Nowadays, the proportion of renewable energy is progressively becoming substantial in many sectors such as power generation, heating and cooling, transport fuels, and off-grid energy services. Indeed, reductions of the greenhouse gas emissions and dependency to the fossil-fuels constitute a priority for many countries.
In order to reduce its emissions and secure its energy supply, the European Commission set ambitious objectives to promote the exploitation of renewable energy resources. The European Council, thereby, imposed national targets to increase the EU average share of renewable to 20 % of the final energy consumption by 2020 (EREC, 2007). United Kingdom has been set an objective of 15% of its energy consumption coming from renewable sources. EU renewable shares of final energy consumption in 2005 and 2009 as well as the 2020 targets are shown on the Figure 1.
Figure - EU renewable shares of final energy (From REN21, 2011, p.50)
Besides those objectives, the observation of the EU energy consumption shows that households and services sectors contribute respectively for 25.4 % and 13.1 % to the total energy consumption (Market Observatory for Energy, 2010) (See Figure 2). The consumption for these two sectors is mainly linked to building demands: houses, catering and hostels, office and administrative buildings, etc (DECC, 2012).
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Figure - EU-27 final energy consumption by sector (From Market Observatory for Energy, 2010, p.13)
At the time of the construction or the refurbishment, two strategies can be applied in order to reduce the primary energy consumption of fossil-fuels (Fieber, 2005). The first strategy consists to support a transition towards renewable energy sources allowing keeping an equivalent level of consumption while the second one focus on energy conservation to obtain sustainable development. Solar energy technologies have the advantage that they can be seen as representatives of both strategies of renewable and energy consumption.
Furthermore, building integration of solar energy can be made via active and passive solar systems. Among the solar power technologies, concentrating solar power technologies presented significant developments the last years. Figure 3 shows the average annual growth rates of renewable energy capacity and biofuels production (REN21, 2011).
Figure - Average annual growth rates of renewable energy capacity and biofuels production, 2005-2010 (From REN21, 2011, p.18)Solar_growth_rates.png
On the other hand, many studies on the potential of organic fluids with low boiling point are led in order to improve heat transfer capacities of the actual solar thermal technologies; notably for systems using Rankine cycle to combine electricity and heat production. The use of specific organic fluid allows recovering heat from lower temperature heat sources (Chen, Goswani and Stefanakos, 2010).
The present master thesis joins this research interest around the organic rankine cycle by studying and modelling an integrated system using compounds parabolic concentrators (CPC) as energy source for the needs of a five storeys office building in London. The organic working fluid used in this study is the 1, 1, 1, 3, 3-Pentafluoropropane (R245-fa) and has been used for its interesting properties.
The objective of this project is to model and optimise using Matlab a combined Compound Parabolic Concentrator-Organic Rankine Cycle (ORC) using R245-fa as working fluid to ensure a part of the needs in electricity, heat and cooling for an office building in London. The building has five storeys, a ground floor area of 300 m² and is 22.5 m high. The occupancy throughout the building is one person per 14 m², so this results in 214 workers throughout the five floors.
Considering the local conditions and the building specifications as the size, insulation, materials properties and electricity needs, the energy demand for a typical year can be calculated for every period. In addition, the local conditions and building restrictions allows assessing the heat which can be recovered by CPCs installed on the roof of the building. Thirdly, modelling the ORC using the heat recovered by the CPC as heat source permits to assess the electricity and heat which can be produced from this kind of system.
This project allows assessing the potential of such a system and its contribution to the energy supply for a typical office building. However, efficiency of the system, integrative and technological aspects must be considered as well to assess its feasibility.
The main objectives of the project are listed below:
Always on Time
Marked to Standard
CPC and ORC: literature review and background
Modelling energy demand
Modelling CPC heat recovering
Modelling ORC using R245-fa
Optimise CPC-ORC system for the considered building
Propose integrated system for production of electricity, heat and cooling.
Assess relevance of the system and of the use of R245-fa as working fluid
Compound parabolic concentrators
Despite a growing interest for concentrating solar technologies during the last decades, concentrated solar exists since Antiquity (Acquasol, 2012). More recently, Auguste Monchout was the first in 1866 to use a parabolic through to produce steam for a solar steam engine (Butti and Perlin, 1981). Following Monchout, inventors as Allessandro Battaglia, John Ericsson and Frank Shuman developed concentrating solar devices for irrigation, refrigeration and locomotion. In 1913, Shuman finished to build a 55 horsepower parabolic solar thermal station in Meadi in Egypt for irrigation. This station is shown on the Figure 4.
