PV systems are generally divided into two major categories: grid - connected
(also known as grid - tied ) systems that are interfaced to an electricity grid;
and stand - alone systems that are self - contained. Over the years it has been
customary for books on PV to describe stand - alone systems fi rst, probably
because they are seen as ‘ pure PV ’ . Also we should remember that stand -
alone systems, including those launched into space and the solar home
systems (SHSs) that supply electricity to individual families in developing
countries, accounted for much of the PV industry in its early days. But since
the 1990s the market has shifted decisively towards PV power plants and
installations on buildings connected to an electricity grid. By the year 2000
grid - connected PV had overtaken stand - alone systems in global market
share and by 2009 more than 95% of solar cell production was being
deployed in grid - connected systems. In many ways such systems are
simpler to design and describe than their stand - alone cousins. For both
these reasons our own story begins with grid - connected PV.
Since most people have seen PV arrays mounted on the roofs of homes,
this seems a good place to start. Figure 4.1 shows the elements of a domestic
PV installation, typically with an array power between 1 and 5 kW p ,
interfaced to the local electricity grid. The major advantage of this arrangement
is that the output from the PV array is fed into the grid when not
required in the home; conversely, when the home needs power that cannot