Ziyad M. Salameh

Methodology for optimally sizing the combination of a battery bank and PV array in a wind/PV hybrid system

In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the average power generated by a wind turbine and a PV module for every hour of a typical day in a month. A load of a typical house in Massachusetts, USA, was used as a load demand of the hybrid system. For a given load and a desired loss of power supply probability, an optimum number of batteries and PV modules was calculated based on the minimum cost of the power system.

A mathematical model for lead-acid batteries

A mathematical model of a lead-acid battery is presented. This model takes into account self-discharge, battery storage capacity, internal resistance, overvoltage, and environmental temperature. Nonlinear components are used to represent the behavior of the different battery parameters thereby simplifying the model design. The model components are found by using manufacturers specifications and experimental tests. A comparison between the model and experimental results obtained from a battery evaluation test system was used for verification. This model can be used to accurately evaluate battery performance in electrical systems. >

Optimum photovoltaic array size for a hybrid wind/PV system

A methodology for calculation of the optimum size of a PV array for a stand-alone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the probability density functions of the wind speed and the irradiance for each hour of a typical day in a month. The wind speed and irradiance probability density functions and manufacturers specification on a wind turbine and a PV module were used to calculate the average power generated by the wind turbine and the PV module for each hour of a typical day in a month. The least square method is used to determine the best fit of the PV array and wind turbine to a given load. On the basis of the energy concept an algorithm was developed to find the optimum size of the PV array in the system. >

Dynamic response of a stand-alone wind energy conversion system with battery energy storage to a wind gust

A mathematical model of each element of a stand-alone wind energy conversion system is developed. The model variables are expressed in the d-q rotor reference frame. The wind turbine was considered as the only source of power in this study. Using this model, the system response to a recorded wind gust is investigated by calculating the generator current, the rectifier current, the load current, the battery charging current and the battery voltage. The calculated results are then verified by comparing them with actual values obtained from a data acquisition system. Good agreement was achieved between the experimental and analytical results.

Step-up maximum power point tracker for photovoltaic arrays

Abstract This paper discusses a new maximum power point tracker (MPPT), which has been devised and tested at the laboratory. This MPPT is a high-frequency set-up dc-to-dc power conditioning unit. Simple and inexpensive analog circuitry is used to continually maximize the true PV array output power rather than maximizing the current or voltage at either the PV array or load. The control circuit is designed such that the actual current and voltage are sensed directly from the PV array. These two signals are then multiplied by a single-chip multiplier. The multiplier output charges or discharges two separate RC circuits of different time constants. These two RC signals are then mixed to set the duty cycle of a pulse width modulated signal to continually track the array maximum power point. This MPPT is simple and inexpensive; and it continuously tracks the true PV array maximum power point regardless of the load type.

Photovoltaic module-site matching based on the capacity factors

In this paper, a methodology for the selection of the optimum photovoltaic module for a specific power plant site is developed. The selection is based on the capacity factors (CF) of the available PV modules. Long term irradiance data recorded for every hour of the day for 30 years are used. These data are used to calculate the probability density function of the irradiance for different hours of a typical day in a month. The irradiance probability density function and the manufacturers specifications on PV modules are used to calculate the capacity factors for the PV modules. The PV module with the highest average capacity factor for the specific site is the optimal and recommended PV module. In this paper, the price per installed maximum peak watt is approximately the same for different modules and hence the cost is not an issue. >

Sizing of a stand-alone hybrid wind-photovoltaic system using a three-event probability density approximation

Abstract The PV-array and battery storage sizing of a stand-alone hybrid wind-photovoltaic system is being addressed here. A probabilistic approach is used to arrive at the results. A new technique using a three event probability density instead of the traditional two event approximation is developed. This technique is then used to determine the optimum relationship between the number of PV panels and the number of storage batteries required for the stand-alone hybrid wind-photovoltaic system, to meet a certain loss of power probability. This method uses long term data of wind speed, irradiance and ambient temperature taken every hour for 30 yr and the load specifications for a “typical New England house” that is going to be powered by the hybrid system.

Step-down maximum power point tracker for photovoltaic systems

Abstract A design of a simple, inexpensive, and efficient maximum power point tracker (MPPT) is presented. This design calls for a fixed voltage and a pilot cell to track the maximum power point voltage (Vmp). The tracking is done by changing the duty cycle of a step-down chopper, which is controlled by a direct feedback analog circuit. The control voltage of the tracker is the open circuit voltage (Voc) of the pilot cell multiplied by a constant. This constant is preadjusted so that it tracks the Vmp of the array in response to any changes due to temperature or insolation. This MPPT can also function as a voltage regulator for battery charging.

Determination of lead-acid battery capacity via mathematical modeling techniques

The evaluation of the ampere-hour capacity of a lead-acid battery using a mathematical modeling technique is presented. The battery model was used to simulate a battery cycle at different temperatures, at different rates of charge and discharge, and at different end voltages to determine how the battery parameter of ampere-hour capacity was affected. The parameter obtained from the model simulation was compared with experimental results for verification. It is shown that the mathematical model accurately depicts ampere-hour capacity under various operating conditions. >

Analysis of the effects of a passing cloud on a grid-interactive photovoltaic system with battery storage using neural networks

In this paper, a combined radial-basis-functions (RBF) and backpropagation network is used to predict the effects of passing clouds on a utility-interactive photovoltaic (PV) system with battery storage. Using the irradiance as input signal, the network models the effects of random cloud movement on the electrical variables of the maximum power point tracker (MPPT) and the variables of the utility-linked inverter over a short period of time. During short time intervals, the irradiance is considered as the only varying input parameter affecting the electrical variables of the system. The advantages of artificial neural network (ANN) simulation over standard linear models is that it does not require the knowledge of internal system parameters, involves less computational effort, and offers a compact solution for multiple-variable problems. The model can easily integrated into a typical utility system and resulting system behavior can be determined. The viability of the battery-supported PV power system as a dispatchable unit is also investigated. The simulated results are compared with the experimental results captured during cloudy days. This model can be a useful tool in solar energy engineering design and in PV-integrated utility operation.