Consider a multiple-array design with bypass diodes shown in the figure below Sh

Question

Consider a multiple-array design with bypass diodes shown in the figure below Shaded M1 M1 M1 M1 Inverter 240VAC GRID Shaded Shaded M2 M2 M2 M2 The technical data are as follows. Array 1: 4 series-connected modules M1, each module has an open-circuit voltage of 18V and short-circuit current of 6A Array 2: 4 series-connected modules M2, each module has an open-circuit voltage of 25V and short-circuit current of 8A The arrays are connected to grid via an inverter. Assume that, for each module, the maximum power voltage is 80% of Voc and the maximurm power current is 90% of Isc. The inverter outputs power to the grid at 240 VAC, power factor of 1.0, and efficiency of 90%. Assume that 3 modules are shaded, as shown in the figure. Under this condition, calculate the following parameters for the PV system: 1) PV source circuit voltage for Array 1 and Array 2 (i.e. Source 1 and 2) 2) PV source circuit current for Array 1 and Array 2 (i.e. Source 1 and 2) 3) PV output circuit voltage(i.e. the voltage at point C in the above figure) 4) The maximum-possible power output from the inverter to the grid. Assume that the inverter rating is sufficient to convert all power from the PV system.

Explanation / Answer

Multiple array design with bypass diodes.

Given data:

Module 1

open circuit voltage, Voc1 =18V

Short circuit current, Isc1 = 6A

Module 2

Open circuit voltage, Voc2 = 25V

Short circuit current, Isc2 = 8A

General data

  Maximum power voltage = 80% of Voc

Maximum power current = 90% of Isc

power factor = 1.0

efficiency = 90%

output power of inverter = 240VAC

Calculations:

1) The maximum circuiit voltage for array 1 and array 2,

Maximum circuit voltage is 25V.

2). The maximum circuit current for pv source circuits was calculated by taking the short circuit current and multiplying it by 125%.

For module 1

Isc1*125% = 6*125%

=6*(125/100)

=7.5A

For module 2:

Isc2*125% = 8*125%

= 8*(125/100)

=10A

PV source circuit current for array 1 and array 2( source 1 and 2) = 7.5+10 = 17.5A

(Determining the maximum source circuit current is important because when adding several arrays in parallel, the current is additive)

3). The PV output circuit must have a maximum voltage for that circuit calculated as the sum of the rated open circuit voltage

Voc1 + Voc2 = 18+25 = 43V

The voltage at point C = 43V

4).The maximum possible power output from the inverter to grid

Operated voltage * rated efficiency = 43*90% = 38.7W

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