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 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 cell's surface area (approximately 7A
for a 6 inch square multicrystalline 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 to
charge a 12, 24 or 48 volt battery bank.
Will
solar work in 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 averages 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 from others, so
they will have more "full sun hours" per day. The solar insolation
zone map on the right will give you a general idea of the "full sun hours
per day" for your location.
How
much will a system cost for my 2000 square foot 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, we need to know what breakers are in your service and the AMP ratings. Call 1.866.786.6979 to have a EcoStar Specialist help you calculate costs.
Can
I use all of my normal 120/240 VAC appliances?
Yes. 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. Appliances that operate at 240 VAC (such as electric water
heaters, cook-stoves, furnaces and air conditioners) are, in most cases,
impractical 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 (unless the AC is above 14 seer) 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.
What
components do I need?
There
are many components that make up a complete solar system, but the 4 main items
are: solar modules, charge controller(s), batteries 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 day or night. Batteries come in many sizes and grades. The inverter
takes the DC energy stored in the battery bank and inverts it to 120 VAC to run
your AC appliances.
Where
should I mount the solar modules and what direction should I face them?
If your site
is in the Northern Hemisphere you need to aim your solar modules to the true
south direction (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 below 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 to go by is latitude minus 15? in the summer, latitude in
the spring/fall and latitude plus 15? in the winter. Most mount structures
provide for a seasonal adjustment of the tilt angle from horizontal to 65?.
Should
I set my system's battery bank up at 12, 24 or 48 VDC?
Should
I wire my home for AC or DC loads?
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 counterparts. Small cabin and RV systems are
typically wired DC while most home systems are wired for AC loads exclusively.
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.
Can
I use PV to heat water or for space heating?
No.
Photovoltaics converts the sun's energy into DC electricity, so trying to
operate a high power electric heating element from PV panels would be very
inefficient and expensive. Though running it through the high voltage inverter
this can be achieved.
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 to a minimum, which is good. But they also require
roof penetrations in multiple locations (a potential source of leakage) and
they require an expensive ground fault protection (GFP- 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 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.
What does a power inverter do, and what can I use one for?
A power inverter changes
DC power from a battery into conventional AC power that you can use to operate
all kinds of devices ... electric lights, kitchen appliances, microwaves, power
tools, TVs, radios, computers, to name just a few. You just connect the
inverter to a battery, and plug your AC devices into the inverter ... and
you've got portable power ... whenever and wherever you need it.
The inverter draws its
power from a 12 Volt battery (preferably deep-cycle), or several batteries
wired in parallel. The battery will need to be recharged as the power is drawn
out of it by the inverter. The battery can be recharged by running the
automobile motor, or a gas generator, solar panels, or wind. Or you can use a
battery charger plugged into an AC outlet to recharge the battery.
Using an Inverter for
Emergency Home Backup Power
A very simple way to use
an inverter for emergency power (such as during a power outage), is to use
a car battery (with the vehicle running), and an extension cord running into
the house, where you can then plug in electrical appliances.
What size inverter should I
buy?
Short Answer: The size you choose depends on the
watts (or amps) of what you want to run (find the power consumption by
referring to the specification plate on the appliance or tool). We recommend
you buy a larger model than you think you'll need (at least 10% to 20% more
than your largest load).
Example: You want to power
a computer with a 17" monitor, some lights,
and a radio.
|
Computer:
|
300
Watts |
|
2
- 60 Watt lights: |
120
Watts |
|
Radio: |
10
Watts |
|
Inverter
Watts Needed: |
430
Watts |
For this application, you
would minimally need a 500 W inverter, and should give some thought to a larger
one, as there will likely be a time when you wish you'd bought a bigger model
... in this example, you might decide you'd like to run a fan while you
compute, or let the kids watch TV.
Longer Answer: Determine Continuous Load and
Starting (Peak) Load: You need to determine how much power your tool or
appliance (or combination of them that you would use at the same time) requires
to start up (starting load), and also the continued running requirements
(continuous load).
What is meant by the terms
"continuous-2000 watts" and "peak surge-4000 watts" is that
some appliances or tools, such as ones with a motor, require an initial surge
of power to start up ("starting load" or "peak load"). Once
started, the tool or appliance requires less power to continue to operate
("continuous load")
Helpful
formulas:
To
Convert AMPS to WATTS:
Multiply:
AMPS X 120 (AC voltage) = WATTS
This formula yields a close approximation of the continuous load of the
appliance
To
Calculate approximate Startup Load:
Multiply:
WATTS X 2 = Starting Load
This formula yields a close approximation of the starting load of the
appliance, though some may require an even greater starting load. NOTE: Induction motors such as air
conditioners, refrigerators, freezers and pumps may have a start up surge of 3
to 7 times the continuous rating.