Figure - Parabolic solar collector thermal station for irrigation built by Shuman in Meadi (From Solarhaven, 2012)Shuman_solar_thermal.png
Parabolic concentrators came back in the 1980s in response to the two 1970s oil crisis (Acquasol, 2012). Following encouraged investments in alternative and renewable energy production, Luz Solar Partners Ltd. built nine parabolic through power plants in the California Desert between 1983 and 1989 with a total capacity of 354 MW. Those power plants are still in operation today and remain among the largest collection of concentrating solar power plants in the world. Some pilot concentrating solar power plants have also been built in Australia but as the oil price fell, incentives have been shortened.
Nowadays, Compound parabolic concentrators are mainly used for power generation applications and constitute the most mature technology among the solar thermal electricity (STE) methods of generation (ESTELA, 2010). Figure 5 shows the actual STE power plants and research facilities in Europe and North Africa.
Moreover, Y. Zhang et al. argued that thermal concentrating solar power (CSP) technologies might progress from current hybrids plants to plants with a modest amount of heat storage and potentially even to plants with sufficient thermal storages to provide based load generation capacity (2010). The actual plants use synthetic aromatic fluid as working fluid but they can be improved by using either molten salt as working fluid either direct steam generation (ESTELA, 2010) (Fernandez-Garcia et al., 2010).
STE solar Europe Map.png
Figure - Map of the research and constant solar thermal power plants in Europe and North Africa (From ESTELA, 2012)
Nevertheless, CPC collectors are not only used for electricity production. They can be used for applications such as industrial process heat, domestic hot water and space heating, air-conditioning and refrigeration, pumping and irrigation, desalination or solar chemistry (Fernandez-Garcia et al., 2010). Besides, many researches are led in order to use CPC to improve the performance of PV cells (Guiqiang et al., 2012) (Chemisana, 2011). Indeed, concentrating solar photovoltaic can offer many advantages compare to traditional PV panels as higher electrical conversion efficiency, better use of space, and ease of recycling materials. Heat can eventually removed by cooling the cells depending on the concentration ratios.
In parallel, researches are led with the aim to improve the characteristics of the compounds parabolic concentrators or the working fluid used to extract heat (Sani et al., 2010) (Oommen and Jayaraman, 2001). For instance, Yuehong Su et al. present recently a ray tracing analysis of lens-walled compound parabolic concentrator, which has a thin CPC-shaped lens attached to a common mirror (2011).
Organic Rankine Cycle
As concentrating solar technologies, Organic Rankine Cycles exists since the end of 19th century. Frank Ofeldt was the first in 1883 to develop a power cycle using an organic high molecular fluid, naphta, as working fluid (Turboden, 2012). His naphta engines were steam engines boiling naphta instead of water to drive pistons and were used to power boats. However, the ORC was seriously studied during the 20th century, notably in Italy, Russia, USA and Israel.
Nowadays, ORC is a well-known and widely spread form of energy production for different applications, notably using renewable energy as heat source.It is mostly developed for biomass power plants, geothermal plants and waste heat recovery (Quoilin, 2011). Figure 6 shows the ORC market shares (Quoilin and Lemort, 2009).
Although ORC constitutes a mature technology in those fields, many researches are led to improve existing technologies or develop new processes. For instance, Taljan et al. presented recently a novel methodology for optimal sizing of biomass-fired ORC combined heat and power system with heat storage (2011). Wang et al. studied the different working fluid which can be used for waste heat recovery in vehicles (2011) while Shengjun, Huaixin and Tao did a performance comparison and parametric optimisation of subcritical ORC and transcritical power cycle system for low-temperature geothermal power generation (2011).
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Figure - Share of each application in the ORC market (From Quoilin and Lemort, 2009, p.6)
Nevertheless with the environmental concern and rising oil prices, many investments and researches are led into new applications such as solar thermal and PV, fuel cells, waste heat recovery, reverse osmotic desalination ... to produce clean and reliable electricity. Figure 7 shows the market evolution from 1984 to 2009 in terms of power installed and identified projects (Quoilin and Lemort, 2009).
Figure - ORC market evolution (From Quoilin and Lemort, 2009, p.6)
About solar PV, studies are led in order to combine concentrating PV with an ORC (Kosmadakis, Manolakos and Papadakis, 2010). The concentrator allows increasing the efficicency of the PV while by cooling the cells; heat can be furnished to an attached ORC. Many researches are also led to combine solar with an ORC to drive reverse osmosis processes for water desalination (Karellas, Terzis and Manolakos, 2010) (Penate and Garcia-Rodriguez, 2011) (Nafey and Sharaf, 2010).
Systems combining ORC with fuel cells are as well investigated in order to recover heat from the electrolyte for additional power production (Sanchez et al., 2010) (Zhao et al., 2011). Furthermore, Al-Sulaiman, Dincer and Hamdullahpur did the analysis of a trigeneration plant based on solid oxide fuel cell and ORC (2009). In another domain, Schoenmaker, Rey and Pirota investigated a modified ORC using buoyancy force of a working fluid (2010).
