PV powered universities literature review/Fab Pitfalls with "Green Energy" at University and Government Campuses

Fab Pitfalls with "Green Energy" at University and Government Campuses[1][1][1][1][1][edit | edit source]

Abstract Many university and government campuses have rapidly expanding "Green Energy" programs. These programs often include a mix of solar photovoltaic power, wind power, fuel cells, and other low-carbon sources. Unfortunately, practical experience has shown serious problems with these sources powering sensitive fab tools. A better solution is to operate the fab tools from traditional utility-provided power, then use the "green" power to operate less-sensitive fab support equipment: chillers, CDA compressors, CDW pumps, and so forth. This less-sensitive equipment often consumes half or more of the entire fab energy budget, and is readily adaptable - with some small technical effort - to tolerate the power disturbances found on a "green" grid.

• Practical experience has shown serious problems with renewable sources powering sensitive fab tools
• Switching frequency of a DC/AC inverter in PV installation create a large level of noise which can significantly affect metrology tools
• Green energy has a higher source impedance than utility energy which means that disruptive voltage sags tend to be deeper and longer

Forecasting of photovoltaic power yield using dynamic neural networks[2][2][2][2][2][edit | edit source]

Abstract The importance of predicting the output power of Photovoltaic (PV) plants is crucial in modern power system applications. Predicting the power yield of a PV generation system helps the process of dispatching the power into a grid with improved efficiency in generation planning and operation. This work proposes the use of intelligent tools to forecast the real power output of PV units. These tools primarily comprise dynamic neural networks which are capable of time-series predictions with good reliability. This paper begins with a brief review of various methods of forecasting solar power reported in literature. Results of preliminary work on a 5kW PV panel at King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia, is presented. Focused Time Delay and Distributed Time Delay Neural Networks were used as a forecasting tool for this study and their performance was compared with each other.

• The output of PV plants shows non-linear behavior which varies from day to day
• Data from smaller smaller scale solar systems recording time intervals of 10min exhibits output of more vivid nonlinearity
• FTDNN and DTDNN can be used to forecast power yield of a PV system connected to a local load
• FTDNN has been found to be a more attractive candidate for forecasting PV output in comparison with DTDNN

Evaluation and verification of an intelligent control system with modelling of green energy devices by constructing a micro-grid system in university campus (report I)[3][3][3][3][3][edit | edit source]

Abstract This paper presents a simulation model of green energy devices, which is developed for analyzing energy balance of a micro-grid and for optimizing its management. Several renewable energy based electricity production and storage are modeled and analyzed in the making of strategies for sustainable micro-grid management. In this study, two different simulation models are described, which call a "long-term simulation model", and a "detailed short-term simulation model". The first one is a high speed simulation model; it aims for prediction of the energy supply and demand balance of the micro-grid. In contrast, the second one is an accurate verification model; it use for detailed signal analysis of the devices and system. A case study, renewable energy model using photovoltaic, fuel cell, biomass and tidal power generation, is conducted and its simulation result is presented.

• The home and building energy management system (HEMS and BEMS) has been growing in Japan, and it enables resident to save energy and lower electricity bill payment
• The power supply emulator is software which runs on an emulation server, and is for copying the putput of a green energy device
• The information of power consumption, power supply, and various environmental data is stored in the EMS database server
• Based on the information and on prediction of power consumption and power supplies, EMS controls power generation systems and power consumption within possible limits
• Efficiencies of DC/DC converters are higher than full-wave rectifier efficiency
• The bidirectional DC/AC inverter controls the active power transferred from the DC bus to the AC bus

Centralized and modular architectures for photovoltaic panels with improved efficiency[4][4][4][4][4][edit | edit source]

