The present work is focused on the development of a simulation model for an existing cogeneration power plant, which utilizes a solar thermal field with parabolic trough solar collectors coupled to an Organic Rankine Cycle engine. The power plant is modeled in the trnsys v.17 software package and its performance has been validated with real operating conditions. The simulated system (concentrated solar power (CSP) field and ORC engine) is the main part of a hybrid power plant located near “Ziloti” village of the Municipality of Xanthi, in northeastern Greece. The construction of the hybrid power plant was funded by the Strategic Co-Funded Project of the European Territorial Cooperation Program Greece–Bulgaria 2007–2013 with the acronym ENERGEIA. The power plant simulated in this paper includes a 234 kW th solar parabolic trough collector (PTC) field, a 5 m 3 thermal energy storage tank, and a 5 kW e ORC engine for the production of thermal and electrical energies. The results of the simulations present small deviation in contrast to the real operating data of the CSP power plant coupled with the ORC engine, therefore the simulation model is considered as reliable.

This paper proposes an efficient single-stage photovoltaic (PV) fed permanent magnet brushless DC (PMBLDC) motor water pumping system with grid power interface. The power conditioning system used in the conventional two-stage system is eliminated, and the maximum power point tracking (MPPT) scheme is incorporated within the inverter used for the electronic commutation of the BLDC motor. The BLDC motor pumping is advantageous than the conventional induction motor-aided water pumps. The proposed system is the first of its kind to employ a grid power export scheme utilizing the same inverter drive which in turn reduces the complexity of adding new inverter circuitry and thereby making the system economically viable. The BLDC pump and grid power export scheme is realized in both simulation and hardware environment for a power rating of 1 kW. The results reveal that the proposed system is highly viable.

A two-dimensional numerical model is developed to simulate the transient response of a heat pipe-assisted latent heat thermal energy storage (LHTES) unit integrated with dish-Stirling solar power generation systems. The unit consists of a container which houses a phase change material (PCM) and two sets of interlaced input and output heat pipes (HPs) embedded in the PCM. The LHTES unit is exposed to time-varying concentrated solar irradiance. A three-stage operating scenario is investigated that includes: (i) charging only, (ii) simultaneous charging and discharging, and (iii) discharging only. In general, it was found that the PCM damps the temporal variations of the input solar irradiance, and provides relatively smooth thermal power to the engine over a time period that can extend to after-sunset hours. Heat pipe spacing was identified as a key parameter to control the dynamic response of the unit. The system with the greatest (smallest) heat pipe spacing was found to have the greatest (smallest) temperature drops across the LHTES, as well as the maximum (minimum) amount of PCM melting and solidification. Exergy analyses were also performed, and it was found that the exergy efficiencies of all the systems considered were greater than 97%, with the maximum exergy efficiency associated with the system having the minimum heat pipe spacing.

The proper alignment of facets on a dish engine concentrated solar power system is critical to the performance of the system. These systems are generally highly concentrating to produce high temperatures for maximum thermal efficiency so there is little tolerance for poor optical alignment. Improper alignment can lead to poor performance and shortened life through excessively high flux on the receiver surfaces, imbalanced power on multicylinder engines, and intercept losses at the aperture. Alignment approaches used in the past are time consuming field operations, typically taking 4–6 h per dish with 40–80 facets on the dish. Production systems of faceted dishes will need rapid, accurate alignment implemented in a fraction of an hour. In this paper, we present an extension to our Sandia Optical Fringe Analysis Slope Technique mirror characterization system that will automatically acquire data, implement an alignment strategy, and provide real-time mirror angle corrections to actuators or labor beneath the dish. The Alignment Implementation for Manufacturing using Fringe Analysis Slope Technique (AIMFAST) has been implemented and tested at the prototype level. In this paper we present the approach used in AIMFAST to rapidly characterize the dish system and provide near-real-time adjustment updates for each facet. The implemented approach can provide adjustment updates every 5 s, suitable for manual or automated adjustment of facets on a dish assembly line.

