The environmental impacts and the carbon intensity of geothermal energy: A case study on the Hellisheiði plant

Geothermal energy, alongside other low-carbon and renewable energies, is set to play a key role in decarbonising the power generation industry to meet the Paris Agreement goal. Thus far the majority of Life Cycle Assessment (LCA) studies focused on enhanced geothermal plants. However, conventional geothermal plants that harness hydrothermal reservoirs dominate the production of electricity from geothermal energy worldwide. This article focuses on Hellisheiði, a combined heat and power double flash geothermal plant located in Iceland, with an installed capacity of 303.3 MW of electricity and 133 MW of hot water. The study has a twofold goal: (i) identify hot spots in the life cycle and, where possible, suggest improvements, and (ii) understand the potential of geothermal energy to decarbonise the power generation industry. First, a detailed LCA study has been performed on Hellisheiði, with cradle-to-grave system boundaries and detailed site-specific data obtained from the literature. The analysis identifies consumption of diesel for drilling and use of steel for wells casing and construction of the power plant as the main hot spots. Second, carbon intensities of electricity production for various possible configurations of the Hellisheiði power plant (including single flash, and power-only production) have been compared with those of other geothermal plants and other energy sources. Different allocation procedures have been used to allocate impacts between electricity and hot water where necessary, and Monte Carlo simulations have been used to estimate uncertainties of Hellisheiði's carbon intensities. The comparison shows that the carbon intensity of Hellisheiði is in the range of 15–24 g CO2-eq./kWh, which is similar to those of binary cycle geothermal plants, solar (photovoltaic) and hydropower, lower than other geothermal technologies and fossil-based technologies, and higher than nuclear and onshore wind

Data on the environmental impacts of the Hellisheiði geothermal plant and on the carbon intensity of geothermal energy and other energy technologies

This data article is related to the research article “The environmental impacts and the carbon intensity of geothermal energy: A case study on the Hellisheiði plant”. The article reports numerical values of the results of the Life Cycle Assessment (LCA) study, which are reported only graphically and in an aggregated form in the main article. Data include normalised impacts, unaggregated environmental impacts of each life-cycle phase and activity in the foreground system, and results of Monte Carlo simulations. The article also includes data on the carbon intensity of other geothermal studies and alternative energy technologies, which were used for comparison in the associated research article

Reprocessing vs direct disposal of used nuclear fuels: The environmental impacts of future scenarios for the UK

The UK recently switched from a “nominal” twice-through cycle - whereby used nuclear fuels were reprocessed, but uranium and plutonium were not routinely reintroduced in the fuel cycle – to a once-through cycle, where used nuclear fuels are stored pending disposal. However, it is also the current strategy to keep other options open, including a twice-through cycle based on a different chemical separation process from the conventional PUREX. This article presents a comprehensive Life Cycle Assessment study of future scenarios for the back-end of the UK nuclear fuel cycle that aims at informing policy- and decision-makers. The study considers the direct disposal approach and four reprocessing scenarios envisaging different strategies for disposal and/or reuse of reprocessed uranium and plutonium, and adopts a consequential approach including only short-term effects. These primarily represent reductions in demand for uranium mining due to recycling of uranium and plutonium, and are modelled upon identification of a marginal technology. Several marginal technologies are explored because of the uncertainty regarding the actual response of the market. Results of the study show that recycling of uranium, but especially of plutonium is of paramount importance because of the avoided burdens associated with production of nuclear fuel from mined uranium. The reprocessing scenarios envisaging reprocessing of used nuclear fuels and recycling of both plutonium and uranium represent the most favourable options. The direct disposal approach may be advantageous only in terms of radiological impacts depending on the marginal technology chosen

Can the use of captured CO2 lower the environmental impacts of formate production?