Abstract The most common type of photovoltaic (PV) installation in residential applications is the centralized architecture. This realization aggregates a number of solar panels into a single power converter for power processing. The performance of a centralized architecture is adversely affected when it is subject to partial shading effects due to clouds or surrounding obstacles, such as trees. An alternative modular approach can be implemented using several power converters with partial throughput power processing capability. This paper presents a detailed study of these two architectures for the same throughput power level. The study compares the overall efficiency of these two different topologies, using a set of rapidly-changing real solar irradiance data collected by the Solar Radiation Research Laboratory (SRRL) at the National Renewable Energy Laboratory (NREL). This provides an opportunity to study both schemes using real measured data. The output power of both the topology is compared against the panel ideal power. Hence, the efficiency is overall in nature. The electrical efficiency is another form of computation which uses the panel maximum available power as input instead of panel ideal power. The paper uses overall efficiency for all analysis. The buck converter along with the Perturb & Observe maximum power point tracking algorithm were selected to perform the study. A detail power loss analysis is also presented in the paper. Analytical results are validated through detailed computer simulations using the Matlab/Simulink mathematical software package.

• The modular architecture has resulted in more overall efficiency than its counterpart CMPPT under shading conditions such as clouds
• P&O fails to track the maximum power under a sharp change in irradiation patterns even in the case of modular topology
• The sharp changes only occurs for a very short duration, once the solar irradiance settles to a new value, the MPPT will stabilize to new operating point
• The change in temperature will not likely to affect the function of MPPT because the power electronics operates much faster than the weather or temperature change

Greenhouse gases emissions and energy payback of large photovoltaic power plants in the northeast united states[5][5][5][5][5][edit | edit source]

Abstract The majority of large-scale solar farms have so far been constructed in the Southwest of the United States due to the intense insolation there. However, the high cost of electricity and the desire to increase the portion of renewables in the electric supply have generated interest in developing large-area plants in other areas. The environmental impact of building such large-scale solar farms in the northern United States has not yet been evaluated; we do so in this paper. This work discusses the life-cycle environmental impact from constructing and operating a 37-MWp solar-photovoltaic power-plant on the forested campus of Brookhaven National Laboratory, New York. We use the results from our assessments of its life-cycle emissions of greenhouse gases are then compared with those generated by similar plants in other regions to assess the net impacts of photovoltaics' life cycles in areas where trees are removed to accommodate the power plant.

• Single axis solar panels made of multi crystalline silicon have an average efficiency of 13.5% and its total power is about 37MWdc
• 10% of inverters' part must be replaced every 10 years
• Photovoltaic would reduce at least 68% of the green house gases which would be emitted from the current electricity system

A green prison: The Santa Rita Jail campus microgrid[6][6][6][6][6][edit | edit source]

Abstract A large microgrid project is nearing completion at Alameda County's twenty-two-year-old 45 ha 4,000-inmate Santa Rita Jail, about 70 km east of San Francisco. Often described as a green prison, it has a considerable installed base of distributed energy resources (DER) including an eight-year old 1.2 MW PV array, a five-year old 1 MW fuel cell with heat recovery, and considerable efficiency investments. Fig. 1 is an aerial depiction of the Jail with the PV rooftop modules clearly visible.

• Round-trip losses are significant for NaS batteries, and 30 percent is the average here
• In general, the battery is charged in the early morning hours and discharged during the following afternoon

A green campus project and advances in semiconductor nanostructures for photovoltaic applications[7][7][7][7][7][edit | edit source]

Abstract We provide an overview of the various campus wide "Green" projects at the University of California, San Diego aiming for higher energy saving and efficiency for buildings and facilities. We present results on novel photovoltaic and photoelectrochemical cells based on semiconductor nanostructures, including compound semiconductor quantum wells and Si-based nanowires, for solar energy generation and storage.

