Solar Organic Rankine Cycle Research Articles

Estimation of the Solar Organic Rankine Cycle System Technology Potential in Developing Countries

The use of a solar organic Rankine cycle (ORC) system in small-scale power generation has attracted recent interest for powering rural areas in developing countries. The technology uses a parabolic trough solar thermal collector, heat exchangers and scroll expanders (for the expansion process) coupled with a generator for electricity production. This paper describes the solar potential for the ORC systems in South Asian countries with different working fluids to fulfill the present and future energy demands of these countries. The solar potential for the ORC system has not been assessed appropriately in earlier studies. The solar potential includes the geographic and technological potential for ORC system power generation. In addition, this paper discusses the existing energy policies of South Asian countries. These policies provide the major motivation and interest for the development and use of solar ORC technology. This article shows that solar ORC technology can meet the energy needs of rural areas of South Asian countries and can provide a sustainable energy base.

A small-scale solar Organic Rankine Cycle power plant in Thailand: Three types of non-concentrating solar collectors

Power generation from solar energy is one of many alternative ways to solve the current energy crisis and environmental problems affecting our world. In this study, a system that utilizes low-temperature heat (under 100 °C) from solar energy to generate electricity by a small-scale Organic Rankine Cycle system is proposed. The system is analyzed using three different capacities of the ORC system with R-245fa (20, 40 and 60 kWe) in combination with solar water heating system (SWHS), using four different models (SORC-I, SORC-II, SORC-III, and SORC-IV). Compound parabolic concentrator (CPC), evacuated-tube and flat-plate collectors were used to generate heat with optical efficiency (FR(τα)e) of 0.72, 0.57, 0.74, overall heat transfer coefficient (FRUL) of 0.97, 0.75, 3.62 W/m2-K, and collector area of 2.16, 2.37, 2.08 m2 per unit, respectively. The maximum power output, the CO2 emission, and the economic analysis in terms of levelized cost of electricity (LCOE) were evaluated by a mathematical model. The weather data from Bangkok, a representative city in the central part of Thailand, was used for simulations. The simulation results shown that, if the number of collectors is the same on all systems, the system can produce the highest power output when combined with the CPC collectors. In terms of the economic analysis, the 60 kWe ORC system has the lowest LCOE value of 0.20 USD/kWh if coupled with 950 units of evacuated-tube collectors without initial investment of the collectors into consideration. In this case, the system can produce the power output of 113.5 MWh/Year, and reduce CO2 emission of 62.2 Ton CO2 eq./Year. If investment cost is taken into account, a LCOE of 0.67 USD/kWh can be achieved by the same system but coupled with 900 units of the same collectors. In this case, the system power output is 110.0 MWh/Year, and CO2 emission are reduced by 60.3 Ton CO2 eq./Year.

Analysis of a solar Rankine cycle powered refrigerator with zeotropic mixtures

A solar organic Rankine cycle (ORC) powered vapor compression cycle (VCC) for refrigeration is under investigation in this paper. To improve the overall system performance, zeotropic mixtures are proposed to be used in the integrated ORC-VCC system for the first time. A thermodynamic model is developed, and a total of eight pure fluids and five zeotropic mixtures with various compositions are evaluated and compared to identify the best combinations of fluids for yielding high system efficiencies. Besides, the influences of generating temperature, refrigerating temperature, superheating and internal heat exchanger (IHE) in ORC on the system performance are analyzed. For the ORC-VCC operating between −5 and 80 °C, dry fluid R600a shows the highest system efficiency (0.2212) among the pure fluids. For zeotropic mixtures, there exists a composition range within which binary mixtures always show higher system efficiency than the component pure fluids. Mixture R161/R600a with an R161 mass fraction of 0.25 shows the highest system efficiency (0.3089) among all fluids, which is increased by 39.6% and 54.7% comparing with R600a and R161, respectively. Adding IHE in ORC benefits the system efficiency, and the benefit is much more evident for dry fluids. Superheating makes wet fluids become applicable in ORC-VCC, but it becomes ineffective in improving the system efficiency when there is no IHE in system.

Thermal analysis of a Phase Change Material for a Solar Organic Rankine Cycle

Organic Rankine Cycle (ORC) is a promising technology for low temperature power generation, for example for the utilization of medium temperature solar energy. Since heat generated from solar source is variable throughout the day, the implementation of Thermal Energy Storage (TES) systems to guarantee the continuous operation of solar ORCs is a critical task, and Phase Change Materials (PCM) rely on latent heat to store large amounts of energy.In the present study, a thermal analysis of a PCM for a solar ORC is carried out. Three different types of PCMs are analyzed. The energy equation for the PCM is modeled by using the heat capacity method, and it is solved by employing a 1Dexplicit finite difference scheme. The solar source is modeled with a time-variable temperature boundary condition, with experimental data taken from the literature for two different solar collectors. Results are presented in terms of temperature profiles and stored energy. It has been shown that the stored energy depends on the heat source temperature, on the employed PCM and on the boundary conditions. It has been demonstrated that the use of a metal foam can drastically enhance the stored energy due to the higher overall thermal conductivity.

