How can I normalize FFT in frequency domain?

Hi, I've FFT Voltage of a solar panel and get weird amplitude in frequency domain. I've read some previous questions about FFT and it seems like you have to normalize the magnitude of FFT to get better values. Thank you in advance, Here is my code:

     [X1,TXT,RAW] = xlsread('FFT_starkutansno effekt.xlsx');
     time = X1(:,1); 
     Voltage = X1(:,2);
     f1 = fft(X1(:,2));
     DT = 0.1;
     Fs = 1/DT;              %sampling frequency
     DF = Fs/size(X1,1);
     freq = 0:DF:Fs/2;
     f1 = f1(1:length(f1)/2+1);    %frequency vector
     figure(1);
     plot(freq,abs(f1));
     grid
     ylim([0 360]); 
     ylabel(' Magnitude ');
     xlabel('Frequency (Hz) ');
     title('Fast Fourier Transform Without Snow And High Light Intensity');

     figure(2); 
     plot(time,Voltage); 
     xlabel(' Time (s) '); 
     ylabel(' Voltage (V) ');
     ylim([3.2 5.2]);
     title(' Voltage Without Snow And High Light Intensity ');

[David Goodmanson]

Hi Sahaphol,

The csv file and your code are not working well together, and even if they were it appears that the time array is not in the file.

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/matlab/ref/fft.html