• The solar cell efficiency is improved 250 percent by SiNx surface passivation, and conformal ITO contact reduces the series resistance and improves the energy conversion efficiency about 5 times compared to bare Si p/n junction solar cells and about 2.3 times to that of SiNx passivated devices
• The use of Ag mesh grid on ITO top contact reduces the series resistance and increase of efficiency
• High quality Al2O3 passivation gives the best energy conversion efficiency

An innovative approach for determining PV cost convergence in the 25 Solar America Cities[8][8][8][8][8][edit | edit source]

Abstract This presentation introduces the PV cost convergence calculator (PV CCC) developed under a contract supporting the U.S. Department of Energy's (DOE) Solar America Cities (SAC) program. The PV CCC is the first tool of its kind to provide a means to compare solar PV levelized costs and the timing of PV cost convergence with conventional energy sources for inter-city residential and commercial systems. The model reveals the specific impacts of various types of incentives on grid parity, and provides valuable input for strategic planning activities.

• The PV CCC is the first tool of its kind to compare the timing of PV cost convergence for inter-city residential and small commercial-scale solar PV systems for the 25 U.S
• The PV CCC model considers other important regional information such as local energy prices and local incentives, both of which vary widely throughout the United States

Large-scale photovoltaic solar power integration in transmission and distribution networks[9][9][9][9][9][edit | edit source]

Abstract The province of Ontario in Canada has embarked on a major initiative to promote the grid interconnection of photovoltaic (PV) solar power systems. The Ontario Centres of Excellence, Centre of Energy, has recently approved a $6 million project for this purpose to a team of two Universities — University of Western Ontario and University of Waterloo, together with the support of four major industry partners who are involved in this technology in Ontario. A new technology has been developed for the utilization of PV solar farms in the nighttime and also during daytime as STATCOM. This paper will present the scope, objectives, research activities and commercialization potentials of this transformative project.

• Large solar power plants can cause reverse power flow in the feeder transformers which results a transformer maloperation
• Feeder losses can be reduced when properly sized and placed photovoltaic systems match the feeder peak load
• Fluctuations can happen in the output power of photovoltaic systems by random variations of solar irradiance which is caused by environmental conditions
• In order to predict the solar power that can be transmitted to the grid, real-time models of weather and metrological data are superimposed
• For determining the wind load, solar panels need to be instrumented with pressure taps

Simulation and experimental study of shading effect on series and parallel connected photovoltaic PV modules[10][10][10][10][10][edit | edit source]

Abstract Partial shading of photovoltaic modules is a widespread phenomenon in all kinds of Photovoltaic (PV) systems. In many cases the PV arrays get shadowed, completely or partially, by the passing clouds, neighboring buildings and towers, trees or the shadow of one solar array on the other, etc. This further leads to nonlinearities in characteristics. In this study, the simulation and experimental results of uniform and partial shading of PV modules are presented. Different shading pattern have been investigated on series and parallel connected photovoltaic module to find a configuration that is comparatively less susceptible to electrical mismatches due shadow problems. Simscape simulation model is employed to model the solar cell taking into account its series and parallel resistance.

• The output characteristics of a PV module get more complicated if the entire array does not receive uniform insolation
• A bypass diode can be added in parallel with solar cell in order to overcome the effects of partial shading
• Shaded cells absorb power and act as a load which means that power is dissipated in shaded cells as heat and cause hot spots

Assessing the effect of variable atmospheric conditions on the performance of photovoltaic panels: A case study from the Vaal Triangle[11][11][11][11][11][edit | edit source]

Abstract The purpose of this paper is to present a practical setup which is used to determine the availability of power from a singular stationary photovoltaic panel for variable atmospheric conditions in the Vaal Triangle, located in southern Gauteng, South Africa. Atmospheric conditions in this paper are characterized by air pollution and cloud movements, both which impact negatively on the operation of photovoltaic panels as shown by a number of scientific studies. Power regulation is achieved through the use of a DC-DC converter with a constant load resistance being employed to ensure reliability of the results for repeated measurements. The performance of the system is determined by considering the amount of time in which the DC-DC converter delivers power to the load resistance over a one week period, given as a percentage. Initial results indicate that the performance of this system varies by as much as 26% over a three month period stretching from March through May of 2011.

