Elsevier

Solar Energy

Volume 99, January 2014, Pages 203-214
Solar Energy

Hybridisation optimization of concentrating solar thermal and biomass power generation facilities

https://doi.org/10.1016/j.solener.2013.10.041Get rights and content

Highlights

  • Comparison of 17 different CSP–biomass hybrid concepts using mature CSP & biomass technologies.

  • 13% Net efficiency increase between different scenarios.

  • Up to 69% cost reduction with hybrids when comparing annual generation with standalone CSP.

  • Technical, economic, environmental analysis comparing hybrid and standalone CSP systems.

  • Consideration of thermal storage to increase annual generation.

Abstract

Recently, the first concentrating solar power–biomass hybrid power plant commenced operation in Spain and the combination of both energy sources is promising to lower plant investment. This assessment investigates 17 different concentrating solar power–biomass hybrid configurations in regards their technical, economic and environmental performance. The integration of molten salt thermal storage is considered for the best performing hybrid configuration. While thermal storage can increase plant output significantly even 7 h full-load thermal storage plants would generate the majority of the electricity, 70%, from the biomass resource.

Only mature technologies with references >5 MWe are considered in this assessment to ensure that the scenarios are bankable. The concentrating solar power technologies selected are parabolic trough, Fresnel and solar tower while the biomass systems include grate, fluidised bed and gasification with producer gas use in a boiler.

A case study approach based on the annual availability of 100,000 t of wood biomass is taken to compare the different plant configurations but the results are transferable to other locations when updating site and cost conditions. Results show that solar tower–biomass hybrids reach the highest net cycle efficiency, 32.9%, but that Fresnel-biomass hybrids have the lowest specific investment, AU$ 4.5 m/MWe. The investment difference between the 17 scenarios is with up to 31% significant. Based on the annual electricity generation CSP–biomass hybrids have an up to 69% lower investment compared to standalone concentrating solar power systems. The scenario with the best technical performance, being solar tower and gasification, is at this point in time not necessarily the best commercial choice, being Fresnel and fluidised bed, as the lower Fresnel investment outweighs the additional electricity generation potential solar towers offer. However, other scenarios with different benefits rank closely.

Introduction

Concentrating solar power (CSP)–biomass hybrid plants are a well accepted solution for comparatively low cost base-load/dispatchable renewable energy but are a niche market considering the limited areas with a sufficiently high direct normal irradiance, >1700 kW h/m2/year, and biomass resources. Countries such as Australia, Spain, Italy, Greece, Thailand, India, and Brazil are, amongst others, prime candidates for such projects as these countries have locations that meet both criteria. To maximize the commercial viability and efficient biomass use the power plant concepts should be as efficient as possible considering the economic realities of obtaining finance for such projects.

Recently, the first CSP–biomass hybrid plant commenced operation near Barcelona, Spain (Protermosolar, 2012), which proves that such concepts work technically and are bankable solutions. Despite other CSP–biomass configurations being investigated in the past, including Fresnel and tower systems, no other projects commenced construction at this point in time.

This paper investigates different possible CSP–biomass hybrid configurations with the aim of identifying the best in regards to technical, economic, and environmental performance, such as cycle efficiency, investment, and CO2 abatement potential. The efficient use of biomass is not only necessary to maximize plant output, but also to optimize usage as biomass has to be purchased competitively against other users, such as pulp and paper industry. Understanding the different CSP–biomass hybrid options will enable project developers to concentrate on the most promising ones therewith increasing chances to successfully implement such projects.

All scenarios investigated in this paper assume that the biomass boiler is operating constantly at full capacity, that the CSP system provides additional capacity during the daytime when electricity demand/prices are typically higher in Australia (Lekovic et al., 2011), and that the CSP and biomass systems can operate independent of each other by providing identical steam flows/parameters to the joint turbine. To minimize plant investment molten salt thermal storage is considered only for one high temperature scenario as its cost are still comparatively high and the biomass component can generate electricity at lower cost during the night and extended cloud coverage. Future work could investigate CSP–biomass hybrids with thermal storage in more detail by considering other storage media, such as pressurized water or steam, and tank configurations, such as single tanks.

Section snippets

Current hybrid proposals

First proposals to combine CSP with biomass/waste materials using dish systems were investigated briefly in the 1980s (McDonald, 1986). However, due to technical and financial issues no plants were built. It took more than two decades before the first commercial CSP–biomass hybrid plant, Termosolar Borges 22.5 MWe (Morell, 2012), commenced operation near Lleida, ca. 150 km west of Barcelona, Spain, see Fig. 1. The plant is located further north than any other CSP project in Spain and uses the

Methods

The assessment aims to identify the best CSP–biomass hybrid plant configuration by investigating the technical, economic and environmental performance of 17 different scenarios. A case study approach is chosen to compare the scenario differences but the assessment is transferable to other locations when adapting site and cost conditions.

Water–steam cycle analysis

Several options exist to increase the efficiency of a Rankine cycle systems, such as optimized feedwater heating, blowdown heat recovery and flue gas condensation. This section briefly outlines the effects of these options on the net cycle efficiency and provides the base case scenario (scenario 1) for the following CSP–biomass hybrid assessment.

Results

The technical, economic and environmental results shown for the 17 different scenarios are based on triple feedwater heating and blowdown heat recovery. Some information is provided on the impact of molten salt TS and less mature plant concepts.

To clearly identify the scenarios and its different results in Table 3, Table 4, Table 5 an abbreviation code is used where for example 1−PT+TO stands for scenario 1 using the parabolic trough technology with thermal oil. Each CSP technology is paired

Conclusion

The assessment shows that at the moment the best technical and environmental CSP–biomass hybrid configuration, being solar tower and gasification, is not the best commercial choice, being Fresnel and fluidised bed. While the efficiency differences for the 17 scenarios reach 13% the investment variations are with 31% significantly larger. The results also show that, based on identical annual electricity generation, the CSP–biomass hybrid plant investment is up to 69% lower compared to a

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