There are a few different types of photovoltaic
(PV) cells produced under many different brand
names. The key point is that all PV uses sunlight
to generate a direct electrical current (DC).
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Homeowners should first decide whether
their electricity-generating solar systems
will (a) stand-alone or (b) be connected
to the electricity grid. |
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Stand-alone systems, which require specialized
batteries to store electricity, are most
often found in rural settings or projects
where the closest grid connection is a half-mile
or more away. |
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Photovoltaic array installation
on the Captain Planet Zero Energy Home in Atlanta,
Georgia
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| Grid-connected
systems, which allow homes to become “power
providers” to the electrical grid network
are discussed below |
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| The first steps towards
owning a grid-connected photovoltaic system are: |
| • |
Pursue home energy efficiency—seal
leaky ductwork, install efficient appliances and
compact fluorescent light bulbs, and properly insulate
your home. This could reduce the size and cost of
your PV system by 20 to 50 percent |
| • |
Assess your rooftop or property for an area that
receives direct sunlight daily for a minimum of 6
hours. This area should face due south, but this
can vary by about 15 degrees. A typical residential
PV system which produces about 2 kilowatts (2kW)
requires an area of about 8 feet by 25 feet to accommodate
solar panels. |
| • |
Determine how much energy your home uses.
Online energy use calculator on the Energy Star website |
| • |
Determine what percentage of your home’s
energy supply you want from photovoltaics. |
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| A Word about Sizing |
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If you go to purchase a PV system, the first question
you’ll be asked is “How much?” The
size of a PV system is given as the maximum direct
current (DC) output of the solar system in kilowatts.
So, a 2-kilowatt (kW) system generates 2,000 watts
of DC electricity when fully exposed to the sun’s
rays. After this direct current is converted to usable
alternating current (AC) through an inverter, the
output is reduced to about 1.7kW. |
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System size is based on available area and budget. |
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A Residential Photovoltaic
System
A good aim is to install a system that
will, at peak production, supply one-half
to three-fourths of your household’s
energy demand. This is typically a system
between 1kW and 3kW.
Each home requires a different amount
of electricity to meet its demands. Every
season and time of day will likewise mean
a different energy load. So, it’s
impossible to give a uniform system size
for homeowners.
| It’s best to install
the largest system your budget will
permit for two reasons: |
| • |
installation costs are about the
same whether you’re installing
a small 0.5kW or a large 3kW system |
| • |
inverters, a vital component to every
PV system, are usually sized for systems
up to 5kW. The closer your system is
to 5kW, the more cost-effective your
inverter purchase. |
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Jason Hercules illustrates
the scale of the solar shingle array at
the Southface Energy and Environmental
Resource Center.
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This is a typical grid-connected photovoltaic system. |
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| This system: |
| • |
generates usable AC current after passing through
the inverter |
| • |
is connected to the conventional electricity grid |
| • |
offsets energy that would normally come in through
the conventional grid with clean solar energy |
| • |
can provide power back to the grid |
| Features this system includes: |
| • |
photovoltaic panels (number and size depend on
desired system capacity) |
| • |
mounting hardware and connecting cables |
| • |
inverter to change direct current (DC) into alternating
current (AC) |
| • |
disconnects (basically big on/off switches) that
automatically isolate the system from the grid in
accordance with local electrical and safety codes
and utility requirements |
