Analysis of off-grid hybrid wind turbine/solar PV water pumping systems

While many remote water pumping systems exist (e.g. mechanical windmills, solar photovoltaic, wind-electric, diesel powered), few combine both the wind and solar energy resources to possibly improve the reliability and the performance of the system. In this paper, off-grid wind turbine (WT) and solar photovoltaic (PV) array water pumping systems were analyzed individually and combined as a hybrid system. The objectives were to determine: (1) advantages or disadvantages of using a hybrid system over using a WT or a solar PV array alone; (2) if the WT or solar PV array interfered with the output of the other; and (3) which hybrid system was the most efficient for the location. The WT used in the analysis was rated at 900 W alternating current (AC). There were three different solar PV arrays analyzed, and they were rated at 320, 480, and 640 W direct current (DC). A rectifier converted the 3-phase variable voltage AC output from the WT to DC before combining it with the solar PV array DC output. The combined renewable energies powered a single helical pump. The independent variable used in the hybrid WT/PV array analysis was in units of W/m². The peak pump efficiency of the hybrid systems at Bushland, TX occurred for the 900 W WT combined with the 640 W PV array. The peak pump efficiencies at a 75 m pumping depth of the hybrid systems were: 47% (WT/320 W PV array), 51% (WT/480 W PV array), and 55% (WT/640 W PV array). Interference occurred between the WT and the different PV arrays (likely due to voltage mismatch between WT and PV array), but the least interference occurred for the WT/320 W PV array. This hybrid system pumped 28% more water during the greatest water demand month than the WT and PV systems would have pumped individually. An additional controller with a buck/boost converter is discussed at end of paper for improvement of the hybrid WT/PV array water pumping system.     

Performance analysis of water cooled concentrated photovoltaic (CPV) system

The concentrated photovoltaic (CPV) system focuses solar radiation on the solar cells. CPV systems need to track the sun for keeping the reflected radiation focussed on the solar cell. A CPV module and its active water-cooling system are developed at the School of Energy and Environment, Southeast University, China and its performance has been reported here. This developed system has been used for testing the PV module's performance for different parameters such as operating temperature, power output, and efficiency. The experimental results show that the operating temperature of the CPV module under water cooling is reduced under 60 °C and therefore the efficiency of the CPV has increased and produced the more electric power output. The effect of water flow rate has been analyzed for the CPV efficiency and output.     

Energy matrices analyses of hybrid photovoltaic thermal (HPVT) water collector with different PV technology

In this paper, an attempt has been made to evaluate and compare the energy matrices of a hybrid photovoltaic thermal (HPVT) water collector under constant collection temperature mode with five different types of PV modules namely c-Si, p-Si, a-Si (thin film), CdTe and CIGS. The analysis is based on overall thermal energy and exergy outputs from HPVT water collector. The temperature dependent electrical efficiency has also been calculated under composite climate of New Delhi, India.It is observed that c-Si PV module is best alternative for production of electrical power. Maximum annual overall thermal energy and exergy is obtained for c-Si PV module. The maximum and minimum EPBT of 1.01 and 0.66 years on energy basis is obtained for c-Si and CIGS respectively, whereas on exergy basis maximum EPBT of 5.72 years is obtained for a-Si and minimum of 3.44 in obtained for CIGS PV module. EPF and LCCE increase with increasing the life time of the system.     

The effect of hybrid photovoltaic thermal device operating conditions on intrinsic layer thickness optimization of hydrogenated amorphous silicon solar cells

Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favorable operating temperatures for the thermal system. Amorphous silicon not only has a smaller temperature coefficient than c-Si, but also can display improved PV performance over extended periods of higher temperatures by annealing out defect states from the Staebler–Wronski effect. In order to determine the potential improvements in a-Si:H PV performance associated with increased thicknesses of the i-layers made possible by higher operating temperatures, a-Si:H PV cells were tested under 1 sun illumination (AM1.5) at temperatures of 25 °C (STC), 50 °C (representative PV operating conditions), and 90 °C (representative PVT operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840 nm were evaluated at each temperature. Results show that operating a-Si:H-based PV at 90 °C, with thicker i-layers than the cells currently used in commercial production, provided a greater power output compared to the thinner cells operating at either PV or PVT operating temperatures. These results indicate that incorporating a-Si:H as the absorber material in a PVT system can improve the thermal performance, while simultaneously improving the electrical performance of a-Si:H-based PV.     

