Solar Rankine Research Articles

A comparative study of pure and zeotropic mixtures in low-temperature solar Rankine cycle

The paper presents an on site experimental study of a low-temperature solar Rankine cycle system for power generation. The cycle performances of pure fluid M 1 (R245fa) and zeotropic mixtures M 2 (R245fa/R152a, 0.9/0.1) and M 3 (R245fa/R152a, 0.7/0.3) are compared, respectively, based on the experimental prototype. The experiments have been conducted under constant volume flow rate of different fluids. The results show that, with the component of R152a increasing, the system pressure level increases and the power output varies accordingly, which provides an additional means of capacity adjustment. The collector efficiency and thermal efficiency of zeotropic mixtures are comparatively higher than pure fluid of R245fa in the experimental condition, which indicates that zeotropic mixtures have the potential for overall efficiency improvement. Due to the non-isothermal condensation of zeotropic mixture, the condensing heat could be partially recovered by adding an external heat exchanger. Thus, compared with pure fluid R245fa the system overall efficiency of zeotropic mixtures could be improved.

Performance evaluation of a low-temperature solar Rankine cycle system utilizing R245fa

A low-temperature solar Rankine system utilizing R245fa as the working fluid is proposed and an experimental system is designed, constructed and tested. Both the evacuated solar collectors and the flat plate solar collectors are used in the experimental system, meanwhile, a rolling-piston R245fa expander is also mounted in the system. The new designed R245fa expander works stably in the experiment, with an average expansion power output of 1.73 kW and an average isentropic efficiency of 45.2%. The overall power generation efficiency estimated is 4.2%, when the evacuated solar collector is utilized in the system, and with the condition of flat plate solar collector, it is about 3.2%. The experimental results show that using R245fa as working fluid in the low-temperature solar power Rankine cycle system is feasible and the performance is acceptable.

Analysis of zeotropic mixtures used in low-temperature solar Rankine cycles for power generation

This paper presents the analysis of low-temperature solar Rankine cycles for power generation using zeotropic mixtures. Three typical mass fractions 0.9/0.1 (Ma) 0.65/0.35 (Mb), 0.45/0.55 (Mc) of R245fa/R152a are chosen. In the proposed temperature range from 25 °C to 85 °C, the three zeotropic mixtures are investigated as the working fluids of the low-temperature solar Rankine cycle. Because there is an obvious temperature glide during phase change for zeotropic mixtures, an internal heat exchanger (IHE) is introduced to the Rankine cycle. Investigation shows that different from the pure fluids, among the proposed zeotropic mixtures, the isentropic working fluid Mb possesses the lowest Rankine cycle efficiency. For zeotropic mixtures a significant increase of thermal efficiencies can be gained when superheating is combined with IHE. It is also indicated that utilizing zeotropic mixtures can extend the range of choosing working fluids for low-temperature solar Rankine cycles.

Technical and economic comparison between PV-RO system and RO-Solar Rankine system. Case study: Thirasia island

This paper presents the technical characteristics as well as an economic comparison of two autonomous desalination systems. The first system concerns the laboratory experimental results of a direct coupled PV-SWRO desalination system without batteries equipped with a hydraulic energy recovery device of the Clark pump type. The PV system consists of 18 Arco-Solar monocristaline PV panels, with total peak power of 846 W. These panels are directly connected to a brushless DC motor of 510 W, powering a rotary vane pump as low pressure pump. The clark pump utilizes the high pressure brine to intensify the feed pressure to the RO desalination system. The desalination system has a capacity of 0.1 m 3/h. The specific energy recovery of this system has been experimentally found to be in the range of 3.8–6 kWh/m 3 depending on the feed water temperature and the feed water salinity. The second system is an organic solar Rankine system for RO desalination. The heat produced by the solar collectors’ field is transformed to mechanical power through an organic Rankine cycle process. The shaft power produced drives the high pressure pump of the RO unit, initiating the desalination process. The prototype system consists of vacuum tube solar collectors 90 m 2, a Rankine engine of 100 kW and an RO unit of 0.3 m 3/h. The energy recovery system of the RO unit consists of a pair of axial piston pumps (APP) manufactured by Danfoss. One of them operates reversely, as turbine, exploiting the hydraulic energy of the brine stream. The aim of the economic analysis is not only to estimate the cost of each system but also to compare them on the same basis, in order to allow a meaningful comparison. Hence, each system cost is determined having utilised the same economic assumptions like interest, operating expenses, etc. Moreover, these desalination systems can provide sufficient amounts of potable water for the local needs of a small island, like Thirasia, (Cyclades, Greece) at a cost as low as 7.77 ɛ/m 3, very close to that of water hauling.

