The sight of a steaming power station on the lava fields of Iceland might be what springs to mind when the topic of geothermal power is raised - but what if we were to set that narrative in Glasgow instead?
Natural Power’s heat team looked at doing just that. Working in conjunction with several other parties to study the viability of using deep geothermal energy from circa 5km under Glasgow, aiming to provide low carbon heat and power into the centre of the city.
Deep geology assessments undertaken by a third-party specialist indicated that injected geothermal brine might be recovered at the surface in significant volumes at a temperature of 210°C. Natural Power’s task was to assess what surface equipment would be required to facilitate use of this to generate heat and power, in what respective quantities, and how and to whom it might be distributed.
It so happens that 210°C straddles the zones where it might be practical to use a steam turbine with flashed steam (rapidly depressurising and vaporising the brine in a dedicated vessel); or using binary cycle generation systems. Our first tasks were therefore to determine which system might generate the best balance of heat and power, and to find off-takers to engage with.
Utilising existing contacts and data sets (for example Scotland Heat Map), we identified 9 large energy users in the vicinity of the project and made direct contact to gauge their interest in being connected to such a system. All of these were very open to a heat connection and a somewhat mixed response to an electricity connection.
Natural Power’s Heat team undertook detailed analysis of flash steam systems, ORC systems, and combinations of these to assess the most beneficial energy production to meet the identified demands. Extensive and detailed discussions with manufacturers, enabled us to develop accurate cost build ups for the various generation and distribution systems.
The team carried out detailed routing and sizing assessments for the proposed district heat network, including a buried services review, pinch point analysis and initial discussions with the City Council. The process of systems design to a good level of detail, and interfacing with suppliers, enabled a financial model to be developed alongside the technical assessment work.
Ultimately, a single stage ORC system was identified to be the best technoeconomic solution with a preliminary design as follows:
Hot brine used to generate steam for the brewery
Ultimately, a single stage ORC system was identified to be the best technoeconomic solution, with steam generated from the part of the brine being supplied to the brewery, the balance of the brine offtake then used to heat to the water in the district heat network and drive the ORC system. The ORC plant was expected to generate electricity to be exported to a local substation and sleeved to customers via PPA agreements, thus avoiding significant private wire resilience costs. The low temperature hot water (LTHW) district heat network was designed to feed all the non-steam buildings contributing to the delivery of some 88GWh of heat and 135GWh of electricity projected to be producible from the scheme.
The main constriction to the project was the large land take for heat rejection and the surface support equipment (pumps, brine treatment, air cooled condensers), the concerns over the impact of a somewhat industrial installation at the proposed location, and the confidence in sub-surface temperatures. That said, parties in Glasgow still have a keen interest in geothermal heat at all depths, so we may yet see wisps of steam rising over the city from a geothermal heat and power plant (although lava fields are, hopefully, less likely).