Optimal sizing of array and inverter for grid-connected photovoltaic systems

Optimum PV/inverter sizing ratios for grid-connected PV systems in selected European locations were determined in terms of total system output, system output per specific cost of a system, system output per annualised specific cost of a system, PV surface orientation, inclination, tracking system, inverter characteristics, insolation and PV/inverter cost ratio. Maximum total system output was determined for horizontal, vertical and 45° inclined surfaces for a low efficiency inverter for sizing ratios of 1.5, 1.8 and 1.3, respectively; and for a medium efficiency inverter with sizing ratios of 1.4, 1.5 and 1.2. PV surface orientation and inclination have little impact on the performance of a high efficiency inverter. For different PV tracking systems and for different inverter characteristics, the optimum sizing ratio varied from 1.1 to 1.3. The PV/inverter cost ratio and the PV and inverter lifetimes have significant impact on the optimum PV/inverter sizing ratio. A correlation relating optimum sizing ratio and PV/inverter cost ratio has been developed; the correlation coefficients were found to be functions of insolation and inverter type. The impact of PV/inverter sizing ratio on PV array performance was less when PV array has a much higher cost than the inverter. The optimum sizing ratio for PV/inverter cost ratio of 6 and low efficiency inverter system varied from 1.4 to 1.2 for low to high insolation sites. For a high efficiency inverter system, the corresponding variation was from 1.3 to 1.1.     

Measures for diffusion of solar PV in selected African countries

This paper investigates how African governments are considering supporting and promoting the diffusion of solar PV. This issue is explored by examining so-called ‘technology action plans (TAPs)’, which were main outputs of the Technology Needs Assessment project implemented in 10 African countries from 2010 to 2013. The paper provides a review of three distinct but characteristic trajectories for PV market development in Kenya (private-led market for solar home systems), Morocco (utility-led fee-for service model) and Rwanda (donor-led market for institutional systems). The paper finds that governments’ strategies to promoting solar PV are moving from isolated projects towards frameworks for market development and that there are high expectations to upgrading in the PV value chain through local assembly of panels and local production of other system elements. Commonly identified measures include support to: local production; financing schemes; tax exemptions; establishment and reinforcement of standards; technical training; and research and development.     

Comparative analysis of different supporting measures for the production of electrical energy by solar PV and Wind systems: Four representative European cases

In the 9th of March 2007, the European Council decided a fixing goal of 20% contribution of the renewable energy sources (RES) on the total European electric energy production in 2020.In order to reach such an ambitious goal, all the European countries are adopting different support policies for encouraging the installations of RES-based generation systems.In this paper, after a brief review on the main support policies for RES in Europe, the specific situations of four representative countries (France, Germany, Italy and Spain) are examined, with the purpose of putting into evidence the main differences in the support policies adopted for Photovoltaic (PV) and Wind systems.In particular, a comparison based on the calculation of the pay-back-period (PBP), the net present value (NPV) and the internal rate of return (IRR), for different sized PV and Wind systems, shows that in some situations a support policy can be not convenient for the owner of the RES-based generation system and that, in many cases, the differences between the way of implementation of the same support policy in different countries, can give place to significantly different results.     

Why is there overcapacity in China's PV industry in its early growth stage?

China has rich solar energy resources with great potential for future development. In recent years, encouraged and guided by China's central and local governments as well as international market, China's PV industry has seen a fast development, with increasingly expanded output. A complete industrial chain has taken shape. In 2011, the PV industry of China saw an annual output value of more than 300 billion RMB and total exports and imports of 142 billion RMB, providing jobs for 300,000 people. The development of China's PV industry mainly relies on the European market. Major factors driving the increase of its production capacity include: huge profits at early stage; great support of governments; lack of effective development planning; low-end processing and manufacturing; low admittance standards. The overcapacity in China's PV industry here refers to overcapacity of PV products such as silicon, polycrystalline silicon, solar cells and PV modules. Impacted by the US Financial Crisis and the European Debt Crisis, the market demand for PV products has been shrinking, resulting in more serious overcapacity of the industry. The Chinese government had hoped that the domestic PV market could absorb the overproduced PV products. However, it seems that, due to insufficient development and uncoordinated incentive system, the domestic PV market may not be able to promote significant change of the situation in a short period. Therefore, it should take a long time to solve the problem of overcapacity.     

