Economic feasibility of solar pumping

Two major questions concerning the economic feasibility of solar pumping are addressed. The first of these is concerned with finding a least-cost solar system by considering the alternative use of either thermal or water storage. The second involves the determination of areas where solar energy would be economically competitive with electricity or fuel as a power source for pumping installations.A linear programming solution is developed to find the optimal combination of thermal and water storage for a solar installation. The formulation is then extended to determine a least-cost system when hybrid systems are considered. A hybrid system may incorporate a combination of solar, electric and fuel power inputs. The concept of a breakeven “critical” distance from existing infastructure for solar installations is developed, and an example problem is provided to illustrate typical values of this distance and to show its sensitivity to the base energy costs and rate of inflation for those costs. It appears that electrical pumping is probably the most economical alternative provided that electric infrastructure is located nearby. Fuel power will also be more economical than solar if there is a source of fuel near the proposed pumping site. However, solar systems may be economically competitive when considered for installation at realistic distances from existing infrastructure.     

Optimal thermohydraulic performance of a wire mesh packed solar air heater

This paper is concerned with thermohydraulic investigations on a packed bed solar air heater having its duct packed with blackened wire screen matrices of different geometrical parameters (wire diameter and pitch). The thermohydraulic performance of an air heater in terms of effective efficiency is determined on the basis of actual thermal energy gain subtracted by the primary energy required to generate power needed for pumping air through the packed bed. Based on energy transfer mechanism in the bed, a mathematical model is developed to compute effective efficiency. A design criterion is also suggested to select a matrix for packing the air flow duct of a solar air heater which results in the best thermal efficiency with minimum pumping power penalty. Resulting values of effective efficiency clearly indicate that the packed bed solar air heater investigated is thermohydraulically efficient as compared to flat plate collectors.     

Solar thermal heat engines for water pumping: An update

Solar thermal-driven heat engines for water pumping have been previously reviewed for some authors in the past century. However, some devices have not been treated as metal hydride-based systems or the pumping subsystems of solar thermal-driven reverse osmosis desalination systems. Following the typical classification given in the previous literature, in this work an update of the solar heat engines for water pumping based in thermodynamic methods (conventional and unconventional) is presented. Besides small remarks about systems previously quoted by other authors, new designs found in the literature are described. In general, the main characteristics of these systems is their low efficiency, low power output and, in the case of unconventional designs, its simplicity. This work in conjunction with previous review papers make up reference point for the knowledge of the use of solar thermal energy for liquid pumping purpose.     

Exergy optimization of flow rates in flat-plate solar collectors

The optimal flat-plate collector mass flow rate is determined by maximizing the exergy (available energy) delivery of the collector as the objective function. Collector and storage dynamics are neglected. Although the case where the pumping power loss is ignored results in bang-bang control, the case where this loss is included in the exergy equation results, after some assumptions, in an optimal mass flow rate that is a function of collector parameters, inlet and ambient temperatures and solar heat gain. Daily performance of a typical flat-plate solar collector with optimum mass flow rate is compared with the performance of the same collector using the mass flow rate obtained by maximizing the difference between the collected thermal energy and the required pumping power.     

Performance characterisation and energy savings of uncovered swimming pool solar collectors under reduced flow rate conditions

The effects of reduced flow rates on the performance and effectiveness of domestic unglazed, uninsulated pool solar collector heaters are investigated. The study shows electrical energy savings in excess of 80% are achievable for typical solar collectors operating at flow rates reduced by up to 75% while collector efficiency is only reduced by approximately 10–15%. The reduction of electrical energy required for pumping and the increased COP of reduced flow through typical pool solar thermal collectors is shown to far outweigh the small loss of collector performance attributable to the change in flow rates. The ratio of thermal energy delivered to the electrical energy supplied was improved in the order of 400% for the collector tested.     

