Backup Generators for PV Systems We typically use generators as
a supplement to photovoltaic power. There are some very large
applications for which continuous-use generators may prove more
cost effective than a PV system, but in almost all of the
applications with which we work, the economics of generators are
maximized by restricting them to providing backup power.
Generators are used for backup in situations where seasonal
variability of insolation is substantial as in a cloudy climate,
or for systems where occasional very large loads are powered, as
for intermittent use of large shop tools or a deep well pump in
a residence. We typically design residential PV systems to
provide 80 to 90 percent of the home's annual electrical power.
The last 10 to 20 percent is more economically supplied by a
generator. The reason for this is simply economics. In many
cases we would double the cost of the system to provide this
last 10 to 20 percent of annual power. It is much more Cost
effective to employ a backup source