Renewable Energy Sources for the mCCHP-SE-RES Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 123

Fig. 20 Cross section of a
PV/T collector

maximum ef 20 %. The electric and thermal performance of thermo-

photovoltaic collectors is smaller than that of photovoltaic panels and separate
classic solar thermal collectors, but two thermophotovoltaic collectors together
produce more energy on the surface unit than a photovoltaic panel and a solar
thermal collector situated close to each other [ 19 ]. This is important when the
available surface is important. Thermophotovoltaic collectors may be level plan or
with concentration, and may work with water or with air.

ciency of 5 -

6.2 Performances of Thermal Solar Collectors

The thermal effi- -

ciency and on the collector time constant, which depends on the thermal capacity of
the collector and is shown by equation:

ciency of the collector depends on the instantaneous thermal effi-

2

g ¼ g 0 k 1 T i

T a
H k 2

ð T i T a Þ

ð 12 Þ

H

were:

T i is the temperature of the inlet fluid;

T a is the ambient temperature;
H is the irradiance [W/m 2 ];
ʷ 0 is the optical ef

ciency of the collector
at the point where the average collector temperature is equal to the ambient
temperature.
k 1 and k 2 are the heat loss coef

ciency. The optical ef ciency is the ef

cients.

ned by the EN 12975 on the aperture area
of the collector shall meet, or exceed the following conditions: optical ef

The ef ciency of the collector, as de

ciency at

least 0.75, k 1 heat loss not more than 1.18 W/m 2

° C, k 2 heat loss not more than

0.010 W/m 2 C 2 .

°