I am using pvlib.clearsky.detect_clearsky to detect if it’s clear sky, I am sure the inputs are series data with time, but it returns ‘ValueError: index can’t contain negative values’.

Here’s my code:

d_GHI = pd.read_excel(ghi_f)['GHI']
d_cr = pd.read_excel(clr_f)['GHI']
d_time_utc = pd.read_excel(ghi_f)['time']

d_GHI.index = d_time_utc
d_cr.index = d_time_utc

series_ghi = pd.Series(d_GHI)
series_cr = pd.Series(d_cr)




clearsky = pvlib.clearsky.detect_clearsky(d_GHI,d_cr)

I tried to change the input arguments as array and assigned times seperately, but still doesn’t work