REELCOOP project: developing renewable energy technologies for electricity generation

Transcription

1 12 th International Conference on Sustainable Energy Technologies (SET-2013) 26-29th August, 2013 Hong Kong Paper ID: SET REELCOOP project: developing renewable energy technologies for electricity generation Armando C. Oliveira 1,* and Bruno Coelho 1 1 Dept Mechanical Eng, University of Porto, Rua Dr Roberto Frias, Porto, Portugal * Corresponding acoliv@fe.up.pt ABSTRACT REELCOOP stands for REnewable ELectricity COOPeration and is a recently approved EU-FP7 project under the Energy 2013 call to develop renewable energy technologies for electricity generation. The REELCOOP project will address different technologies: photovoltaics, concentrated solar power, solar thermal and bioenergy. The impacts on the grid due to electricity generated by these technologies will also be assessed. Three REELCOOP prototypes using the different technologies will be built and tested,, representing both micro-scale (distributed) and large-scale (centralised) approaches to electricity generation. The decentralised systems will be a Building Integrated PV (BIPV) system - using ventilated façades to improve cell efficiency, and an ORC-CHP system driven by solar thermal and biomass. The centralised electricity generation system will be a small-size Concentrating Solar Power (CSP) plant, running with hybrid energy sources (solar/biomass). REELCOOP also aims to reinforce cooperation between EU and MENA countries. KEYWORDS: renewable energy, electricity generation, solar thermal, PV, CSP plant 1 INTRODUCTION REELCOOP is a recently approved EU-FP7 R&D project. It stands for REnewable ELectricity COOPeration and it addresses 5 renewable energy areas: photovoltaics (PV), concentrated solar power (CSP), solar thermal (ST), bioenergy, grid integration. The REELCOOP partners are: University of Porto (Portugal), University of Reading (UK), German Aerospace Centre (Germany), University of Évora (Portugal), Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (Spain), École Nationale d'ingénieurs de Tunis (Tunisia), Maroccan Institut de Recherche en Energie Solaire et Energies Nouvelles (Morocco), Yaşar University (Turkey), Onyx Solar (Spain), MCG Solar (Portugal), Termocycle (Poland), Soltigua (Italy), Zuccato Energia (Italy), Alternative Energy Systems (Tunisia), Centre de Développement des Energies Renouvelables (Algeria). The REELCOOP approach will be to develop decentralised (distributed) building integrated PV systems (BIPV) and ST micro-cogeneration systems, as well as centralised generation of electricity in combined (hybrid) solar/biomass power plants. This is in accordance with the EU SET-Plan approach of developing a European electricity grid able to integrate renewable and decentralised energy sources. BIPV systems have been increasingly used as a means to generate electricity on-site, and their diffusion will increase in the near future, taking into account the future EU regulation on nearly net zero energy buildings (ZEB). The ZEB concept usually requires on-site electricity generation and sale to the electrical grid. Systems that will enhance electrical efficiency and reduce cost will be considered. ST micro-cogeneration may combine solar and biomass energy sources, as a means of achieving the best competitiveness with, for instance, PV systems. Organic Rankine Cycles (ORC) driven by solar thermal collectors coupled to biomass/biogas boilers will be developed, and the use of different micro-turbine types will be taken into consideration, in order to achieve the best efficiency and the lowest costs. The use of cogeneration, with the production of useful heat, will maximise system efficiency and reduce the cost per kwh of useful energy. This also complies with the EU Directive on the Promotion of Cogeneration (2004/8/EC), [1]. The combination of solar and biomass (waste) sources in CSP centralised plants will allow maximisation of plant operating time, contributing to lower electricity production costs. This has been demonstrated by previous simulation work, [2], and will be experimentally demonstrated during REELCOOP. Three prototype systems will be developed and tested in REELCOOP, based on different technologies, and with the goals presented in Table 1. The 3 systems are representative of both micro-scale (distributed) and large-scale (centralised) approaches to electricity generation: prototypes 1 and 2 are representative of typical micro-generation systems, while prototype 3 is representative of a large-scale power plant on a reduced scale. The 3 systems to be built in REELCOOP project are: 1. BIPV: 6 kw integration of PV modules into ventilated façades (decentralized electricity generation for new buildings or major refurbishments); 2. ORC-CHP: 6 kw solar thermal and biomass organic Rankine cycle combined heat and power system (decentralized electricity generation for existing or new buildings); 3. CSP: 60 kw hybrid biomass / concentrated solar power parabolic trough with direct steam generation (centralized electricity generation).