Dynamic performance analysis of solar organic Rankine cycle with thermal energy storage

This paper discusses the dynamic performance in a small-scale solar organic Rankine cycle (SORC) with thermal energy storage (TES) considering solar disturbance. A dynamic model of SORC is developed. The factor FSR (Fluctuation Suppression Ratio) is defined to reflect the effect of TES on suppressing the dynamic impact. The dynamics of the SORC are found to contain resonance characteristics. With the interaction between solar disturbances and system thermal inertia (mainly determined by TES capacity), the energy superposition could cause dynamic resonance. In order to study the dynamic performance of the SORC, the influence factor including TES capacity, solar fluctuation (period, amplitude, average solar) and evaporation temperature were analysed, while FSR and the total system efficiency were the indicators which represent the system stability and performance respectively. The simulation result shows that within a certain solar period, there is a specific TES capacity range leading to resonance. The proper TES capacity should be selected according to local solar fluctuations to effectively suppress dynamic impact in the initial design phase.

Exergy and economic analysis of organic Rankine cycle hybrid system utilizing biogas and solar energy in rural area of China

ABSTRACTDue to the existing huge biogas resource in the rural area of China, biogas is widely used for production and living. Cogeneration system provides an opportunity to realize the balanced utilization of the renewable energy such as biogas and solar energy. This article presented a numerical investigation of a hybrid energy-driven organic Rankine cycle (ORC) cogeneration system, involving a solar ORC and a biogas boiler. The biogas boiler with a module of solar parabolic trough collectors (PTCs) is employed to provide heat source to the ORC via two distinct intermediate pressurized circuits. The cogeneration supplied the power to the air-condition in summer condition and hot water, which is heated in the condenser, in winter condition. The system performance under the subcritical pressures has been assessed according to the energy–exergy and economic analysis with the organic working fluid R123. The effects of various parameters such as the evaporation and condensation temperatures on system performance were investigated. The net power generation efficiency of the cogeneration system is 11.17%, which is 25.8% higher than that of the base system at an evaporation temperature 110°C. The exergy efficiency of ORC system increases from 35.2% to 38.2%. Moreover, an economic analysis of the system is carried out. The results demonstrate that the profits generated from the reduction of biogas fuel and electricity consumption can lead to a significant saving, resulting in an approximate annual saving from $1,700 to $3,000. Finally, a case study based on the consideration of typical rural residence was performed, which needs a payback period of 7.8 years under the best case.

Performance assessment of a solar trigeneration system for residential applications by means of a modelling study

Concentrated solar technologies coupled with ORC system is a well-known topic in temperature ranges lower than 200°C. However, the integration to an efficient and economic working system is still a challenge especially at small scale. Efforts exist to achieve higher overall efficiencies but they are solely focused on thermal and electrical production while few of these is encompassing small-scale solar trigeneration systems. In the present article, the potential of a small scale concentrated solar Organic Rankine Cycle plant coupled with an absorber is investigated using a simulation analysis of a small scale 50 m2 CPC solar field, a 3.5 kWe ORC and a 17.6 kWc absorption chiller to satisfy respectively heating, electricity and cooling needs of a residential user. The simulation analysis of the overall system has been carried out in TRNSYS and an own model of the ORC system has been developed by the authors in Matlab thus improving the previous general model. The final aim of the proposed work is indeed the performance assessment of the small scale integrated system in order to evaluate the potential feasibility of such a system for residential applications.

Thermodynamic comparison and dynamic simulation of direct and indirect solar organic Rankine cycle systems with PCM storage

A thermodynamic comparison between a novel direct solar ORC system (DSOS) and indirect solar ORC system (ISOS) is carried out in this study. A phase change material (PCM) heat storage unit is integrated with both systems to ensure the stability of power generation. Water and R245fa are selected as a heat transfer fluids (HTFs) for ISOS and DSOS respectively. However, R245fa is used as working fluid for both systems. Weekly, monthly and annual dynamic simulations are carried out to compare the performance of both systems using hourly weather data of Islamabad, Pakistan. ISOS has shown 1.71% system efficiency and able to provide 34.02 kW/day power while DSOS has shown 4.5 times higher system efficiency and 2.8 times higher power on annual basis. Numerical model for the PCM storage is developed and validated with the previous experimental data. Average annual amount of energy stored by PCM during charging phase for ISOS is 4.24 MW/day higher than DSOS. However, in comparison with ISOS, DSOS has delivered 33.80 kW/day more power to HTF during discharging phase of the PCM on annual basis. Maximum benefits of PCM storage are observed during the summer season compared to the winter season at selected operating conditions. Furthermore, average annual increment in capacity factor by using PCM storage are found to be 21.71% and 17% for DSOS and ISOS respectively.

