Summary of Thesis Aim and Objectives

The central aim of this thesis is to design, develop and test an efficient and effective proof of concept tri-generation system based on SOFC and liquid desiccant air conditioning technology for building applications. The integration of SOFC and liquid desiccant air conditioning technology will be the first of its kind system, and serves to progress the field of low carbon sustainable energy conversion techniques for building applications.

Seven thesis objectives have been established with the purpose of achieving the thesis aim, and are summarised as follows:

  • (1) Highlight the current gap in the literature surrounding SOFC liquid desiccant tri-generation systems, particularly for building applications.
  • (2) Justify the selection of an appropriate working fluid for the liquid desiccant air conditioning system.
  • (3) Numerically evaluate the liquid desiccant air conditioning system, with particular regards to its suitability for integration in an SOFC tri-generation system.
  • (4) Development of a system model to evaluate the feasibility of integrating SOFC and liquid desiccant air conditioning technology, and to establish how performance varies with operational changes in the system.
  • (5) Evaluation based on experimental data, of the SOFC and liquid desiccant air conditioning components.
  • (6) Tri-generation system integration with energetic, economic and environmental evaluation.
  • (7) Recommendations for future work related to SOFC liquid desiccant tri-generation systems, particularly for building applications.

Originally, before the technical and economic issues were encountered with the building-installed SOFC CHP system; several technical objectives for the final building-installed SOFC tri-generation system were selected. These are detailed in Table 1.1, and are based upon the EU TriSOFC project (Riffat 2012).

Due to it being laboratory based and of a lower electrical capacity the experimental tri-generation system does not meet the technical objectives set out in Table 1.1. However, the simulations presented in Chap. 4 and the theoretical trigeneration system integration analysis, based on empirical data presented in Sect. 7.2, does aim to maintain the technical objectives.

An electrical output of 1.5 kWe has been selected based on its appropriateness for providing baseline power in domestic building applications; a value used extensively in the domestic fuel cell CHP sector (Ellamla et al. 2015). Furthermore, 1.5 kWe is within the 2 kWe maximum limit to be considered for the UK feed-in-tariff (FiT), therefore increasing the incentive to adopt the developed tri-generation system. Depending on thermal utilisation in the developed tri-generation system, combined efficiency could reach 85 %, similar to that of combustion based systems. However, as demonstrated in Sect. 2.4, for the developed system to compete with current combustion based tri-generation systems it needs to have a higher electrical efficiency. At the proposed scale i.e. <2 kWe, a combustion based

Table 1.1 Summary of technical objectives of the tri-generation system

Technical parameter


SOFC electrical power

~1.5 kWe

System efficiency (based on natural gas)

>85 %

Electrical efficiency (LHV)

>45 %

system could not meet the 45 % electrical efficiency target, an SOFC can, and is therefore a technical objective of the work. Steinberger-Wilckens (2013) states, for hydrogen fuel cells to produce a marked effect on the stationary market they need to match and surpass the performance of current CHP/tri-generation systems. A high electrical efficiency target strengthens the case for hydrogen based energy conversion in building applications.

Reduced system efficiency is often experienced by CHP systems operating in hot and humid climates where the demand for dehumidification/cooling outweighs heating. As a result, the first of its kind SOFC liquid desiccant tri-generation system has been proposed. The novel system aims to overcome the issue of reduced thermal energy utilisation in summer months and thus improve system performance. Although the proposed system operates on a hydrocarbon fuel, it is expected to significantly reduce the associated CO2 emissions compared to an equivalent separate generation system consisting of a boiler, grid electricity and vapour compression air conditioner. The development of the novel tri-generation system serves to provide an essential stepping stone in developing and refining the necessary technology for when the wide-spread transition to clean zero carbon hydrogen production can occur.

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