2 Table 1. Target characteristics of REELCOOP prototype systems. Prototype system Energy sources Electricity output a 1- BIPV solar 6 kw 2- ORC-CHP solar thermal/biomass 6 kw Overall efficiency b 15% Levelised electricity cost 10% c /kwh e /kwh e d 3- CSP plant solar/biomass 60 kw 10% /kwh e a nominal useful output b average, source(s) to electricity c electrical only not including heat output d only additional cost above heat production cost The environmental sustainability and economics of the prototype systems will be assessed by means of Life Cycle Assessment studies, and the results obtained will be disseminated to industry and research, as proof-of-concept of renewable electricity generation solutions. Grid integration will also be assessed and developed. Apart from the main technical objectives given above, further major objectives of the REELCOOP project are listed below: Improvement of PV cell technology with respect to efficiency and cost; Improvement of BIPV operation under real-life situations with lower electricity costs; Improvement of micro ORC-CHP system efficiency, using high efficiency solar collectors and micro-turbines, with lower electricity costs; Improvement of CSP plant operation with lower electricity costs; Testing of prototype systems both in the lab and in field trials under real-life context to improve the whole-system design and operation; Economic assessment and investigation of spin-off opportunities into related market sectors; Dissemination of information to industry and research, both in EU and Mediterranean Countries (MENA region), via a regularly updated website as well as publications and presentations at relevant conferences / seminars; Development of exploitation routes for bringing improved technologies to market; Strengthening of the European and MENA position in the technological fields involved. 2 PROTOTYPE DESCRIPTION This section describes the principles of the 3 prototype systems to be developed in REELCOOP: system 1 BIPV: decentralised electricity generation for new buildings or major refurbishments; system 2 ORC-CHP: decentralised electricity generation for existing or new buildings; system 3 CSP: centralised electricity generation. 2.1 SYSTEM 1 BIPV System 1 is based on the integration of PV modules into ventilated façades. The use of two different types of solar cells will be considered: commercially existing c-si cells and Dye-sensitized Solar Cells (DSCs). DSCs are able to convert both direct and diffuse light, which makes them highly adapted to cloudy or dusty weather. Additionally, DSCs are semi-transparent, with various possibilities of colours and diverse patterns, being aesthetically pleasant. They are scalable to large size cell application and with an optimized distribution of the active areas. DSCs are also less sensitive to temperature, enabling a stable efficiency for a temperature range up to 80ºC. The DSC photovoltaic element uses mainly organic raw-materials (non-toxic and cheap) and spends less energy during the manufacturing process than conventional PV technologies. Due to the low manufacturing cost, DSC cells have a very interesting application in BIPV, being able to significantly reduce the electricity cost (LEC). Presently, DSCs have an efficiency around 12 % up to temperatures of 70-80ºC; in fact, their efficiency increases from ambient temperature up to 70-80ºC. In the REELCOOP prototype, the PV module is cooled by outdoor air flowing in both front and rear surfaces, increasing the electrical efficiency of c-si cells, which decreases with temperature increase. Recent testing as shown that an increase in efficiency of about 10% is expected, compared to an enclosed building integrated PV module, [3]. DSCs can be installed in windows, but if placed in a ventilated façade, they may operate at higher temperature, thus increasing their efficiency. Air ventilation also allows to limit the maximum temperature level. This temperature control is particularly important in MENA countries, where cell temperatures are potentially very high, due to high ambient temperature and solar radiation levels. System 1 (BIPV) is schematically shown in Figure 1 and will be installed and tested in a real building in Turkey. 2.2 SYSTEM 2 ORC/CHP The ORC-CHP system is driven by solar thermal collectors and an auxiliary biomass boiler, allowing cogeneration of electricity and heat. The system can be applied both to new or existing buildings. The power circuit of Figure 2 (Rankine cycle) uses an organic refrigerant as working fluid, like methanol, n-pentane, or others, [4]. Thus, it uses a CFC-free refrigerant with no ODP or other environmental adverse effects. The solar collector circuit uses evacuated tube or low-concentrating (CPC) solar thermal collectors, providing heat at temperatures above 150ºC, able to boost system efficiency. The system uses an auxiliary boiler running on biomass. Therefore, it may be a totally renewable energy system. A minor electricity consumption for pumps may

3 come from the electrical grid or solar PV. As the ratio of system output heat to power is moderately high, in the range of 8 to 9, the system is most adequate for buildings where a larger consumption of heat occurs, either in the residential, commercial or industrial sectors. Therefore, the system may also contribute to supply/replace traditional HVAC systems. Cooling needs may be supplied through thermal heat pumps, using output heat from the CHP system. REELCOOP prototype system 2 is presented in figure 2 and will be installed and tested in Morocco. The interest of the system comes from the fact that, despite its moderate electrical efficiency, only additional (initial and operating) costs are needed, by reference to a conventional system providing the same amount of heat. In order to compete with decreasing costs of solar PV systems, an ORC-CHP system needs an efficient micro-turbine. Beyond conventional centrifugal turbines, new micro-turbine types have been developed and applied in recent years, such as scroll, screw or gas engine expanders. High efficiency expanders, specially adapted to ORC cycles/refrigerants will be used with isentropic efficiencies in the range of 75 to 80% are now feasible, with further advantages of modularity, small vibration and noise levels. glazing indoor space PV module ventilated façade outdoor air Fig. 1 Schematic representation of a BIPV system integrated in a ventilated façade prototype 1. Fig. 2 Schematic representation of REELCOOP prototype system 2.