A small-scale solar organic Rankine cycle combined heat and power system with integrated thermal energy storage

In this paper, we examine integrated thermal energy storage (TES) solutions for a domestic-scale solar combined heat and power (S-CHP) system based on an organic Rankine cycle (ORC) engine and low-cost non-concentrating solar-thermal collectors. TES is a critical element and distinct advantage of solar-thermal systems. It can allow, depending on how it is implemented, improved matching to the end-user demands, improved load factors, higher average efficiencies and overall performance, as well as reduced component and system sizes and costs, especially in climates with high solar-irradiance variability. The operating temperature range of the TES solution must be compatible with the solar-collector array and with the ORC engine operation in order to maximise the overall performance of the system. Various combinations of phase change materials (PCMs) and solar collectors are compared and the S-CHP system’s performance is simulated for selected months in the contrasting climates of Cyprus and the UK. The most important performance indicator of the ORC engine, i.e., net-power output, and the required TES volume are compared and discussed. The PCM-TES solutions that enable the best summer performance from an ORC engine sized for a nominal ∼1-kWe output in combination with a 15-m2 solar collector array result in diurnal volume requirements as low as ∼100L in Cyprus and 400–500L in the UK. However, the required TES volume is strongly influenced by the choice of operational strategy for the system in matching the domestic load profiles. In a full-storage strategy in which electrical energy generation from the ORC engine is offset to match the week-day evening peak in demand, it is found that a ∼20% higher total daily electrical output per unit storage volume can be achieved with a PCM compared to water as a sensible storage medium. The isothermal operation of the PCMs during phase-change allows for smaller diurnal storage temperature swings and higher energy conversion efficiencies from the solar collector array. These results are useful in informing the development of small-scale solar-thermal heat and power systems and of suitable integrated TES solutions for such applications.

Techno-economic comparison of solar organic Rankine cycle (ORC) and photovoltaic (PV) systems with energy storage

In this work, we compare the technical and economic performance of a solar organic Rankine cycle (s-ORC) system with thermal energy storage (TES) and a solar photovoltaic (PV) system with battery storage at a capacity of 50 kWe. A two-dimensional variable space, comprising solar field area and storage capacity is swept for optimum operational zones of five performance indicators, namely annual energy generation, capacity utilization factor (CUF), capital cost, levelized cost of electricity (LCOE) and energy wasted. Minimum LCOE estimated for the s-ORC system was 0.19 USD/kWh with a CUF of 0.56. For the same CUF value, the PV system incurs a LCOE of at least 0.26 USD/kWh. The minimum LCOE of the PV system yields an attractive value of 0.12 USD/kWh, but it includes no battery storage and thus delivers a significantly lower CUF of 0.27. The results indicate that for achieving minimum LCOE, the operational zones of the two technologies differ in terms of storage requirement. The s-ORC technology potentially offers improved reliability of power supply through cost-effective TES. Visualization of annual energy and costs in the form of contour maps facilitates a holistic comparison of the two technologies with their storage options.

Experimental Assessment of a Helical Coil Heat Exchanger Operating at Subcritical and Supercritical Conditions in a Small-Scale Solar Organic Rankine Cycle

In this study, the performance of a helical coil heat exchanger operating at subcritical and supercritical conditions is analysed. The counter-current heat exchanger was specially designed to operate at a maximal pressure and temperature of 42 bar and 200 °C, respectively. The small-scale solar organic Rankine cycle (ORC) installation has a net power output of 3 kWe. The first tests were done in a laboratory where an electrical heater was used instead of the concentrated photovoltaic/thermal (CPV/T) collectors. The inlet heating fluid temperature of the water was 95 °C. The effects of different parameters on the heat transfer rate in the heat exchanger were investigated. Particularly, the performance analysis was elaborated considering the changes of the mass flow rate of the working fluid (R-404A) in the range of 0.20–0.33 kg/s and the inlet pressure varying from 18 bar up to 41 bar. Hence, the variation of the heat flux was in the range of 5–9 kW/m2. The results show that the working fluid’s mass flow rate has significant influence on the heat transfer rate rather than the operational pressure. Furthermore, from the comparison between the experimental results with the heat transfer correlations from the literature, the experimental results fall within the uncertainty range for the supercritical analysis but there is a deviation of the investigated subcritical correlations.

