• Energy Research

The implications of intensive use of shallow geothermal energy resources in shallow urban aquifers are still not known for waterborne pathogens relevant to human health. Firstly, we hypothesized that waterborne enteric pathogens would be relatively increased in heated groundwater plumes. To prove this, microbiological sampling of 31 piezometers covering the domain of an urban groundwater body affected by microbiological contamination and energetically exploited by 70 groundwater heat pump systems was performed. Mean differences of pathogenic bacteria contents between impacted and non-impacted monitoring points were assessed with a two-tailed independent Student's t-test or Mann-Whitney U and correlation coefficients were also calculated. Surprisingly, the results obtained revealed a significant and generalized decrease in waterborne pathogen contents in thermally impacted piezometers compared to that of non-impacted piezometers. This decrease is hypothesized to be caused by a heat shock to bacteria within the heat exchangers. The statistically significant negative correlations obtained between waterborne pathogen counts and temperature could be explained by the spatial distribution of the bacteria, finding that bacteria start to recover with increasing distance from the injection point. Also, different behavior groups fitting exponential regression models were found for the bacteria species studied, justified by the different presence and influence of several aquifer parameters and major, minor and trace elements studied, as well as the coexistence with other bacteria species. The results obtained from this work reinforce the concept of shallow geothermal resources as a clean energy source, as they could also provide the basis to control the pathogenic bacteria contents in groundwater bodies.

Abstract One solution for reducing the current consumption of fossil fuels is a more frequent use of shallow geothermal energy. However, particularly regarding urban subsurface resources, increased use conflicts are predictable. Consequently, reasonable exploitation of subsurface resources requires an assessment of technologically achievable energy potentials with scientific based tools. We present application-oriented management tools which target on deriving shallow subsurface energy potentials. 3D groundwater flow and heat-transport models are used to capture groundwater flow and heat-transport dynamics on the city- and quarter-scale, 2D box models are used to quantify technically feasible extraction rates of well doublets for groundwater heat pump systems. For Basel (Switzerland), prospective large theoretical energy potentials can be derived for areas with high advective heat flux and high temperature gradients. Likewise, single city quarters are suitable for ‘active’ thermal use with well doublets, whereas thermal power potentials reach 1.2 MW. Regarding ‘passive’ installations of energy absorbers in subsurface structures located within the groundwater, energy potentials amount to 4 and up to 40 W m−2. The assessment results can be integrated into urban energy plans and support architects, city planners and potential users to acquire initial site-specific information on the technical feasibility of shallow geothermal energy systems.

AbstractThe integral urban water cycle of the Balearic Islands (Spain) is composed of desalination plants, extraction wells, water distribution networks, treatment plants and sewerage systems. This article presents the results of the carbon and water footprint of each of the islands that form the Balearic archipelago, finding differences between those islands with a greater contribution of groundwater, such as Mallorca, and those that are fed exclusively with desalinated water, such as Formentera. Water consumption on these islands is highly seasonal, which results in peaks in demand, which are mainly supplied by desalination. This article aims to be the starting point for assessing the water and energy status of the facilities related to drinking water consumption in the archipelago to be able to take measures aimed at ecological transition in this sector. The results obtained show that seawater desalination plants have the largest carbon footprint, mainly due to their high electricity consumption.

[EN] Solar photovoltaic energy is increasingly positioned as an excellent renewable energy source to be implemented in energy communities. However, studies on photovoltaic potential are still required in order to enhance the clean energy transition in energy dependent systems, such as oceanic islands. This work is a study of photovoltaic potential of public building roofs in the World Heritage city of San Cristóbal de La Laguna in Tenerife (Canary Islands). The buildings selected for the study are sports centres, educational centres and civic centres, considering optimum and maximum production scenarios. The results showed the electricity generation capacity of each building, with 8811 and 861 MWh capacity for the maximum and optimum scenarios, respectively. In the optimal scenario, 56% of energy would be generated, of which 31% would be consumed on site, and the remaining 25% would be sent to the grid. The main difference is that in the case of optimal photovoltaic systems, economic profitability criteria take precedence, while in the case of maximum photovoltaic systems, the environmental benefits in terms of CO2 emissions into the atmosphere increase considerably. In the latter case, CO2 emissions are reduced by 771%, compared to 75% in the case of optimal photovoltaic systems. This research was supported by the European Union's Horizon 2020 research and innovation programme under grant agreement 101037424, project ARSINOE (Climate-resilient regions through systemic solutions and innovations). Peer reviewed

