Thermodynamic assessment of photovoltaic systems

In this paper, an attempt is made to investigate the performance characteristics of a photovoltaic (PV) and photovoltaic-thermal (PV/T) system based on energy and exergy efficiencies, respectively. The PV system converts solar energy into DC electrical energy where as, the PV/T system also utilizes the thermal energy of the solar radiation along with electrical energy generation. Exergy efficiency for PV and PV/T systems is developed that is useful in studying the PV and PV/T performance and possible improvements. Exergy analysis is applied to a PV system and its components, in order to evaluate the exergy flow, losses and various efficiencies namely energy, exergy and power conversion efficiency. Energy efficiency of the system is calculated based on the first law of thermodynamics and the exergy efficiency, which incorporates the second law of thermodynamics and solar irradiation exergy values, is also calculated and found that the latter is lower for the electricity generation using the considered PV system. The values of “fill factor” are also determined for the system and the effect of the fill factor on the efficiencies is also evaluated. The experimental data for a typical day of March (27th March 2006) for New Delhi are used for the calculation of the energy and exergy efficiencies of the PV and PV/T systems. It is found that the energy efficiency varies from a minimum of 33% to a maximum of 45% respectively, the corresponding exergy efficiency (PV/T) varies from a minimum of 11.3% to a maximum of 16% and exergy efficiency (PV) varies from a minimum of 7.8% to a maximum of 13.8%, respectively.     

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.     

Review of the performance of residential PV systems in France

The main objective of this paper is to review the state of the art of residential PV systems in France. This is done analyzing the operational data of 6868 installations. Three main questions are posed. How much energy do they produce? What level of performance is associated to their production? Which are the key parameters that most influence their quality? During the year 2010, the PV systems in France have produced a mean annual energy of 1163 kWh/kW_p. As a whole, the orientation of PV generators causes energy productions to be some 7% inferior to optimally oriented PV systems. The mean Performance Ratio is 76% and the mean Performance Index is 85%. That is to say, the energy produced by a typical PV system in France is 15% inferior to the energy produced by a very high quality PV system. On average, the real power of the PV modules falls 4.9% below its corresponding nominal power announced on the manufacturer's datasheet. A brief analysis by PV modules technology has led to relevant observations about two technologies in particular. On the one hand, the PV systems equipped with heterojunction with intrinsic thin layer (HIT) modules show performances higher than average. On the other hand, the systems equipped with the copper indium (di)selenide (CIS) modules show a real power that is 16% lower than their nominal value.     

Performance comparison of a double-axis sun tracking versus fixed PV system

In the present study, performance results of two double axis sun tracking photovoltaic (PV) systems are analyzed after one year of operation. Two identical 7.9 kWp PV systems with the same modules and inverters were installed at Mugla University campus in October 2009. Measured data of the PV systems are compared with the simulated data. The performance measurements of the PV systems were carried out first when the PV systems were in a fixed position and then the PV systems were controlled while tracking the sun in two axis (on azimuth and solar altitude angles) and the necessary measurements were performed. Annual PV electricity yield is calculated as 11.53 MW h with 1459 kW h/kWp energy rating for 28 fixed tilt angle for each system. It is calculated that 30.79% more PV electricity is obtained in the double axis sun-tracking system when compared to the latitude tilt fixed system. The annual PV electricity fed to grid is 15.07 MW h with 1908 kW h/kWp for the double axis sun-tracking PV system between April-2010 and March-2011. The difference between the simulated and measured energy values are less than 5%. The results also allow the comparison of different solutions and the calculation of the electricity output.     