Exergetic optimization for solar heat receiver with heat loss and viscous dissipation

The exergetic efficiency of heat receiver in solar thermal power system is optimized by considering the heat loss outside the receiver and fluid viscous dissipation inside the receiver. The physical models of heat loss and pumping power consumption for solar heat receiver are first proposed, and associated exergetic efficiency is further induced. As the flow velocity rises, the pumping power consumption and heat absorption efficiency significantly rises, and the maximum absorption efficiency and optimal incident energy flux also increase. Along the flow direction of solar receiver, the exergy flux increment and the flow exergy loss almost linearly increase, while the exergetic efficiency varies very slowly at high flow velocity. According to the exergetic efficiency loss from flow viscou’s dissipation, the exergetic efficiency of solar heat receiver will first increase and then decrease with the flow velocity. Because of the coupling effects of heat absorption efficiency and exergetic efficiency from fluid internal energy, the exergetic efficiency of solar heat receiver will approach to the maximum at proper inlet temperature. As a result, the exergetic efficiency of solar heat receiver will reach the maximum at optimal inlet temperature, incident energy flux and flow velocity.     

Thermohydraulic performance of solar air heaters with roughened absorber plates

Artificial roughness has been found to enhance the heat transfer from the absorber plate to the air in a solar air heater duct. However, this improvement is invariably accompanied by increased pumping power. In this work, the effect of roughness and operating parameters on the thermal as well as the hydraulic performance of roughened solar air heaters is discussed and the thermohydraulic performance of roughened solar air heaters is compared with that of conventional smooth solar air heaters. The optimum design and operating conditions have been determined. On the basis of thermohydraulic considerations it has been found that the systems operating in a specified range of Reynolds number show better thermohydraulic performance depending upon the insolation. A relationship between the system and operating parameters that combine to yield optimum performance has been developed.     

Thermo-hydraulic performance of solar air heaters having integral chamfered rib roughness on absorber plates

This paper presents results of an experimental investigation of the performance of solar air heaters with chamfered repeated rib-roughness on the airflow side of the absorber plates. The roughened elements have a relative roughness pitch of 4.58 and 7.09 while the rib chamfer angle is fixed at 15°. For the airflow duct depths of 21.8, 21.5 and 16 mm, the relative roughness heights for the three roughened plates used are 0.0197, 0.0256 and 0.0441, respectively. The airflow rate per unit area of absorber plate has been varied between 0.024 to 0.102 kgs⁻¹ m⁻² (flow Reynolds number ranges from 3750 to 16 350). The study shows substantial enhancement in thermal efficiency (10 to 40%) over solar air heaters with smooth absorber plates due to the enhancement in the Nusselt number (50% to 120%). The thermal efficiency enhancement is also accompanied by a considerable enhancement in the pumping power requirement due to the increase in the friction factor (80% to 290%). At low flow rates, corresponding to applications requiring air at a high temperature, the solar air heater with roughness elements having a high relative roughness height, yields a better performance. However, at high flow rates the increase in the pumping power is greater than the relative gain in the energy collection for a greater relative roughness height and, hence, the net gain is higher for smaller roughness heights. At still higher flow rates, the smooth duct air heater has better effective efficiency. A mathematical model for thermal performance prediction of solar air heaters with absorber plate having integral chamfered rib-roughness has been presented. The experimental and predicted values of thermal efficiency lie within ±7% with a standard deviation of ±5.8%.     

Small hybrid solar power system

This paper introduces a novel concept of mini-hybrid solar power plant integrating a field of solar concentrators, two superposed Organic Rankine Cycles (ORC) and a (bio-)Diesel engine. The Organic Rankine Cycles include hermetic scroll expander-generators¹ and the sun tracking solar collectors are composed of rows of flat mirror bands (CEP) arranged in a plane, that focus the solar energy onto a collector tube similar to those used in SEGS plants in California. Waste heat from both the exhaust gases and the block cooling of the thermal engine are also heat sources for the ORCs. Such units meet electricity, cooling and pumping needs of remote settlements. The thermal engine guarantees a minimum level of both power and heat availability at night or during cloudy periods. Laboratory tests, made with the superposed ORCs only, confirmed adequate operational characteristics with good performances over a broad range of conditions. A few preliminary tests on the site of the solar power plant when coupled with the engine confirmed a reasonable behavior and the interest of the concept even at part load or during sharp variations of the thermal supply.     

Cascading pressure thermal reduction for efficient solar fuel production

Efficient two-step solar-thermochemical fuel production requires vacuum pumping or inert gas sweeping to lower the oxygen pressure in the thermal reduction step. Pumping is hampered by large oxygen volumetric flows, whereas sweeping is energy-intensive, requiring heat recovery at high temperature, and a dedicated inert gas purification plant. A novel pumping approach—using a cascade of chambers at successively lower pressures—is analyzed and shown to lead to over an order of magnitude pressure decrease compared to a single-chambered design. The resulting efficiency gains are substantial, and represent an important step toward practical and efficient solar fuel production on a large scale.     