Improving the effectiveness of a photovoltaic water pumping system by spraying water over the front of photovoltaic cells

The photovoltaic cells will exhibit long-term degradation if the temperature exceeds a certain limit. Photovoltaic cells are the heart of photovoltaic water pumping systems. In order to utilize PV power and increase photovoltaic water pumping system efficiency, it is necessary to keep PV cell temperature and cell reflection as low as possible. The purpose of this study is to investigate the possibility of improving the performance of a photovoltaic water pumping system. This is performed by spraying water over the photovoltaic cells. The results are compared with traditional systems. Experimental results show that the cells power is increased due to spraying water over the photovoltaic cells. This can significantly increase the system and subsystem efficiency and the pump flow rate when operating under different heads. Measurements of the short circuit current of the module, which is nearly temperature-independent, indicated that the water spray improved the system optical performance.     

Empirical study on thermal performance through separating impacts from a hybrid PV/TE system design integrating heat sink

A hybrid system design integrating a thermoelectric (TE) module has recently represented the advanced photovoltaic (PV) prototype with promoted efficiency for utilizing solar energy from the surroundings. Our present work during development of such a hybrid PV/TE system evaluates the thermal behaviors and the cooling performance associated with when integrating TE and heat sink modules. It has been noticed that a more effective structure through combining a heat sink with a TE module profits heat dissipation by cooling down the whole cell by ~ 8 °C, wherein the TE module itself demonstrates the cooling performance by ~ 27% enhancement in addition to its conventional role for electricity generation. Therefore, the PV/TE with a proper design can be used as a passive method for improving the cell efficiency as well as alleviating hot spot, which is typically occurring when the cell is unevenly heated during its operation. These results could be useful for further advancement on stability of power generation of a hybrid PV/TE system and may also be important for developing high-powered light emit diode.     

A probabilistic method for calculating the usefulness of a store with finite energy capacity for smoothing electricity generation from wind and solar power

This paper describes a novel method of modelling an energy store used to match the power output from a wind turbine and a solar PV array to a varying electrical load. The model estimates the fraction of time that an energy store spends full or empty. It can also estimate the power curtailed when the store is full and the unsatisfied demand when the store is empty. The new modelling method has been validated against time–stepping methods and shows generally good agreement over a wide range of store power ratings, store efficiencies, wind turbine capacities and solar PV capacities.Example results are presented for a system with 1 MW of wind power capacity, 2 MW of photovoltaic capacity, an energy store of 75% efficiency and a range of loads from 0 to 3 MW average.     

Feasibility of the green energy production by hybrid solar + hydro power system in Europe and similar climate areas

This paper analyses the hybrid solar and hydro (SHE) system as a unique technological concept of the sustainable energy system that can provide continuous electric power and energy supply to its consumers and the possibilities of its implementation in Europe and areas with similar climate. The sustainability of such system is based on solar photovoltaic (PV) and hydroelectric (HE) energy as renewable energy sources (RES). For the purpose of connecting all relevant values into one integral SHE system, a mathematical model was developed for selecting the optimal size of the PV power plant as the key element for estimating the technological feasibility of the overall solution. Sensitivity analysis (parameter analysis) was made for the model, where local climate parameters were varied: solar radiation, air temperature, reservoir volume, total head, precipitation, evaporation and natural water inflow. It has been established that, apart from total head (which is to be expected), solar radiation, hydro accumulation size and natural water inflow have the biggest effect on the calculated power of the PV power plant. The obtained results clearly show a wide range of implementation of the new energy source (SHE system), i.e. from relatively cold climates to those abundant in solar energy, but also with relatively small quantity of water, because it only recirculates within the system. All this points to the necessity for further development of hybrid systems (RES + HE systems) and to the fact that they could play an important role in achieving climate objectives.     

