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Solar
panels convert sunlight to DC electricity, which is stored via a
charge regulator into batteries; DC loads can be run directly off
these batteries. Cables from the batteries go to an
inverter, which changes the DC to AC to run the conventional
household loads. Occasional large loads (welder, table saw,
240VAC pumps, etc.) might necessitate the addition of a generator,
which can also charge batteries (in low light conditions) while
you're powering AC loads. And, if you have a good site for
wind (10-12 mph average wind speeds or greater), a wind generator
can be easily added for additional battery charging. Now,
the technology exists for you to have solar
modules, or certain wind generators, with a special
grid-interactive inverter--without batteries. And, as the months
pass, these technologies will become more readily available.
Below is a variety of alternate
energy components, and an overview is given of their function and
how they interact in a system.
CONTROLLERS AND REGULATORS:
Even if you have DC-only power requirements (as with a small
cabin or RV system), you will still need a regulator for any
module 10 watts or larger. The nominal output voltage of
most solar modules ranges from 16 to 20 volts--enough to
"cook" a 12V battery system! A regulator (or
controller) is sized to accommodate the amperage of your incoming
power from the solar array and its voltage output (12, 24 or 48V)
and keep from OVERCHARGING your batteries. You can also get
a regulator that handles a greater amount of amps than currently
required, if you wish to add more solar modules down the
line. Ideally, you will be using slightly less power than
your array's daily output; your regulator will keep your batteries
charged by dumping your array's input to the batteries until they
are "fat", then keep them in that topped-off mode until
your usage lowers the voltage. The next day, when the sun
shines, the process starts again. Controllers come with
quite an amperage range, and a variety of options. E-mail us
for your specific system requirements!
Controllers are also used to optimize voltage in
water
pumping systems, basically enabling the system to produce more
water in lower light conditions by converting voltage to
amperage. In a wind generator, the regulator may be built
into the unit or may be stationed at the battery bank depending
on how the unit is configured.
INVERTER and INVERTER SIZING:
Your inverter takes DC power from your charged battery bank and
converts it to AC power for your typical household lights and
appliances. Once you've determined the number of watt-hours
a day you require, your peak loads need to be
ascertained to properly size the inverter. This is the
amount of watts used based on all appliances and loads that will
be running at one time. A water pump and washing machine
motor is an example of what may be the peak load
requirements. A 1/2 HP pump and washing machine will use
about 1875 (adjusted) watts per hour. If this represents your
total peak loads, you'll need an inverter that will be able to
supply at least 1875 watts of continuous power from your battery
bank--say one in the 2000 watt range. It's a good idea to
start out your system with the size of inverter you plan to grow
into, as upgrading to newer, larger models is costly.
SOLAR MODULES: We
offer a wide variety of modules, with output warranties varying
from 20 to 25 years for the larger panels. Solar modules
should be mounted facing due south with NO shading; if you plan
to adjust the array seasonally, the winter angle will be
latitude plus 15%, in summer, latitude minus 15%. Since we
typically expect the solar modules to last a minimum of 20 to as
many as 40 years, do
not skimp on a mount structure. The panels are too expensive
to let blow away!
Different sizes and makes of modules can generally be mixed in a
12V system. However, in a 24V system, identical modules will have
to be acquired in sets of two, and wired in series. Most
battery-based home systems are 48V configuration, and most solar
modules now have higher voltage. Our 24V modules can be series
wired to easily achieve the 48V configuration, and the MPPT
charge controllers will accept high input voltage and then step
it down to whatever your battery bank needs.
The amount of power a solar module produces is equal to the
intensity of the sunlight it receives; also, the output of the
module is based on the load it's powering. If you are
charging batteries, the battery's internal resistance will affect
the panel's voltage. A module may be able to produce up to
20 volts, but the working voltage will be lower--around 12 to 15
volts. This will reduce the real output of the module.
A 75 watt module working at 14 volts will produce a maximum
of 61.6 watts (the module puts out 4.4 amps X 14V = 61.6
watts).
While there are some modules that perform
better in lower light conditions than others, shading will
reduce the output of any solar panel. By no means should
any shade fall on the modules for two hours before or two hours
after solar noon, and preferably not at all during the day.
BATTERIES:
The size of
the battery bank will be determined by the daily watt-hour
requirements and the desired days of storage capacity
required. Here's a formula for calculating your battery
needs: Take your adjusted watt-hours per day x the number of
days of storage required; take that figure x 2 (for 50% depth of
battery discharge); then divide by the system voltage = amp hours
(ah) of storage needed. FOR EXAMPLE, let's say you need
2000 watt-hours per day and want 5 days of battery back-up; take
2000 x 5 = 10000; x 2 = 20000; divide by 24 (for a 24V system) =
833 amp hours of storage required. If you're looking at
220ah capacity, 6V golf cart deep cycle batteries, we'd divide 833
by 220 to come up with four sets of 4 (as it takes one set of four
6V batteries to supply a 24V system). So you'd need 16 of
those 220ah 6V batteries to provide 5 days of back-up, at the
discharge rate of 2000 watts per day, in a 24V system.
Ideally, we'd prefer that you not take your batteries below 30%
depth of discharge, and NEVER below 50% depth of discharge.
