Page 117 - Advances in Renewable Energies and Power Technologies

90 CHAPTER 3 Forecasting of Intermittent Solar Energy Resource

1000
900
Global horizontal irradiance (Wh/m 2 ) 600
800
700

500
400
300
200
100 Measure
Forecast
0
1400
1340 1360 1380 Time (hours) 1420 1440
Forecasted global horizontal irradiance (Wh/m 2 ) 1000
900
800
700
600
500
400
300
200
100
0
0 100 200 300 400 500 600 700 800 900 1000
2
Measured global horizontal irradiance (Wh/m )
FIGURE 3.6
Upper: Time series of predicted and measured global irradiations e bottom: Scatter plot of
predicted vs. measured global irradiations.

concerning models’ performances for short-term renewable energy forecasting.
They concluded that: “More work using more test cases, data and models needs
to be performed to achieve a global overview of all possible situations. Test cases
located all over Europe, the US and other relevant countries should be considered,
trying to represent most of the possible meteorological conditions.” This paper
very well illustrates the difficulties associated with performance comparisons.
The usually used statistics include:
• The mean bias error (MBE):

N
1 X
MBE ¼ ðb yðiÞ yðiÞÞ (3.1)
N
i¼1