Hybrid photovoltaic/thermal (PV/T) solar systems simulation with Simulink/Matlab

The purpose of this work consists in thermodynamic modeling of hybrid photovoltaic–thermal (PV/T) solar systems, pursuing a modular strategy approach provided by Simulink/Matlab.PV/T solar systems are a recently emerging solar technology that allows for the simultaneous conversion of solar energy into both electricity and heat. This type of technology present some interesting advantages over the conventional “side-by-side” thermal and PV solar systems, such as higher combined electrical/thermal energy outputs per unit area, and a more uniform and aesthetical pleasant roof area. Despite the fact that early research on PV/T systems can be traced back to the seventies, only recently it has gained a renewed impetus. In this work, parametric studies and annual transient simulations of PV/T systems are undertaken in Simulink/Matlab. The obtained results show an average annual solar fraction of 67%, and a global overall efficiency of 24% (i.e. 15% thermal and 9% electrical), for a typical four-person single-familiar residency in Lisbon, with p-Si cells, and a collector area of 6 m². A sensitivity analysis performed on the PV/T collector suggests that the most important variable that should be addressed to improve thermal performance is the photovoltaic (PV) module emittance. Based on those results, some additional improvements are proposed, such as the use of vacuum, or a noble gas at low-pressure, to allow for the removal of PV cells encapsulation without air oxidation and degradation, and thus reducing the PV module emittance. Preliminary results show that this option allows for an 8% increase on optical thermal efficiency, and a substantial reduction of thermal losses, suggesting the possibility of working at higher fluid temperatures. The higher working temperatures negative effect in electrical efficiency was negligible, due to compensation by improved optical properties. The simulation results are compared with experimental data obtained from other authors and perform reasonably well.The Simulink modeling platform has been mainly used worldwide on simulation of control systems, digital signal processing and electric circuits, but there are very few examples of application to solar energy systems modeling. This work uses the modular environment of Simulink/Matlab to model individual PV/T system components, and to assemble the entire installation layout. The results show that the modular approach strategy provided by Matlab/Simulink environment is applicable to solar systems modeling, providing good code scalability, faster developing time, and simpler integration with external computational tools, when compared with traditional imperative-oriented programming languages.     

太阳能光热与光电/光热系统在中国不同建筑气候带下的性能研究

文章利用TRNSYS动态模拟软件研究了在我国不同建筑气候带条件下,不同类型的太阳能PV/T集热系统和普通太阳能PT集热系统的各项性能.其中,太阳能PV/T集热系统分为基于普通玻璃型太阳能PV/T集热系统和基于Low-e型太阳能PV/T集热系统.文章探究了基于普通玻璃型太阳能PV/T集热系统和基于Low-e型太阳能PV/...     

Design and transient-based analysis of a power to hydrogen (P2H2) system for an off-grid zero energy building with hydrogen energy storage

In this study, zero energy building (ZEB) with four occupants in the capital and most populated city of Iran as one of the biggest greenhouse gas producers is simulated and designed to reduce Iran's greenhouse emissions. Due to the benefits of hydrogen energy and its usages, it is used as the primary energy storage of this building. Also, the thermal comfort of occupants is evaluated using the Fanger model, and domestic hot water consumption is supplied. Using hydrogen energy as energy storage of an off-grid zero energy building in Iran by considering occupant thermal comfort using the fanger model has been presented for the first time in this study. The contribution of electrolyzer and fuel cell in supplying domestic hot water is shown. For this simulation, Trnsys software is used. Using Trnsys software, the transient performance of mentioned ZEB is evaluated in a year. PV panels are used for supplying electricity consumption of the building. Excess produced electricity is converted to hydrogen and stored in the hydrogen tank when a lack of sunrays exists and electricity is required. An evacuated tube solar collector is used to produce hot water. The produced hot water will be stored in the hot water tank. For supplying the cooling load, hot water fired water-cooled absorption chiller is used. Also, a fan coil with hot water circulation and humidifier are used for heating and humidifying the building. Domestic hot water consumption of the occupants is supplied using stored hot water and rejected heat of fuel cell and the electrolyzer. The thermal comfort of occupants is evaluated using the Fanger model with MATLAB software. Results show that using 64 m² PV panel power consumption of the building is supplied without a power outage, and final hydrogen pressure tank will be higher than its initial and building will be zero energy. Required hot water of the building is provided with 75 m² evacuated tube solar collector. The HVAC system of the building provided thermal comfort during a year. The monthly average of occupant predicted mean vote (PMV) is between ?0.4 and 0.4. Their predicted percentage of dissatisfaction (PPD) is lower than 13%. Also, supplied domestic hot water (DHW) always has a temperature of 50 °C, which is a setpoint temperature of DHW. Finally, it can be concluded that using the building's rooftop area can be transformed to ZEB and reduce a significant amount of greenhouse emissions of Iran. Also, it can be concluded that fuel cell rejected heat, unlike electrolyzer, can significantly contribute to supplying domestic hot water requirements. Rejected heat of electrolyzer for heating domestic water can be ignored.     

