11:40
Session 17: Use of solar energy
Chair: Matthew Orosz
11:40
20 mins
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A NOVEL HYBRID SOLAR POWER GENERATION SYSTEM USING A-SI PHOTOVOLTAIC/THERMAL COLLECTORS AND ORGANIC RANKINE CYCLE
Jing Li, Pengcheng Li, Gang Pei, Jie Ji, Jahan Zeb Alvi
Abstract: A novel hybrid solar power generation system (HSPGS) is proposed. It mainly consists of photovoltaic/thermal (PV/T) collectors based on amorphous silicon (a-Si) cells, organic Rankine cycle (ORC), and inner-type heat storage unit. The PV/T collectors produce electricity directly via the cells, and the waste heat is carried away to the ORC for thermal power generation. Owing to the unique effect of thermal annealing, a-Si cells together with the ORC benefit from high temperature operation. Steady power generation is guaranteed by the heat storage unit. Compared with the conventional PV and solar ORC systems, the HSPGS can avoid or greatly reduce the usage of expensive battery, and has a much higher power efficiency. This work presents a close view of the HSPGS. Mathematic models are built and the system performance in the temperature range from 80°C to 150°C is estimated. Efficiency of about 12.5% can be achieved with a hot side temperature of 100°C.
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12:00
20 mins
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OPTIMISATION OF A DOMESTIC-SCALE SOLAR-ORC HEATING AND POWER SYSTEM FOR MAXIMUM POWER OUTPUT IN THE UK
James Freeman, Klaus Hellgardt, Christos Markides
Abstract: A model is presented of a domestic-scale solar combined heating and power (S-CHP) system, featuring an Organic Rankine Cycle (ORC) engine and a 15-m2 solar-thermal collector array. The system is configured for operation in the UK, incorporating high-efficiency non-concentrating solar collectors and an ORC working fluid buffer vessel to maintain continuous electrical power output during periods of intermittent solar irradiance. The solar collector array configuration and choice of ORC working fluid are examined, and the system electrical performance is optimised over an annual period of operation by simulating with London UK climate data. By incorporating a two-stage solar collector/evaporator configuration, a maximum net annual electrical work output of 1070 kWh yr-1 (continuous power of 122 W) and a solar-to-electrical efficiency of 6.3% is reported with HFC-245ca as the ORC working fluid and an optimal evaporation temperature of 126 °C. This is equivalent to ~32% of the electricity demand of a typical (average) UK home, and represents an improvement of more than 50% over a recent effort by the same authors based on an earlier S-CHP system configuration and HFC-245fa.
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12:20
20 mins
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IDENTIFICATION OF ORC PARAMETERS FOR OPTIMIZATION OF THERMAL STORAGE MEDIUM COST IN SOLAR ORC
Abhishek Kshirsagar, Pardeep Garg, Pramod Kumar, Matthew Orosz
Abstract: Organic Rankine cycle (ORC) provides the means to convert low grade energy to useful work in an efficient manner. The ORC system can be integrated with renewable energy source such as a concentrated solar thermal system using parabolic trough collectors. However, in case of solar ORCs, issues like fluctuating nature of solar insolation are reported to adversely affect the ORC performance. Thermal storage in this regard can help in suppressing the fluctuations and also provide an option for power generation during non-solar hours. Among the various possible thermal storage technologies, pebble bed system is found to be economical and hence, is studied in this paper in conjunction to ORC with two different working fluids in it.
This paper analyzes the effect of ORC working fluid on the cost associated with the pebble bed based thermal energy storage (PB-TES) tank. The physical layout considered here consists of two closed loops, a) heat transfer fluid (HTF) and b) working fluid loop. Cold HTF from a PB-TES is pumped to a parabolic trough collector where it gets heated and is then sent for the storage in a PB-TES tank. Working fluid loop is a regenerative ORC where the expander exhaust heat is recovered to heat up the pump outlet fluid. The two loops interact via a boiler where the HTF coming from a PB-TES tank is cooled and working fluid in turn is heated up to the expander inlet temperature. A case study of the above mentioned physical system is carried out using R-245fa and R-134a as working fluids for a 100 kWe ORC, with ethylene glycol (for temperatures up to 180 °C) or Therminol VP-1 (beyond 180 °C) as an HTF. DNI calculations are performed for the latitude corresponding to the tropic of Cancer (approximately mean of extreme latitudes of India) and the day of vernal equinox using ASHRAE clear sky model while using single axis tracking scheme for parabolic trough. Control strategy followed in the solar field is has been adopted to regulate HTF mass flow rate to achieve steady HTF temperature (also equal to HTF maximum temperature) throughout the day.
A procedure is developed to calculate the mass of HTF required in a PB-TES tank to suppress inlet temperature fluctuations in the expander. For a given energy storage, the temperature difference of HTF across the boiler and the mass of HTF stored in a PB-TES tank are found to be inversely co-related. This temperature difference is further found to be dependent on ORC working fluid. In case of R-245fa cycle, the temperature difference is~15 °C, whereas it can be as high as 75 °C for an R-134a transcritical cycle, with a pinch temperature of 5 °C in the boiler for the both cases. This affects the mass of HTF required in a PB-TES tank which is a major cost factor. In case of R-134a, cost of HTF is found to be ~5 times lower than that for an R-245fa system.
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12:40
20 mins
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ANALYSIS OF THERMAL ENERGY STORAGE SOLUTIONS FOR A 1 MWe CSP-ORC POWER UNIT
David Sánchez, Hicham Frej, Gonzalo S. Martínez, José María Rodríguez, El Ghali Bennouna
Abstract: Organic Rankine Cycle (ORC) power generation blocks have been principally used in the past couple of decades to recover medium grade heat from sources such as geothermal steam, biomass boilers and the exhaust of a realm of different industrial processes. In the past few years, a new philosophy of integrating thermal solar energy to an organic Rankine cycle has been assessed, the purpose of which is to develop a compact, water free and decentralized solution that offers the advantages of solar thermal power with low intermittency and the possibility to extend power generation to the night time at a relatively reasonable cost. To achieve these objectives, a proper storage system that is thermodynamically fit to the heat profile captured by the solar collector and to that of the power cycle must be identified.
This paper covers the selected criteria and the analysis done to identify the potential storage solutions adapted to a thermal solar – ORC system operating at temperature range between 170 C min and 300 °C max, while receiving energy in the form of sensible heat from the collector in order to eventually deliver it to a power organic Rankine cycle (ORC) that uses Cyclopentane as a working fluid. The system so developed will be integrated in the 1 MWe CSP-ORC facility based on Fresnel technology which is currently under construction at Iresen’s facilities in Morocco.
The paper covers the optimisation process carried out to best match the characteristics of the thermal Energy storage system to the features of the ORC power block. Two alternative solutions are looked into: sensible heat storage and latent (phase-change) heat storage. A parallel analysis is presented from a multiple fold perspective (technical, economic…) showing that both technologies have particular advantages.
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