A modular phase change heat exchanger for a solar oven

A modular energy storing heat exchanger designed to use pentaerythritol for thermal storage (solid-solid phase change at 182°C) is tested in an oven by circulating heat transfer oil which is electrically heated in a manner to simulate a concentrating solar collector. Three efficiencies for heating the system under controlled and measured power input are determined—the heat exchanger efficiency, the efficiency of the heater with distribution lines, and the total system efficiency. Thermal energy retention times and cooking extraction times are determined, and along with the efficiencies, are compared with the results previously reported for a nonmodular heat exchanger. The modular configuration provides a highly improved extraction rate for cooking due to its wrap-around character and its increased surface-to-volume ratio. A full scale glass model of the copper tubing of the system is described and flow observations reported demonstrating how uniformly the parallel pumping branches perform and how trapped air pockets affect pumping power. A technique for measuring pumping power is described and its application to our system is quantified to show that less than 1 watt is required to circulate the heat transfer oil even when the system includes the solar collector and its longer connecting tubes.     

Use of solar assisted geothermal heat pump and small wind turbine systems for heating agricultural and residential buildings

The main objective of the present study is twofold: (i) to analyze thermal loads of the geothermally and passively heated solar greenhouses; and (ii) to investigate wind energy utilization in greenhouse heating which is modeled as a hybrid solar assisted geothermal heat pump and a small wind turbine system which is separately installed in the Solar Energy Institute of Ege University, Izmir, Turkey. The study shows 3.13% of the total yearly electricity energy consumption of the modeled system (3568 kWh) or 12.53% of the total yearly electricity energy consumptions of secondary water pumping, brine pumping, and fan coil (892 kWh) can be met by using small wind turbine system (SWTS) theoretically. According to this result, modeled passive solar pre heating technique and combined with geothermal heat pump system (GHPS) and SWTS can be economically preferable to the conventional space heating/cooling systems used in agricultural and residential building heating applications if these buildings are installed in a region, which has a good wind resource.     

Performance evaluation of solar air heaters having v-down discrete rib roughness on the absorber plate

This paper presents results of a study of the performance of solar air heaters with 60 ° v-down discrete rectangular cross-section repeated rib roughness on the air flow side of the absorber plate. A detailed investigation has been carried out using a mathematical model to study the effects of various ambient, operating and design parameters on the thermal efficiency and effective efficiency (based on the net gain after taking account of the pumping power) of such air heaters. The study shows that, at air mass flow rates less than about 0.04 kg s⁻¹ per m² of the absorber plate, roughened duct solar air heaters provide significant performance advantage over the smooth duct air heater. The thermal and effective efficiencies differ only marginally at low flow rates. With the increase in the flow rate, the difference between the thermal and effective efficiencies increases because of the increase in the pumping power. At the mass flow rate of about 0.045 kg s⁻¹ m⁻², the effective efficiencies of the roughened and smooth duct solar air heaters are practically the same. The results of the study are presented in the form of design plots.     

Effect of solar radiation correlations on system sizing: PV pumping case

The precise determination of solar radiation intensity is important for accurate system sizing. For PV pumping system case, the issue becomes more important since inaccurate solar radiation data nonlinearly reflected to the calculations. Inappropriate solar radiation model selection for a specific design site is a major cause for inaccurate system sizing. The differences in power output of a PV pumping system due to using some solar radiation correlations are examined here. The results are then compared with those of long-term solar radiation measurements. It is reported that the system sizing with the measurements and the most appropriate correlation for the application site significantly differ since the errors in predicting solar radiation data are nonlinearly propagated to the system power output.     

