Zero peaks in fft data even after subtracting mean

1. What does FFT peak at 0 mean?
2. Why is there a peak at 0Hz FFT?

What does FFT peak at 0 mean?

This is a constant value along with the time. This is to say that there is a strong component at 0 Hz compared with the variation around this constant value. You need only to interpret the results. Solution: try to subtract the average value from the signal in the time domain.

Why is there a peak at 0Hz FFT?

A peek at 0Hz represents the DC bias of the signal. If your signal has more area above 0 then below it you will get a peek at 0Hz.