Solar power is arguably the cleanest, most reliable
form of renewable energy available, and it can be
used in several forms to help power your home or business. Solar-powered photovoltaic
(PV) panels convert the sun's rays into electricity by exciting
electrons in silicon cells using the photons of light from the sun. This
electricity can then be used to supply renewable energy to your
home or business.
In most solar systems, solar panels are placed on the roof. An ideal site
will have no shade on the panels, especially during the prime sunlight
hours of 9 a.m.
to 3 p.m.; a south-facing installation will usually provide the optimum
potential for your system, but other orientations may provide sufficient
production. Trees or other factors that cause shading during the day will
cause significant decreases to power production. The importance of shading and
efficiency cannot be overstated. In a solar panel, if even just one of its 36
cells is shaded, power production will
be reduced by more than half.
Not every roof has the correct orientation or angle of inclination to take
advantage of the sun's energy. Some systems are designed with pivoting panels
that track the sun in its journey across the sky. Non-tracking PV systems
should be inclined at an angle equal to the site’s latitude to absorb the
maximum amount of energy year-round. Alternate orientations and/or
inclinations may be used to optimize energy production for particular
times of day or for specific seasons of the year.
Solar
panels, also known as modules, contain photovoltaic cells made from silicon that transform incoming sunlight into
electricity rather than heat. (”Photovoltaic” means electricity from light — photo
= light, voltaic = electricity.)
Solar photovoltaic cells consist of a positive and a negative film of
silicon placed under a thin slice of glass. As the photons of the sunlight beat
down upon these cells, they knock the electrons off the silicon. The negatively-charged
free electrons are preferentially attracted to one side of the silicon cell,
which creates an electric voltage that can be collected and
channeled. This current is gathered by wiring the individual solar
panels together in series to form a solar photovoltaic array. Depending on the
size of the installation, multiple strings of solar photovoltaic array cables
terminate in one electrical box, called a fused array combiner. Contained
within the combiner box are fuses designed to protect the individual module
cables, as well as the connections that deliver power to the
inverter. The electricity produced at this stage is DC (direct current) and
must be converted to AC (alternating current) suitable for use in your home or
business.
To use the energy
from the array, you may also need other components, such as inverters, charge
controllers and batteries, which make up a solar-electric system.
The components required are dependent on the system type designed. System types
include:
PV-DIRECT
SYSTEMS: These are the simplest of solar-electric systems, with the fewest
components (basically the PV array and the load). Because they don’t have
batteries and are not hooked up to the utility, they only power the loads when
the sun is shining. This means that they are only appropriate for a few select
applications, notably water pumping and ventilation—when the sun shines, the
fan or pump runs.
OFF-GRID
SYSTEMS: Although they are most common in remote locations without utility
service, off-grid solar-electric systems can work anywhere. These systems
operate independently from the grid to provide all of a household’s
electricity. These systems require a battery bank to store the solar
electricity for use during nighttime or cloudy weather, a charge controller to
protect the battery bank from overcharge, an inverter to convert the DC PV
array power to AC for use with AC household appliances, and all the required
disconnects, monitoring, and associated electrical safety gear.
GRID-TIED
SYSTEMS WITH BATTERY BACKUP: This type is very similar to an off-grid system in
design and components, but adds the utility grid, which reduces the need for
the system to provide all the energy all the time.
BATTERY LESS
GRID-TIED SYSTEMS: These most common PV systems are also known as on-grid,
grid-tied, utility-interactive, grid-intertied, or grid-direct. They generate
solar electricity and route it to the loads and to the electric utility grid,
offsetting a home’s or business’s electricity usage. System components are
simply comprised of the PV array, inverter(s), and required electrical safety
gear (i.e., fuses/breakers/disconnects/monitoring). Living with a
grid-connected solar-electric system is no different than living with utility
electricity, except that some or all of the electricity you use comes from the
sun. (The drawback of this battery less systems is that they provide no outage
protection—when the utility grid fails, these systems cannot operate.)
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