4 2.3 SYSTEM 3 CSP CSP is, due to its electricity dispatchability possibilities, one of the most promising centralized electricity generation technologies. One of the CSP technologies with great acceptance by the investors is the conventional parabolic trough, with 2275 MW in operation worldwide, and an additional 2062 MW in construction and a further 4185 MW planned [5], with typical sizes of 25 and 50 MW. All these power plants use thermal fluids as heat transfer fluids (HTF), circulating in the parabolic collector and exchanging heat in a downstream boiler, which generates steam to run the power cycle (Figure 3a). A new perspective is to generate steam directly at the solar field, eliminating the need of thermal oils (Figure 3b). a b Fig. 3 Schematic representation of a parabolic trough CSP plant: conventional (a) versus direct steam generation (b), [adapted from 6]. Fig. 4 Schematic representation of REELCOOP prototype system 3. Solar direct steam generation has several advantages such as improved efficiency and lower investment costs, mainly for large systems. On the other side, the main technological problems are the receiver tube performance and durability, the pressurized storage of steam for long periods and the power plant overall behaviour during solar transients. For smaller prototypes it is an innovation to generate superheated steam and the use of small saturated steam turbines presents a technological challenge. System 3 will use parabolic trough concentrating solar collectors for direct steam generation. Energy backup will be provided by a biogas boiler and a storage device. The biomass digestor will be fed by organic waste locally available contributing to the improvement of environmental and living conditions for the population. Energy storage is essential for CSP power plant operation and has higher efficiency and lower costs than conventional electricity storage solutions. Hybridization with bioenergy will eliminate the need for large storage devices to extend power plant operation during the night. There is however the need for storage to compensate the biomass boiler start-up and short transients from solar power. The combination of solar and bioenergy sources in CSP power plants will allow maximisation of plant operating time, contributing to lower electricity production costs. The consortium objective is to build a fully hybrid prototype, with high solar share (over 30%),

5 high conversion efficiencies for both solar and biomass parts, and a large capacity factor, up to 24 hours/day of operation. Prototype system 3 (CSP) is presented in Figure 4 and, after development and design, will be installed and tested in Tunisia. 3 CONCLUSION REELCOOP will develop 3 different systems of renewable electricity generation, all involving improvements or innovations compared to existing technologies. Novel DSC solar cells will be developed and tested, and compared with c-si cells in terms of efficiency and cost, with tests in ventilated façades in a real building; novel vacuum-cpc solar collectors for medium temperature applications will be developed and integrated with high efficiency expanders for ORC-CHP systems; parabolic trough CSP systems with direct steam generation will be developed and tested, using a novel storage solution and hybridized with biomass to increase capacity factors and reduce levelized electricity costs. The REELCOOP project will start in September 2013 and will end in September The 3 presented prototypes will be ready for installation during 2015, with field testing starting in ACKNOWLEDGMENTS The REELCOOP project will receive funding from the European Union Seventh Framework Programme (FP7/ ), under grant agreement nº The authors are also grateful to all the partners for their participation in REELCOOP and to the Calouste Gulbenkian Foundation for grant ref REFERENCES [1] EU Commission, Directive 2004/8/EC on the Promotion of Cogeneration Based on a Useful Heat Demand in the Internal Energy Market, Official Journal of the European Union, [2] Coelho, B.; Schwarzbözl, P.; Oliveira, A.C.; Mendes, A.M., Biomass and Central Receiver System (CRS) Hybridization: Volumetric Air CRS and Integration of a Biomass Waste Direct Burning Boiler on Steam Cycle, Solar Energy 2012, 86 (10), [3] SolarWall website, (accessed on 7 September 2012). [4] Facão, J.; Palmero-Marrero, A.; Oliveira, A.C., Analysis of a Solar Assisted Micro-Cogeneration ORC System, Int J Low Carbon Technologies 2008, 3 (4), [5] CSP today, CSP Today World Map 2012, (accessed on 4 July 2012). [6] Pitz-Paal, R.; Dersch, J.; Milow, B., ECOSTAR roadmap document, DLR 2005.