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About
Solar Energy - FAQ
What
is solar electricity?
Solar electric or photovoltaic (PV) technology converts sunlight
directly into electricity.
You may be more familiar with PV cells as solar cells that power watches
and calculators.
But PV can do much more. It can provide electricity for your home and
provide the opportunity for you to take advantage of net metering.
Why
use PV?
The sun generates enough clean energy in one day to provide a year’s
supply of energy for your home. Why not tap into this abundant
resource of clean energy? PV preserves the earth’s finite fossil-fuel resources-coal
oil, natural gas-and reduces air and noise pollution associated with
those energy sources. Considering the state incentive program along
with the state and federal tax credit program, have greatly reduced
the cost of PV ownership. PV system reliability and durability are
outstanding typical PV systems may last 40 years with minimal
maintenance.
How
does solar electricity or “PV” systems work?
Photo-voltaic, also known as “PV,” produce electricity from the sun.
The solar “cell” is the basic building block of PV technology.
Solar cells are wired together to form a PV module.
PV systems begin with the solar module. Modules gather solar energy in
the form of sunlight and
convert it into direct current (DC) electricity. The more sunlight they
receive, the more electricity they produce. Solar modules are the
heart of the PV system. In essence, they are the power generators.
To convert DC power to alternate current (AC) power, the type of
electricity used in your home, a device called an inverter is used.
Depending upon the size of the PV system, inverters may be mounted
by the PV manufacturer right on the back of a PV module. Inverters may
also be wall-mounted separately from the PV system, but within
close proximity to the solar panels.
This type of inverter’s location can be in the basement, attic or
garage. If an excess of electricity is produced through the PV
system, the power will flow back through your meter for distribution
back to the grid system. This is known as “net metering".
How
does Net Metering work?
Your electric meter spins forward when electricity is flowing from your
utility provider into your home. The meter spins backward when
power is flowing from your home back to utility provider. That is, if
more electricity is generated through a PV system than your home
requires, the excess energy flows back to provider’s electric
grid system, which turns your electric meter backwards. At the end of
the month, you are billed only for net consumption - the amount of
electricity consumed less the amount of electricity distributed
back to your utility provider’s grid.
What
does a typical PV panel look like?
A typical PV panel consists of solar cells connected electrically to
form a module that can measure two to four feet wide and four to
six feet long. Some solar modules look just like traditional roof
shingles. Many interconnected PV modules are called an array.
What
happens if the sun doesn’t shine?
Your PV system will continue to produce electricity during cloudy
weather, although the total amount will be reduced. Power will
automatically be provided through your utility provider at night or
during inclement weather.
How
does shading affect my PV system?
Proper placement of your Photo Voltaic (PV) system is critical to the
success of the PV systems output. Having even one cell in a PV
module in the shade, especially during the best sun hours of the day,
can decrease the output for the entire module and possibly the
entire system.
Since the shaded cell is not producing any moving electrons, it
acts like an open circuit to the entire string. This is similar to
having one Christmas tree light burned out in a string of lights.
No current can flow!
When looking to place your PV system, please watch for any type of
shading. Shading can include trees, chimneys, TV
antennas/satellite dishes, dormers of the house.
Step
1- Review your roof for good access to the sun. Does the area for
PV system receive full sunlight with no shading?
Step
2- If you have 100% of sunlight on a south facing roof, you have
an ideal roof for PV, although east and west facing roofs are very good
also. If there is shading on your roof, consult with a person trained on
PV.
Is
my home right for a PV system?
A PV system needs unobstructed access to the sun’s rays for most, or
all of the day, throughout the year. PV panels are relatively
unaffected by changing weather. In fact, some PV cells actually work better
at colder temperatures. PV modules are angled to catch the sun, not
snow, so any snow that does collect melts quickly. To maximize the
energy production of photovoltaic electricity, PV systems are
installed on a southern exposed roof and mounted parallel with the roof
at a 35 degree roof pitch with no shading. However, roofs that face
east or west may also be acceptable. PV panels should have their
surfaces exposed to the sun’s rays for most or all of the day, with
minimal or no shadows from trees, chimneys and gables between 9 AM
and 4 PM.
Home
Energy Efficiency and PV: An energy efficient home means you can
install less PV. Every dollar on energy efficiency in the home saves
$20 on your PV electric panels. To become energy efficient in the home,
use compact fluorescent light bulbs, which use 75% less energy than
the equivalent incandescent. A 15 watt compact fluorescent will
produce as much light as a 60 watt incandescent. Also look for energy
saving appliances (clothes washers, refrigerators, room A/C,
dishwashers. Refrigerators before 1990 are power hogs!
Can
my home accommodate a PV system?
