Report
Teaser, summary, work performed and final results
Periodic Reporting for period 1 - a-Si PVT-ORC (A novel amorphous silicon cell-based solar cogeneration system using the coupled thermal storage/organic Rankine cycle as an alternative to battery)
Teaser
The organic Rankine cycle (ORC) is a technology for low-grade heat to power conversion. Solar thermal power generation is one field of application for the ORC. Solar ORC can be driven by vacuum-tube or low-concentration solar collectors, and is applicable in the regions...
Summary
The organic Rankine cycle (ORC) is a technology for low-grade heat to power conversion. Solar thermal power generation is one field of application for the ORC. Solar ORC can be driven by vacuum-tube or low-concentration solar collectors, and is applicable in the regions without rich direct radiation resource. Photovoltaic/thermal(PV/T) technology is another way to utilize solar energy. A PV/T module can provide more energy than a sole PV module. The heat captured from the PV/T module helps to accelerate the return on investment. Notably, cooperation of the two technologies will be beneficial. To achieve this, a PV/T collector can be operated at a higher temperature, at which heat collected and stored can be used to drive the ORC when required. Combination of low-cost thermal storage and ORC will be a more economical and environmentally-friendly alternative to battery. Water is an ideal working fluid for thermal storage in the temperature range below 150°C.
The a-Si PVT-ORC system has the potential to be more cost-effective than sole PVT or solar ORC systems. Compared with the c-Si PVT system, it has additional power output (WORC) but more initial investment on ORC and heat storage. The cost of water storage shall be small. The ORC working at about 120°C is already commercialized in the fields of geothermal power generation and waste heat recovery, and the payback period is expected to be less than 5 years. The a-Si PVT-ORC system has an overall electrical efficiency close to that of c-Si PVT at 75°C, which is about 12.8% as shown subsequently. Particularly, it is resilient via thermal storage, and expensive battery is eliminated or greatly reduced. Compared with a sole solar ORC system, the a-Si PVT-ORC system has the integrated PVT collector to provide heat for the ORC, and this will make solar ORC more cost-effective regarding the highly increased solar power efficiency.
The project aims to investigate a medium temperature photovoltaic/thermal (PVT) system incorporated with the coupled thermal storage/organic Rankine cycle (ORC) as a novel alternative to battery. The overall scientific objectives are: (1) Experiments of a-Si cell performance and its stability at the temperature up to 150°C. (2) Prototype development of a-Si PVT collector for medium-high temperature application. (3) Feasibility demonstration of fast prototyping of small scale turbine by 3D printing technology. (4) Modelling of a-Si cell, PVT collector, ORC, and the whole system. (5) Economic and environmental assessment of the a-Si PVT-ORC system.
Through the development of the project, it is concluded that the a-Si PV/T system is technically feasible and promising especially in tri-generation applications.
Work performed
W1: Experimental investigation on the performance of the a-Si cells for medium-high temperature applications has been conducted. The experimental results show that the fill factor (FF) of the a-Si cells is about 56%-57%. The preliminary tests indicate that the a-Si cells shall be able to keep an acceptable efficiency when used in the medium temperature application without technical failure.W2:In March 2017, an a-Si PV/T system was constructed. It was the first time that a-Si cells deposited on stainless steel was used in a practical PV/T system. Preliminary outdoor experiments were conducted and no significant degradation on cell performance or technical failure has been observed over one year operation. The feasibility of the a-Si PV/T technology was demonstrated accordingly. Meanwhile, the constructed collector (1100 mm×820 mm) was designed to be smaller than a common c-Si PV/T collector to reduce the risk of electric conduction between the stainless steel and the aluminum absorber. The thermal performance of the first prototype was expected to be low due to its small size. Following the success of the first prototype, a new a-Si PV/T system with a standard dimension of 1950 mm × 950 mm was recently developed with enhanced thermal and electrical performances. Long term (>1 year) tests have been carried out on the system.W3: A prototype of ORC turbine wheel was produced by 3D printer. The feasibility of ORC turbine partially produced with the assistance of 3D printer has been demonstrated. Parametric optimization of the ORC expander using the semi-empirical models and CFD simulation on the ORC expander have been conducted. The results indicate that the developed mathematical models have an acceptable accuracy.W4 : The a-Si PVT-ORC system consists of the PV/T collector and ORC. The thermal energy output from the PV/T is the input for the ORC. Modelling of the solar ORC system has been carried out. Aside from the modelling of the ORC system, distributed parameter models for the a-Si PV/T collectors have been established. W5: Economic estimation has been conducted. It is shown that even at a temperature as high as 250oC, water is more cost-effective than thermal oil in the solar ORC system applications. The horizontal pressure vessels appear to save more material of steel than the vertical ones. And the total occupied mass tends to decrease with the decrement in the vessel diameter. Multi-vessels functioning in parallel can effectively reduce the device length. Further investigation indicate that the expanders in a tandem configuration is more suitable for large volume ratio situations. Compared with the cascade steam-organic Rankine cycle system, the tandem system has simpler structure, easier control strategy and lower technical requirements, less operating and maintenance fees, more stable power output and higher security. The hybrid PV/T-ORC systems have an advantage over conventional s-ORC and PV systems. It is proved that the proposed a-Si PV/T-ORC system is more environmentally friendly. W6: Since the project started, 9 papers have been published in the prestigious journals as follows. 3 more papers have been submitted to the journals for possible publication. All the papers have acknowledged this MSCA project. 4 patents applications have been submitted. As the organising committee, panel member, scientific committee or presenter, Dr.Li has participated in 7 conferences/seminars. More than 12 academic visits/meetings have been implemented.
Aside from the above work packages as agreed in the Annex 1 to the Grant Agreement, additional works have been done during the reporting period.
Final results
The project has achieved its objectives.Experiments on a-Si cells deposited on stainless steel have been implemented;Four prototypes of a-Si PVT collectors have been developed;Technical feasibility of turbine wheel manufactured by 3D printing technology has been demonstrated; Mathematical models of a-Si cell, PVT collector, ORC, and the whole system have been established;Distributed parameter models have been built to predict the performance of a-Si PV/T system in the medium temperature range; Economic and environmental assessments of the a-Si PVT-ORC system have been carried out. Aside from the above objectives/deliverables/milestones, additional achievements have been made. In particular, a novel approach to the thermal storage through two-step heat discharge has been devised. In regard to the potential for solving the storage problem that is currently restricting the development of DSG technology, this approach is believed to be a scientific breakthrough and may have a significant impact.