21.2.2
21.2.3
Energy yield ratio
We now are going to introduce several indicators that are used to judge the different
ecological aspects. The energy yield ratio is defined as the ratio of the total energy yield of
a PV module or system throughout its lifetime to all the energy that has to be invested in
the PV system in that time. This invested energy not only contains the energy for
producing the components, transporting them to the location and installing them, but also
the energy that is required to recycle the different components at the end of their lifecycle.
As the energy required for producing a PV system depends strongly on the PV
technology and also on the quality of the panels, the energy yield ratio for the different
technologies varies a lot. While the energy yield ratio for PV modules can be as large as
10 to 15, PV systems usually have a lower ratio because of the energy invested in the
components other than the modules.
Energy payback time
A very important concept is the Energy payback time, which is defined as the total
required energy investment over the lifetime divided by the average annual energy yield of
the system,
Note that the energy payback time is different from the economic payback time introduced
in Section 21.1.
The energy payback time of typical PV systems is between one and seven years and
depends on location issues such as the orientation of the PV array as well as the solar
irradiance throughout the year.
Figure 21.4 shows the specific primary energy required for producing PV modules
with different technologies, where the term specific refers to the energy required per kW p
of produced modules. As we can see, the differences between the technologies are large.
The specific energy required for producing thin-film modules from materials such as
amorphous silicon, cadmium telluride and CIGS is significantly below that of modules
made from polycrystalline and monocrystalline silicon, where the specific energy can
reach values up to 12,000-18,000 kWh/kW p . Because of further improvements in the
module efficiency and the manufacturing process, we may expect that the specific energy
follows a decreasing trend.
21.2.3
Energy yield ratio
We now are going to introduce several indicators that are used to judge the different
ecological aspects. The energy yield ratio is defined as the ratio of the total energy yield of
a PV module or system throughout its lifetime to all the energy that has to be invested in
the PV system in that time. This invested energy not only contains the energy for
producing the components, transporting them to the location and installing them, but also
the energy that is required to recycle the different components at the end of their lifecycle.
As the energy required for producing a PV system depends strongly on the PV
technology and also on the quality of the panels, the energy yield ratio for the different
technologies varies a lot. While the energy yield ratio for PV modules can be as large as
10 to 15, PV systems usually have a lower ratio because of the energy invested in the
components other than the modules.
Energy payback time
A very important concept is the Energy payback time, which is defined as the total
required energy investment over the lifetime divided by the average annual energy yield of
the system,
Note that the energy payback time is different from the economic payback time introduced
in Section 21.1.
The energy payback time of typical PV systems is between one and seven years and
depends on location issues such as the orientation of the PV array as well as the solar
irradiance throughout the year.
Figure 21.4 shows the specific primary energy required for producing PV modules
with different technologies, where the term specific refers to the energy required per kW p
of produced modules. As we can see, the differences between the technologies are large.
The specific energy required for producing thin-film modules from materials such as
amorphous silicon, cadmium telluride and CIGS is significantly below that of modules
made from polycrystalline and monocrystalline silicon, where the specific energy can
reach values up to 12,000-18,000 kWh/kW p . Because of further improvements in the
module efficiency and the manufacturing process, we may expect that the specific energy
follows a decreasing trend.