Assesment of grid-connected photovoltaic systems in the Kuwaiti climate

Grid-connected photovoltaic (PV) systems is one of the most promising applications of PV systems. Till now, no detailed studies have been carried out to assess the potential of grid-connected systems in Kuwait. This work investigates the feasibility of implementing grid-connected PV systems in the Kuwaiti climate. The proposed system consists of crystalline solar modules mounted on the building roof and an inverter to convert PV dc output to ac voltage. The building receives electricity from both the PV array and the utility grid. In this system, the load is the total electrical energy consumption in the building.The objective of this work is to examine the performance as well as the economic feasibility of grid-connected PV systems in the Kuwaiti climate. A program is written to evaluate the performance as well as the economic feasibility of such systems in Kuwait. The input to the program is the weather data for Kuwait, time dependent building loads, as well as the utility rates for Kuwait. Weather data generator subroutine included in the program is used to generate hourly weather conditions from the monthly average values of daily radiation on horizontal surface, and ambient temperature available for Kuwait. The five-parameter PV model, which is applicable to both crystalline and amorphous PV modules, is used to determine the performance of the solar modules used in this study.The transient simulation program ( ) is used to link the components of the grid-connected PV system together. The inverter efficiency is represented as a linear function of input power. In this case, it is assumed that the AC output from the system will never be greater than the building load. Electricity tariffs will have an important impact on the cost-effectiveness of the system studied. The tariff used for electric utility is a flat rate per unit kWh of electrical energy. Simulations of the proposed system were carried out over the academic year.The building examined in this study is a flat roof building with a single story. The building roof area is large enough so that the PV arrays can be spaced widely to minimize shading losses. Different array slopes, and azimuth angles were studied to maximize the annual energy generated by the PV modules. Finally, the economic feasibility of grid-connected PV systems in Kuwait are examined.     

Valorization of the waste heat given off in a system alkaline electrolyzer-photovoltaic array to improve hydrogen production performance: Case study Antofagasta,Chile

The efficiency of an electrolyzer can be improved by preheating the water consumed, which is generally done by means of solar energy in PVT panels. In this research, the first objective is to determine whether it is possible to preheat the consumed water by using the residual heat given off by the electrolyzer itself fed by a PV array, and if the above is met, the second objective consists of quantify the benefits obtained in the performance of the system. The simulation is carried out over a period of one year, considering the meteorological conditions of the city of Antofagasta, Chile. The results indicate that it is possible to constantly maintain the water temperature consumed by the electrolyzer at its nominal value of 80 °C, since the energy contained in the waste heat is about 30 times higher than this hot water demand. Continuous operation at 80 °C compared to operation at variable temperature achieves an annual increase of 0.22% in hydrogen production and an average of 0.33% in electrolyzer efficiency. Moreover, by considering the thermal energy given off by the electrolyzer as useful output of the system, the overall energy efficiency increases by a relative percentage of 13%.     

Projected costs of a grid-connected domestic PV system under different scenarios in Ireland,using measured data from a trial installation

This paper presents results of a study of projected costs for a grid-connected PV system for domestic application in Ireland. The study is based on results from a 1.72 kWp PV system installed on a flat rooftop in Dublin, Ireland. During its first year of operation a total of 885.1 kWh/kWp of electricity was generated with a performance ratio of 81.5%. The scenarios employed in this study consider: a range of capital costs; cost dynamics based on a PV module learning rate of 20±5%; projections for global annual installed PV capacity under an advanced and moderate market growth conditions; domestic electricity cost growth of 4.5% based on historic data; and a reduction of 25% or 50% in the CO₂ intensity of national electricity production by 2055. These scenarios are used to predict when system life cycle production costs fall to grid prices (grid parity).     