Conference paper published in the Proceedings of the 1st Mediterranean Geosciences Union (MedGU-21) Conference organized in Istanbul, Turkey, in 2021. Geothermal energy comes in many different forms depending on the specific conditions of the resource. For example, in volcanic areas (such as the Canary Islands) or with subduction of tectonic plates, deposits of water/steam of very high energy and temperatures (150°–350 °C) are sometimes produced, known as high enthalpy resources. Due to their high quality, these can be used for electricity production in binary cycles. The design of a geothermal heat pump system to replace conventional cæold and heat production systems in a winery on the island of Lanzarote (Canary Islands, Spain) is presented. First, a calculation system based on the Matlab program was designed to review the influences of the winemaker’s decisions on the cold and heat consumption of the winery. After calculating hot and cold water consumption and heat pump requirements, a field of geothermal probes was designed using available software. Subsequently, the dimensions of the liquid impulsion equipment were estimated, and an electrical installation was created for the whole system. The data considered are related to winery logistics, must properties, environment, tank dimensions, and energy needs (cooling and heating). Finally, it was decided to use a reversible heat pump with exhaust heat recovery. This system allows heat extracted by the cooling system to be partly used to produce hot water instead of all of it being discharged to the ground. The cooling system will be operated for 18 h daily as a design criterion. The pump selected for the final project installed has an exhaust heat recovery system that allows domestic hot water to be produced in cooling mode. Hot water generation, when the heat pump is cooling, is 15 kW, and the temperature provided is 60 °C, which is adequate to meet the hot water needs of the winery. In addition, the heat pump’s heat sink is in the ground, which remains in practically constant conditions throughout the year, so the effect of outside temperature is minimized. In general, the main advantages of installing a geothermal system are energy savings and reduction in CO2 emissions. Peer reviewed

Managed aquifer recharge (MAR) and, in particular, recharge by direct injection into the aquifer through wells or boreholes allows for a series of very interesting solutions to solve various technical and environmental problems related to management of the urban water cycle. These problems include the overexploitation of water resources, marine intrusion or contamination of groundwater by irrigation returns. The island of Gran Canaria presents several of these problems; thus, the feasibility of implementing a recharge system has been studied to provide a solution to some of them, using a resource of great potential such as reclaimed water. A detailed characterization of groundwater quality in the study area was carried out, complemented by a field campaign with water sampling from the surrounding catchments, in situ analysis and subsequent laboratory analysis. Specifically, an MBR treatment with disinfection is proposed, where the final conclusions indicate that this is a technically and economically viable project, innovative in its application on islands, a priori with an acceptable productive recharge capacity, possibly scalable after the experimental phase and extrapolable to other locations with similar conditions. In addition, it presents a set of important environmental benefits with respect to conservation of and improvement of the state of the groundwater bodies in the studied area, as well contributing to knowledge of and research into water management in volcanic lands and islands. 1,075 Q1 9,3

AbstractThe island of El Hierro is the smallest and youngest island in the Canary archipelago. It has been recognized as a UNESCO Biosphere Reserve since 2000, and it has a population of approximately 10,000 inhabitants. The aim of this study was to determine the amount of CO2 emissions absorbed by the forest stands of the island of El Hierro and compare it to the emissions generated by the population. It is noteworthy that there is a hydro‐wind energy production project on the island that has significantly minimized the emissions linked to energy production. In short, El Hierro's forest stands are capable of capturing 46,785 tons of CO2 annually, while emissions associated with electricity production and emissions linked to road mobility are below the island's carbon sequestration capacity since the Gorona del Viento renewable energy project was built. By working on investment in renewable energies to produce energy and changing mobility with the use of electric vehicles, a small island like El Hierro can adapt to ecological transition by the year 2040. This is a goal set by the government to drastically reduce emissions in the Canary Islands.