What a Good Open Loop Geothermal Feasibility Study Covers

Most organisations exploring open loop geothermal don't start with a blank page. They start with a target. Net zero commitments. Funding windows. Ageing plant that needs replacing. A campus, estate or site that looks like it should be suitable.

At that point, feasibility is often treated as the next step. Commission a study. Get an answer. But the quality of that answer varies enormously.

A good feasibility study doesn't just explore whether open loop geothermal is possible. It gives you enough clarity to decide whether it is worth pursuing and what it will take to make it work on your site, under your constraints.

If it doesn't do that, it hasn't really done its job.

Understanding the Ground: Beyond "There's an Aquifer"

The starting point is always the ground, but not in the simplistic sense of "is there an aquifer?" Most sites in the UK sit over some form of groundwater resource. That alone tells you very little. What matters is how that resource behaves when it is used.

A credible feasibility study should move beyond presence and into performance. It should set out, as clearly as the available data allows, what level of abstraction might be achievable, how the aquifer is likely to respond under sustained pumping, and how confident those assumptions are. Just as importantly, it should be explicit about uncertainty. What is based on data. What is inferred. And what still needs to be proven.

That distinction is critical, because geothermal projects carry their highest risk early on. The less that is properly understood at feasibility stage, the more that risk is carried forward into design, drilling, testing and delivery. In large-scale geothermal development, this is well recognised: feasibility exists specifically to reduce uncertainty to a level where informed investment decisions can be made. But the same principle applies to smaller, direct-use schemes.

Testing and Regulation: Where Projects Are Won or Lost

This is where feasibility studies can begin to lose their value. Many acknowledge the need for test drilling and pump testing, but stop short of defining what that looks like in practice - how yield will be proven, how long testing will need to run, what infrastructure is required, or how water will be managed during the process. Those details matter.

On a live site testing isn't an isolated activity. It needs space, discharge routes, environmental controls, and regulatory approval. It may involve temporary storage, controlled discharge, or negotiated arrangements with regulators. If those elements aren't considered early, they don't disappear. They reappear later as constraints.

Regulation sits alongside this, and it is often underplayed. Open loop geothermal schemes rely on permissions covering groundwater investigation, abstraction and discharge. These are not just procedural steps. They shape what is possible, how testing is carried out, and whether a system can ultimately operate.

A strong feasibility study brings both together, defining how the resource will be proven, and how that process will work within real regulatory constraints.

The Reality of the Site: Where Theory Meets Delivery

Beyond the ground and regulation, the site itself becomes the defining factor.

Every site brings its own constraints. Access for drilling plant. Space for rigs, compounds and testing infrastructure. Interaction with existing buildings, services and operations. Traffic management. Working within a live environment.

On paper, these can look like secondary considerations. In practice, they shape layout, sequencing, programme and cost. They influence where boreholes can be located, how systems are configured, and how disruption is managed.

This is often where well-intentioned designs start to diverge from reality. A layout that works conceptually may not work operationally. A location that looks suitable on a drawing may not be accessible or practical when delivery is considered.

A useful feasibility study brings those factors in early. It doesn't wait until detailed design to discover them.

From Feasibility to Decision: What You Should Be Left With

Open loop geothermal projects do not exist in isolation. They sit within funding frameworks, procurement routes and long-term estate strategies. A feasibility study should reflect that.

It should give you a clear sense of whether there is a credible path from concept to operation, not just technically, but commercially and practically as well. That includes how a scheme might align with funding, how it could be phased, and how risk can be managed as the project develops. In larger geothermal projects, feasibility work is specifically used to support funding decisions by making risks visible and understood.

When all of this is brought together properly, you should be in a very different position to where you started. You should understand whether open loop geothermal is likely to work on your site. You should know what still needs to be proven, how that proof will be obtained, and what constraints will shape the project. And you should be able to decide whether to proceed, pause, or rethink the approach entirely.

Because that is the real purpose of feasibility. Not to justify a scheme, but to give you enough clarity to make a decision with confidence.

Open Loop Geothermal Feasibility: FAQs

What is an open loop geothermal feasibility study?

It's an early-stage assessment that looks at whether an open loop system can realistically be developed on a specific site. It brings together groundwater conditions, testing requirements, regulatory constraints and site considerations to determine whether a scheme is viable, and what would be required to deliver it.

Is open loop geothermal suitable for my site?

It depends on your ground conditions, available space and regulatory constraints. Many sites can support open loop systems in principle, but feasibility is about understanding whether it will work here, under real conditions, not just on paper.

How do you prove an open loop geothermal system will work?

By drilling and testing. Pump testing is used to confirm groundwater yield, behaviour and sustainability. Until that testing's done, performance is based on informed assumptions rather than proven data.

What is pump testing in geothermal projects?

Pump testing involves abstracting water from a borehole over a sustained period to measure flow rates, drawdown and aquifer response. It's the key step in understanding how the ground will behave in operation. Once single boreholes have been tested the system is subjected to operational testing where water is abstracted from a borehole field and reinjected into the reinjection boreholes, this simulates the system operationally and is undertaken to confirm how the aquifer performs and what effect it may have on surrounding water features or other abstraction boreholes.

What permits are needed for open loop geothermal?

Most schemes require consent for groundwater investigation, an abstraction licence, and a permit for discharge or reinjection. These are not just formalities, they shape how a system can be tested and operated.

What can stop an open loop geothermal project?

Common constraints include insufficient groundwater yield, lack of a viable discharge route, regulatory limitations, and practical site issues such as access or space for drilling and infrastructure.

Can open loop geothermal be used on existing buildings?

Absolutely yes - including hospitals, universities and commercial buildings. The main considerations are how the system fits within a live site, and whether the ground and layout can support it.

How long does an open loop geothermal feasibility study take?

Typically a few weeks to a couple of months, depending on the complexity of the site and how much data is already available.

How long does it take to deliver an open loop geothermal system?

From feasibility through to operation, projects can take anything from months to years. Timescales depend on size, complexity, testing, permitting, design and construction.

How much does a feasibility study cost?

Costs vary depending on scope, but are usually small compared to overall project value. More detailed studies provide greater clarity and reduce risk later.

Does a feasibility study guarantee that open loop geothermal will work?

No. It reduces uncertainty rather than removing it. A good study makes clear what is known, what still needs to be tested, and what risks remain.

What happens after a feasibility study?

If the outcome is positive, the next stage typically moves into early-stage design and planning, alongside regulatory engagement and the definition of a testing strategy. This leads into drilling and pump testing to prove the resource, followed by detailed design and delivery.

What should I look for in a good feasibility study?

Clarity over optimism. It should reflect real site conditions, define how the resource will be tested, consider regulatory constraints early, and set out a practical route forward.