Due to their high relative cost, solar-electric energy systems have yet to be exploited on a widespread basis. It is believed in the energy community that a technology similar to photovoltaics, but offered at about $1/W, would lead to widespread deployment at residential and commercial sites. This paper addresses the feasibility study of a low-cost solar-thermal electricity generation technology, suitable for distributed deployment. Specifically, we discuss a system based on nonimaging solar concentrators, integrated with free-piston Stirling engine devices incorporating integrated electric generation. We target concentrator collector operation at moderate temperatures, in the range of 120 ° C to 150 ° C . This temperature range is consistent with the use of optical concentrators with low-concentration ratios, wide angles of radiation acceptance which are compatible with no diurnal tracking and no or only a few seasonal adjustments. Therefore, costs and reliability hazards associated with tracking hardware systems are avoided. This paper further outlines the design, fabrication, and test results of a single-phase free-piston Stirling engine prototype. A very low loss resonant displacer piston is designed for the system using a very linear magnetic spring. The power piston, which is not mechanically linked to the displacer piston, forms a mass-spring resonating subsystem with the gas spring, and has a resonant frequency matched to that of the displacer. The design of heat exchangers is discussed, with an emphasis on their low fluid friction losses. Only standard low-cost materials and manufacturing methods are required to realize such a machine. The fabricated engine prototype is successfully tested as an engine, and the experimental results are presented and discussed. Extensive experimentation on individual component subsystems confirms the theoretical models and design considerations. Based on the experimental results and the verified component models, an appropriately dimensioned Stirling engine candidate is discussed.

Analysis, design, fabrication, and experimental assessment of a symmetric three-phase free-piston Stirling engine system is discussed in this paper. The system is designed to operate with moderate-temperature heat input that is consistent with solar-thermal collectors. Diaphragm pistons and nylon flexures are considered for this prototype to eliminate surface friction and to provide appropriate seals. In addition, low loss diaphragm pistons, etched and woven-wire screen heat exchangers, and plastic flexures, as the main components of the system, are outlined. The experimental results are presented and compared with design analysis. Experiments successfully confirm the design models for heat exchanger flow friction losses and gas spring hysteresis dissipation. Furthermore, it is revealed that gas spring hysteresis loss is an important dissipation phenomenon for low-power Stirling engines and should be carefully addressed in design. Analysis shows that the gas hysteresis dissipation is reduced drastically by increasing the number of phases in a multiphase Stirling engine system. It is further shown that for an even number of phases, half of the engine chambers could be eliminated by utilizing a reversing mechanism within the multiphase system. The mathematical formulation and modal analysis of multiphase Stirling engine system are then extended to a system that incorporates a reverser. By introducing a reverser to the fabricated prototype, the system successfully operates in engine mode. The system proves its self-starting capability and validates the computed start-up temperature.

The CNRS-Promes dish∕Stirling system was erected in Jun. 2004 as the last of three country reference units built in the “Envirodish” project. It represents the latest development step of the EuroDish system with many improved components. With a measured peak of 11 kW electrical output power, it is also the best performing system so far. The measurement campaign to determine the optical and thermodynamic efficiency of the system is presented. The optical quality of the concentrator and the energy input to the power conversion unit was measured with a classical flux-mapping system using a Lambertian target and a charge coupled device camera system. An efficiency of the concentrator including the intercept losses of 74.4% could be defined for this particular system. For the thermodynamic analysis all the data necessary for a complete energy balance around the Stirling engine were measured or approximated by calculations. For the given ambient conditions during the tests, a Stirling engine efficiency of 39.4% could be measured. The overall efficiency for the conversion of solar to electric energy was 22.5%.

One parabolic dish—Stirling engine system—has been in operation at the Engineering School of Seville since March 2004. The unit, based on the Eurodish system, is one of the several Country Reference Units of the EnviroDish project. The system has achieved a maximum thermal efficiency (solar to electricity) close to 20% during operation. The analysis of the different parameters suggests a high potential for improvement. A thermal model of the main components of the engine package (cavity, receiver, and Stirling engine) can help to evaluate possible modifications of the system and identify the most promising ones. The development of such a thermal model and its comparison with experimental data gathered during this period are reported in this work. Model results exhibit a good qualitative agreement with the available measurements. However, the validation of the model will require measuring more parameters at the cavity, receiver, and engine.