A novel thermal water pump for circulating water in a solar water heating system

This research purpose was to perform a parametric study of a novel thermal water pump well fitted in a simulated solar water heating system (SWHS). The SWHS was composed of a heating tank (HT), a hot water storage tank (ST) and an overhead tank (OT). The HT together with a specially designed valve act as a novel thermal water pump that gets power from hot water vapor and air pressure produced by a built-in electric heater in order to transfer heat from the HT to ST. The general operation of this pump has four stages for each cycle: heating, water circulating, vapor circulating and water supplying. The discharge water heads were varied with an increment of 0.25 m from 0.75 to 3 m. According to the experiment, it was found that the pump could operate at an average HT temperature of about 80–95 °C leading to 70–80 °C ST temperatures and 20–35 pumping cycles and consumed 17 MJ energy input during 9-h period. The overall thermal efficiency of the SWHS was 33–42% and the mean pump efficiency was about 0.005–0.011% depending upon the discharge heads.     

Analysis of the maximum power point tracking in the photovoltaic grid inverters of 5 kW

The aim of this article is to describe how closely PV grid-connected inverters (of around 5 kW) operate at the actual maximum power point. These inverters could be installed at any low voltage, PV grid-connected systems. To carry this study out, twelve 50 Hz single-phase inverters were selected from the European market. Each one of them was put into an outdoor grid-connected system installed in Spain. PV power generation with respect to irradiance, ambient temperature and local time was measured under different meteorological conditions. DC voltage and maximum power point tracking efficiency were analyzed. From the results obtained it has been possible to see that the MPPT algorithms used in some inverters do not bring the optimum utilisation of the PV array.     

太阳能电池与热泵热水器联合运行系统性能分析

为了降低太阳能光伏电池的温度,同时提升热泵热水器的蒸发温度,利用循环水路冷却太阳能光伏电池,并将热量传递给热泵热水器的蒸发器,构成联合运行系统。针对杭州市的夏季和冬季气象条件,对该联合运行系统的性能进行了计算,分析了对应不同太阳能电池温度下的系统运行参数的变化情况,包括太阳能电池发电效率和所需换热量,热泵热水器的制热量以及热泵效率等。计算结果表明,该联合运行系统能够同时提高太阳能电池光伏转换效率和热泵效率。     

Overview of the state of technique for PV inverters used in low voltage grid-connected PV systems: Inverters below 10 kW

An analysis has been made of the most important electrical parameters related to photovoltaic grid-connected inverters below 10 kW. To achieve this, a compilation of up to 50 manufacturers, various brands and up to 500 different models has been prepared and updated to February 2008. Datasheet and manuals have been compiled, noting down their electrical output and input characteristics. Different and important aspects with respect to performance of some PV grid-installation have been analyzed: the number of different models for values of power; topology option; operational DC parameters range (such as nominal power, maximum power, nominal current, voltage), operational AC parameter range (such as nominal power, maximum power, nominal current, voltage), inverter conversion efficiency vs nominal power and normalized inverter size and weight.     

Techno-economic analysis and modelling of a remote photovoltaic water pumping system in the desert of Tunisia

For estimating the performance of a photovoltaic (PV) water pumping system without battery storage, a simple algorithm has been developed. This simulation program uses the hourly global solar radiation, the hourly ambient temperature and the hourly wind speed as the input, moreover the characteristics of region (latitude, longitude, ground albedo) and characteristics of PV water pumping system (orientation, inclination, nominal PV module efficiency, NOCT, PV array area, PV temperature coefficient, miscellaneous power conditioning losses, miscellaneous PV array losses, temperature of reference, moto-pump efficiency and inverter efficiency). This work allows evaluating the economic interest of a remote PV water pumping systems in the desert of Southern Tunisia, which will have to satisfy an average daily volume of 45 m³ throughout the year compared to another very widespread energy system in the area, the diesel genset (DG), by using the method of the life-cycle cost (LCC). The cost per m³ of water was calculated for this system. It is found that the LCC for PV system is 0.500 TND/m³ and the LCC DG is 0.837 TND/m³. The present study indicates economic viability of PV water pumping systems in the desert of Tunisia.     