Experimental study on the performance of solar Rankine system using supercritical CO 2

An experimental study is carried out to investigate the performance of a solar Rankine system using supercritical CO 2 as a working fluid. The testing machine of the solar Rankine system consists of an evacuated solar collector, a pressure relief valve, heat exchangers and CO 2 feed pump, etc. The solar energy powered system can provide electricity output as well as heat supply/refrigeration, etc. The system performance is evaluated based on daily, monthly and yearly experiment data. The results obtained show that heat collection efficiency for the CO 2-based solar collector is measured at 65.0–70.0%. The power generation efficiency is found at 8.78–9.45%, which is higher than the value 8.20% of a solar cell. The result presents a potential future for the solar powered CO 2 Rankine system to be used as distributed energy supply system for buildings or others.

Design of an autonomous low-temperature solar Rankine cycle system for reverse osmosis desalination

The present paper regards the design outline, of a low temperature solar organic Rankine cycle system for reverse osmosis (RO) desalination. The thermal processing taking place is described briefly below: Thermal energy produced from the solar collectors array evaporates the working fluid (HFC-134a) in the evaporator surface, changing the fluid state from sub-liquid to super heated vapour. The super-heated vapour is then driven to the expanders where the generated mechanical work produced by the processing drives the high pressure pump of the RO unit, circulation pumps of the Rankine cycle (HFC-134a, cooling water pump), and the circulator of the collectors. The saturated vapour at the expanders' outlet is directed to the condenser and condensates. HFC-134a condensation is necessary in the Rankine process. On the condenser' s surface, seawater is pre-heated and directed to the seawater reservoir. Seawater pre-heating is applied to increase the fresh water recovery ratio. The saturated liquid at the condenser outlet is then pressurised by the HFC-134a pump. Specific innovations of the system are low temperature thermal sources can be exploited efficiently for fresh water production; solar energy is used indirectly and does not heat seawater; the RO unit is driven by directly mechanical work produced from the process; the system condenser acts as sea water pre-heater and this serves a double purpose; (1) increase of feed water temperature implies higher fresh water production, (2) decrease of temperature of “low temperature reservoir” of Rankine cycle implies higher cycle efficiencies. Such a system can be an alternative to PV-RO systems, while low temperature energy sources like thermal wastes may be used for RO desalination. Based on the design results, a prototype installation is going to be realised.

A new concept for integrating a thermal air power tube with solar energy and alternative, waste heat energy sources and large natural or man-made, geo-physical phenomenon

A method for power generation combining a solar concentration system and a pneumatic power tube system in a large open pit is described. Solar energy is concentrated by a plurality of heliostat mirrors placed along the embankment of the pit, which tends to be spherical in contour. The pneumatic tubes recover waste heat energy from the solar Rankine power cycle system and from a variety of sources that originate from or are in close proximity to the very deep, man-made open-pit mine or from other naturally occurring geo-physical chasms. The man-made or naturally formed chasms provide structural support for the pneumatic power tubes. The air in the tubes is heated by the recovered waste energy, and in so doing, its density is sufficiently reduced so as to produce air drafts from which mechanical power can be recovered from wind turbines and converted into electrical power by suitable electric generators. The deep chasms can be from a man-made phenomenon such as commissioned, open-pit mines or from naturally occurring fissures in the earth. The waste heat can be from solar energy, ground source energy or products of combustion from waste products that are to be mitigated or destroyed. The concept is novel in its integration of a solar powered heat engine with recoverable waste heat via the proposed pneumatic power tube as well as in the means of structural support that the geo-physical phenomenon provides and the modularity (for ease in manufacturing and installation) that makes the pneumatic power tube economically viable. The complete system uses state-of-the art wind turbine power recovery, solar reflective surfaces for solar energy collection, heat pipe arrays for ground source heat recovery, and air diffuser subsystems for enhanced wind turbine efficiency.