The interest to combine compound parabolic concentrators with a Organic Rankine Cycle is to generate electricity by converting low-grade heat. In this idea, the working fluid choice is important in the design of the system. Chen, Goswani and Stefanakos investigated the different thermodynamics cycles and working fluids for the conversion of low-grade heat (2010) while Rayegan and Tao established a procedure to select working fluids for solar organic Rankine cycles (2010).
In 2008, Zhang and Li investigated the possibilities for a solar-heated generation system using CPC collectors in terms of storage capacities, thermal efficiencies and layout for the collectors. Later, Gang and Jie analysed the performances and efficiencies of a low temperature solar thermal electric generation system using regenerative ORC and CPCs (2010). Regarding Quoilin et al., they assessed the performances and performed design optimisation of a low-cost solar ORC for remote power generation (2011). On the other hand, a solar thermal ORC electric system with two stages collectors and heat storages units was proposed in 2011 (Gang and Jie). Finally, He and al. performed simulation of a parabolic through solar thermal power generation system with an ORC (2012). Figure 8 shows a schematic of the system proposed by He et al.
Figure - Schematic diagram of parabolic through SEGS system with ORC (From He and al., 2012, p. 632)
In order to achieve the objectives of this project, the following methodology will be applied. The project has been divided in four main groups, or set of tasks: Initiation, Modelling, Report and Seminar. For each of these groups, the different tasks and subtasks will be achieved in a chronological order.
The initiation determines the nature and the scope of the project. It starts with a pre-research on the subject considered. Once this pre-research is made, the objectives of the project can be established and a schedule is built. Then, researches are made on the subject to state the background of the project and the literature review. An intermediate report or pilot-study is written.
During this phase of the project, the functions or parts of the model to establish are implemented in Matlab. The first task consists to capture and organise the data needed for the model. Then, the functions corresponding to the calculations of the energy demand, the CPC collector heat absorption and the ORC are implemented. Each of the function must be tested and adapted to fit the program structure. A central function centralised the results and managed the calculation process. The system is then optimised as well. Finally, an interface allows a better use of the model.
When the model has been established and its running gives satisfactory results, the report of the project can be written. In this part, it is important to state the frame of the project, the assumptions made and the model developed. The simulations and their results are presented. It is followed by a discussion of the results and further work. The conclusion allows summarising the project and what has been achieved.
At the end of the project, a seminar allows showing to the colleagues the results and the key points of the project via an academic paper and a presentation. In this part, it is important to focus on the most relevant part of the project as the background, what has been achieved and the main results.
At this stage of the project, the initiation group of tasks including pre-research, project objectives, schedule, background and literature review as well as methodology has been achieved and are stated in this report. The second phase of the project, the modelling part, has been initiated and some results have been obtained. First of all, the structure of the program is shown on the Figure 9.
Figure - Structure of the program
The function Capture.m has been implemented and allows picking up the building environment data from an Excell file and sorts them in matrix which can easily be used in further calculation. A first version of the functions demand.m and CPC.m has also been implemented. The first one gives an overview of the heat which can be absorbed by the CPC collectors without taking into account the conductive losses. Figure 10 shows the gross result for the potential heat absorbed during the year per m² for every hour.
Figure - Heat absorbed by the CPC
The second one gives the energy consumption of the studied building in terms of electricity and heat, the cooling being ensured by electrical devices with a COP = 3. The temperatures have been maintained between 22°C and 24°C during the office hours considered in this case as 10 am to 10 pm. This result takes into account for the moment the losses through the envelope of the building except the ground slab. Figure 11 and 12 show respectively the electricity and heat demand through the year while Figure 13 shows the temperature evolution in the building.
Figure - Electricity demand
Figure - Heat consumption
Figure - Temperature in the building
Until the end of the project, a program giving a good overview of the proportion of the energy which can be supplied by a combined CPC-ORC system, using R245-fa as working fluid for the building considered in London can be obtained. The functioning conditions will be analysed and an optimum can be found. An assessment of the system efficiency can be processed in order to evaluate the relevancy to develop and install this kind of system in the London or similar climatic regions. This will be achieved through a report reviewing the principles and assumptions linked to the model developed as well as technological considerations.
The project has been planned by going in a first time through a project breakdown. In a second time, a Gantt chart has been built to organise accurately the project. The project breakdown and the Gantt chart are shown respectively in the Table 1 and on the Figure 14 below. A copy of the initial project planning is also included in the Appendix.
Literature review and background
Modelling Energy demand
Building energy demand
Results and discussion
Seminar article and presentation
The present report stated the background, the literature review, the objectives, the schedule, the methodology as well as the progression of the project at this stage. Some results have also been presented and an appraisal of what can be achieved until the end of the project has been stated. It gives an overview of the progression and evolution of this master thesis.
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