Most often the start up
load of the appliance or power tool determines whether an inverter has the
capability to power it.
For example, you have a
freezer with a continuous load of 4 amps, and a start up load of 12 amps:
4 amps x 120 volts = 480
watts continuous
12 amps x 120 volts = 1440 watts starting load
You would need an inverter
with peak-surge rating greater than 1440 watts.
FORMULA
to convert AC Watts to DC Amps:
AC Watts divided by 12 x
1.1 = DC Amps
(this is the size vehicle alternator you would need to keep up with a specific
load; for example, to keep up with a continuous draw of 1000 watts, you would
need a 91 amp alternator)
Do I need Modified Sine Wave, or Pure Sine Wave?
Advantages of Pure Sine
Wave inverters over modified sine wave inverters:
a) Output voltage wave
form is pure sine wave with very low harmonic distortion and clean power better
than utility-supplied electricity.
b) Inductive loads like
microwave ovens and motors run faster, quieter and cooler.
c) Reduces audible and
electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game
consoles, Fax, and answering machines.
d) Prevents crashes in
computers, weird print out, and glitches and noise in monitors.
e) Reliably powers the
following devices that will normally not work with modified sine wave
inverters:
- Laser printers, photocopiers, magneto-optical hard
drives
- Certain laptop computers (you should check with your
manufacturer)
- Some fluorescent lights with electronic ballasts
- Power tools employing "solid state" power
or variable speed control
- Some battery chargers for cordless tools
- Some new furnaces and pellet stoves with
microprocessor control
- Digital clocks with radios
- Sewing machines with speed/microprocessor control
- X-10 home automation system
- Medical equipment such as oxygen concentrators
Modified Sine Wave works
well for most uses, and is the most common type of inverter on the market, as
well as the most economical. Pure Sine Wave inverters (also called True Sine
Wave) are more suited for sensitive electrical or electronic items such as
laptop computers, stereos, laser printers, certain specialized applications
such as medical equipment, a pellet stove with an internal computer, digital
clocks, bread makers with multi-stage timers, and variable speed or
rechargeable tools (see "Appliance
Cautions" below). If you wish to use those items with an inverter,
then choose a Pure Sine Wave inverter. If you mostly want to run lights, TV,
microwave oven, tools, etc, a Modified Sine Wave inverter is fine for your
needs.
We often are asked if
computers will work with Modified Sine Wave. It's been our experience that most
(with the exception of some laptops) will work (though some monitors will have
interference such as lines or a hum). However, if you have any doubt about any
appliance, tool or device, particularly laptop computers and medical equipment
such as oxygen concentrators, we recommend that you check with its manufacturer
to be sure it is compatible with a Modified Sine Wave inverter. If it is not,
choose one of our Pure Sine Inverters instead.
The difference between
them is the Pure Sine Wave inverter produces a better and cleaner current. They
are also considerably more expensive. You might find it practical to get a
small Pure Sine Wave inverter for any "special need" you may have,
and also a larger Modified Sine Wave inverter for the rest of your
applications.
How do I hook up the Inverter? What size cable should I
use?
The small inverters (400
watts and under) come with a cigarette lighter adapter, and may be plugged into
your car's lighter socket (although you will not be able to draw more than 150
to 180 watts from the cigarette lighter socket). The small units also come with
cables that can be clamped directly to a battery. If you want an inverter that
will plug into your cigarette lighter, you must choose one that is 400 watts or
less.
Larger inverters (500
watts and over) must be hard-wired directly to a battery. The cable size
depends on the distance between battery and inverter, and will be specified in
the Owner's Manual.
When connecting the
inverter to the battery use the thickest wire available, in the shortest
length practical.
General recommendations —
Inverters 1500 watts and under: If battery and inverter are within 4', use #4
gauge AWG. If 4'-6', use #2. If more than 6', use #0 gauge wire (#0 gauge wire
may require a "0 to 4 Gauge Adapter"). The maximum length generally
recommended is 10', and shorter is better. If you need more length, it is much
better to put it on the AC side (as with an extension cord from inverter to
appliance) than on the DC side.
Inverters over 1500 watts
will require #1/0 or larger cable, in the shortest possible length.
What type of battery should I use (automotive or deep
cycle)?
True deep cycle only!
