PV Array 
By J. Eckstein 1990

	This subroutine represents a four parameter model of a Photovoltaic
Array.  It is capable of predicting the complete current-voltage 
characteristic over the entire operating voltage range of a flat-plate,
non-sunconcentrated collector.  While a series resistance is taken into
account, a shunt resistance is assumed to be infinite and thus neglected 
in the model.
	A routine is implemented which determines the voltage and current at
maximum power point. The operating current is found for a given voltage, 
irradiance and ambient temperature as input.  An option is provided to 
evaluate the series resistance with the bisection method, if not given as
input.  To overcome convergence problems which appear when simulating direct
coupled systems, a bisection method type of convergence promotion is 
included.  It is turned off, if input FLAG is equal to zero.  Sample input
and output are included in the source code following the variable 
identification.

	The model requires 18 parameters, 4 inputs and generates 10 outputs. Each is described below with units as required by the TYPE62. Parameters typical of a Siemens 100W panel are noted for reference sake.

PARAMETERS 18
1 Reference Short Circuit Current (6.5 A)
2 Reference Open Circuit Voltage (21.6 V)
3 Reference Cell Temperature (298 K)
4 Radiation at Reference Conditions (1000 W/m^2)
5 Voltage at Max Power (Reference Condition) (17 V)
6 Current at Max Power (Reference Condition) (5.9 A)
7 Temperature Dependence Coefficient of Open Circuit Voltage (ref cond) (-0.079 V/K)
8 Temperature Dependence Coefficient of Short Circuit Current (ref cond) (0.02 A/K)
9 Number of Cells in Series in module (36)
10 Number of modules in series
11 number of modules in parallel
12 Cell Temperature of Nominal Operating Cell Temperature (NOCT) Test (318 K)
13 Ambient Temperature of NOCT Test (293 K)
14 Radiation Level of NOCT Test (800 W/m^2)
15 Area (0.89 m^2)
16 Average tau alpha product (0.9)
17 Semiconductor Bandgap (1.12 eV)
18 Shunt Resistance (-1) (-1 indicates that it is very large)

INPUTS 4
1 Radiation (kJ/m^2)
2 Ambient Temperature (K)
3 Load Voltage 
4 Convergence Promoter on (1) or off (0)
(leave this last input "off" if you have battery storage)

OUTPUTS 10
1 Voltage (V)
2 Current (A)
3 Power (W)
4 Max power (W)
5 Power Output/Max Power output
6 Voltage at Max Power (V)
7 Current at Max Power (I)
8 Open Circuit Voltage (V)
9 Short Circuit Current (I)
10 Fill Factor (Ratio of area under PV curve to what it would be if it were a rectanlge)

REF: Detailed Modeling of Photovoltaic System Components by J. Eckstein
     Masters Thesis  at University of Wisconsin at Madison