Hill of Banchory geothermal energy project: feasibility report

17. Conclusion and Recommendations

The work reported here has confirmed that there is indeed a promising prospect for augmenting the heat supplied to the customers of the Hill of Banchory heat network by developing a deep geothermal well doublet system exploiting the radiothermal Hill of Fare granite nearby. Appraisal of pre-existing geological data, and new data on heat production rates and thermal conductivity gathered during this study, reveal that the Hill of Fare Pluton is somewhat more promising as a geothermally prospect than had hitherto been supposed.

The HOBESCO network is unusually cost-effective as it sources its biomass locally, and geothermal energy would not be able to out-compete that energy source. However, financial appraisal indicates that it could out-compete the use of gas (which is already used or back-up and peak-up purposes by HOBESCO), and would be an attractive alternative to gas to support future network expansion once the limits of local sustainable biomass availability are exceeded. In otherwise analogous situations elsewhere in Scotland where cheap, sustainable local biomass is not available, geothermal from similar granites would likely emerge as the prime option for low-carbon, renewable district heating.

Given the limited time and funds available for this project, it has not been possible to eliminate all sources of uncertainty relating to the Hill of Fare / Hill of Banchory geothermal prospect. In particular, we lack site-specific information on several important aspects of hydrogeology and geothermics, including:

• the geothermal gradient within the Hill of Fare;
• possible decrease in heat production rates over depth, and the rate thereof;
• fracture patterns in the granite;
• permeability of fractured zones; and
• chemistry of native ground water at depth in the granite (which has implications for corrosion control and reinjection practices).

This study has markedly increased confidence in the viability of developing renewable heat from Scotland's radiothermal granites. It has made ever more poignant and pressing the need to finally catch up with other parts of the UK with similar prospects (i.e. Cornwall and the North Pennines) and sink some boreholes to resolve some of the above questions in a rigorous and timely manner. The next steps for the Hill of Banchory project (see Chapter 19) are therefore focused on addressing this need, and removing the principal remaining barrier to project development for this promising source of low-carbon, renewable heat.