Advances in reduction of total harmonic distortion in solar photovoltaic systems: A literature review

The use of photovoltaic (PV) systems has increased in recent years due to the high demand for clean energy sources. PV systems can utilize abundant and free energy from the sun, which is a substantial advantage. However, compared with other renewable technologies, the PV system still faces major obstacles such as high cost and low efficiency. In addition, fluctuating incident energy from the sun creates harmonics in the generated power that might lead to undesirable system performance. Total harmonic distortion (THD) is the ratio of distorted power to the main power of the signal, and is most commonly used to indicate the amount of signal distortion. THD has become a serious concern as more PV systems are integrated into grid systems. Previous research and reviews have attempted to reduce THD and its effect, but unfortunately focused on reducing THD at individual parts of the PV system. For the first time, this study holistically and systematically reviews the advances in THD reduction techniques for the entire PV system. The causes of harmonics, current solutions, and research gaps for further investigation are described in detail. Moreover, the current THD reduction techniques used in each stage of the PV system are compared, including their main benefits and drawbacks. Finally, this study recommends the use of adaptive filters as a possible solution for THD reduction because these filters have effectively reduced noise and disturbance in other systems.     

Review and comparison study of hybrid diesel/solar/hydro/fuel cell energy schemes for a rural ICT Telecenter

In this paper, the rural electrification study of an ICT Telecenter in particular reference to the Kelabit Highland of Sarawak is presented. The use of diesel generator and its associated environmental implications is first discussed. The cost-effectiveness of the present solar PV system and the solar/hydro schemes for rural electrification of the rural ICT are evaluated employing the HOMER simulation software, considering sustainability factors such as system efficiency, weather, fuel costs, operating and maintaining costs. Subsequently, simple novel Hybrid Energy Performance Equations and the associated Energy Performance Curves are derived and introduced, respectively, which provide a visualization model, simplifying hybrid system analysis. Results obtained in this study have shown that combined power schemes is more sustainable in terms of supplying electricity to the Telecenter compared to a stand-alone PV system due to prolong cloudy and dense haze periods. The hybrid systems can have efficiency range of ∼15%–75% compared to PV stand-alone of only ∼10%, indicating hybrid systems are more reliable and sustainable – in minimizing both energy losses and excess energy.     

Experimental results of controlled PV module for building integrated PV systems

Last issues about Building Integrated Photovoltaic Systems (BIPV) still show average Performance Ratio (PR) values in the range of 0.75–0.80. The main causes well known: partial shadows, temperature effects, PV inverter losses, thermal losses, etc. and mismatching losses. Ideally, all the modules work in the same conditions, but differences between modules really exist due to differences in the working temperature, the inclination or orientation angles, differences in the I–V characteristic coming from the manufacturing process, etc. The effect is that the output power of the complete PV system is lower than the addition of the power of each PV module.These mismatching losses can be decreased by means of suitable electronics. This paper presents the experimental results obtained over PV systems equipped with controlled PV modules, PV modules with low cost and high efficiency DC–DC converters, including MPPT algorithm and other functions, such as power control and Power Line Communications (PLC).Tests have been divided into two great categories: tests on the electronic performance of the DC–DC converter and tests on grid-connected PV systems with multiple DC–DC converters. Many of these tests have been carried out taking advantage of the PV System Test Platform, a powerful tool especially designed by Robotiker to evaluate all kind of PV systems, especially systems with differences between modules. Aspects of the DC–DC converter performance have been detailed and among the most important experiments, the paper analyses different situations such as partial shadows, different inclined planes, PV systems with different PV modules, and finally a comparison between a conventional system and a system composed by controlled PV modules have been described. To sum up, the importance of a good system dimensioning is analysed, with very interesting results.     