The majority of bulk chemicals (e.g. olefins and alcohols) are organic compounds that are almost exclusively produced from fossil feedstocks such as natural gas. Utilisation of carbon dioxide captured from anthropogenic sources, which are both inexpensive and abundantly available, represents an alternative pathway that is drawing increasing attention, mainly for its potential to decreasing emissions of greenhouse gases and resource depletion of chemicals production. Notably, carbon utilisation does not represent an approach to CO2 mitigation because it only delays its emissions rather than removing it over a long timescale; hence, the relevant question that we aim to address is: "Can captured CO2 be used as feedstock to reduce the environmental impacts of chemicals' production?". As a case study, this work focuses on the production of formate and presents a prospective comparative life cycle assessment (LCA) between the conventional fossil-based pathway and an innovative, CO2-based process, that involves the electro-catalytic reduction of CO2 using an ionic liquid as solvent. CO2 is assumed to originate from a natural gas-fired power plant and captured after combustion, through a conventional monoethanolamine absorption system. Ionic liquids are used to enanche the reduction of CO2 and its conversion to formate. The study adopts a cradle-to-gate perspective and analyses multiple impact categories including, but not limited to, global warming and resources depletion

A brief overview on valorization of industrial tomato by-products using the biorefinery cascade approach

The industrial processing of tomato leads to substantial amounts of residues, typically known as tomato pomace or by-products, which can represent as much as 10% by weight of fresh tomatoes. At present, these residues are either used as feedstock for animals or, in the worst case, disposed of in landfills. This represents a significant waste because tomato pomace contains high-value compounds like lycopene, a powerful antioxidant, cutin, which can be used as a starting material for biopolymers, and pectin, a gelling agent. This article presents an overview of technologies that valorize tomato by-products by recovering added-value compounds as well as generating fuel for energy production. These technologies include operations for extraction, separation, and exploitation of lycopene, cutin and pectin, as well as the processes for conversion of the solid residues to fuels. Data collected from the review has been used to develop a biorefinery scheme with the related mass flow balance, for a scenario involving the tomato supply chain of Regione Campania in Italy, using tomato by-products as feedstock

Geothermal energy in the UK: The life-cycle environmental impacts of electricity production from the United Downs Deep Geothermal Power project

The UK is rich in heat-producing granites, especially in the county of Cornwall, suggesting the potential for energy production with low environmental footprint. The United Downs Deep Geothermal Power (UDDGP) project aims to demonstrate the technical and commercial viability to produce electricity from the Cornish geothermal resource, exploiting the natural permeability of a significant deep structural fracture zone known as the Porthtowan Fault Zone. Drilling of the first well started at the end of 2018, and the plant is expected to be operational by mid-2020. A relevant question is whether deep geothermal energy is truly environmentally benign. This article presents a comprehensive and detailed Life Cycle Assessment study that i) identifies the main life-cycle sources of environmental impacts for the production of electricity in the UDDGP plant; ii) investigates the effects on the environmental impacts of significant uncertainties surrounding the project, such as availability of geothermal fluid and configuration of the power plant, and iii) compares the performance of the UDDGP operation, and by extension of the putative geothermal energy production in the UK, with other key energy sources in the country. The life cycle inventory relies on a combination of site-specific data for wells construction and literature data for above-surface facilities and stimulation techniques. We validated our model by comparing climate change impacts of UDDGP with those reported by other studies on enhanced geothermal systems. Our results show that the greatest portion of environmental impacts originates from the construction phase (primarily due to steel for wells casing and diesel used during drilling), whilst the scenario analysis demonstrates that increasing installed capacity and cogenerating heat and power are the most effective strategies for improving the environmental performance. Our analysis also suggests that the environmental impacts may increase by ∼35% if stimulation techniques are required to increase the geothermal wells productivity. Compared to alternative energy sources, in the category climate change, UDDGP performs better than solar energy and is comparable with wind and nuclear. It is shown that the environmental benefits of geothermal energy are not straightforward and that a number of trade-offs needs to be considered when other impact categories are quantified

The life-cycle environmental performance of producing formate via electrochemical reduction of CO_{2} in ionic liquid

