Alternative and sustainable heat production for drinking water needs in a subarctic climate (Nunavik, Canada): Borehole thermal energy storage to reduce fossil fuel dependency in off-grid communities

Abstract

Highlights-First-time design of borehole thermal energy storage in a subarctic climate -Best scenarios provide 50 % solar fraction and 60 % heat recovery at the 3 rd year -Annual savings of 7 000 l of diesel and 19 tonnes of equivalent CO2 are achieved -A novel type of borehole connection reduces advection heat loss by 60 % -Underground storage is a key technology towards energy and food security in the Arctic ABSTRACTThe development of renewable energy technologies in the Arctic faces technical barriers mainly related to extremely cold temperature. Moreover, storage issues to bridge the gap between supply and demand are more compelling than in temperate climates. Can underground thermal energy storage be efficiently used in such a cold environment to offer a viable seasonal storage alternative? This working hypothesis was tested by designing and simulating for the first time a borehole thermal energy storage facility in a subarctic climate. A system comprising a 1000 m 2 gross solar area and one hundred 30-m-deep borehole heat exchangers was simulated in TRNSYS to cover part of the heating demand of a pumping station that supplies drinking water in Kuujjuaq (Northern Québec, Canada). The Nunavik capital is characterized by more than 8000 heating degree days below 18 ºC and average spring-summer solar radiation of 4.6 kWh m -2 d -1 . Despite the presence of discontinuous scattered permafrost in the area, the study site is free of frozen ground, likely due to a talik that developed around a nearby lake. A number of scenarios reveal that solar fraction of 45 to 50 % and heat recovery of more than 60 % can be achieved by the 3 rd year of operation, resulting in annual savings of 7 000 l of regular diesel consumption. A 50-years life-cycle cost analysis demonstrates that a specific incentive program can guarantee similar net present cost and levelized cost of energy compared to the current dieseldependent situation, or better if electricity comes from renewable source. An additional 10 % loss of thermal energy occurs when groundwater advection is a factor. FEFLOW simulations demonstrate that square-shaped storage together with a newly-proposed borehole connection design can reduce advection heat loss by 60 % and improve the overall performance of the system. This work validates the technical viability of underground thermal energy storage in subarctic climates and indicates it could help reduce fossil fuel consumption in

Long-Term Temperature Evaluation of a Ground-Coupled Heat Pump System Subject to Groundwater Flow

“…Thermal conductivity of gabbro was measured in another case study and ranged between 1.65 and 2.29 W m −1 K −1 [45], which is consistent with our results. Shale samples have an average thermal conductivity ranging between 2.4 and 2.9 W m −1 K −1 (Table 2), which is in agreement with a value of 2.8 W m −1 K −1 measured for other samples of similar lithology in the St. Lawrence lowlands [10,12,44,46]. The calcarenite sample has the highest thermal conductivity among all the samples collected in the quarry, with a value of 3.5 W m −1 K −1 .…”

“…However, the impact of groundwater flow on underground thermal energy storage systems is negative because it increases heat loss around GHEs used as a heat storage medium. Giordano and Raymond [10] demonstrated that~10% of the energy lost by the bore field of an underground energy storage system can be due to advection when the Darcy flux is 8 × 10 −7 m s −1 , while this heat loss can be reduced bỹ 60 % if the connection and layout of the GHEs is designed considering the magnitude and direction of groundwater flow.…”

“…Previous studies have been conducted to evaluate the impact of groundwater flow on the operating temperature of GHEs. For example, different authors simulated the operation of thermal energy storage systems with GHEs influenced by groundwater flow [9][10][11], while similar modelling was completed for GCHP systems by Dehkordi et al [1]. However, most available studies are based on theoretical modelling exercises and have not been validated with operational data from systems that are influenced by significant groundwater flow conditions.…”

Availability and Feasibility of Renewable Resources for Electricity Generation in the Arctic: The Cases of Longyearbyen, Maniitsoq, and Kotzebue

“…Excess electrical energy can heat a thermal reservoir, which can then release heat when required after an extended period. Thermal underground storage has been tested under sub-Arctic conditions but not in Arctic areas with permafrost [29]. For short-term or immediate solutions, water can be electrically heated and fed into the district heating system [26].…”

Thermophysical properties of surficial rocks: a tool to characterize geothermal resources of remote northern regions

“…Geothermal investigations with a focus on the Canadian northern communities facing critical energy challenges have additionally been carried out (e.g., Comeau et al 2017;Giordano and Raymond 2019;Grasby et al 2013;Gunawan et al 2020;Majorowicz and Grasby 2014;Majorowicz and Minea 2015b;Minnick et al 2018). These studies indicate promising geothermal energy development for the off-grid communities due to the cold climate and the high energy cost.…”