Exergetic performance evaluation of heat pump systems having various heat sources

In this study heat pump systems having different heat sources were investigated experimentally. Solar‐assisted heat pump (SAHP), ground source heat pump (GSHP) and air source heat pump (ASHP) systems for domestic heating were tested. Additionally, their combination systems, such as solar‐assisted‐ground source heat pump (SAGSHP), solar‐assisted‐air source heat pump (SAASHP) and ground–air source heat pump (GSASHP) were tested. All the heat pump systems were designed and constructed in a test room with 60 m² floor area in Firat University, Elazig (38.41°N, 39.14°E), Turkey. In evaluating the efficiency of heat pump systems, the most commonly used measure is the energy or the first law efficiency, which is modified to a coefficient of performance for heat pump systems. However, for indicating the possibilities for thermodynamic improvement, inadequate energy analysis and exergy analysis are needed. This study presents an exergetic evaluation of SAHP, GSHP and ASHP and their combination systems. The exergy losses in each of the components of the heat pump systems are determined for average values of experimentally measured parameters. Exergy efficiency in each of the components of the heat pump systems is also determined to assess their performances. The coefficient of performance (COP) of the SAHP, GSHP and ASHP were obtained as 2.95, 2.44 and 2.33, whereas the exergy losses of the refrigerant subsystems were found to be 1.342, 1.705 and 1.942 kW, respectively. The COP of SAGSHP, SAASHP and GSASHP as multiple source heat pump systems were also determined to be 3.36, 2.90 and 2.14, whereas the exergy losses of the refrigerant subsystems were approximately 2.13, 2.996 and 3.113 kW, respectively. In addition, multiple source heat pump systems were compared with single source heat pump systems on the basis of the COP. Exergetic performance coefficient (EPC) is introduced and is applied to the heat pump systems having various heat sources. The results imply that the functional forms of the EPC and first law efficiency are different. Results show that Ex_loss,total becomes a minimum value when EPC has a maximum value. Copyright © 2008 John Wiley & Sons, Ltd.     

Inverter sizing of grid-connected photovoltaic systems in the light of local solar resource distribution characteristics and temperature

Inverter sizing strategies for grid-connected photovoltaic (PV) systems often do not take into account site-dependent peculiarities of ambient temperature, inverter operating temperature and solar irradiation distribution characteristics. The operating temperature affects PV modules and inverters in different ways and PV systems will hardly ever have a DC output equal to or above their STC-rated nominal power. Inverters are usually sized with a nominal AC output power some 30% (sometimes even more) below the PV array nominal power. In this paper, we show that this practice might lead to considerable energy losses, especially in the case of PV technologies with high temperature coefficients of power operating at sites with cold climates and of PV technologies with low temperature coefficients of power operating at sites with warm climates and an energy distribution of sunlight shifted to higher irradiation levels. In energy markets where PV kW h’s are paid premium tariffs, like in Germany, energy yield optimization might result in a favorable payback of the extra capital invested in a larger inverter.This paper discusses how the time resolution of solar radiation data influences the correct sizing of PV plants.We demonstrate that using instant (10 s) irradiation values instead of average hourly irradiation values leads to considerable differences in optimum inverter sizing. When calculating inverter yearly efficiency values using both, hourly averages and 1-min averages, we can show that with increased time resolution of solar irradiation data there are higher calculated losses due to inverter undersizing. This reveals that hourly averages hide important irradiation peaks that need to be considered.We performed these calculations for data sets from pyranometer readings from Freiburg (48°N, Germany) and Florianopolis (27°S, Brazil) to further show the peculiarities of the site-dependent distribution of irradiation levels and its effects on inverter sizing.     

Medium scale photovoltaic applications forBarbados

A major obstacle to the implementation of significant photovoltaic applications in theCaribbean region is the unavailability of adequate analyses of the PV installations and theirappropriateness for the particular application, especially in terms of estimates of reliability,maximum and minimum as well as average performances. In this article we outline the currentsituation in Barbados, and show an example of the type of calculation which may be sufficient tointerest architects and engineers in the installation of significant PV systems. We calculate theinstantaneous beam solar energy incident on the four vertical faces of a building at fifteen minuteintervals for every day of the year assuming zero cloud cover. Cloud cover is estimated to reducethe beam contribution by about 15% over a year counterbalanced by the estimated diffusecomponent which increases the total available solar energy by about 30%. We thus determine theavailable energy for PV and find that it compares favourably with that on a horizontal surfaceunder the same conditions. These results indicate that replacing structural glass by PVglass—which incurs no additional cost—leads to worthwhile energy collection and cansignificantly reduce expenditure on electricity.     

