DBK CORPORATION
"The Energy Family - Low Cost Electricity"
DBK SOLAR DIVISION
1-(619) 692-2145
Q1...
How do solar cells generate electricity?
A1...
Photovoltaics (PV) 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.
Q2...
Will solar work in my location?
A2...
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.
DBK's crystalline solar cell efficiencies are around 70% that means we
can expect to generate about 2900 - 3000 watts 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.
Q3...
How much will solar cost for a 2000 square foot home?
A3...
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. If not, you can fill out the “load evaluation form” Using this
information, DBK Solar can design a system to meet your needs.
Q4...
What components do I need for an off-grid system?
A4...
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 (see question 7) and the DC power they produce is
wired through a charge controller before it goes on to the battery bank where it
is stored. The two main functions of a charge controller are to prevent the
battery from being overcharged and eliminate any reverse current flow from the
batteries back to the solar modules at night. The battery bank stores the energy
produced by the solar array during the day for use at anytime of the day or
night. The inverter takes the DC energy stored in the battery bank and inverts
it to 120 or 240 VAC to run your AC appliances.
Q5...
What components do I need for a grid-tie system?
A5...
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.
Q6...
Can I use all of my normal 120/240 VAC appliances?
A6...
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
unless you are using DBK 3000 solar panels. You no longer have to consider using alternatives such as LP or natural gas for water/space
heating or cooking with the purchase of DBK 3000 solar panel. 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.
Q7...
What type of solar module mounting structure should I use?
A7...
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. However, if you are in the southern U.S. and
your energy usage peaks in the summer, then a tracker may be beneficial to match
the time of your highest energy consumption with a tracking solar array’s
maximum energy output.
Q8...
Should I wire my home for AC or DC loads?
A8...
It depends on the size of the system and what type of
loads you want to run. DC appliances are usually more efficient than AC since
you don’t have to worry about the loss through the inverter, but DC loads are
typically more expensive and harder to find than their AC counter parts. Small
cabin and RV systems are typically wired DC while most home systems are wired
exclusively for AC loads. With improvements in inverter efficiency and
reliability in the last 5 years, AC is the way to go for a home system. Another
advantage AC has over DC is that the voltage drop for a 120VAC circuit is much
less than a 12VDC circuit carrying the same power, which allows you to use
smaller gauge wire.
Q9...
Can I use PV to heat water or for space heating?
A9...
No. Photovoltaics converts the sun’s energy into DC electricity at a relatively
low efficiency level (14-16%), so
trying to operate a high power electric heating element from PV would be very
inefficient and expensive. Solar
thermal (or passive solar) is the direct heating of air or water from the heat
of the sun and is much more efficient
for heating applications than photovoltaics.
Q10...
Where should I mount the solar modules, and what direction should I face them?
A10...
If your site is in the northern
hemisphere you need to aim
your solar modules to true
south (the reverse is true for
locations in the southern
hemisphere) to maximize your
daily energy output. For many
locations there is quite a
difference between magnetic
south and true south, so please
consult the declination map
before you setup your mount
structure. The solar modules
should be tilted up from
horizontal to get a better angle
at the sun and help keep the
modules clean by shedding rain
or snow. For best year round
power output with the least
amount of maintenance, you
should set the solar array facing
true south at a tilt angle equal
to your latitude with respect to
the horizontal position. If you
plan to adjust your solar array tilt angle seasonally, a good rule of thumb is:
- latitude minus 15° in the summer
- latitude in the spring/fall
- latitude plus 15° in the winter
Most mount structures are available with a seasonal adjustment of the tilt angle
from horizontal to 65°.To determine if your proposed array site will be shaded
at any time of the day or year you should consider using the Solar System.
Q11...
Should I set my system’s
battery bank up at 12, 24,
or 48 VDC?
A11...
The PV industry really began with the 12V
radio communications market. These systems were typically small (1-2 solar
modules) and had all 12 VDC loads. As the solar industry matured and entered the
home market, systems became much larger (16+ solar modules) and no longer used
DC loads exclusively Most home systems today are 24 or 48 VDC since the higher
system voltage gives you a lot more flexibility as to how far away you can place
your solar modules from the battery bank as compared to a 12V system. For a
given power output, a higher system voltage reduces your amperage flow (but not
your power) which allows you to use a smaller and less expensive gauge wire for
your solar to battery and battery to inverter wire runs. Of course, if you
already have a lot of 12VDC loads, that may be your deciding factor as to what
voltage you set your system up at. Most grid-tie systems operate at 48 volts or
higher.