Photovoltaic research and demonstration activities at New EnglandElectric

From 1985 onward, New England Electric has carried out and supported a wide range of research, development and demonstration projects related to the use of solar photovoltaic (PV) energy. This paper describes each project and summarizes performance to date. Several projects embody the concepts of distributed generation (DG) and demand-side management (DSM) as well as utilization of renewable energy. These residential and commercial grid-connected PV systems have reduced electrical demand at each site during the Company's summer peak hour from 1986 through 1993. In addition, during many of the hours around noon the residential systems have provided all of the energy for neighboring homes without PV systems. Transmission and distribution losses associated with the normal supply of energy to these sites was therefore minimized during these hours. On-site production of electricity via photovoltaics may also result in significant environmental benefits, particularly in summer, through displacement of energy from fossil-fueled peaking units. Other types of projects discussed include (1) a solar monitoring network, with simulation of electrical output for three types of PV systems, (2) a unique PV-assisted DC lighting system for a commercial building, (3) a large (100 kW) ground-mounted PV system, (4) a combination solar-PV and solar-thermal system, and (5) development of a single-module inverter     

A simple photo-voltaic tracking system

This paper describes a simple photo-voltaic (PV) tracking system which has been designed and manufactured using a pyramidal stand as a base. A rotating unit consisting of two pairs of modules fixed at an angle of 170° between them was installed at the upper edge of the stand. The four modules and a DC motor were connected to a bridge circuit making the system sensitive to solar tracking. The PV tracker has a DC–DC (24/2 V) converter, DC–AC (24/220 V) inverter and a battery. The modules are able to provide a maximum power of 100 W, which feeds the converter, inverter and DC motor. Wind resistance of the tracker is quite low. The total area of the four modules is 1.26 m². The inclination angle between the modules and the horizontal plane is adjustable (34°±11°) and the tracking angle is 120°. The system can track solar motion with an error of ±10°. The designed PV tracking system, with modules fixed at an angle of 170° to feed the load as well as the DC motor, exhibited it to be an efficient energy-conversion system. The fabricated system offers low wind resistance. The cost analysis data revealed that the proposed design was very economical and cost effective.     

Direct power control of grid connected PV systems with three level NPC inverter

This paper presents the control of a three-level Neutral Point Clamped (NPC) voltage source inverter for grid connected photovoltaic (PV) systems. The control method used is the Extended Direct Power Control (EDPC), which is a generic approach for Direct Power Control (DPC) of multilevel inverters based on geometrical considerations. Maximum Power Point Tracking (MPPT) algorithms, that allow maximal power conversion into the grid, have been included. These methods are capable of extracting maximum power from each of the independent PV arrays connected to each DC link voltage level. The first one is a conventional MPPT which outputs DC link voltage references to EDPC. The second one is based on DPC concept. This new MPPT outputs power increment references to EDPC, thus avoiding the use of a DC link voltage regulator. The whole control system has been tested on a three-level NPC voltage source inverter connected to the grid and results confirm the validity of the method.     

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.     

Review of international standards for grid connected photovoltaic systems

Photovoltaic power systems are unique in their characteristics and in their mode of application to buildings. Grid connected PV is being applied in a variety of applications including large centralised stations, commercial buildings and individual houses. There is a need for specific standards to address distinctive new issues created by grid connected PV power systems. Internationally many countries are attempting to develop standards for building integration, DC side issues and grid connection issues. This paper surveys the current developmental state of the major countries’ standards in this area, comparing and contrasting, standards and guidelines under development.     

