A critical review of the greenhouse gas emissions associated with parabolic trough concentrating solar power plants

Preliminary thermoeconomic analysis of combined parabolic trough solar power and desalination plant in port Safaga (Egypt)

Design and comparative analysis of photovoltaic and parabolic trough based CSP plants

In the United States, concentrating solar power (CSP) is one of the most promising renewable energy (RE) technologies for reduction of electric sector greenhouse gas (GHG) emissions and for rapid capacity expansion. It is also one of the most price-competitive RE technologies, thanks in large measure to decades of field experience and consistent improvements in design. One of the key design features that makes CSP more attractive than many other RE technologies, like solar photovoltaics and wind, is the potential for including relatively low-cost and efficient thermal energy storage (TES), which can smooth the daily fluctuation of electricity production and extend its duration into the evening peak hours or longer. Because operational environmental burdens are typically small for RE technologies, life cycle assessment (LCA) is recognized as the most appropriate analytical approach for determining their environmental impacts of these technologies, including CSP. An LCA accounts for impacts from all stages in the development, operation, and decommissioning of a CSP plant, including such upstream stages as the extraction of raw materials used in system components, manufacturing of those components, and construction of the plant. The National Renewable Energy Laboratory (NREL) is undertaking an LCA of modern CSP plants, starting with those of parabolic trough design. Our LCA follows the guidelines described in the international standard series ISO 14040-44 [1]. To support this effort, we are comparing the life-cycle environmental impacts of two TES designs: two-tank, indirect molten salt and indirect thermocline. To put the environmental burden of the TES system in perspective, one recent LCA that considered a two-tank, indirect molten salt TES system on a parabolic trough CSP plant found that the TES component can account for approximately 40% of the plant’s non-operational GHG emissions [2]. As emissions associated with plant construction, operation and decommissioning are generally small for RE technologies, this analysis focuses on estimating the emissions embodied in the production of the materials used in the TES system. A CSP plant that utilizes an indirect, molten salt, TES system transfers heat from the solar field’s heat transfer fluid (HTF) to the binary molten salts of the TES system via several heat exchangers. The “cold tank” receives the heat from the solar field HTF and conveys it to the “hot tank” via another series of heat exchangers. The hot tank stores the thermal energy for power generation later in the day. A thermocline TES system is a potentially attractive alternative because it replaces the hot and cold tanks with a thermal gradient within a single tank that significantly reduces the quantity of materials required for the same amount of thermal storage. An additional advantage is that the thermocline design can replace much of the expensive molten salt with a low-cost quartzite rock or sand filler material. This LCA is based on a detailed cost specification for a 50 MWe CSP plant with six hours of molten salt thermal storage, which utilizes an indirect, two-tank configuration [3]. This cost specification, and subsequent conversations with the author, revealed enough information to estimate weights of materials (reinforcing steel, concrete, etc.) used in all components of the specified two-tank TES system. To estimate embodied GHG emissions per kilogram of each material, two life cycle inventory (LCI) databases were consulted: EcoInvent v2.0 [4], which requires materials mass data as input, and the US Economic Input-Output LCA database [5], which requires cost data as input. IPCC default global warming potentials (GWPs) give the greenhouse potential of each gas relative to that of carbon dioxide [6]. Where certain materials specified in Kelly [3] were not available in the LCI databases, the closest available proxy for those materials was selected based on such factors as peak process temperature, and similar input materials and process technology. The thermocline system was modeled using the two-tank system design as the foundation, from which materials were subtracted or substituted based on the differences and similarities of design [7]. Table 1 summarizes the results of our evaluation. Embodied emissions of GHGs from the materials used in the 6-hour, 50 MWe two-tank system are estimated to be 17,100 MTCO2e. Analogous emissions for the thermocline system are less than half of those for the two-tank: 7890 MTCO2e. The reduction of salt inventory associated with a thermocline design thus reduces both storage cost and life cycle greenhouse gas emissions. While construction-, operation- and decommissioning-related emissions are not included in this assessment, we do not expect any differences between the two system designs to significantly affect the relative results reported here. Sensitivity analysis on choices of proxy materials for the nitrate salts and calcium silicate insulation also do not significantly affect the relative results.