Design and performance of a solar-powered heating and cooling system using silica gel/water adsorption chiller

In this paper, a solar-powered compound system for heating and cooling was designed and constructed in a golf course in Taiwan. An integrated, two-bed, closed-type adsorption chiller was developed in the Industrial Technology Research Institute in Taiwan. Plate fin and tube heat exchangers were adopted as an adsorber and evaporator/condenser. Some test runs have been conducted in the laboratory. Under the test conditions of 80 °C hot water, 30 °C cooling water, and 14 °C chilled water inlet temperatures, a cooling power of 9 kW and a COP (coefficient of performance for cooling) of 0.37 can be achieved. It has provided a SCP (specific cooling power) of about 72 W/(kg adsorbent). Some field tests have been performed from July to October 2006 for providing air-conditioning and hot water. The efficiency of the collector field lies in 18.5–32.4%, with an average value of 27.3%. The daily average COP of the adsorption chiller lies in 33.8–49.7%, with an average COP of 40.3% and an average cooling power of 7.79 kW. A typical daily operation shows that the efficiency of the solar heating system, the adsorption cooling and the entirely solar cooling system is 28.4%, 45.2%, and 12.8%, respectively.     

Optimal inverter sizing considering cloud enhancement

A study of a photovoltaic (PV) array and inverter system installed in San Diego, California, was conducted in order to determine the energy losses due to inverter saturation (capping of inverter power output due to the PV array power output exceeding the inverter maximum power rating). Two mechanisms of saturation were considered: cloud enhancement (refers to an increased diffuse component of irradiance caused by clouds surrounding the unobstructed solar disk) and clear sky exceedance. For inverter sizing ratios (defined as R = inverter maximum AC output rating/PV DC rating) of R = 0.81 and R = 0.87 the annual energy losses as a percent of annual energy production were 2.65% and 2.20% using 1-s measurement resolution. Annual energy losses were calculated by aggregating the difference between modeled power (assuming no saturation occurred) and measured power. Losses due to cloud enhancement dominated the total losses, especially for R = 0.87. Increasing inverter size reduces saturation losses during high irradiance conditions, but decreases inverter conversion efficiency under low irradiance conditions. Increasing the sizing ratio to R = 1.22 would result in a maximum amount of energy production at our site. Averaging on timescales from 1-s to 1-h was performed to demonstrate that cloud enhancement losses can only be quantified using 10-s or finer measurements.     

Performance of a multi-bed adsorption heat pump using SWS-1L composite adsorbent and water as the working pair

An analysis of the coefficient of performance (COP), specific cooling power (Q_scp) and exergy losses for a four-bed adsorption heat pump is presented. A composite adsorbent (SWS-1L) and water are the adsorption pair. An optimum cycle time, corresponding to a maximum specific cooling power, was found. This maximum specific cooling power increases almost linearly with the regeneration temperature. For the operation corresponding to the maximum specific cooling power at the regeneration temperature of 120 °C, using the SWS-1L composite adsorbent to substitute a regular-density silica gel in the adsorbers, the COP and Q_scp values can be increased by 51% and 38.4%, respectively. At the regeneration temperature of 100 °C and the mode operating time of 360 s, the second-law efficiency of the adsorption heat pump is 20.4%. The cycle exergy loss mainly occurs in the adsorbers. The exergy losses in the condenser and evaporator are small. Among the four processes in the adsorbers, the precooling and preheating processes result in 41.55% and 28.96% of the cycle exergy loss, respectively, while the adsorption and regeneration processes cause 8.44% and 18.97%, respectively. The exergy losses in the precooling and preheating processes mainly result from heat transfer through a significant temperature difference.     

