I have the error Attempted to access Irs(1.21516); index must be a positive integer or logical.

while the code is

 clc 

 close all 

 Gref = 1000; %reference irradiance

 Tcref=25+273; % reference temperature in Kelvin

 Tc=45+273; % opertion temperature in Kelvin 

 G=800; % operation irradiance

 Rs=0.39383;

 vocref=36.3;

 Eg=1.12; % band gap of material

 Iscref=7.84;

 A=0.98117; % ideality factor of diode

 q = 1.6e-19; 

 k = 1.38e-23;

 Ns=60;

 Ki=0.102;

 Ipv=(G/Gref)*(Iscref+Ki*(Tc-Tcref));

 vtn=(A*k*Tcref*Ns)/q;

 Irs= Iscref/(exp(vocref/(A*vtn))-1);

 Io= Irs((Tc/Tcref)^3)*exp(((Eg*q)/(A*K))*((1/Tcref)-(1/Tc)));

 Id=Io(exp((q*(v+I*Rs)/(A*K*Tc*Ns))-1));

 i = 0;   % Set initial current

 x=1;

 I = zeros(1,30);

 for v=0:0.005:36.3

 I(x)= Ipv - Io*(exp((q*(v+i*Rs)/(A*K*Tc*Ns))-1)) - ((v+Rs)/Rsh);

 i = I(x) %Update Current

 x=x+1;

 end

 v=0:0.005:36.3;

 P = I.*v; 

 plot(v,P)

 grid on

what should I do ?. P.S: I am still beginner.

[Stephen23]

Where do you imagine that the 1.21516th element of an array is?

Here is an array with three elements:

X = [   1,   2,   3]
        ^1st ^2nd ^3rd element

Where is the 1.21516th element of that array?

[shrik kader]

Stephen Cobeldick, As I said I am beginner, what do you suggest to do ?

[Stephen23]

@shrik kader: I don't know what your algorithm is, so unless you describe exactly what you are trying to achieve, I can only guess. My guess is that you might need interpolation of your data:

https://www.mathworks.com/help/matlab/interpolation.html

Answer 1

[Steven Lord]

If on this line of code:

Io= Irs((Tc/Tcref)^3)*exp(((Eg*q)/(A*K))*((1/Tcref)-(1/Tc)));

you're attempting to multiply Irs by ((Tc/Tcref)^3) and multiply the result by the exponential of another quantity, you're missing the first multiplication.

Io= Irs*((Tc/Tcref)^3)*exp(((Eg*q)/(A*K))*((1/Tcref)-(1/Tc)));

If instead you have a vector Irs containing data and an associated "index" vector and want to interpolate the Irs vector to obtain data at some point that is not present in the "index" vector, as Stephen said you will need to interpolate.