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Solar panels are
what produces
electric from the
sun. They
come in various
sizes ranging from
as little as 5 watts
up to as much as 187
watts. Most
panels are normally
12 volts DC with
panels above 140
watts usually being
24 volts DC.
We are dealers
for a number of
different
manufactures and
like most dealers,
we have our panels
delivered directly
from our
distributors or from
the manufacturers.
Since about the
beginning of 2004
most of the worlds
production of solar
panels has been
bought up by the
European market
making availability
in the United States
and the rest of the
world very low.
As a result, in some
cases there are
panels in stock and
in others they are
back-ordered.
We can not guarantee
when your panels
will be shipped but
your panels will be
shipped in the order
they are received.
When we see that
an order has
been placed for a
certain size panel,
we will let you know
the shipping status
of that panel and
also that of similar
size panels that may
be available sooner.
We are sorry
about this
situation, many
of the manufactures
we have talked with
are in the process
of either gearing up
their production
levels or allocating
more panels to the
American market
(which only
represents about 10
percent worldwide).
We are hoping that
this crunch will
ease up soon.
We recommend
that you move
forward with your
solar plans and
place your solar
panel order as soon
as you can (with
either us or
whoever) because to
some degree or
other, this problem
may be around for
awhile. We
recommend that while
you are waiting for
your panels that you
could use wind,
hydroelectric (if
you have a water
source), or a
propane backup
generator to keep
your batteries
charged.
Once your order has
been placed we
will make every
effort to get you
your panels as
quickly as possible.
However due to the
overwhelming demand
on the panel
industry we can not
tell you how long it
will take, until an
order has come
across our desk |
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Solar Module Power Characteristics |
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The current and
power output of photovoltaic modules are
approximately proportional to sunlight intensity. At
a given intensity, a module’s output current and
operating voltage are determined by the
characteristics of the load. If that load is a
battery, the battery’s internal resistance will
dictate the module’s operating voltage.
A module which
is rated at 17 volts will put out less than its
rated power when used in a battery system.This is
because the working voltage will be between 12 and
15 volts. As wattage (power) is the product of volts
times amps, the module output will be reduced. For
example: a 50 watt module working at 13.0 volts will
produce 39.0 watts (13.0 volts x 3.0 amps = 39.0
watts).This is important to remember when sizing a
PV system.
An I-V curve as
illustrated to the right is simply all of a
module’s possible operating points, (voltage/current
combinations) at a given cell temperature and light
intensity. Increases in cell temperature increase
current slightly, but drastically decrease voltage. |
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Maximum power is
derived at the knee of the curve. Check the amperage
generated by the solar array at your battery’s
present operating voltage to better calculate the
actual power developed at your voltages and
temperatures. |
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Shading |
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PV modules are
very sensitive to shading. Unlike a solar
thermal panel which can tolerate some shading, many
brands of PV modules cannot even be shaded by the
branch of a leafless tree.
Shading obstructions can be defined as soft
or hard sources. If a tree branch, roof vent,
chimney or other item is shading from a distance,
the shadow is diffuse or dispersed. These soft
sources significantly reduce the amount of light
reaching the cell(s) of a module. Hard sources are
defined as those that stop light from reaching the
cell(s), such as a blanket, tree branch, bird
dropping, or the like, sitting directly on top of
the glass. If even one full cell is hard shaded the
voltage of that module will drop to half of its
unshaded value in order to protect itself. If enough
cells are hard shaded, the module will not convert
any energy and will, in fact, become a tiny drain of
energy on the entire system.
Partial-shading even one cell of a 36-cell
module, such as the KC120, will reduce its power
output. Because all cells are connected in a series
string, the weakest cell will bring the others down
to its reduced power level. Therefore, whether ½ of
one cell is shaded, or ½ a row of cells is shaded as
shown above, the power decrease will be the same and
proportional to the percentage of area shaded, in
this case 50%.
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When a full
cell is shaded, it can act as a consumer of
energy produced by the remainder of the cells, and
trigger the module to protect itself. The module
will route the power around that series string. If
even one full cell in a series string is shaded, as
seen on the right, it will likely cause the module
to reduce its power level to ½ of its full available
value. If a row of cells at the bottom of a module
is fully shaded, as seen in Figure 7, the power
output may drop to zero. The best way to avoid a
drop in output power is to avoid shading whenever
possible. |
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Tilt Angle |
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To capture the
maximum amount of solar radiation over a year,
the solar array should be tilted at an angle
approximately equal to a site's latitude, and facing
within 15º of due south. To optimize winter
performance, the solar array can be tilted 15º more
than the latitude angle, and to optimize summer
performance, 15º less than the latitude angle. At
any given instant, the array will output maximum
available power when pointed directly at the sun.
To compare the energy output of your array to
the optimum value, you will need to know the site's
latitude, and the actual tilt angle of your
array-which may be the slope of your roof if your
array is flush-mounted. If your solar array tilt is
within 15º of the latitude angle, you can expect a
reduction of 5% or less in your system's annual
energy production. If your solar array tilt is
greater than 15º off the latitude angle, the
reduction in your system's annual energy production
may fall by as much as 15% from its peak available
value. During winter months at higher latitudes, the
reduction will be greater. |
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Azimuth Angle and
Magnetic Declination |
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If a
south-facing roof is unavailable, or the total
solar array is larger than the area of a
south-facing roof section, an east or west-facing
surface is the next best option. Be aware that solar
power output decreases proportionally with a
horizontal angle, or "azimuth," greater than 15º
from due south. The decrease in annual power output
from a latitude-tilted east or west-facing array may
be as much as 15% or more in the lower latitudes or
as much as 25% or more in the higher latitudes of
the United States. Avoid directing your tilted solar
panels northwest, north or northeast, as you'll get
little power output.
Magnetic
declination, the angle difference between
magnetic south and true solar south, must also be
taken into account when determining proper solar
array orientation. If a magnetic compass alone is
used to determine where to point the array, you may
not capture the maximum amount of solar radiation.
For a general view of the magnetic declination field
lines in North America, see the map on the right.
If you have access
to the Internet, and wish to calculate the exact
magnetic declination of your site, visit the
following website:
http://www.gwolab.nrcan.gc.ca/geomag/e_cgrf.html.
If you wish to gain
in-depth information about magnetic
declination, visit the following website:
http://www.ngdc.noaa.gov/seg/potfld/faqgeom.html. |
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