The use of computational fluid dynamics (CFD) models significantly extends the capabilities for the detailed analysis of the complex heat transfer and gas dynamic processes that occur in the internal gas circuit of a Stirling engine by more accurately predicting the engine’s performance. This accurate data on operational characteristics of the engine can then contribute to more precise calculations of the dimensions of a parabolic concentrator in a dish/Stirling engine installation. In this paper a successful axisymmetric CFD simulation of a solar “V”-type Stirling engine is described for the first time. The standard κ - ε turbulence model, with a moving mesh to reflect the reciprocating motion of the pistons, has been employed for the analysis of the engine’s working process. The gas temperature and pressure distributions and velocity fields in the internal gas circuit of the machine have been obtained and the pressure-volume diagrams have been calculated. Comparison of the numerical results produced from the axisymmetric CFD simulation of the engine’s working process with those computed with the use of second-order mathematical analysis shows that there are considerable differences. In particular, analysis of the data obtained indicates that the gas temperature in the compression space depends on the location in the cylinder for the given moment in the cycle and it may differ substantially from being harmonic in time.

A solar stirling engine based on a horizontal selective flat-plate converter is analyzed in this work. A detailed model for the heat losses towards the atmosphere is presented. The engine’s output power is maximised numerically. The analysis is based on meteorological data measured at Viking Landers sites during clear sky and dust storm conditions. All the computations were performed for a solar collection area similar in size with that of Mars Pathfinder’s Sojourner. The efficiency of converting solar energy into mechanical work at noon is as high as 18%. The power provided by the engine is as high as 16 W during autumn and winter. These results suggest that under the Martian environment the performance of properly designed solar Stirling engines is comparable with that of PV cell power systems.

The Minto engine is a liquid piston heat engine that converts heat energy into mechanical energy. Evaporation of the heated, volatile working fluid pushes it upwards against gravity. This causes the device to tip over and rotate. A 500 mm diameter Minto engine which used petroleum ether as the working fluid, was built and was operated between 344 K and 294 K. Thermal efficiencies of up to 0.25% (i.e. 1.7% of the Carnot maximum) were measured. This engine behaves as a power amplifier. It absorbs low grade heat over a long period of time and suddenly releases it as a pulse of mechanical energy over a short period of time.

Dish-Stirling systems have demonstrated the highest efficiency of any solar power generation system by converting nearly 30% of direct-normal incident solar radiation into electricity after accounting for parasitic power losses[1]. These high-performance, solar power systems have been in development for two decades with the primary focus in recent years on reducing the capital and operating costs of systems. Even though the systems currently cost about $10,000 US/kW installed, major cost reduction will occur with mass production and further development of the systems. Substantial progress has been made to improve reliability thereby reducing the operating and maintenance costs of the systems. As capital costs drop to about $3000 US/kW, promising market opportunities appear to be developing in green power and distributed generation markets in the southwestern United States and in Europe. In this paper, we review the current status of four Dish-Stirling systems that are being developed for commercial markets and present system specifications and review system performance and cost data. We also review the economics, capital cost, operating and maintenance costs, and the emerging markets for Dish-Stirling systems.

Thermal Integral Micro-Generation (TIMGen) systems on the scale of a few Watts are proposed for use with solar or fuel-derived heat. The optics, the thermal receiver, and several alternative generation technologies, including MEMS heat engines (Stirling and Brayton cycles), thermal photovoltaics, and thermoelectric, are discussed. Analysis of system performance shows the potential for efficiency comparable to photovoltaic cells and large-scale thermal plants. A major advantage of thermal systems over PV cells is the possibility of hybrid operation, both with sunlight and with another heat source when sunlight is not available. The alternative heat source can be another renewable or conventional fossil fuel. TIMGen plants compared to large-scale centralized thermal plants offer the advantages of modularity, scalability, redundancy and low cost via mass production. They can prove to be a very attractive option both for remote, self-contained electricity generation, and as an alternative to large-scale centralized plants.

