Ideal rooftop location points
south and permits the solar
modules to tilt at an angle
equivalent to the latitude.
Where the utility company
makes them available, a smart
meter can optimize your
power use and tell you exactly
how much power the house is
using and producing.
Service
Inverter should be mounted in a rela-
panel
tively cool, weather-protected spot —
under a shading eave, for instance.
KuRt StRuve
electric power is measured
in watts. a kilowatt (kw) is
Microinverters: Some newer grid-tied systems replace a large central inverter with several microinvert-
ers, individually attached to the back of each PV module. Power coming off the module/inverter com-
1,000 watts, and a megawatt
bination is 230 volts AC and can tie directly to the household service panel. A major advantage is that if
(mw) is 1 million watts. you
one module is shaded or broken, performance of the rest of the system is unaffected. You can monitor
buy electricity in kilowatt-
the performance of each individual panel, on a home computer or your smart phone. DC to DC opti-
hours (kwh), which is energy
mizers are also now available, which help to optimize the power from a string of PV modules, but do not
(as opposed to power). For
convert to AC as inverters do.
instance, if you run a 100-watt
light bulb for an hour, you’ve
used 100 watt-hours of energy.
if you run it for 10 hours, you’ve
used 1 kwh, for which the aver-
age household would be billed
11 cents (at $0.11/kwh). a 1-kw
Pv array can produce 1 kw in
direct sun. if sunlight falls on it
five hours a day, it may produce
5 kwh that day.
Know your load. If your family uses 600 k Wh of electricity
each month, that works out to
about 20 k Wh per day. If you get
an average of five hours of direct
sunlight daily, you’d balance your
electric use with about 4 k W of
net-metered PV power. A 2-k W
system would offset about 50 percent of your bill.
System components must be matched. a 3-kilowatt
(kw) inverter can’t handle the power produced by a 5-kw dC
array. if you install a 3-kw array, you may consider putting in a
5-kw inverter to allow for expansion of the array in the future.
also be aware of economies of scale. Labor costs may be lower,
per unit, for a large system. if a 5-kw system can be installed
in a day, you won’t save labor costs by buying a 3-kw system,
which may also take a day.
