fuel imports or volatile international markets. That improves energy security for the counties served and reduces reliance on the waste-to-energy plant for base load heat.
Operational flexibility
- As a continuous thermal source, geothermal complements dispatchable heat from combustion plants. Operators can use geothermal heat to cover base and mid-level loads while retaining fossil or waste-fired units for peak shaving and rapid response.
Emissions and climate goals
- Each megawatt-hour replaced by geothermal reduces local combustion emissions. Over an operating year, a 10 MW geothermal input corresponds to substantial avoidance of CO2 and other pollutants, helping municipal climate targets and improving urban air quality.
Local economic and social co-benefits
- Long-term, stable heat costs can support local industry and households, and geothermal projects often create skilled local jobs during construction and long-term technical roles for operation and maintenance.
Integration advantages from the Geiselbullach site
One of the project’s highlighted advantages is its siting at an active power-generation complex. Using existing infrastructure offers multiple efficiency gains:
- Shorter grid and piping distances: Proximity to the district heating network minimises distribution losses and reduces trenching and piping costs.
- Shared electrical and control systems: Existing substation, SCADA and grid interconnection points can be adapted for geothermal plant controls and pump power.
- Co-location with heat consumers: Large industrial or municipal loads already connected to the site simplify offtake arrangements and accelerate revenue realization.
- Streamlined permitting and stakeholder engagement: Working within a site already zoned for energy reduces planning friction and leverages existing operational safety and environmental oversight.
These practical synergies have a measurable effect on timetable and total investment required to reach commercial delivery.
Next steps: commissioning, pump installation and commercial start
Following dismantling of the drilling rig, the project is executing the mechanical phase: installing submersible production pumps, constructing the heat transfer station and completing hydraulic and thermal commissioning. Key near-term actions include:
- Pump installation and testing: Correct pump selection and commissioning will ensure the desired 90 L/s flow is sustainable while minimizing electricity use. Variable-speed drive configuration will allow operators to match flow to demand.
- Heat transfer station construction: Heat exchangers, filtration, chemical conditioning and safety systems will enable efficient energy transfer to the district heating loop while protecting the network from reservoir water impurities.
- Reinjection well and reservoir balancing: Completing reinjection infrastructure and confirming injection capacity ensures long-term reservoir health and minimizes thermal breakthrough risks.
- Grid trials and thermal balancing: Stepwise integration tests will verify supply temperatures, return-temperature management and tariff metering ahead of commercial handover.
- Regulatory and safety certifications: Final approvals, environmental monitoring plans and operational permits will be required before regular commercial operation.
Project planners currently target the 2027 heating season as the deadline for commercial deliveries. Given the current status—drilling complete and mechanical installation underway—the schedule appears achievable barring unforeseen technical or permitting delays.
Longer-term outlook: scaling geothermal for regional heat
Geiselbullach is a concrete example of how municipal-scale geothermal can fit into a broader decarbonization strategy. If the wells perform over the long term as currently measured, the site will not only displace existing fossil-derived heat but also provide a platform for incremental network expansion.
Scaling considerations:
- Replication at other sites: Success at Geiselbullach can justify further exploration of geothermal opportunities in nearby basins and under similar infrastructure co-location strategies.
- Hybridization: Combining geothermal with short-term flexible assets—thermal storage, heat pumps, peak boilers—can optimize network efficiency and reduce the need for large spinning reserves.
- Industrial heat offtake: Beyond residential and commercial district heating, available geothermal heat can serve nearby industrial processes, increasing load-factor and project economics.
- Innovation and secondary revenues: Opportunities such as low-temperature heat-driven absorption chillers, aquifer thermal energy storage (ATES), or mineral extraction (e.g., lithium from brines where geology permits) could add revenue streams.
Long-term reservoir management will drive sustainable output. Operators must monitor temperature, pressure and chemical composition and adapt injection strategies to avoid thermal depletion or scaling issues.
Governance, collaboration and lessons learned
The successful testing is the product of coordinated work by multiple parties: the drilling contractor, engineering and consultancy teams, Amperland Thermalwärme GmbH and GfA, together with the sponsoring district authorities. It underlines several lessons applicable to other projects:
- Early and iterative engineering reduces surprises: Trenching, integration and mechanical design that anticipate reservoir parameters speed commissioning.
- Local stakeholder engagement matters: Working with municipal operators and county authorities smooths permitting and offtake contracting.
- Choose partners with geothermal experience: Skilled drilling teams and consultants reduce both schedule slips and drilling-related risks.
- Reuse of infrastructure is a high-impact strategy: Co-locating geothermal projects at existing energy sites lowers cost and complexity compared with greenfield sites.
The project’s less-than-five-year trajectory from first concrete considerations to near-operation demonstrates that municipal geothermal projects can reach maturity within feasible funding and planning cycles when technical risk is managed effectively.
Environmental monitoring and responsible operation
Sustainable geothermal exploitation depends on ongoing monitoring and environmental stewardship. Key environmental measures for Geiselbullach will include:
- Water quality monitoring: Reservoir water can carry dissolved minerals and gases; continuous sampling protects surface infrastructure and ensures safe reinjection.
- Seismicity surveillance: Although the risk of induced seismicity is low in many shallow geothermal projects, continuous monitoring is best practice.
- Thermal impact assessment: Tracking reinjection temperatures and subsurface thermal plumes ensures neighboring wells and ecosystems remain unaffected.
- Emissions and effluent controls: Proper handling of any gases or brines prevents local contamination and adheres to regulatory limits.
Transparent public reporting of monitoring results builds trust with communities and regulators.
Conclusion: a decisive step for regional heat transition
The 90 L/s at 79–80 °C performance from the second deep well is a technical and symbolic milestone. It confirms the project’s core assumptions, materially reduces development risk, and supports a rapid move to pump installation, heat-station construction and commissioning. When online, roughly 10 MW of geothermal heat will lower fossil-fuel dependence, enhance system flexibility and strengthen regional energy security ,while providing a blueprint for additional geothermal deployment in the region.
If Geiselbullach proceeds to smooth commercial commissioning for the 2027 heating season, it will stand as a practical example of how municipal utilities and energy companies can integrate deep geothermal into mixed-generation heat systems to deliver resilient, lower-carbon urban heating
Related : Closed-Loop Geothermal Systems: Companies, Technology, Investment, Power
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Source : Amperland
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