This paper describes the experimental study carried out on a Permanent Magnet Brushless DC (PMBLDC) motor coupled to a pump load powered by a Photo Voltaic (PV) Array for a Water Pumping System. A simple low cost controller has been designed and developed without any current and position sensors. This drastically reduces the over all cost of the drive system. This controller is used to test the dynamic behavior of the PMBLDC motor drive system. The mathematical model of the system is developed with a view to carry out a comparison between experimental and simulated response of the drive system. The necessary computer algorithm is developed to analyze the performance under different conditions of varying solar irradiance for a pump load. The developed state space equations are simulated to obtain the performance characteristics which are also verified by conducting suitable experiments on the developed system. [S0199-6231(00)01002-9]

In this paper a second level mathematical model for the computational simulation of the working process of a 1-kW Stirling engine has been used and the results obtained are presented. The internal circuit of the engine in the calculation scheme was divided into five chambers, namely, the expansion space, heater, regenerator, cooler and the compression space, and the governing system of ordinary differential equations for the energy and mass conservation were solved in each chamber by Euler’s method. In additional, mechanical losses in the construction of the engine have been determined and the computational results show that the mechanical losses for this particular design of the Stirling engine may be up to 50% of the indicated power of the engine.

Various solar electric system performance codes are used to predict the power generated by different solar power systems in the Southern Nevada area during 1990 by using the National Solar Radiation Data Base (NSRDB) for Las Vegas. The system types evaluated along with the prediction codes (shown in parenthesis) are as follows: a central receiver or a power tower system with various amounts of storage (SOLERGY), a Luz-type SEGS parabolic trough system without fossil fuel backup or storage (LUZERGY), a dish-Stirling system (DISH2, a conversion of direct beam radiation with constant collector/engine efficiency was used for this), and various arrangements of nonconcentrating photovoltaic devices (PVFORM). Comparisons of these results are made with the daily variations of load requirements of an electrical utility operating in the same geographical area. These comparisons are made for summer and winter periods. It is shown that several of the power generation schemes have summer peak outputs that occur at times very near to, but not coincident with, the peak utility load requirements. The power tower with a relatively small amount of thermal storage was the only scheme able to provide full power output at the times of summer peak demands. Winter peaks in this region occur during the night. Two comparisons are made that illuminate the summer load serving capability of solar generation in addition to simply showing time-variations of outputs. Included in these comparisons are the determination of the difference in time between the peak power output and the peak demand, as well as the normalized fraction of the peak power generated at the peak demand times.

Wind turbine technology has been used to pump water since ancient history. Direct mechanically coupled wind turbines are the most common method for pumping water to croplands and livestock. Many more recent wind turbines are electrically coupled, with the water pump connected to the wind turbine via a motor-generator connection. With electrical coupling, the distance and location of the water pump is independent of the location of the wind turbine. Therefore, the wind turbine can be located at an optimal wind energy site while the water pump is close to the water well or water tank. This paper analyzes a water-pumping system consisting of a wind turbine, a permanent magnet synchronous generator, an induction motor, and a centrifugal-type water pump.

This paper addresses thermodynamics of phase-change storage elements in series with heat engines. It is assumed that the duration of the heat storage and the discharge are equal. It is also assumed that the same heat transfer fluid (HTF) with a constant flow rate is used for the whole cycle. The major constraint imposed on these systems is the stability of the temperature of the HTF supplied to the engine during the storage-discharge cycle. It is shown, for this setup, that the freezing point of the phase-change material (PCM) is defined by the First Law. Maximal stability corresponds to the freezing point equal to the arithmetic mean of the inlet temperatures of the hot and the cold streams. An analytic expression is developed for the Second Law efficiency of the heat storage-removal cycle for the phase-change element in series with an engine. It yields maximal entropy production in the absolute stability limit. Two analytically tractable models of a phase-change storage in series with a heat engine are studied in detail. One involves a PCM slab, and the second involves a PCM tube-and-shell heat exchanger.

A solar dynamic ground test demonstrator space power system is being developed. The system comprises a complete Brayton engine—a heat receiver, concentrator, radiator, recuperator, heat rejection gas cooler, and turboalternator compressor. All of these components will be operated inside a vacuum tank. The engine is powered by simulated sunlight from an external bank of lights. Successful completion of the testing will indicate the readiness of solar dynamic power for space applications. This paper discusses the thermal and structural analysis of the heat receiver component. The analysis performed indicates that all components comfortably meet the life and cold start requirements, while maintaining the necessary overall performance.