Page 96 - Design of Solar Thermal Power Plants

84 2. THE SOLAR RESOURCE AND METEOROLOGICAL PARAMETERS

Earth undergoes significant changes; in addition, due to different atmo-
spheric environments in the calculation area, solar radiation that reaches
the surface has significant regional characteristics that are far less sig-
nificant than the corresponding astronomic radiation. Many scholars have
estimated respective local solar radiation resources by establishing
mathematical models and empirical relationships. Many meteorological
parameters, such as atmospheric turbidity, relative humidity, clearness
index, cloud amount, and sunshine duration, have been proven to have
impacts on local solar irradiation resources, among which the most crucial
influencing factor is sunshine duration.
By utilizing meteorological data (including solar radiation data and
sunshine duration) from typical climatic regions of eight typical cities
during the period of 1994e2003, the mathematical relationship between
the monthly mean clearness index and the sunshine percentage was
established to estimate global solar radiation. The results indicate a
model with excellent estimation accuracy. In order to further demon-
strate the model’s precision, comparisons were made between estima-
tion results of the established model and other mathematical models in
terms of mean percentage error (MPE), mean bias error (MBE), and root-
mean-square error (RMSE). The results proved that the estimation
model based on local meteorological data samples is more reliable
than the estimation model that has already been published for global
applications.
Many scholars have proposed ways to estimate solar radiation re-
sources based on the mathematical relationship between global solar ra-
diation and sunshine percentage on the horizontal surface through linear
regression, among which the most representative is the Angstrome
Prescott model. Here, a mathematical relationship applicable for full-site
single-month estimation of domestic solar radiation resources estimation
is established by utilizing meteorological data of eight typical cities in
different climatic regions of China to estimate the domestic solar radiation
resources.
Refer to Eq. (2.16) [5] for the mathematical expression of the Angstrom-
Prescott model:

H S
¼ a þ b (2.16)
H 0 S 0
In which H refers to the monthly mean value of daily global radiation
1
on the horizontal surface, MJ$m 2 d ; H 0 refers to the monthly mean
value of the daily total astronomic radiation within the calculation area,
1
MJ$m 2 d ; S refers to the monthly mean value of sunshine duration; S 0
refers to the maximum value of the monthly mean value of sunshine
duration; a and b are coefficients.