FAQs - Solar
Powered Energy
The Federal
Government has a Renewable Energy Tax Credit available
to homeowners and business. Up to 30% of the installed
cost for a wind or solar system may be used for a tax
credit.
1)
How do solar cells generate electricity?
Photovoltaics or PV for short can
be thought of as a direct current (DC) generator powered
by the sun. When light photons of sufficient energy
strike a solar cell, they knock electrons free in the
silicon crystal structure forcing them through an
external circuit (battery, inverter or direct DC load),
and then returning them to the other side of the solar
cell to start the process all over again. The voltage
output from a single crystalline solar cell is about
0.5V with an amperage output that is directly
proportional to the cell’s surface area (approximately
7A for a 6 inch square multi-crystalline solar
cell). Typically 30-36 cells are wired in series (+ to
-) in each solar module. This produces a solar module
with a 12V nominal output (~17V at peak power) that can
then be wired in series and/or parallel with other solar
modules to form a complete solar array.
2)
Will Solar work at my location?
Solar is universal and will work
virtually anywhere, however some locations are better
than others. Irradiance is a measure of the sun’s power
available at the surface of the earth and it peaks at
about 1000 watts per square meter. With typical
crystalline solar cell efficiencies around 14-16%, that
means we can expect to generate about 140-160W per
square meter of solar cells placed in full sun.
Insolation is a measure of the available energy from the
sun and is expressed in terms of "full sun hours" (i.e.
4 full sun hours = 4 hours of sunlight at an irradiance
level of 1000 watts per square meter). Obviously
different parts of the world receive more sunlight than
others, so they will have more “full sun hours ”per day.
The solar insolation zone map will give you a general
idea of the full sun hours per day during the summer for
your location.
3)
How much will solar cost for a 2000 sq. ft. home?
Unfortunately there is no per square foot “average”
since the cost of a system actually depends on your
daily energy usage and how many full sun hours you
receive per day; and if you have other sources of
electricity. To accurately size a system to meet your
needs, you need to know how much energy you use per day.
If your home is connected to the utility grid, simply
look at your monthly electric bill.
4)
What components do I need for a off grid system?
There
are many components that make up a complete solar
system, but the 4 main items on a stand-alone system
are: solar modules, charge controller(s), battery(s) and
inverter(s). The solar modules are physically mounted on
a mount structure and the DC power they produce is wired
through a charge controller before it goes on to the
battery bank where it is stored.
5)
What components do I need for a grid tie system?
Grid-tie systems are inherently simpler than either
grid-tie with battery back-up or stand-alone solar
systems. In fact, other than safety disconnects,
mounting structure and wiring, a grid-tie system is just
solar modules and a grid-tie inverter! Today’s
sophisticated grid-tie inverters incorporate most of the
components needed to convert the direct current from the
modules to alternating current, track the maximum power
point of the modules to operate the system at peak
efficiencies and terminate the grid connection if grid
power is interrupted from the utility.
6)
Can I use all of my normal 120/240 volt AC appliances?
Maybe. Many older homes were not designed or built with
energy efficiency in mind. When you purchase and install
a renewable energy system for your home, you become your
own power company, so every kWh of energy you use means
more equipment (and hence more money) is required to
meet your energy needs. Any appliance that operates at
240 VAC (such as electric water heaters, cook stoves,
furnaces and air conditioners) are expensive loads to
run on solar. You should consider using alternatives
such as LP or natural gas for water/space heating or
cooking, evaporative cooling instead of compressor based
AC units and passive solar design in your new home
construction if possible. Refrigeration and lighting are
typically the largest 120 VAC energy consumers in a home
(after electric heating loads) and these two areas
should be looked at very carefully in terms of getting
the most energy efficient units available. Great strides
have been made in the past 5 years towards improving the
efficiency of electric refrigerators/freezers. Compact
fluorescent lights use a quarter to a third of the power
of an incandescent light for the same lumen output and
they last ten times longer. These fluorescent lights are
now readily available at your local hardware or discount
store. The rule of thumb in the renewable energy
industry is that for every dollar you spend replacing
your inefficient appliances, you will save three dollars
in the cost of a renewable energy system to run them. So
you can see that energy conservation is crucial and can
really pay off when considering a renewable energy
system.
7)
What type of solar module mounting structure should I
use?
There
are four basic types of mount structures: roof/ground,
top-of pole, side-of-pole and tracking mounts, each
having their own pros and cons. For example roof mount
structures typically keep the wire run distances between
the solar array and battery bank or grid-tie inverter to
a minimum, which is good. But they may also require roof
penetrations in multiple locations, and they require an
expensive ground fault protection device to satisfy
article 690-5 of the National Electrical Code-NEC. On
the other hand, ground mounted solar arrays require
fairly precise foundation setup, are more susceptible to
theft/vandalism and excessive snow accumulation at the
bottom of the array. Next are top-of-pole mounts which
are relatively easy to install (you sink a 2-6 inch
diameter SCH40 steel pole up to 4-6 feet in the ground
with concrete). Make sure that the pole is plumb and
mount the solar modules and rack on top of the pole.
Top-of-pole mounts reduce the risk of theft/vandalism
(as compared to a ground mount). They are also a better
choice for cold climates because snow slides off easily.
Side of pole mounts are easy to install, but are
typically used for small numbers of solar modules (1-4)
for remote lighting systems where there already is an
existing pole to attach them to. Last but not least are
the trackers, which increase the daily number of full
sun hours and are usually used for solar water pumping
applications. Trackers are extremely effective in the
summer time when water is needed the most. In the
northern U.S., typical home energy usage peaks in the
winter when a tracker mount makes very little difference
as compared to any type of fixed mount (roof, ground or
top-of-pole). In this situation, having more modules on
a less expensive fixed mount will serve you better in
the winter than fewer modules on a tracker.
Call now
for a site survey or home inspection.
DNL Energy, LLC 603-536-2461 or email us at
hortond@dnlenergy.com.