Integrated solar pump design incorporating a brushless DC motor for use in a solar heating system

Most solar thermal hot water heating systems utilize a pump for circulation of the working fluid. An elegant approach to powering the pump is via solar energy. A “solar pump” employs a photovoltaic module, electric motor, and pump to collect and convert solar energy to circulate the working fluid. This article presents an experimental investigation of a new integrated solar pump design that employs the stator of a brushless DC motor and a magnetically coupled pump that has no dynamic seal. This design significantly reduces total volume and mass, and eliminates redundant components.The integrated design meets a hydraulic load of 1.7 bar and 1.4 litres per minute, equal to 4.0 watts, at a rotational speed of 500 revolutions per minute. The brushless DC motor and positive displacement pump achieve efficiencies of 62% and 52%, respectively, resulting in an electric to hydraulic efficiency of 32%. Thus, a readily available photovoltaic module rated 15 watts output is suitable to power the system.A variety of design variations were tested to determine the impact of the armature winding, pump size, pulse width modulation frequency, seal can material, etcetera. The physical and magnetic design was found to dominate efficiency. The efficiency characteristics of a photovoltaic module are such that over-sizing is wasteful.The integrated design presents a robust, efficient package for use as a solar pump. Although focus has been placed on application to a solar thermal collector system, variations of the design are suitable for a wide variety of applications such as remote location water pumping.     

Capillary pumping systems for solar heating application

Capillary pumping two-phase loops have been continuously investigated for electronic cooling systems, satellite thermal control and other space applications. Most tests were performed in capillary evaporators using plastic or metallic porous wick as capillary structure and anhydrous ammonia as the working fluid. In this work, capillary pumping system assisting flat solar collectors is proposed as an alternative to residential and commercial water heating systems, using fine circumferential grooves as capillary structure and acetone as the working fluid. The experimental results are obtained for a small-scale solar heating system, using one capillary pump attached to a flat copper plate of 46 cm in length and 6 cm in width. The capillary pump consists of a 19 mm OD and 500 mm long aluminium tube, with fine internal circumferential groves as the capillary structure. The working fluid is pumped from a condenser designed to delivery heat to the water storage. Heat inputs up to 14 W (507 W/m²) were estimated for heating purpose. The system presented reliable start-ups and good performance in continuous operation. The measurements were found to be in good agreement with theoretical results for the temperature field and solar power absorbed by the system.     

Solar water pumping

The principles of solar water pumping are briefly described. The mechanical energy needed for pumping water may be produced by thermodynamic, or direct-conversion methods. In thermodynamic conversion a fluid with high internal energy is produced in solar collectors or concentrators. The internal energy of the fluid may be utilized in Rankine-, Brayton-, or Stirling-cycles or in specially designed devices. The nature of irrigation in the arid regions calls for scattered water pumping stations, hence small solar pumps. These pumps may be mass produced and delivered to the site. The direct conversion includes photovoltaic, themoelectric and thermionic processes. With the current prices of solar cells photovoltaic water pumping seems to be economically competitive with the current solar Rankine-cycle system in the power ranges of below 5 kW, especially when both systems have to be imported by a developing country.     

基于空间矢量PWM法的光伏水泵变频控制系统

介绍一种基于空间矢量PWM控制的光伏水泵变频控制系统。该空间矢量PWM算法具有对光伏阵列母线电压的动态补偿功能，保证在光伏阵列工作电压大范围变化条件下，变频驱动电机满足恒磁通调速控制。同时结合光伏水泵系统的工作特点，提出了一种简单实用的光伏阵列最大功率点跟踪控制方式，稳定可靠地实现了系统的最大功率点跟踪控制。     

Solar water pumping clean water for Sudan rural areas

The Republic of Sudan in Eastern Africa has one of the fastest growing economies in Africa. However, its remotely isolated rural areas pose problems to rural energy management and development because of poor road links with the urban centres, and remoteness from the national electrical transmission grid. Development of renewable energy sources, therefore, has a vast potential in Sudan. Solar energy, with excellent sunshine of over 3000 h per year, is of paramount importance, the applications of which are already quite siginficant and are growing at steady rate. Solar energy is suitable for small-scale water pumping in remote areas where the demand is regular, such as for drinking water, but it may also be used for irrigation. Most areas in Sudan have climates suitable for solar pumping. A review is given of the use of solar energy for water pumping to improve the living conditions of the population in rural areas and to develop techniques for utilization of solar energy in a tropical environment condition. Results, suggests that, solar powered water pumping must be encouraged, promoted, invested, implemented, and demonstrated by full scale in Sudan.     

Small solar (thermal) water-pumping system

A small solar (thermal) water pump prototype was tested. The pump works on an organic Rankine cycle using refrigerant R113. The design of the pump is described. Detailed temperature and pressure measurements of the working fluid for different operating conditions are performed. The behaviour of the cycle is analysed to get a clear picture of the thermodynamic process. Power-characteristic curves are obtained by a systematic variation of water temperature, pumping head and heat input.