Environmental Engineering Reference
In-Depth Information
Electric Energy Yield of Photovoltaic systems
A rough calculation of the quantity of energy fed in annually by a grid-connected
photovoltaic system can be made on the basis of the annual solar radiation
H
solar
in
kWh/(m
2
a) from Figure 5.15, the losses or gains through orientation and tilt angle
f
orientation
(Figure 5.16), the rated or MPP power
P
MPP
of photovoltaic modules in kW
p
and the performance ratio PR (compare Table 5.3):
Hf PR
⋅
⋅
⋅
solar
orientation
MPP
E
=
.
electric
1
kW
m
2
The yield of a photovoltaic system in Berlin that is orientated approximately 20°
towards the south-southeast and tilted approximately 20° towards the south-south-
west and has an MMP power of 4 kW
p
will be used as a sample calculation. The
annual solar radiation according to Figure 5.15 is around 1020 kWh/(m
2
a). According
to Figure 5.16, the tilt gains are
f
orientation
= 110% = 1.1 based on the south orienta-
tion. Based on the performance ratio of an average system
PR
= 0.75, the annual
quantity of fed-in electric energy is:
1020
kWh
ma
⋅
1 1 4
.
⋅
kW
⋅
0 75
,
kWh
a
p
2
E
electric
=
=
3366
.
1
kW
m
2
This corresponds approximately to the consumption of an average German house-
hold. Therefore, as a yearly average about 30 m
2
of roof area is necessary for a
household to cover its total electricity requirements using a solar system. The spe-
cifi c yield related to 1 kW
p
is often given for a system. In the example above, the
total is 825 kWh/(kW
p
a).
The rough calculation of yield described here naturally incorporates certain inac-
curacies. However, the order of magnitude of the system yield is correct. It can be
used in the following section to examine the economic viability. Internet tools and
computer programmes are available to conduct a more precise analysis. Professional
fi rms also offer to carry out calculations of this type. In any case, if a large system
is to be installed, it is advisable to get an expert to produce an appraisal on yield to
avoid unpleasant surprises later on. Banks also often require a copy of the relevant
appraisal.
■
http://www.valentin.de/onlineberechnung/pv
PV online calculations
■
http://www.nrel.gov/rredc
Renewable Resource Data
Centre
■
http://re.jrc.ec.europa.eu/pvgis/
Photovoltaic Geographical
Information System PVGIS
It is not necessary for a grid-connected system to be large enough to cover the total
electricity requirements of a household. Depending on the roof size and how much
money is available, the system can turn out to be larger or smaller than optimally