Technico-economic analysis of off grid solar PV/Fuel cell energy system for residential community in desert region

A technico-economic analysis based on integrated modeling, simulation, and optimization approach is used in this study to design an off grid hybrid solar PV/Fuel Cell power system. The main objective is to optimize the design and develop dispatch control strategies of the standalone hybrid renewable power system to meet the desired electric load of a residential community located in a desert region. The effects of temperature and dust accumulation on the solar PV panels on the design and performance of the hybrid power system in a desert region is investigated. The goal of the proposed off-grid hybrid renewable energy system is to increase the penetration of renewable energy in the energy mix, reduce the greenhouse gas emissions from fossil fuel combustion, and lower the cost of energy from the power systems. Simulation, modeling, optimization and dispatch control strategies were used in this study to determine the performance and the cost of the proposed hybrid renewable power system. The simulation results show that the distributed power generation using solar PV and Fuel Cell energy systems integrated with an electrolyzer for hydrogen production and using cycle charging dispatch control strategy (the fuel cell will operate to meet the AC primary load and the surplus of electrical power is used to run the electrolyzer) offers the best performance. The hybrid power system was designed to meet the energy demand of 4500 kWh/day of the residential community (150 houses). The total power production from the distributed hybrid energy system was 52% from the solar PV, and 48% from the fuel cell. From the total electricity generated from the photovoltaic hydrogen fuel cell hybrid system, 80.70% is used to meet all the AC load of the residential community with negligible unmet AC primary load (0.08%), 14.08% is the input DC power for the electrolyzer for hydrogen production, 3.30% are the losses in the DC/AC inverter, and 1.84% is the excess power (dumped energy). The proposed off-grid hybrid renewable power system has 40.2% renewable fraction, is economically viable with a levelized cost of energy of 145 $/MWh and is environmentally friendly (zero carbon dioxide emissions during the electricity generation from the solar PV and Fuel Cell hybrid power system).     

Effects of large-scale photovoltaic power integration on electricity distribution networks

The public support in photovoltaic (PV) technologies and increasing markets have resulted in extensive applications of grid-connected PV, in particular in the consumer side and electricity distribution grid. In this paper, the effects of a high level of grid connected PV in the middle voltage distribution network have been analyzed. The emphasis is put on static phenomena, including voltage drop, network losses and grid benefits. A multi-purpose modeling tool is used for PV analysis in Lisbon and Helsinki climates. All network types studied can handle PV without problems with an amount of PV equaling at least up to the load (1 kW_p/household). The comb-type network showed the best performance. The PV is unable to shave the domestic load peak in the early evening hours but through orientating the PV panels both to east and west, the noon peak from PV can be reduced by 30%. PV integration reduces network losses positively up to a 1 kW_p/hh (100% of annual domestic load) level. For 2 kW_p/hh all but the comb-type networks demonstrate clear over-voltage situations and the annual network losses are much higher than without PV.     

Properties and uses of storage for enhancing the grid penetration of very large photovoltaic systems

In this third paper, which studies the hourly generation data for the year 2006 from the Israel Electric Corporation, with a view to incorporating very large photovoltaic (PV) power plants, we address the question: What properties should storage have in order to enhance the grid penetration of large PV systems in an efficient and substantial manner? We first impose the constraint that no PV energy losses are permitted other than those due to storage inefficiency. This constraint leads to powerful linkages between the energy capacity and power capacity of storage, and PV system size, and their combined effect on grid penetration. Various strategies are then examined for enhancing grid penetration, based upon this newfound knowledge. Specific strategies examined include PV energy dumping and baseload rescheduling both on a seasonal basis and shorter time periods. We found, inter alia, that at high grid flexibilities (in the range ff=0.8–1), PV grid penetration levels could be possible in the range 60−90% of annual requirements. Moreover, with appropriately designed storage and accurate forecasting, a future grid could be operated at ff=1.