Environmental Engineering Reference
Figure 5.11 Principle of grid-connected photovoltaic system.
wrong with their solar system. Technically, a solar system can still be kept running
in island operation if the grid fails. However, as power failures are very infrequent,
hardly anyone makes the additional technical provisions that would be necessary.
An inverter does not only convert voltage. It also ensures that photovoltaic modules
are working with optimal voltage and delivering the maximum possible power. The
setting of optimal voltage is also called MPP tracking. When a system is planned,
it is important that the number of photovoltaic modules is coordinated with the
inverter. The leading manufacturers of inverters usually offer relevant design pro-
grammes free of charge.
Shadowing can also cause problems. Photovoltaic systems react sensitively and
performance suffers even if only part of a system is in the shade. If two cells are in
shade, the entire photovoltaic module can stop working. Therefore, a site that has
minimal shade is more important for the installation of a system than an optimal
orientation towards the sun.
Large grid-linked photovoltaic systems feed all generated electricity into the public
grid. They function as pure solar power plants. With large systems it can be benefi -
cial to track them towards the sun (Figure 5.12). Systems that use tracking can
increase power output by 30% on an annual average. However, tracking also
increases the investment cost and requires additional maintenance because of the
mechanical parts required. Therefore, tracking pays particularly in situations where
large, well-maintained systems are installed.
The neatest looking installations of photovoltaic systems are those on roofs and
façades (Figures 5.13 and 5.14). Less building material is also needed for this type
of installation, which is a cost advantage as these systems are still very expensive.
Furthermore, compared to expensive marble façades, photovoltaics can sometimes
turn out to be a real bargain.