The influence of the solar radiation and operating temperature

After the analysis of the internal structure of the photo voltaic array, we began to study the external influence to the photo voltaic array. There are mainly two factors that restrict the operation of the photo voltaic: the solar irradiation level and the ambient temperature. These can be affected by sudden change in the weather and the seasons. In this project, the influence of these factors must be researched and designed in the circuit.

It was told that the solar cell operation temperature is changed as a function of solar irradiation level and the ambient temperature.The function is shown below:

The temperature coefficient C_TV is the temperature influence on the photovoltaic cell voltage and the temperature coefficient C_TI is the temperature influence on the photovoltaic cell current.

It should be noted that the constant T_a is used as the reference temperature and the constant S_c is the reference solar irradiation at the temperature T_a. Then the temperature change T_x is made. The value of β_T­ is 0.004 and the value γ­_T is 0.06. The reference temperature T_a is 20 centigrade and the irradiation at this temperature S_c is 100. To make the temperature unit same, the temperature in Celsius should be converted into Kelvin: T_aK=T_ac +273.

Then considering the change in solar irradiation, the solar irradiation change can cause the change of cell temperature and this change also should be considered. It can be found that due to the variation of the solar irradiation level, the photovoltaic voltage and current change factors is expressed by the following equations:

The constant α_s is the change in temperature due to the variation of the irradiation level. It is equal to 0.2 for the solar cells used. S_x is the change value of the irradiation level. The coefficient C_SV is the irradiation influence on the photovoltaic cell voltage and the coefficient C_SI is the irradiation influence on the photovoltaic cell current.

According to above analysis, the new photovoltaic voltage and the current can be obtained after the change in the solar irradiation level and the ambient temperature. The equations for the new value are shown below:

The value V_c and I_ph is used as the benchmark reference cell output voltage and the reference cell photocurrent. V_cx and I_phx is the new value at the new temperature Tx and the new irradiation level S_x.