DC current injection into the network from PV inverters of <5 kW for low-voltage small grid-connected PV systems

The present paper is focused on the study of DC current injection for low-voltage small grid-connected PV systems, which is one of the power quality requirements of utility companies. To achieve this aim, the existing status of guidelines and regulations in six selected countries where the development in the grid PV sector has evolved rapidly over the last decade (Australia, Germany, Japan, Spain, the United Kingdom and the United States) has been reviewed according to the DC current injection into the grid. Furthermore, a grid-connected system installed in Spain has been used to carry out measures concerning possible DC current injection into the grid. Thus, 12 single-phase inverters <5 kW (according to the transformer options: 50 Hz LF transformers, HF transformers or transformerless) from the European market have been tested. Many groups of measurements were made under different conditions. The results show that in all cases there is DC current injection, even if an LF transformer inverter is used.     

Building-integrated PV installations in the Netherlands: Examples and operational experiences

Building-integrated PV started receiving attention in the Netherlands around 1990. Attention has ever since been focusing on the integration of PV into new dwellings. Efforts have resulted in cost reductions, performance improvements, the development of new integration products and the creation of a network with utilities, property developers, architects, building companies and local authorities. PV system costs have been reduced by one third, to 5 Euro in 2000. System performance has gone up slightly during the reporting period, further reducing the costs per unit energy produced. Inverter costs have gone down from 1.5 Euro/Wp in 1991 to 0.5 Euro/Wp in 2000. Concerning integration into buildings and the building process, the Netherlands PV programme has been concentrating on developing products for low-cost integration into sloped roofs of new buildings. Watertight profile systems have been developed, tested, and applied in projects on a growing scale. The costs for building integration have come down due to improvements in integration systems, the electric system and in installation procedures. Projects have also been carried out on an increasing scale to learn about the integration of PV into the building process. In total, a capacity of more than 8 MW was installed by the end of the year 1999, with projects ranging from individual dwellings and offices to solar cities such as the Nieuw Sloten project in Amsterdam (250 kWp) and Nieuwland in Amersfoort (1 MW). Now, at the turn of the century, plans are being derived to give PV the ‘boost’ to become commercially viable within the next 7 to 10 years. For this, an ambitious goal is being formulated by government together with the PV industry, utilities, the building sector and others involved in PV in the Netherlands. Already in the mid-1990s, the long-term energy programme of the ministry of Economic Affairs set the target at an installed PV capacity of 250 MWp by the year 2010. In order to achieve a commercially viable market within the next 7 to 10 years, however, a goal of 500 MWp installed PV capacity would be required. Recent research shows that such a target is ambitious, but achievable if supported by dedicated government programmes, investments by industry and contributions of the building and utility sector.     

Solar Power 2006, San José, CA

The Solar Power 2006 conference in San José was the largest solar conference event in United States history. This meeting marks a new awakening of the United States to Solar Power, since the peak in interest in it during the 1970s. This editorial reviews the highlights of the meeting, with an emphasis on the companies that participated, and the areas where further research is crucially needed. Primarily, the meeting was focused on a review of the industries currently involved in solar conversion-related manufacturing and development, and the factors that limit market introduction of products. Some of the key outcomes of the meeting include the realization that large-scale concentrating solar thermal installations, rather than photovoltaic (PV) systems, will likely dominate utility-scale energy production (i.e. system outputs of over 100 MWe). It was noted that there has been a steady cost reduction in silicon PV modules, and the goal of a PV module cost near US$1.44/W (in 2002 dollars) is expected around 2013, at which time there will have been a cumulative module production of over 10,000 MW. However, the current shortage of silicon feedstock (polysilicon) will drive PV research directions for many years to come. Many venture-capital funded start-up companies have arisen to develop commercial approaches to thin film solar cells and modules that use less silicon.     

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.     

