EuroSun2008-13

Comparative models

The results of this proposed model are compared with three other previously reported models which are believed to be applicable anywhere in the world and yield superior results for cloudy

conditions.

( і) Rietveld model [2]

Rietveld examined several published values of a and b, and noted that a is related linearly and b hyperbolically to the mean value of S / S0 such that

(9)

Substituting a and b in Eq (1), one

(10)

(ii) Ogelman et al model [2, 4]

Ogelman et al proposed the use of a correlation which relates the global solar radiation to S / S0 in a quadratic form as

(11)

(iv) Page model [8]

Page quoted a correlation which was believed to be suitable anywhere.

H c

= 0.23+0.48 H S0

The three models listed above were applied to the sunshine data in China. The calculated and measured values of average daily global radiation on the horizontal surface were compared using the following parameters.

1.2. Comparative parameters

In order to compute the deviation and compare the results of above models, this paper makes use of following parameters.

RMSE
(13)
estimated______ measured H measured
/ N
(14)

N

MBE = [I (Hestimated - Hmeasured )] / N

i=1

RMSE: Root Mean Square Error MABE: Mean Absolute Bias Error

MBE: Mean Bias Error

Hestimated : the estimated value of the global solar radiation Hmeasured: the measured value of the global radiation

He: the arithmetic mean value of the m estimated values of the global solar radiation

Hm : the arithmetic mean value of the m measured values of the global solar radiation N: the number of the data

2. Results and Discussion