Experimental validation of autonomous PV-based water pumping system optimum sizing

The progress met in the world market of photovoltaics underlines the maturity of investments realized, guarantees the reliability of the technology utilized and designates the variety of applications in covering the energy demands of both stand-alone and grid connected consumers. Concerning stand-alone systems, the incorporation of photovoltaic systems in water pumping applications is thought to be one of the most popular and ideal uses of solar energy exploitation, especially under the common allegation of coincidence between insolation and water demand. In this study, an attempt to investigate the opportunities of a PV powered water pumping system able to meet additional – apart from the water pump – electricity loads, results in the development of an optimum sizing methodology which is accordingly validated by experimental measurements. From the results obtained, it becomes clear that a properly designed PV-pumping configuration of 610 W_p is capable of covering both the electricity (max 2 kWh/day) and the water (max 400 L/h) management demands of a large variety of remote consumers.     

An experimental study on using natural vaporization for cooling of a photovoltaic solar cell

This study attempts to investigate a new way for cooling PV cell using natural vapor as coolant. The performance of solar cell was examined on simulated sunlight. The natural vapor encountered backside of PV cell vertically in various distribution and different mass flow rates. Also, the effect of natural vapor temperature in cooling performance was analyzed. Results indicated that the temperature of PV cell drops significantly with increasing natural vapor mass flow rate. In detail, the PV cell temperature decreased about 7 to 16 °C when flow rate reaches 1.6 to 5 gr min^− 1. It causes increasing electrical efficiency about 12.12% to 22.9%. The best performance of PV cell can be achieved at high natural vapor flow rate, low natural vapor temperature and the obtained optimum distribution condition.     

Hot water cooled electronics: Exergy analysis and waste heat reuse feasibility

We report an experimental study on exergetically efficient electronics cooling using hot water as coolant. It is shown that water temperatures as high as 60 °C are sufficient to cool microprocessors with over 90% first law (energy based) efficiency. The chip used in our experiment is kept at temperatures of 80 °C or below so as not to exceed any allowable industrial specifications for maximum microprocessor chip temperature. The use of hot water as coolant will eliminate the requirement for chillers typically used in air-cooled data centers and, therefore, significantly reduce the power consumption. An exergy analysis shows that a six fold rise in second law (exergy based) efficiency is achieved by switching the water inlet temperature from 30 °C to 60 °C. The resulting high exergy at the heat sink outlet is a measure of the potential usefulness of the waste heat of data centers, thereby helping to design data centers with minimal carbon footprint. A new metric for the economic value of the recovered heat, based on costs for electricity and fossil fuels, heat recovery efficiency and an application specific utility function, is introduced to underscore the benefits of hot water cooling. This new concept shows that the economic value of the heat recovered from data centers can be much higher than its thermodynamic value.     

Overall thermal energy and exergy analysis of hybrid photovoltaic thermal array

In this paper, overall thermal energy and exergy analysis has been carried out for different configurations of hybrid photovoltaic thermal (PVT) array. The hybrid PVT array (10.08 m × 2.16 m) is a series and parallel combinations of 36 numbers of PV modules. A one-dimensional transient model for hybrid PVT array has been developed using basic heat transfer equations. On the basis of this transient model, an attempt has been made to select an appropriate hybrid PVT array for different climatic conditions (Bangalore, Jodhpur, New Delhi, and Srinagar) of India. On the basis of high grade energy (i.e. overall exergy gain), case-III has been selected as the most appropriate configuration because overall exergy for case-III is 12.9% higher than case-II. The overall thermal energy and exergy gain for Bangalore is 4.54 × 10⁴ kW h and 2.07 × 10⁴ kW h respectively which is highest in comparison to the other cities.