Thermodynamic modelling and analysis of a solar organic Rankine cycle employing thermofluids

This paper presents thermodynamic modelling and simulation study of a small scale saturated solar organic Rankine cycle (ORC) which consists of a stationary, flat plate solar energy collector that is utilised as a vapour generator, a vane expander, a water-cooled condenser and a pump. Simulations are conducted under constant condensing temperature/pressure and various cycle pressure ratios (PR) for 24 organic thermofluids including Hydrocarbons (HCs), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), Hydrofluoroethers (HFEs) and Hydrofluoroolefins (HFOs). Special attention is given to the influence of PR and fluids’ physical properties on the solar ORC performance as well as fluids’ environmental and safety impacts including global warming potential (GWP), flammability and toxicity. The simulation results indicate that when the same fluid is considered, pressure ratio of the cycle leads to various operating conditions such as collector (evaporating) pressure which results in various collector, expander and cycle efficiency. For instance, increasing the pressure ratio of the cycle enhances the net work output and the thermal efficiency of the cycle, whereas it decreases the flat plate collector efficiency. The results also indicate that the proposed system produces the maximum net work output of 210.45W with a thermal efficiency of 9.64% by using 1-butene. Furthermore, trans-2-butene, cis-2-butene, R600, R600a, R601, R601a and neopentane (HC), R227ea and R236fa (HFC), RC318 (PFC) and R1234ze (HFO) show promising solar ORC thermal performances. However, the flammability problem of HCs and global warming potential issue of HFCs and PFCs limit their applications, owing to the safety and environmental concerns.On the other hand, in terms of the environmental impact, thermofluids such as RE347mcc, RE245fa2 (HFEs) and R1234ze, R1233zd (HFOs) offer an attractive alternative, yet they were neither the most efficient, nor generated the highest amount of net work output. This paper provides thermofluids’ selection guidelines to achieve maximum efficiency within solar thermal energy technologies while keeping environmental impacts into considerations.

Optimisation of a small solar organic Rankine cycle based on the exergetic analysis

A mathematical model is written for a solar organic Rankine cycle (ORC) taking into account the Pinch temperature differences in the system heat exchangers. The (exergetic factor)-(variation in enthalpy) diagram of the hot and cold composite curves of the heater-evaporator and the superheater of the ORC gives information about the strategy to be followed in order to improve the structure of the system. The introduction of an internal recuperative heat exchanger to preheat the ORC fluid and the splitting of the solar fluid to balance the heat capacities in the heater and the superheater are also considered. An exergetic analysis reveals the magnitude of the exergy destruction in the key pieces of the system. A comparative simulation of the way, the ORC operates with different organic fluids points out that R245fa gives the highest exergetic efficiency.

Exergy Analysis of a Solar Organic Rankine Cycle with Square Prismatic Cavity Receiver

In this study, a solar organic Rankine cycle (ORC) was empirically modelled. A solar dish collector with a tubular cavity receiver was used as the ORC heat source. The effects of the solar irradiation, the depths of the cavity receiver, and the diameter of the inner cavity tube on the exergetic performance of the tubular cavity receiver were investigated. The exergy parameters such as the receiver exergy rate, the thermal exergy efficiency, the receiver exergy factor, and the electrical exergy efficiency were analysed. The results revealed that the optimum structure of the tubular cavity receiver for achieving the highest receiver exergy rate, thermal exergy efficiency, receiver exergy factor, and electrical exergy efficiency, was the cubical cavity (i.e., cavity depth equal to the side length of the cavity) with the smallest tube diameter.

Exergy analysis of a solar organic Rankine cycle with square prismatic cavity receiver

Exergy analysis of a solar organic Rankine cycle with square prismatic cavity receiver

Optimisation of a small solar organic Rankine cycle based on the exergetic analysis

Optimisation of a small solar organic Rankine cycle based on the exergetic analysis

Optimal design of a hybrid CSP-PV plant for achieving the full dispatchability of solar energy power plants