Study of Phase Change Steam Accumulator and Application to Solar Rankine Cycle System.

Since fossil fuel like petroleum, coal, and natural gases will sooner or later run out in this or next century, natural energy like solar, wind, and biomass will rise as one of alterative energy sources. Most of the conventional solar thermal electric systems utilize high-temperature difference. In the present paper, an advanced solar Rankine cycle system with CPC (Compound Parabolic Concentrator) collector and steam accumulator of phase-change type is newly proposed. The phase-change steam accumulator with high temperature phase change material (PCM) is designed and evaluated both experimentally and theoretically. And this paper reports experimental results of the proposed system under actual solar radiation and under heat stored accumulator condition.

Study on Solar Rankine Cycle Engine of Displacement-type.

Most of the past solar-powered heat engines have been aiming at operating under very high temperature and high pressure. For example, solar Stirling engine is operated at over 700∼800 degrees Celsius and at high pressure exceeding 10MPa. However, in order to obtain such a high temperature and high pressure condition, concentrating collector with large concentration ratio is inevitable. Also sun tracking device was compulsory to achieve high thermal efficiency. This direction requires high cost of the product, and brings low thermal efficiency, which loses competitiveness in the solar market. In this article, the unique solar Rankine cycle engine using displacement-type scroll expander is proposed. The proposed solar Rankine cycle engine has the following features ; 1) The system consists of very simple components similar to the airconditioner. 2) The operational temperature is very low (100∼300°C). 3) The thermal efficiency based on solar radiation is supposed to be about 15%, which is at least twice the conventional photovoltaic (PV) system.

On the optimization of solar-driven refrigerators

The thermodynamic optimization of a solar driven refrigerator, that is, a refrigerator driven by use of the solar Rankine power cycle, is studied in this paper. The system is totally irreversible, i.e. externally and internally irreversible. The effect of the operating conditions on the overall efficiency of the system is evaluated.

Performance of low temperature solar rankine power generation system

The overall performance of a solar thermal electrical power generation system is governed by the performance of the energy collection system and the power conversion unit. Any system operating under given meteorological and solar radiation conditions has a unique energy collection temperature for which the electrical output of the system will be a maximum. An engineering analysis of the system was carried out to obtain general correlations which can be used for determining such an optimum temperature. Factual experience on the design and operation of a Rankine system, using flat plate collectors and the climatological data, was used to obtain numerical estimates for the net energy conversion capability of such systems operating in Kuwait.

Potentialities of the solar-operated rankine engine

Small-capacity solar Rankine engines can operate at low and medium temperature ranges. The performance of this engine depends basically on the collector subsystem, the working fluid and the type of expander. The problems and potentialities of different alternatives of these items are discussed. Three working fluids, toluene, Fluorinol-85 and steam, were selected to examine the performance of the Rankine engine and its potentiality in the medium temperature range (150–350°C). Four types of parabolic trough solar collectors, available in the international market, were considered in this analysis. It was concluded that steam provides the best option while FL-85 still has good advantages. Extensive efforts are needed to find the most suitable expander for this system.

Development and test of solar Rankine cycle heating and cooling systems

This paper describes the design, fabrication and test of a prototype 63.3 kW (18 ton) solar-powered Rankine cycle heat pump, as well as the assembly and field test of a 63.3 kW (18 ton) solar powered chiller.

Second-generation parabolic trough solar energy systems optimization analysis

In the near future high-efficiency, low-cost, parabolic trough collectors will probably become available. The economic feasibility of these parabolic trough solar-energy systems is affected by many parameters which include component cost, load shape, fraction of the load supplied by solar energy, average temperature of the collector field and its axis of rotation, and for solar Rankine cogeneration systems, the electrical-to-thermal energy output ratio. The sensitivity of economic feasibility and system design to changes in these and other relevant parameters is discussed. System design and economics generally were found to be sensitive to component cost. They were also found to be quite sensitive to some of the other parameters in restricted ranges.