• Cloudy conditions and air pollution prevent direct radiation, and they give rise to diffuse radiation which is not conductive to optimum PV performance
• A major drawback of PV energy generation is the low power density and related to solar irradiation and low efficiency of the PV conversion
• A 24 V DC/DC converter can be used to ensure a minimum voltage drop over the converter between its input and output
• The on-time of the system can be determined with a normal probability plot in MS EXCEL using the Data Analysis Toolpak

An experimental investigation of the real time electrical characteristics of a PV panel for different atmospheric conditions in Islamic University of Technology (OIC), Gazipur, Bangladesh[12][12][12][12][12][edit | edit source]

Abstract The electrical characteristics of a 60W, 12V PV panel is presented on this paper for geographical location of Latitude = 23° 43'N and Longitude = 90°25'E (Islamic University of Technology, Gazipur, Dhaka, Bangladesh). The open circuit voltage and short circuit current of the panel are measured and recorded at an interval of three minutes along with the total solar irradiation. The total solar irradiation is measured using the device "UNIKLIMA VARIO" commissioned in the automatic weather monitoring station of the university. Based on the weekly data voltage-times and current-time curves are plotted for three different seasons from which the total available electrical power curve is also derived. Then the electrical efficiency of the panel is calculated using the solar irradiation data. The objective is to observe the variation of efficiency for different weather and atmospheric condition. The voltage generated by a PV panel depends on the geographical location of the site, time of the year, time of the day and local weather condition. The geographical and climatic condition of the chosen site is suitable for PV power systems. The electrical design of the array is influenced by the factors such as- sun intensity, sun angle, load matching for maximum power and operating temperature of the panel. Based on the experiments it has been observed that with increased radiation, the panel current is increased linearly. With a constant irradiation, the output voltage of the panel is increased for a decrease in the panel temperature or vice-versa. Finally the efficiency curve for the three different seasons is plotted and according to the observed data a comparison is carried on based on different factors affecting the efficiency of the panel. The total energy output in kWh is also calculated using the power curve of the panel for three different seasonal variations.

• The most important factor for designing any solar energy system is having the knowledge of quantity and quality of the solar energy at a specific location
• The countries that are located within 3.200 km of the equator, the usage of sun's energy can be economically significant
• The solar energy variations is related to the angle that the sun makes with a horizontal plane on the surface of the earth
• The automatic weather station UNIKLIMA vario is used for storing the climatic data, controlling, and monitoring
• When the cell temperature increases due to the increase in irradiation, the cell starts to operate at a lower efficiency; therefore, the efficiency of the cell is higher in the winters than summers

Analysis of the solar and wind resources for applications in hybrid systems in the Yucatan Peninsula[13][13][13][13][13][edit | edit source]

Abstract The evaluation of PV-Wind hybrid systems under real field conditions is essential to predict their actual capacity to convert the energy available in the solar radiation and wind resources into electrical power. Therefore, detailed studies of these resources play a crucial role to estimate whether electricity can be generated at a reasonable cost for a specific region. The work presented in this paper shows the results of a study of Solar and Wind resources with the purpose of being applied in conjunction for reliable hybrid PV-Wind generators in the Yucatan Peninsula region. The study was undertaken at the Energy Laboratory of the Autonomous University of Yucatan located close to the north coast. Diurnal and seasonal variations were computed for each resource.

• The data collection system used in this research comprises a solar tracker system, solar radiation sensors, a wind and direction sensors, a data-logger and a computer
• The data logger collects, pre-processes and stores the data measured from the sensors every two seconds then compute the averages every one minute
• The solar sensors include a shadow system to measure the diffuse radiation and a support tracking arm to aim the pyheliometer toward the sun position allowing monitoring the direct radiation on the study site