Heat Transfer Fluid Life Time Analysis of Diphenyl Oxide/Biphenyl Grades for Concentrated Solar Power Plants

The Middle East is one among the areas of the world that receive high amounts of direct solar radiation. As such, the region holds a promising potential to leverage clean energy. Owing to rapid urbanization, energy demands in the region are on the rise. Along with the global push to curb undesirable outcomes such as air pollution, emissions of greenhouse gases, and climate change, an urgent need has arisen to explore and exploit the abundant renewable energy sources. This paper presents the design, performance analysis and optimization of a 100 MWe parabolic trough collector Solar Power Plant with thermal energy storage intended for use in the Middle Eastern regions. Two representative sites in the Middle East which offer an annual average direct normal irradiance (DNI) of more than 5.5 kWh/m2/day has been chosen for the analysis. The thermodynamic aspect and annual performance of the proposed plant design is also analyzed using the System Advisor Model (SAM) version 2017.9.5. Based on the analysis carried out on the initial design, annual power generated from the proposed concentrating solar power (CSP) plant design in Abu Dhabi amounts to 333.15 GWh whereas that in Aswan recorded a value of 369.26 GWh, with capacity factors of 38.1% and 42.19% respectively. The mean efficiency of the plants in Abu Dhabi and Aswan are found to be 14.35% and 14.98% respectively. The optimization of the initial plant design is also carried out by varying two main design parameters, namely the solar multiple and full load hours of thermal energy storage (TES). Based on the findings of the study, the proposed 100 MW parabolic trough collector solar power plant with thermal energy storage can contribute to the sustainable energy future of the Middle East with reduced dependency on fossil fuels.

Concentrated solar power (CSP) is viewed as one of the most promising alternatives in the field of solar energy utilization; parabolic trough collector (PTC) solar power plants are the most commercially established among the power plants operating with CSP technology. In this paper, a parabolic trough solar thermal power plant with thermal energy storage was evaluated in terms of design and thermal performance, using the SAM program of NREL (System Advisor Model). This program is used to evaluate the active and economic performance of a plant such as monthly energy production, annual energy production, and level cost of energy (LCOE).one representative site in south Libya, Sebha city, which offers an annual average direct normal radiation (DNI) of more than 6.0 kWh/m2/day, has been chosen for the analysis and optimization of the proposed 100 MWe PTC Solar power plant. The optimization is carried out with solar multiple (SM) and full load hours of thermal energy storage TES as the parameters, to minimize the Levelized cost of electricity and maximize the annual energy yield. Based on the findings of the study, the proposed 100 MW PTC solar power plant with thermal energy storage can contribute to the sustainable energy future of Libya with reduced dependency on fossil fuels. This design and performance analysis of the plant encourages further development and innovation of solar thermal power plants in all regions of Libya.

In this work, a technical and economic analysis concerning the integration of parabolic trough concentrated solar power (CSP) technologies, with or without thermal storage capability, in an existing typical small isolated Mediterranean power generation system, in the absence of a feed-in tariff scheme, is carried out. In addition to the business as usual (BAU) scenario, five more scenarios are examined in the analysis in order to assess the electricity unit cost with the penetration of parabolic trough CSP plants of 50 MWe or 100 MWe, with or without thermal storage capability. Based on the input data and assumptions made, the simulations indicated that the scenario with the utilization of a single parabolic trough CSP plant (either 50 MWe or 100 MWe and with or without thermal storage capability) in combination with BAU will effect an insignificant change in the electricity unit cost of the generation system compared to the BAU scenario. In addition, a sensitivity analysis on natural gas price, showed that increasing fuel prices and the existence of thermal storage capability in the CSP plant make this scenario marginally more economically attractive compared to the BAU scenario. (7 pages)

Analysis of the influence of operational strategies in plant performance using SimulCET, simulation software for parabolic trough power plants

Life cycle analysis of external costs of a parabolic trough Concentrated Solar Power plant

A simplified dynamic model of integrated parabolic trough concentrating solar power plants: Modeling and validation

Utilization of renewable energy resources is currently a global concern due to several reasons that include environmental pollution caused by combustion of conventional fuels, availability of resources in the vicinity, and continuous increase in cost of conventional fuels. Solar energy is the major renewable energy resource that is a basis for the other ones. Since the annual average daily radiation for Ethiopia is 5.2kWh/m2/day and the minimum annual average radiation ranges from 4.5kWh/m2/day in July to a maximum of 5.55kWh/m2/day in February and March [1], [2], parabolic trough collector solar power plants, which are mature technologies among the solar thermal ones, can be feasible to be used in the country for large and small scale applications. An interactive simulation software has been developed by the authors to support designers and researchers who are willing to simulate flow dynamics and power prediction of parabolic trough solar power plants and optimisation of their components. The design of the software began from thorough understanding of the physics governing conversion of energy from solar radiation to electricity using the plant, sizing of plant components, code writing for solving the governing equations and designing an interactive graphical user interface (GUI) for easy communication with the software. Besides giving the basic fuction of simulation and optimisation, the software benefits its users in being freely accessible and open source. The open sourceness of the software package also moitvates others in the energy field to develop their own packages either by modifying the code of this software or by creating a new one. Furthermore, it is a unique method of mapping and identifying conducive environmental localities that are suitable for implementation of solar energy. Over and above this, this project is a unique means of sharing global responsibility of mitigating effect of climate change. The software has been validated by simulating existing power plants for which all the data are available.

