*3.4. Error Measures*

The performance of the reference methods and the different approaches were evaluated with five different error measures for ANNs. The equation shows the mean-square error (MSE) [50,59].

$$\text{MSE}\left(\mathbf{x}',\mathbf{x}\right) = \frac{1}{N} \sum\_{n=1}^{N} \left(\mathbf{x}'\_n - \mathbf{x}\_n\right)^2 \,,\tag{13}$$

In the equations, *x* is the measured power time series, *x*2 is the predicted power time series, and *N* denotes the number of samples of the time series [47,48,59].
