Hybridizing concentrated solar power (CSP) with biogas and biomethane as an alternative to natural gas: Analysis of environmental performance using LCA

Abstract

Concentrating Solar Power (CSP) plants typically incorporate one or various auxiliary boilers operating in parallel to the solar field to facilitate start up operations, provide system stability, avoid freezing of heat transfer fluid (HTF) and increase generation capacity. The environmental performance of these plants is highly influenced by the energy input and the type of auxiliary fuel, which in most cases is natural gas (NG). Replacing the NG with biogas or biomethane (BM) in commercial CSP installations is being considered as a means to produce electricity that is fully renewable and free from fossil inputs. Despite their renewable nature, the use of these biofuels also generates environmental impacts that need to be adequately identified and quantified. This paper investigates the environmental performance of a commercial wet-cooled parabolic trough 50 MWe CSP plant in Spain operating according to two strategies: solar-only, with minimum technically viable energy non-solar contribution; and hybrid operation, where 12 % of the electricity derives from auxiliary fuels (as permitted by Spanish legislation). The analysis was based on standard Life Cycle Assessment (LCA) methodology (ISO 14040-14040). The technical viability and the environmental profile of operating the CSP plant with different auxiliary fuels was evaluated, including: NG; biogas from an adjacent plant; and BM withdrawn from the gas network. The effect of using different substrates (biowaste, sewage sludge, grass and a mix of biowaste with animal manure) for the production of the biofuels was also investigated. The results showed that NG is responsible for most of the environmental damage associated with the operation of the plant in hybrid mode. Replacing NG with biogas resulted in a significant improvement of the environmental performance of the installation, primarily due to reduced impact in the following categories: natural land transformation, depletion of fossil resources, and climate change. However, despite the renewable nature of the biofuels, other environmental categories like human toxicity, eutrophication, acidification and marine ecotoxicity scored higher when using biogas and BM.

Life Cycle Assessment of a HYSOL Concentrated Solar Power Plant: Analyzing the Effect of Geographic Location

“…The use of natural gas instead of biomethane for scenario B was considered to be a likely scenario in countries where natural resources for biogas production are scarce, since the amount of biomethane required per year (3.40ˆ10 9 MJ/yr) exceeds the capacity of most of the biogas facilities installed to date [17]. Environmental impacts derived from the natural gas life cycle were determined by the Ecoinvent v.3 database, adapting the original CORES data to Spanish natural gas imports [21] as follows: 69% of Algeria; 16% of Nigeria; 10.9% of Norway and 3.9% of Netherlands.…”

“…Life Cycle Assessment (LCA) is an appropriate methodology to evaluate the environmental performance of renewable technologies, as has been proven in scientific literature [7][8][9]. The environmental impacts of conventional CSP plants have been previously evaluated by the scientific community [10][11][12][13][14][15][16][17][18][19][20]. These analyses are all based on LCA methodology, and evaluate the environmental performance of CSP plants of varying capacity, operating with different technologies (parabolic trough/Fresnel reflectors, central tower, Stirling dish), including specific component characteristics (air/wet cooling, thermal storage technology) and hybridization with different fuels.…”

Overlooked impacts of electricity expansion optimisation modelling: The life cycle side of the story

“…SimaPro is an LCA software that allows users to customise inventory libraries of all stages of the life cycle (used materials, fuel extraction, processing and delivery). The inventory data of greenhouse gases (CO 2 , CH 4 , and N 2 O) were collected from EcoInvent database [31], governmental agencies [1,9] and relevant literature [5,6,24,33]. Then, the individual greenhouse gases were aggregated into CO 2 e (carbon dioxide equivalent) emissions in accordance to the GWP (Global Warming Potential) in a time horizon of 100 years as described by IPCC in its 5th assessment report [28].…”

Technical and Environmental Analysis of Parabolic Trough Concentrating Solar Power (CSP) Technologies

“…The minimum amount of auxiliary energy required to operate a commercial parabolic trough CSP installation varies depending on the size of the solar field and the TES, the intensity of solar irradiance, and ambient temperature. For the conditions typically found in southern Spain, this minimum requirement ranges between 100,000 and 130,000 MJ/MW/ year, which represents 6.28E + 06 MJ/year for a typical 50 MWe CSP installation or 1.61E + 05 Nm 3 /year of natural gas [12]. Table 1 (see CSP with TES) shows the main features and operating characteristics of a wet-cooled 50 MWe CSP plant with 7.5 h TES like the ones installed in southern Spain.…”

“…5 Ability of the plant to provide electricity on demand. et al [10], Lovegrove and Pye [11], San Miguel and Corona [12], and Klein and Rubin [13].…”