Basically you need to put a little more power into your
batteries than you use (about 120 watts for every 100 watts you
take out). Batteries can be series wired to achieve the voltage
desired (i.e. four 6V batteries for 24V, two for 12V, etc.).
We offer several sizes and types of batteries to best suit your
system needs.
Most of the batteries we offer are the lead-acid type. They
do require proper maintenance to extend their life and work in an
optimum fashion. They prefer moderate temperatures -
around 70 degrees; for this reason they should be insulated in
cold climates, and well-ventilated in warm climates. They
need to be "equalized" at least three or four times a
year, and as often as monthly. Equalizing refers to a
"controlled overcharging" process whereby the voltage of
the batteries is increased to where the accumulated sulfates are
"cooked" off the plates and mixed back into the
electrolyte solution. During this process, the battery caps
are removed and distilled water is added as necessary.
A hydrometer (tool for checking the specific gravity)
is used to check the electrolyte density of individual battery
cells at this time. The equalization voltage for a 12V
system will usually be around 15 volts; for a 24V system, 30
volts. Some manufacturers suggest their batteries be
equalized monthly. Go to this link,
http://www.oasismontana.com/batteries.html, our new battery
page, for more maintenance information.
We offer several types of 6V batteries and 2V industrial
cells. Once we know the criteria for your back-up power
requirements, we will specify the best batteries for your project,
and, as we have distributor contacts all over the country, we can
have many shipped to you with no freight charges (2V cells and
Surrette batteries excepted).
GENERATORS: A
generator/PV hybrid system may suit your home; many clients feel
the need to have a stand-by or back-up generator for prolonged
low light conditions or for the occasional high energy
demand. Some people just have the generator, inverter and
battery bank (called a gen-verter system), so when they're powering
their big water pump (or some other large load) they can also be
charging their battery bank to run smaller loads (lights, TV,
etc.) after they've shut their generator down--to minimize the
generator run time. These folks do not plan to add solar to
their system. Generators use a gas internal combustion
engine to convert fuel to AC electricity, which can power
large AC loads while batteries are being charged. In fact,
many utilize a generator with batteries and inverter in the
construction phase, then add solar incrementally as can be
afforded. During construction, large power tools can draw
costly amounts of power--and would not be economical to run with photovoltaics. But, while you're running a generator to
power these loads, you can also be charging a battery bank.
When you shut down the generator, you can then, via an inverter, run
smaller loads (lights, TV, microwave, etc.) off the
battery bank. Solar can be added easily to these
generator/inverter/battery systems in order to reduce or negate
generator run time. Let us know your power needs so we can
specify the best generator for your system--or tell us what you
have, and we'll design a system to accommodate your
requirements. It all comes down to how many watts per day
you need. For information and pricing on specific
components, scroll down the price list and also click on the
generator button.
WIND GENERATORS: While
being extremely site specific, wind generators may be a valuable
addition to your battery charging scheme. If you live where
there is an average wind speed of 10-12 mph or greater, and you
can mount your unit 30 ft. above anything else within 400 yards,
you may have a terrific location! In the right situation,
wind generators can be more efficient and cost-effective than
photovoltaics. To find out the wind speeds for your area,
contact your local airports or weather agencies for this
information. E-mail us your site information and power
requirements, and we'll specify the best unit to meet your
needs. See additional information under
wind
generators.
WATER PUMPS: Call us
with your pumping project specifications. We need to know
the following: your well casing size? Well
depth? At what depth will your pump hang in the
casing? What is the output capacity of the well? What
times of year will this be used? Is there a pump now in use
at the site? Will this be pumping to a tank or cistern, or
is it part of a pressurized system? How is the water quality
(sandy, muddy, etc.)? And, lastly, how many gallons per day
(and in what seasons) are needed? With this information we
can propose a water pumping system for you. Many
pumping systems are battery-less, but we can add batteries for
on-demand usage. We offer a variety of DC submersible
and surface pumps, 117VAC pumps, and we can power your existing
230VAC model. E-mail us your pump specifications and power
requirements! We have a basic water pumping system broken
down by components--check out our
water
pumping systems on that page by clicking on the
"Water Pumping" button. For information on
DC
submersibles, click here.
ENERGY EFFICIENT APPLIANCES:
It is a fact that every dollar spent on energy efficiency will
save you three to five dollars with your alternate energy
system. Your heating loads are NOT cost effectively powered
by electricity; your electric stove, water heater, clothes dryer
and furnace are much more efficiently powered by natural gas or
propane. Conventional refrigerators tend to be real energy
hogs, so please consider an energy-efficient unit or even a
propane refrigerator. An energy-efficient refrigerator could
(in many parts of the country) be powered by four 75W solar
modules; a conventional refrigerator might take 8 to 12 MORE
modules, with an appropriately larger battery bank! Compact
fluorescent lights have the look and feel of incandescent bulbs ,
yet use 75% less power. When
you become your own power company, any way you can reduce your
electrical loads will save you money in the cost of your system.
We have info on efficient AC refrigeration as well as information on
LP
or Propane Refrigeration or "Refrigeration"
at this link:
www.eco-fridge.com.
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