Technical information about geothermal energy
Geothermal Energy explained
In the widest sense, geothermal resources may be harnessed to provide power, heating or cooling.
In some areas of the world, quite high subsurface temperatures may be found at moderate depths. If there is also a productive reservoir (a layer of rock through which water can flow) at that location, it may be economic to drill boreholes to access water or steam and to produce electricity (with heat as a by-product). Other settings (such as the UK) provide fewer opportunities for electricity generation, but there are areas with reservoirs at a temperature that can supply heat demands directly (i.e. without a heat pump).
Importantly, in almost any location, heat can be extracted from the ground (or from a water body, or from the air) and raised to the required temperature with a heat pump. Ground Source and Water Source heat pump systems can achieve higher heating performance than Air Source in the winter (when the heat demand is highest) as the ground / water body remains warmer than the air during winter. Similarly, Ground Source and Water Source heat pump systems can achieve higher cooling performance than Air Source in the summer (when the cooling demand is highest) as the ground / water body remains cooler than the air during summer.
Benefits of Geothermal:
- Environmentally friendly – geothermal energy is one of the cleanest forms of renewable energy. Modern geothermal systems produce virtually no CO2 emissions and have minimal impact on the surrounding environment. The majority of infrastructure is built below ground which means a small footprint on land.
- Renewable – geothermal reservoirs are naturally replenished and, unlike traditional fossil fuel energy sources, are sustainable if managed properly.
- Stable – geothermal energy is a reliable source of energy, does not suffer from the weather and seasonal intermittency of wind and solar, is produced locally and is available 365 days a year.
- Affordable – while geothermal energy systems often have a high capital cost at the outset, the operational cost of geothermal energy is low. These low operating costs are steady, predictable and not vulnerable to external markets.
Ground Source heating systems comprise:
- Ground Loop systems. These use shallow-buried coiled pipe to collect heat. The heat is essentially provided by the solar energy that penetrates the first few meters of soil. The heating fluid passes through a heat pump, where it is cooled before returning to the Ground Loop. (For cooling applications, shallow-buried pipe is generally not considered).
- Open Loop Borehole systems. Wells are drilled into a productive aquifer (rock formation) or flooded mine. Water is pumped out of one or more wells and through the heat pump. It may then either flow into a waterway or be re-injected into the aquifer (or mine) via an injection well. An abstraction licence is required for larger offtakes.
- Closed Loop Borehole systems. Wells are drilled to a sufficient depth to provide adequate heat/coolth collection. Water is circulated around the well (or wells) and through the heat pump. Closed Loop systems aim to access a steady year-round ground temperature; they supply less heat than Open Loop systems (but a productive aquifer is not required). They are usually more costly than Ground Loop systems (but can be installed in areas where very limited open ground is available).
Water Source heating systems comprise:
- Open Loop Water systems. Water is generally abstracted from a water body (such as a river, lake or large pond), is pumped through a heat pump, and then discharged back to the water body. They can be very effective for either heating or cooling needs. It is important that the water volume / flow is sufficient, or there will be an unacceptably large cooling of the water body.
- Closed Loop Water systems. This is another option for extracting heat / coolth from water bodies. Coiled pipe heat collectors (similar to those used in Ground Loop systems) may be deployed: these are placed in the river / lake / pond rather than buried in the ground; alternatively, compact heat exchangers may be deployed. Pipe excavation costs are avoided, but the pipes / heat exchangers may be an unwanted obstruction depending on the requirements of other users of the water body.
Deep “Direct Use” Geothermal
True geothermal energy (not ground-source energy which is predominantly solar) exists in the UK in depths generally greater than 200 m. To be eligible for the deep geothermal Renewable Heat Incentive (RHI) subsidy a well / borehole must extend to a depth greater than 500 m.
Abandoned mines, aquifers, and fractured granites or other heat generating bedrock can all be sources of geothermal energy. The key properties are depth, and therefore temperature, and permeability, i.e. the flow rate that can be sustainable pumped from the ground. When the temperature of hot water required at the surface is the same or lower of that found in the ground, not heat pump is required, meaning a huge cost saving on your annual energy bill.
Many areas in the UK are suitable for geothermal heat production, and we are happy to advise you for free if your site is on top of one! More information about these kinds of resources can be found in our brochure.
Can Geothermal work for me?
TownRock Energy will be delighted to help you to answer that question. In any evaluation, we will consider your heating / cooling demands, study the geothermal resources available at / near to your site, and will advise you which, if any, of the above geothermal heating / cooling solutions may be appropriate for your needs. If one or more of these approaches seems promising, we can take the evaluation through to project feasibility and then on to an investment-ready business case so you can proceed with confidence. Our approach is described in our project workflow.