The amount of space needed by a PV system is based on the output of the
PV system and the type of PV system installed. Most residential
systems require as little as 50 square feet (for a small “starter” system)
up to as much as 1,000 square feet for larger systems. A typical
two-kilowatt system could occupy approximately 200 square feet. If
your location limits the physical size of your system, you may want
to install a system that uses more efficient PV modules. Greater
efficiency means that the module uses less surface area to convert
sunlight into a given amount of electric power.
Estimated
Roof Area Needed in Square Feet
| PV
Module Efficiency*
|
PV
Capacity Rating, watts (in bold)
|
|
|
100
|
250
|
500
|
1,000
|
2,000
|
4,000
|
10,000
|
100,000
|
| 4
|
30
|
75
|
150
|
300
|
600
|
1,200
|
3,000
|
30,000
|
| 8
|
15
|
38
|
75
|
150
|
300
|
600
|
1,500
|
15,000
|
| 12
|
10
|
25
|
50
|
100
|
200
|
400
|
1,000
|
10,000
|
| 16
|
8
|
20
|
40
|
80
|
160
|
320
|
800
|
8,000
|
* Although the efficiency (percentage
of sunlight converted to electrical energy) varies with different of
PV Modules available today, higher-efficiency modules typically cost
more. So, a less efficient system is not necessarily less
cost-effective. - The Vermont Renewable Energy Resource Center.
How
much PV will I need?
As a starting point, you might consider how much of your present
electricity needs you would like to meet with your PV system. For
example, suppose that you would like to meet 50 percent of your electricity
needs with your PV system. You could work with your PV provider to
examine past electric bills and determine the size of the PV system
needed to achieve that goal.
You can contact your local utility
provider and request the total electricity usage, measured in kilowatt-hours,
for your household over the last 12 months (or consult your electric
bills if you save them.). Ask your PV provider how much your new PV
system will produce on an annual basis (also measured in
kilowatt-hours) and compare that number to your annual electric demand
to get an idea of how much you will save.
Calculating
Electricity Bill Savings for a Net-Metered PV System
Energy
From the PV System
Determine the size of your PV system in kilowatts (kW). This
value represents the "kW of PV" input for the equations
below.
Based on geographic location, the "Energy Production
Factor" is about 1,900.
To estimate the annual energy
produced by your system, use the following equation:
Energy from the PV system =
(kW of PV ) x (Energy Production Factor) = kWh/year
Divide this number by twelve if you want to determine your estimated
monthly energy reduction.
Energy
Bill Savings
To estimate the annual energy bill savings from your system, use the
following equation:
Energy bill savings =
(Annual kWh/year ) x (Residential Rate) = $/year saved
(The residential rate in the above equation should be in dollars
per kWh; for example, the rate of 17 cents for kWh is input as
$0.17/kWh.)
For example, a 2 kW PV system (assuming a residential rate of .17 cents
per kWh)
would provide the following:
Energy from the PV system = 2kW
x 1,900 = 3,800 kWh/year.
Energy Bill Savings = 3,800 kWh/year x $.17/kWh = $646.00.
Note:
The uncertainty of the
contoured values is generally ±10%.
In mountainous and other areas of complex terrain, the uncertainty may
be higher.
Do
I need to be concerned with the condition of my existing roof?
A PV system can be installed on any well-structured roof. Typically
asphalt shingles are easiest to work with, while slate is the most
difficult. If your roof is older and needs to be replaced in the very near
future, you may want to replace it at the time the PV system is
installed to avoid the future cost of removing and reinstalling
your PV system. PV systems are also available that integrate PV cells
into the roofing materials themselves. This allows the roof itself
to act as the PV collecting device and serves as an excellent
option when replacing a roof or designing and/or building anew home. One benefit
of an integrated PV system is its ability to offset the cost of roofing
materials.
How
much does a PV system cost?
The total cost of a PV system includes the PV system and installation.
Your PV system’s cost will depend on a number of factors,
including system size and the energy efficiency of your home, whether the
home is under construction and whether the PV is integrated into the
roof or mounted on top of an existing roof. The cost also varies
depending on the PV system rating, size, manufacturer, retailer and installer.
Small-scaled PV systems with built-in inverters that produce about 600
watts of power may cost about $10 per watt ($6,000). These small
systems will offset only a small fraction of your electricity bill.
A 2-kilowatt system that will offset the needs of a very
energy-efficiency home may cost $8 to $10 per watt
($16,000-$20,000). At the high end, a 10-kilowatt system that will
completely offset the energy needs of many conventional homes may
cost $7 to $8 per watt ($70,000-$80,000). These prices of course,
are just rough estimates, and your costs will depend on your system's
configuration, your equipment options and other factors.
Remember,
the state incentives can significantly reduce the cost of purchasing a
PV system.
In addition, the state and federal tax credit can reduce your overall
costs much further.
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