Organic Rankine Cycle coupling with a Parabolic Trough Solar Power Plant for cogeneration and industrial processes

In the development of renewable energy sources, there has been a trend toward increasing and stabilising the power output of Concentrated Solar Power Plants (CSPPs) during times of reduced solar resource through the use of Thermal Energy Storage Devices (TESDs). This study investigates whether the use of a molten salt TESD decreases the efficiency of a parabolic trough CSPP due to additional system energy losses despite prolonging the operational time of the CSPP. A theoretical analysis of a simplified CSPP was made to determine if a TESD would impact the efficiency of the CSPP. This was followed up by a survey of currently active parabolic trough CSPPs both with and without molten salt TESDs. The theoretical analysis illustrated that a TESD would have no effect on the efficiency of a CSPP. However, the survey revealed that the use of a TESD improved the efficiency of a CSPP. The results of the study don't support the theoretical analysis or the hypothesis suggesting that a property has been overlooked. This property is most likely to be that generators tend to operate best within a certain temperature range, and in a CSPP the optimum temperature range cannot be maintained. This results in a generator being selected capable of operating for the longest period with the lowest amount of excess solar energy. When a TESD is implemented, the excess solar energy is stored for later use, prolonging the generator's running time and increasing the useable energy. The realisation of the ability of a TESD to increase the efficiency of a CSPP as well as extending its operating time shows a promising area of development in CSPP technology and increasing its application in electricity generation.

Due to the growing world population and its increasing energy demand, the construction of new power plants is inevitable. At the same time, it is necessary to keep the rise of the global average temperature well below 2 °C compared to pre-industrial level in order to significantly reduce the impacts and risks of climate change. Therefore, an environmental friendly energy infrastructure is required to reduce greenhouse gas emissions. Solar thermal power plants are a promising technology, as they provide the possibility to buffer solar energy in a thermal storage. Thus, it can produce electricity according to the demand and is independent of meteorological fluctuations. A life cycle assessment is necessary to assess the environmental impact of a solar thermal power plant and its individual components. This work analyses the extent of the environmental effects of solar thermal tower power plants in the following selected impact categories according to the CML-method: Global Warming Potential (GWP 100 years), Abiotic Depletion potential (ADP elements), Eutrophication potential (EP) and Acidification Potential (AP). The most ecologically relevant components are identified and modelled with different specifications in order to compare the influence of different building types. Furthermore, the life cycle assessment model is applied to different geographical locations in order to enable site-specific considerations. The selected locations are Upington in South Africa, Evora in Portugal and Calama in Chile. The life cycle inventory is generated based on an extensive literature research and forms the foundation for the modelling of solar thermal tower power plants in the LCA software GaBi ts. As a result, the most ecologically relevant components are determined. A comparison of the different locations allows statements on the ecological potential of solar thermal tower power plants at a specific site. The heliostats and the molten salt (MS) as heat transfer fluid and storage medium dominate the impact on the GWP 100 years. The heliostats consist mainly of steel and glass and are needed in large numbers. The molten salt is used in a high amount and consists of a mixture from sodium nitrate and potassium nitrate which both have a high impact on GWP. Moreover, the transport and the construction on site have relevant contributions to GWP. The impact of the transport results from the large mass of all shipped components. The impact of the construction on site has copper cables as the main contributor. The end-of-life scenarios have a significant effect on the total impact. Depending on the recovery of the metals and especially the further use of the molten salt, the environmental impact is decisively influenced.

Under the background of increasing greenhouse effect and decreasing fossil energy, renewable energy power generation has been drawn increasing attention by almost all countries in the world, and especially the solar thermal power generation has received much attention in recent years. As a solar energy utilization pattern different from the photovoltaic power generation, the solar thermal power generation has the advantages such as higher stability and larger scale that other kinds of renewable energy power generations do not have. However, for the current solar thermal power plants, the higher cost of the initial construction and lower concentration efficiency have become obstacles to its advancement in the power generation industry. As a crucial subsystem of the solar thermal power plants, the heliostat subsystem not only occupies nearly half of the cost of the solar thermal power plants, but also directly determines the concentration efficiency of the solar thermal power plants. Therefore, how to reduce the cost of the heliostat field, and distribute and control the heliostat at the same time, so that it can accurately and effectively track the sun in real time, which is one of most important problems. In this paper, a summarize of the current researches on the methods for improving power generation efficiency is given for the heliostat part of the solar tower thermal power plants.