Carbon capture and utilisation provide a means to mitigate climate change caused by anthropogenic greenhouse gas emissions by delaying carbon emissions via temporary storage in goods. This article presents a comprehensive Life Cycle Assessment (LCA) study of a novel process that generates formate via electrochemical reduction of CO_{2} in ionic liquid. We performed a scenario analysis, covering uncertain parameters like the recycling rate of unreacted reagents and the market price of CO_{2}, and compared the environmental performance of the carbon utilisation system with that of the conventional process, which relies on fossil sources. Inventory data is obtained from a mix of literature sources and commercial LCA databases. Our analysis indicates that (i) the system needs to attain a 99.9% recycling rate to be competitive with the conventional process; (ii) a future negative market price of CO_{2} would substantially reduce the environmental impacts associated with formate; (iii) there are significant environmental trade-offs between the carbon utilisation system and the conventional process, with the former outperforming the latter in 6/8 out of the 14 impact categories investigated. It should be noted that our results are conservative because inventory data for the electrochemical reduction process is obtained from laboratory experiments

Life-cycle Inventory data and impacts on electricity production at the United Downs Deep Geothermal Power project in the UK

This data article supports the research article “Geothermal energy in the UK: the life-cycle environmental impacts of electricity production from the United Downs Deep Geothermal Power project”. The article reports inventory data, primarily on the construction of the geothermal wells, that is not reported in the main article, and the complete, disaggregated numerical values of the life-cycle environmental impacts reported only in part and in graphical form in the research article. The article also includes data supporting comparative analyses between deep geothermal energy and other energy technologies in the UK, and between the impacts of the construction of wells in a deep and conventional power plant

The environmental impacts of reprocessing used nuclear fuels: A UK case study

Historically the UK implemented a “nominal” twice-through cycle whereby used nuclear fuels were reprocessed, but uranium and plutonium were not recycled: they were stored pending a future decision by the UK Government. However, the policy for managing higher activity wastes is clear: it envisages their disposal in a Geological Disposal Facility. Consultations for siting a repository - which were suspended in 2013 - have recently restarted, but the repository will not be available for several decades at the earliest. This article presents a comprehensive LCA study on the historical UK approach for managing used nuclear fuels and the UK Government policy for disposal of higher activity wastes. The underpinning purpose is to inform policy and decision-makers concerned with decisions on the future of the UK nuclear fuel cycle. The study relies on a combination of operational data from the Sellafield site – the industrial complex home to the UK reprocessing plants - and literature data on the GDF, and on a number of assumptions regarding the GDF design and disposal of higher activity wastes. The results reveal that a great proportion of the environmental impacts can be linked to two specific causes: indirect burdens from production of uranyl nitrate, which is used to separate plutonium from uranium, and copper, proposed in one scenario to be used as the outer layer of the disposal canister for High Level Waste. The results also demonstrate that the carbon intensity of the management of used nuclear fuels is practically negligible when compared with results from other LCA studies that cover the entire fuel cycle

The environmental performance of protecting seedlings with plastic tree shelters for afforestation in temperate oceanic regions: A UK case study

Restoration of forested land represents an effective strategy to achieve net-zero target emissions by enhancing the removal of greenhouse gases from the atmosphere. The most common afforestation strategy envisages planting seedlings, which are germinated and grown to the desired age at tree nurseries, with plastic shelters to increase growth and survival of trees. This article presents a comprehensive Life Cycle Assessment (LCA) study that compares the environmental performance of current and prospective scenarios for shelter-aided seedling planting compared with a base case where shelters are not employed. The study focuses on the UK, but results and conclusions are valid for other temperate oceanic regions. The scenarios investigated are a combination of different shelters materials and end-of-life (EoL) strategies. Our analysis demonstrates that (i) planting seedling without shelters is the most preferable option across most environmental impact categories (including Climate Change), and in terms of weighted results, (ii) polypropylene shelters are preferable to bio-based alternatives, including polylactic acid-starch blends and bio-polypropylene, (iii) recycling is the most environmentally advantageous EoL treatment. Our study also showed that that the carbon emissions of the scenarios investigated are negligible when compared to the amount of carbon sequestered by a tree in 25 years