Home Environment A Novel SOFC Tri-generation System for Building Applications
Humanity is now at a global tipping point. Serious decisions regarding the future of world energy supply and demand need to be made. We face the challenge of addressing the issues of reducing reliance on dwindling reserves of fossil fuels and rising energy demand. Predictions regarding the finite supply of heavily relied upon fossil fuels are bleak. It has been calculated that total consumption of easily exploitable oil reserves will take place by 2050 (BP 2012), natural gas in 70-100 years and coal in the next few centuries (Marban and Valdes-Solfs 2007). Exploration will then have to move to places such as the Amazon and the Arctic, or in the deep ocean, therefore making it more expensive and technically challenging. Furthermore, global energy demand is set to rise. Currently, countries such as China, India and Brazil have large and ever increasing populations. Presently, energy consumption per capita in these rapidly expanding economies is well below that of more economically developed economies such as the UK or North America. However, with the continued economic development of these nations, their energy consumption per capita is predicted to grow to, or even surpass that, of countries such as the UK. In the current global situation where the majority of energy supply is from finite fossil fuel reserves, this poses a grave problem; supply is falling and demand is increasing. Furthermore, the principal method of global energy conversion is through the combustion of these fossil fuels. This process liberates significant quantities of greenhouse gases (GHG) into the atmosphere. It is now of critical importance that GHG emissions associated with energy conversion are substantially reduced in order to limit the effects of climate change and environmental pollution. Agreements such as the 1997 Kyoto Protocol have been established in order to try and mitigate the effects of climate change by reducing the quantities of GHG released into the atmosphere. More recently the UK set out © Springer International Publishing AG 2017
T. Elmer, A Novel SOFC Tri-generation System for Building Applications, Springer Theses, DOI 10.1007/978-3-319-46966-9_1
in its 2007 Energy White Paper that it would commit to an 80 % GHG emission reduction compared to 1990 levels by 2050 (DECC 2008). The European Union (EU) has committed to reducing CO2 emissions by 20 % by 2020 compared to 1990 levels (Bohringer et al. 2009). Both the UK and EU targets are ambitious; however there is now a common trend amongst many nations towards aspirations of a low carbon future.
Due to the increasing concern over the provision of future energy supply and climate change, there is a significant interest in the development of alternative clean energy sources and efficient power generators. Buildings consume 40 % of the world’s primary energy for cooling, heat and power (DECC 2011). Most of this energy is from electricity generated at centralised power stations; where at present up to 70 % of available energy is wasted. The overall system efficiency is low at 30-40 %, leading to a high waste of energy resources, resulting in considerable CO2 emissions and unnecessarily high running costs. Reducing the energy consumption of buildings can make a substantial contribution towards attaining the EU’s 2020 and the UK’s 2050 carbon emission targets. But this will only be achieved by moving from conventional centralised power generation systems to onsite highly-efficient clean micro-generation technology (Jradi and Riffat 2014d; Ellamla et al. 2015; Elmer et al. 2015).
One of the most promising possibilities for clean micro-generation is solid oxide fuel cell (SOFC) technology, which can generate electricity directly through an electrochemical reaction which brings together hydrogen and oxygen. The only by-products are waste heat, water vapour, and depending on the fuel used a modest amount of CO2. Chemical to electrical energy conversion efficiencies can be over 50 % compared to 30-40 % in combustion processes, such as internal combustion engines and gas turbines. Technical assessments have demonstrated that if combined heat and power (CHP) technology is used with SOFC, the total system efficiency can be as high as 90 % (Berger 2015).
Liquid desiccant systems are used in heating, ventilation, and air conditioning (HVAC) applications where simultaneous maintenance of temperature and humidity control is an important benefit to the user. This technology is often used in tri-generation system applications, where the desiccant system is driven by the heat by-product. If the waste heat from SOFCs is used to drive the liquid desiccant unit, then a tri-generation system will result, supplying not only the power and heat as the conventional CHP technology to the building, but also cooling and humidity control. It has been demonstrated in the literature that the inclusion of liquid desiccant in a tri-generation system configuration can provide significant improvement to total system efficiency (Liu 2004; Jradi and Riffat 2014b).
The 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. The proposed system will be the first of its kind, and can be used for a range of building applications (e.g. domestic, schools, offices), providing power, heating and dehumidification/cooling to the occupied space.
This section has provided some contextual background and the research aim.
This chapter is structured in three main parts:
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