Frequency for a time series
The sampling frequency, or sample rate, is the number of equal-spaced samples per unit of time. For instance, if you have 96 equally spaced observation per day, then you sampling rate is 96/day, or 96/24/3600=0.0011 Hz. Hz, which means per second, is widely used for sample rate.

The frequency of your data is different. I you signal is periodic or approximately periodic (say, the similar energy consumption patterns repeat everyday), the the frequency is the number of occurrence of that repeating pattern per unit of time. More generally, if your data does not look like periodic, it would help to conduct Fourier Analysis to understand the frequency components in your data. The Fourier Analysis (Fourier Transform) is the operation to transform time-domain data into the frequency domain.