Optimum working fluids for solar powered Rankine cycle cooling of buildings

The results of an investigation of possible working fluids suitable for the solar Rankine cycle cooling of buildings are presented. The Underwriter's safety requirements, system operating reliability and fluid thermal stability were the primary factors used in the screening process. Although minimum development problems would appear to exist when using steam, a low power level, multi-stage turbine, having a high degree of superheat, would run at excessive shaft speed resulting in high turbine disc stresses. In addition, the machine would be delicate, expensive, and require tight tolerances thereby complicating its manufacture. Moreover, the presence of two-phase flow in its bearings would cause erratic operation. Water is therefore considered to be an unsuitable fluid for such systems. Among the various organic fluids considered, including those proposed for various prototype developments presently in progress, only the halocarbon compounds R-11, R-113 and R-114 and the fluorinert compounds FC-75 and FC-88 satisfied safety requirements. Their two-phase pressure drops per unit length, mean two-phase heat transfer coefficients and maximum allowable heat flux were determined for Reynolds numbers of 10,000 to 120,000 at an average, fully-developed, liquid-phase velocity of 1.22 m/sec, and 16.6 mm inside tube diameter. A preliminary assessment based on these results, and those available of static, thermal stability tests together with the values of the vapor pressures in the condensing temperature range and the boiling points is presented. It indicates that R-113 followed by FC-88 are the most suitable fluids for such application. A final assessment however, should be based on dynamic thermal stability tests, where boiling, condensing and other stresses are imposed on the fluids.

Current costs of solar powered organic Rankine cycle engines

Solar energy can be used to heat and cool buildings, drive irrigation pumps, make electrical power, desalt sea water, and, in general, reduce energy demands on conventional energy sources. The organic Rankine cycle engine will play an important part in the conversion of solar energy to useful shaft power. Technical feasibility is here now, as shown by several demonstration projects; however, economic feasibility may be some years away. This paper addresses the technical and cost aspects of the organic Rankine cycle and its interaction with the solar collector as a power system. The efficiency and practical considerations of the combined collector and Rankine system show that collector temperatures of 93°C (200°F), 150–200°C (300–400°F), and 315°C (600°F) are optimum operating conditions for flat plate, concentrators, and tracking concentrators respectively. The peak solar conversion efficiencies of these systems are approximately 5, 10 and 11 per cent respectively. When comparing the cost of solar power systems, it is shown that the dominant factor in the system cost is the collector cost. It is estimated that in a production unit the Rankine cycle cost will be approximately one-third of the total system cost with two-thirds going to the collector component. Consequently, low-cost collectors are crucial for commercialization of solar Rankine systems. It is estimated that the installed cost of mass produced solar power systems would be in the neighborhood of $1600–$2500/peak kW output. These values do not relate to a solar cooling system since not all the collectors are charged to the cooling system; hence, the relevant cost comparison is the production costs of the Rankine and the absorption cooling systems. Therefore, the conclusions presented here relate primarily to power systems. Solar power systems are technically feasible now; however, when will they be economically feasible? It is this author's opinion that this will occur when there is no other alternative, which may not be long in coming. When this time does arrive, the organic Rankine engine is available to convert the Sun's heat into useful power.

Flat-plate solar-collector performance evaluation with a solar simulator as a basis for collector selection and performance prediction

The use of a solar simulator for performance determination permits collector testing under standard conditions of wind, ambient temperature, flow rate and sun. The performance results determined with the simulator have been found to be in good agreement with outdoor performance results. The measured thermal efficiency and evaluation of 23 collectors are reported which differ according to absorber material (copper, aluminum, steel), absorber coating (nonselective black paint, selective copper oxide, selective black nickel, selective black chrome), type of glazing material (glass, Tedlar, Lexan, antireflection glass), the use of honeycomb material and the use of vacuum to prevent thermal convection losses. The collectors were given performance rankings based on noon-hour solar conditions and all-day solar conditions. The determination with the simulator of an all-day collector performance was made possible by tests at different incident angles. The solar performance rankings were made based on whether the collector is to be used for pool heating, hot water, absorption air conditioning, heating, or for a solar Rankine machine.