Renewable Energy Sources for the mCCHP-SE-RES Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 97

2.2 Performances of Solar Energy Conversion

To design a device for converting solar energy into thermal or electric energy, it is
necessary to know the incident solar irradiation on the collecting/active surface of
the PV or ST panel. On the other hand, solar irradiation depends on several factors,
such as the latitude and the altitude of the area, the season, the day, the hour, the
degree of nebulosity and the dust content, the water vapors, and the greenhouse
gases in the atmosphere.
That is why, to evaluate the performance level, the notion of multiannual
average value of the horizontal daily solar irradiation is used; this is a unit of the
primary energy existing in this source and is de ned as the solar irradiation energy,

which reaches a horizontal surface of 1 m 2 daily. The value of H is determined from
statistical data, depending on the location of the PV or ST panel.
To exemplify, consider the case in which the location is in the southeastern part
of Romania, where H = 3.95 kWh/m 2 /d.
If, in an ST panel, this energy is converted into heat, the ef ciency of the

conversion might be of approximately 0.7. The thermal energy delivered daily by
an ST panel whose active surface is of 1 m 2 , noted q PT , has the following value:

m 2 q PT ¼ H g ¼ 3 : 95 0 : 7 ¼ 2 : 772 kWh = = d ð 4 Þ

c energy is delivered to a boiler, where it heats the
water, it results then that the mass m of the heated water by 1 m 2 of the ST panel,
with a difference in temperature of

If we consider that this speci

Δ θ

, is:

q PT
c P Dh

m ¼ Kg = d ; ð 5 Þ

°

where c p = 4.187 kJ/(kg c to water.

Considering the concrete case in which the water is heated from 10 to 90

C) is the heat speci

C, it
results that an ST panel, with a surface of 1 m 2 may heat of approximately 25 kg
water daily.
Similarly, the speci

°

c electric energy delivered by a PV panel depends on the
multiannual average value of the horizontal daily solar irradiation and on the
conversion ef ciency of the PV panel.

To exemplify, consider once again the case in which the location of the panel is
in the southeastern part of Romania, where H = 3.95 kWh/m 2 /d. As the ef

ciency is
of about 0.15, it results that the electric energy delivered daily by a panel with a
surface of 1 m 2 , noted e PV , has the following value:

m 2

e PV ¼ H g ¼ 3 : 95 0 : 15 ¼ 0 : 5925 kWh = = d ð 6 Þ

The decision to use equipment for converting solar energy into thermal or
electric energy is determined by the level of solar irradiation energy ux and by the