Figure 20.5: Experimentally measured temperature difference T M − T a as a function of the irradiance on the PV module
G M for two module types. Linear fits and a linear curve for an average PV module are shown as well (adapted from a
figure from NASA [162]).
Equation (20.2) only takes the ambient temperature into account but neglects
influences from wind speed and mounting configuration, which can lead to significant
errors in the predicted cell temperature. In order to take the mounting configuration of the
module into account, the installed nominal operating cell temperature (INOCT) has been
defined [164]. This value is described as the cell temperature of an installed array under
NOCT conditions. Its value can therefore be obtained from the NOCT and the mounting
configuration. The evaluation of how the INOCT varies with the module mounting
configuration has been experimentally determined by measuring the NOCT at various
mounting heights; the results are summarized in Table 20.2.
Table 20.2: Derivation of the INOCT from the NOCT for various mounting configurations [164].
Rack Mount
INOCT = NOCT − 3°C
Direct Mount
INOCT = NOCT + 18°C
Standoff
INOCT = NOCT + X
where X is given by
W (cm)
X (°C)
2.54
11
7.62
2
15.24
− 1