A new feller-buncher for harvesting energy wood: Results from a European test programme

In recent years, some manufacturers have developed new downsized feller-bunchers that are particularly suited to small-tree harvesting. One of these machines was tested in some of the most promising small tree resources of Europe, namely: Finnish young conifer forests, French hornbeam coppice and Italian sycamore plantations. The tests were conducted within the scope of a 3-year long European project, whose goal was to assess the suitability of this new technology to the production of wood biomass from silvicultural operations. Depending on site characteristics, the machine reached an average productivity between 4 and 8 green tonnes per net working hour, comparing favourably with other European shear-type felling heads and qualifying for deployment on a European scale.     

Performance of reverse osmosis pilot plant powered by Photovoltaic in Jordan

This paper presents the work performed within ADIRA project funded by European Union as a consortium of many countries to boost the integration of desalination units with renewable energy in rural areas. The work focused on the study of Water desalination by Reverse Osmosis (RO) and electricity generation using Photovoltaic Technology (PV) with additional battery storage. RO-PV system has been successfully designed, installed and tested in Hartha Charitable Society in northern part of Jordan as part of the ADIRA project. The system is composed of PV panels (433 Wp), softener and compact RO unit with typical daily water production of 500 L. The system produced clean drinking water from a salty water feed with salt content up to 1700 mg/L. The technical details of the RO plant, the energy supply and the operation strategies of the system are presented in this study. The effect of meteorological data like solar insolation, ambient temperature, daily sunshine hours on the performance of the RO-PV system are studied. Furthermore, effect of operating pressure and temperature on recovery percentage, salt rejection and specific energy consumption in addition to details about the PV current and voltage are also discussed.     

Procedure to carry out quality checks in photovoltaic grid-connected systems: Six cases of study

Assessing the correct operation of PV grid-connected systems (PVGCS) is paramount not only for mere energy and profitability concerns but also for safety reasons. Intended to this purpose, the IEC 62446 standard is open to some tests to be required in some circumstances, in addition to those stated in this document. Our work proposes a procedure to carry out quality checks in PVGCS complying with this standard and dealing with some tests not mentioned in it – namely, PV generator peak power measurement, inverter response and earth electrode measurement – so that the verification of the system gets more comprehensive. This procedure was carried out in six PV plants sited in different locations with a Mediterranean climate in Spain. The most remarkable results of this experimental campaign may be summarized as follows: an excellent on-site behavior of the inverters, in general very good figures for the isolation and earth electrode resistance and a scarcely relevant existence of hot spots. On the down side, some figures for the peak power of the tested PV generators well below their nominal value were found. The procedure described in this paper has proved to be a useful tool to assist in the verification of a PVGCS after installation and for subsequent re-inspection or maintenance.     

An intelligent method for sizing optimization in grid-connected photovoltaic system

This paper presents an intelligent sizing technique for sizing grid-connected photovoltaic (GCPV) system using evolutionary programming (EP). EP was used to select the optimal set of photovoltaic (PV) module and inverter for the system such that the technical or economic performance of the system could be optimized. The decision variables for the optimization process are the PV module and inverter which had been encoded as specific integers in the respective database. On the other hand, the objective function of the optimization task was set to be either to optimize the technical performance or the economic performance of the system. Before implementing the intelligent-based sizing algorithm, a conventional sizing model had been presented which later led to the development of an iterative-based sizing algorithm, known as ISA. As the ISA tested all available combinations of PV modules and inverters to be considered for the system, the overall sizing process became time consuming and tedious. Therefore, the proposed EP-based sizing algorithm, known as EPSA, was developed to accelerate the sizing process. During the development of EPSA, different EP models had been tested with a non-linear scaling factor being introduced to improve the performance of these models. Results showed that the EPSA had outperformed ISA in terms of producing lower computation time. Besides that, the incorporation of non-linear scaling factor had also improved the performance of all EP models under investigation. In addition, EPSA had also shown the best optimization performance when compared with other intelligent-based sizing algorithms using different types of Computational Intelligence.     

