Environmental Engineering Reference
In-Depth Information
Figure 5.10
Typical places for using photovoltaic island systems. Left: Electricity supply to a village in
Uganda. Right: Mountain hut.
Source: SMA Technologie AG.
Small solar-operated systems can only contribute minimally, if even at all, to climate
protection. On the other hand, photovoltaic-operated pocket calculators and watches
help reduce the mountain of small spent batteries.
5.3.2 Sun in the Grid
Photovoltaic systems that feed into a public grid are built in a different way from
island systems. First of all, they normally require a larger number of modules. With
crystalline solar modules a top output of 3.5 to 5 kilowatts peak (kW
p
) can be
installed for a 25 square metre area. In Germany this generates between 3000 and
4000 kilowatt hours with the right kind of roof; in Southern Europe or better sites
in the USA the fi gure increases to around 50%. This easily covers the electricity
requirements of an average German household. An ideal surface can usually be
found quite easily on the roofs of single-family homes (Figure 5.11).
As solar modules produce direct voltage but the public grid works with alternating
voltage, an inverter is also required. An inverter converts the direct voltage of a
photovoltaic module into alternating voltage. Modern inverters have high demands
placed on them. They are required to have a high level of effi ciency to ensure that
only very little valuable solar energy is lost during the conversion into alternating
voltage. Modern photovoltaic inverters achieve effi ciency of close to 95% or even
more. What is important is that effi ciency is high even with a partial load, such as
in cloudy weather. European effi ciency describes average inverter effi ciency based
on Central European climate conditions, while CEC effi ciency is for Californian
conditions.
Inverters also have to monitor the grid constantly and switch off the solar feed when
a general grid outage occurs. If the electric company wants to do work on the grid
and needs to shut off the electricity to do this, the solar current still being fed in
could harm the workers. If a public power outage occurs, owners of photovoltaic
systems will unfortunately end up sitting in the dark even though there is nothing
