Guardbridge geothermal technology demonstrator project: feasibility report

13. Conclusions

The following conclusions arise from the Guardbridge geothermal heat feasibility project in terms of estimated water temperatures and flow rates, well design options, investigation of the scale of potential district heating network, the CAPEX, OPEX and REPEX for exploration and DHN network development, and construction of economic models accounting for all predicted financial costs and the revenue from the sale of the heat.

C1. At the end of this study, which corresponds to the Catalyst Stage following the Low Carbon Infrastucture Transition programme project stages, the evaluation has shown a potentially viable scheme both technically and economically, though at low return in the base case.

C2. The geology beneath the Guardbridge site is suitable for geothermal exploration and using available rock characteristics data and the presented geological model, two flow rates are predicted that are 1) low and 2) reasonable-high estimates associated with temperatures in the range of 23 - 27 ^oC.

C3. Several well designs have been considered, all technically achievable, and a single well design has been taken forward for the economic evaluation. The well is estimated to be capable of delivering water at about 25 ^oC with a flow rate of 15 litres/second, producing 418 kw of heat(± 10%).

C4. The economic model developed for this project predicts that the district heating network option that is economic involves the Guardbridge site only, and that with a flow rate of 15 l/s, 50% of the district heat required at Guardbridge could be supplied by geothermal sources.

C5. The combination of geological thickness and depth uncertainty, plus the very large range in porosity and permeability observed at any depth in offset wells, results in an order of magnitude uncertainty in flow rates and corresponding heat potential. Higher temperatures due to deeper aquifers, or higher flow rates due to better permeability, will both significantly improve the project's performance economically.

C6. It is expected that some uncertainty in aquifer depth and thickness can be reduced through undertaking low cost geophysical surveys, which have not been possible within this study. The primary geological uncertainty of flow rate can only be constrained and reduced by drilling and testing the aquifer flow rate.

C7. Developing a wider DHN to surrounding communities is not economic based on the current network density or considering the known future potential network developments. A single well at the relatively low temperature estimated here will not provide sufficient heat to expand the network beyond the Guardbridge site.

C8. The geothermal heat project benefits from the proximity to the biomass energy centre and combining the two systems could provide a dual heating and cooling system, and an opportunity to conduct research on integrating different low carbon energy systems.

C9. The location of the Guardbridge project is ideal for producing critical data on the most productive Hot Sedimentary Aquifers in the Central Belt of Scotland and could be used to significantly de-risk other HSA geothermal exploration projects.

C10. Recycling some of the geothermal water to potable standards for use or sale is worthy of further investigation. A flow rate of 15 l/s equates to 54 m ³/h which is a considerable volume to process, but filtering and chlorination may be low energy and sufficient methods to produce potable water. Waters in excess of 5000 s would need additional treatment at a cost of 5 - 10kW/m ³per day. The Guardbridge site could provide the research focus to advance technology in this area and develop the on-site and off-site customer base, but some disposal-to-sea of treated water will be required, dependent on flow rates and the volume of water that can be utilised or sold.

C11. Any progress to an exploration phase will most likely require an Environmental Impact Statement and assessments from SNH and Fife Council, along with planning permission approval and abstraction licenses from Fife Council and SEPA, and permission to drill under any land that is not part of the Guardbridge site.