Theoretical Study Of Solar Cells Utilization

Circuit is divided into linear circuit and non-linear circuit and solar cell equivalent circuit is a typical nonlinear circuit. The equivalent circuit with single diode five-parameter model is applicable to crystalline silicon (monocrystalline, polycrystalline, amorphous) solar cells, Ⅲ-Ⅴ compound solar cells and organic solar cells. By solar cells circuit analysis, the current equation is established using Kirchhoff’s current law and the voltage equation is established using Kirchhoff’s voltage law. In traditional linear circuit analysis, the maximum output power transfer theorems is stated as, when the load resistance is equal to the Thevenin equivalent resistance or Norton equivalent resistance, the load output the maximum power. In this paper, through the introduction of non-linear model, we obtain general current equation of nonlinear circuit and get the maximum output power transfer theorem, which is universal for linear and nonlinear circuit. It is clearly pointed out that the maximum output power transfer theorem of linear circuit is only a special case of the maximum output power transfer theorem. Maximum output power transfer theorem has been verified in solving the load resistance of maximum output power point cases.The current equation of solar cell establishes the relationship of load current and load voltage. We can plot Ⅰ-Ⅴ characteristic curve in the conventional single origin coordinate system, but we can not describe the current items and voltage items in the equivalent circuit, so a novel dual-origin coordinate system is designed in the second chapter. In dual-origin coordinate system, we mark the line of current equation and voltage equation. Dual-origin coordinate system achieves physical model, mathematical formula and function image in correspondence. Dual-origin coordinate system reveals that photo-generated current power is equal to the diode friction power, series and shunt resistance friction power and the load output power in physics and area of photo-generated current power is equal to the area of total friction power and the area of output power. The proportions of output power and internal friction power may change with photo-generated current; the output power is far less than the friction power with the high light, so solar cell does not apply to high light.In the theoretical study of solar cell utilization, we also need to consider the following four aspects:can the solar cell be transferred from linear to nonlinear? How is the battery power distribution on the load and series-shunt resistance? How to calculate the maximum power operating point and how to track? In order to get the big current and voltage, we need series-parallel array. What mathematical approach is using to study a series-parallel array?Ⅰ-Ⅴ characteristic curve is always expressed as a strict single minus convex curve, when the photocurrent or series resistance increases, Ⅰ-Ⅴ characteristic curve vary from curve to approximate straight line and the solar cell circuit is from non-linear to linear. The third chapter presents a criteria of shape number which is the ratio of the diode-voltage and the open circuit voltage. When the criteria reduce the interval range, it will appear the phenomenon. A necessary condition of this phenomenon is the existence of the series resistance, and we observed this phenomenon through the external series resistance experiment. When the Ⅰ-Ⅴ characteristic curve trends to approximate straight line, the fill factor tends to minimum value0.25.To get the maximum load output power and the friction power of series and shunt resistance is small, it is necessary to analyze solar cell power distribution on the various parts of the resistive element. Chapter IV carried out the study of the maximum output power load range and the gain-loss power load range. The results show that only when the ratio of series and parallel resistance is less than "1/8", the gain-loss power load range exists. When the load of maximum output power point is ’Rml=Rs(1+Rsh/Rs)0.5,we could get the maximum output power and also ensure that the ratio of load output power and series-shunt friction power has the maximum value ’[(1+Rsh/Rs)0.5-1]/2’.Maximum power research of solar cell has two levels:solving the maximum power point, this means that we can numerically calculate the load voltage and current maximum power point at assumed the five-parameter; tracking the maximum power point or determining the maximum power equation, this means that we plot the maximum power curve when the light changes. The fifth chapter gives the maximum power point load resistance iterative equation; computer simulation shows that the smaller series resistance, the greater shunt resistance, the smaller diode reverse saturation current and the larger diode ideality factor would make the output power larger. Theoretical studies indicate that the actual solar cells with increasing light intensity, load current and output power maximum power point are increased, then decreased and showed the phenomenon of voltage normally. Maximum power equation has the same important value as I-V characteristics in solar cell research and it is the mathematical basis of the maximum power tracking. Maximum power curve generally has two voltage extreme points, which are constant voltage tracking points. In Chapters VI and VII, we discuss the maximum power point tracking and suggest that constant resistance tracking could be adopted at low light and high light; under moderate light conditions, we recommend using a linear tracking, which requires slope tracking technology, the slope range is (-Rs,0). Near the two voltage extreme points of maximum power curve, we recommend constant voltage tracking; theoretical studies indicate that the minimum voltage of the constant tracking is’4nVth (1+Rs/Rsh)’.Computer simulation shows that silicon-based solar cells, from non-condensing to condensing multiple a dozen or two dozen suns, we can observe that the load voltage at the maximum power point firstly increases and then decreases with the condensing multiples increasing.In order to obtain a large load voltage and current, we need a series-shunt array consisting of single cells. In the eighth chapter, Lambert W function does not only give a voltage explicit solution with respect of current and a current explicit solution with respect of voltage, but also get the voltage equations of the circuit constituting series array with load and get the current equations of the circuit constituting shunt array with load.