With the aim of providing fully dispatchable power using only solar energy, this paper focuses on a hybrid power generation system based on Concentrating Solar Power (CSP) and Photovoltaic (PV) plants. In particular, the CSP section is based on linear Fresnel collectors using thermal oil as heat transfer fluid, a two-tank direct TES system and an Organic Rankine Cycle (ORC) power plant. In the PV section, the PV array is coupled with a battery bank for electrochemical storage.The study evaluates the optimal design parameters (solar field area, TES capacity and ORC nominal power for the CSP section, nominal power of the PV array and battery capacity for the PV section) that minimize the energy production cost of the hybrid CSP-PV plant while the plant is constrained to follow a power output curve characterized by a constant power level. Moreover, to assess the influence of meteorological conditions, the study considers two different locations: Ottana (Italy) and Ouarzazate (Morocco).The results demonstrate that hybridization of PV and CSP technologies becomes highly cost-effective if a constant power output is required for daily time periods longer than about 16h, when the distinguishing feature of CSP plants of decoupling power generation from sunlight is effectively exploited, independently of the location under study. On the contrary, for production periods shorter than 8h, the use of a PV system coupled with a proper battery bank is the most cost-effective solution for both locations evaluated. Solar energy availability and unmet load fraction remarkably influence the hybrid plant design, especially for load duration periods in the range between 8 and 16h/day. As expected, due to the lower amount of available solar energy, the hybrid solar plant located in Ottana needs larger sizes of both CSP solar field and PV arrays than the same plant located in Ouarzazate resulting in higher energy production costs.

Performance Evaluation of a Helical Coil Heat Exchanger Working under Supercritical Conditions in a Solar Organic Rankine Cycle Installation

Worldwide interest in low grade heat valorization using organic Rankine cycle (ORC) technologies has increased significantly. A new small-scale ORC with a net capacity of 3 kW was efficiently integrated with a concentrated solar power technology for electricity generation. The excess heat source from Photovoltaic (PV) collectors with a maximum temperature of 100 °C was utilized through a supercritical heat exchanger that uses R-404A as working medium. By ensuring supercritical heat transfer leads to a better thermal match in the heat exchanger and improved overall cycle efficiency. A helical coil heat exchanger was designed by using heat transfer correlations from the literature. These heat transfer correlations were derived for different conditions than ORCs and their estimated uncertainty is ~20%. In order to account for the heat transfer correlation uncertainties this component was oversized by 20%. Next, a prototype was built and installed in an integrated concentrated photovoltaic/thermal (CPV/T)/Rankine system. The results from the measurements show that for better estimation of the sizing of the heat exchanger a more accurate correlation is required in order to design an optimal configuration and thus employ cheaper components.

Experimental Study of the Influence of Light Intensity on Solar Organic Rankine Cycle Power Generation System

A low-temperature (<120 °C) solar organic Rankine cycle (ORC) power generation experimental facility is designed and built. The influence of light intensity on the system performance is investigated using the experimental facility. The results indicate that the system efficiency can reach 2.2%. The temperature of heat transfer fluid (HTF) decreases linearly with light intensity (I). However, both system efficiency and thermoelectric efficiency first decrease linearly and then drop sharply as I decreases at working fluid flow rates (Vwf) of 200 and 160 L/hr, while they only decrease slightly with I at Vwf of 120 L/hr. The light intensity of the turning point is 824 W/m2 at Vwf of 200 L/hr, which corresponds to an HTF temperature of 75 °C. In addition, it is found that the influence of light intensity on the performance of ORC becomes stronger for higher working fluid flow rate. Moreover, the light intensity and HTF temperature at the turning point increase with working fluid flow rate. The experimental results are of great significance for the design and operation of low-temperature solar ORC power generation system.

Effect of working fluids on the performance of a novel direct vapor generation solar organic Rankine cycle system

A novel solar organic Rankine cycle (ORC) system with direct vapor generation (DVG) is proposed. A heat storage unit is embedded in the ORC to guarantee the stability of power generation. Compared with conventional solar ORCs, the proposed system avoids the secondary heat transfer intermediate and shows good reaction to the fluctuation of solar radiation. The technical feasibility of the system is discussed. Performance is analyzed by using 17 dry and isentropic working fluids. Fluid effects on the efficiencies of ORC, collectors and the whole system are studied. The results indicate that the collector efficiency generally decreases while the ORC and system efficiencies increase with the increment in fluid critical temperature. At evaporation temperature of 120 °C and solar radiation of 800 Wm−2, the ORC, collector and overall thermal efficiencies of R236fa are 10.59, 56.14 and 5.08% while their values for Benzene are 12.5, 52.58 and 6.57% respectively. The difference between collector efficiencies using R236fa and Benzene gets larger at lower solar radiation. The heat collection is strongly correlated with latent and sensible heat of the working fluid. Among the fluids, R123 exhibits the highest overall performance and seems to be suitable for the proposed system in the short term.