Optimal design and development of PV-wind-battery based nano-grid system: A field-on-laboratory demonstration

The present paper has disseminated the design approach, project implementation, and economics of a nano-grid system. The deployment of the system is envisioned to acculturate the renewable technology into Indian society by field-on-laboratory demonstration (FOLD) and “bridge the gaps between research, development, and implementation.” The system consists of a solar photovoltaic (PV) (2.4 kWp), a wind turbine (3.2 kWp), and a battery bank (400 Ah). Initially, a prefeasibility study is conducted using the well-established HOMER (hybrid optimization model for electric renewable) software developed by the National Renewable Energy Laboratory (NREL), USA. The feasibility study indicates that the optimal capacity for the nano-grid system consists of a 2.16 kWp solar PV, a 3 kWp wind turbine, a 1.44 kW inverter, and a 24 kWh battery bank. The total net present cost (TNPC) and cost of energy (COE) of the system are US$20789.85 and US$0.673/kWh, respectively. However, the hybrid system consisting of a 2.4 kWp of solar PV, a 3.2 kWp of wind turbine, a 3 kVA of inverter, and a 400 Ah of battery bank has been installed due to unavailability of system components of desired values and to enhance the reliability of the system. The TNPC and COE of the system installed are found to be US$20073.63 and US$0.635/kWh, respectively and both costs are largely influenced by battery cost. Besides, this paper has illustrated the installation details of each component as well as of the system. Moreover, it has discussed the detailed cost breakup of the system. Furthermore, the performance of the system has been investigated and validated with the simulation results. It is observed that the power generated from the PV system is quite significant and is almost uniform over the year. Contrary to this, a trivial wind velocity prevails over the year apart from the month of April, May, and June, so does the power yield. This research demonstration provides a pathway for future planning of scaled-up hybrid energy systems or microgrid in this region of India or regions of similar topography.     

Performance monitoring results of the first grid-connected BIPV system in Colombia

This paper summarizes the operational performance results of the first grid-connected building integrated photovoltaic (BIPV) system installed in Colombia (in Bogotá, at 4°35′ latitude and 2.580 m altitude) after two years of monitoring. The performance monitoring was carried out with a sophisticated monitoring system, designed and implemented by us using the virtual instrumentation concept. The following parameters were measured: DC and AC power, inverter and system conversion efficiency, energy generated by the PV array, AC energy produced by the BIPV system, parameters to analyze power quality (%THD, harmonic components, frequency, voltage, flickers, power factor, active power, apparent power and reactive power), solar radiation in the inclination plane of the panels and environment temperature.The data obtained allowed to evaluate the general performance and the quality of the electric power generated by the photovoltaic plant. The results indicated that the power generated by the grid-connected BIPV plant fulfills the specifications demanded for such systems by National and International standards.     

The impact of array inclination and orientation on the performance of a grid-connected photovoltaic system

The impact of PV surface orientation and inclination on grid-connected photovoltaic system performance under maritime climates was investigated using validated TRNSYS simulations. Insolation, PV output, PV efficiency, inverter efficiency, system efficiency, performance ratio (PR) and PV savings were estimated annually, seasonally and on monthly bases for various surface inclinations and orientations. Incident insolation and PV output were maximum for a surface with inclination 30° facing due south and minimum for a vertical surface with orientation 90° east or west from south. The monthly optimum collection angle maximising incident insolation varied from 10° to 70°. For the particular location and system studied, the maximum annual PV efficiency, the inverter efficiency, the PR and the system efficiency were for a south-facing surface with an inclination of 20°. For a horizontal surface, the monthly variation of system parameters was significant over a year. For time-dependent tariff rates, the annual PV savings were higher for a system oriented with same orientation towards the west than east from south while for constants tariff rates, the PV savings was the same for east or west orientation from south.