How
long can I run the inverter on my battery?
Tip: Deep cycle (marine) batteries
generally have the highest reserve ratings. They are also capable of
withstanding repeated drains of power and recharging.
Tip: Engine start batteries should not
be discharged below 90% charged state, and marine deep cycle batteries should
not be discharged below 50% charged state. Doing so will shorten the life of
the battery based on most battery manufacturers recommendations.
Note: If you intend to use power tools
for commercial use, or any load of 200W for more than 1 hour regularly (between
battery recharging) we recommend installing an auxiliary battery to provide
power to the inverter. This battery should be a deep cycle type and sized to
meet your run time expectations with the engine off. The auxiliary battery
should be connected to the alternator through an isolator module to prevent the
inverter from discharging the engine start battery when the engine is off.
How do
I connect two or more batteries?
It may be advisable to
operate the inverter from a bank of 12 Volt batteries of the same type in a
"parallel" configuration. Two such batteries will generate twice the
amp/hours of a single battery; three batteries will generate three times the
amp/hours, and so on. This will lengthen the time before your batteries will
need to be recharged, giving you a longer time that you can run your
appliances.
You can also connect 6
Volt batteries together in "series" configuration to double the
voltage to 12 volts. Note that 6 Volt batteries must be connected in pairs.
|
Operating a Microwave with a Power Inverter
The power rating used with
microwave ovens is the "cooking power" which refers to the power
being "delivered" to the food being cooked. The actual operating
power requirement rating is higher than the cooking power rating (for
example, a microwave with "advertised" rating of 600 watts usually
corresponds to almost 1100 watts of power consumption). The actual power
consumption is usually stated on the back of the microwave. If the operating
power requirement cannot be found on the back of the microwave, check the
owner's manual or contact the manufacturer.
Television
and Audio Suggestions
Although all our inverters
are shielded and filtered to minimize signal interference, some interference
with your television picture may be unavoidable, especially with weak signals.
Here are some suggestions
that may improve reception:
1. First make sure that
the television antenna produces a clear signal under normal operating
conditions (i.e., at home plugged into a standard 110AC wall outlet). Also
insure that the antenna cable is properly shielded and of good quality.
2. Change positions of the
inverter, antenna cables and television power cord.
3. Isolate the television,
its power cord and antenna cables from the 12 volt power source by running an
extension cord from the inverter to the TV set. Insure that any excess AC power
cord is a distance away from the TV set.
4. Coil the television
power cord and the input cables running from the 12 volt power source to the
inverter.
5. Attach a "Ferrite
Data Line Filter" to the television power cord. More than one filter may
be required. These are available at electronic supply stores including Radio
Shack (Radio Shack Part No. 273-105)
NOTE: Some inexpensive
audio systems may discharge a slight "buzzing" sound when operated
with an inverter. This is caused by deficient filters in the audio system. The
only solution to this problem is using a sound system with a higher quality
power supply.
DO NOT plug small
appliances into the inverter AC receptacles to directly recharge their
nickel-cadmium batteries. Always use the re-charger provided with that
appliance.
DO NOT plug in battery
chargers for cordless power tools if the charger carries a warning that
dangerous voltages are present at the battery terminals.
Not all fluorescent lamps
operate properly with an inverter. If the bulb appears to be too bright, or
fails to light, do not use the lamp with an inverter.
Some fans with synchronous
motors may slightly increase in speed (RPM) when powered by an inverter. This
is not harmful to the fan or to the inverter.
Certain rechargers for
small nickel-cadmium batteries can be damaged if plugged into an inverter. In
particular, two types of appliances are susceptible to damage:
- Small, battery-operated appliances such as
flashlights, cordless razors and toothbrushes that can be plugged directly
into an AC receptacle to recharge.
- Certain battery chargers for battery packs that are
used in some cordless hand-tools. Chargers for these tools have a warning
label stating that dangerous voltages are present at the battery
terminals.
DO NOT use an inverter
with the above two types of equipment.
The majority of
portable appliances do not have this problem. Most portable appliances use
separate transformers or chargers that plug into AC receptacles to supply a
low-voltage DC or AC output to the appliance. If the appliance label states
that the charger or adapter produces a low-voltage DC or AC output (30 volts or
less), there should be no problem powering that charger or adapter.
Safety Warning: 110 Volts of current can be lethal. Improper use of a power
inverter will result in property damage, personal injury, or loss of life.
Please read and follow carefully the instructions in the Owner's Manual
provided with every inverter for important safety considerations and
precautions.
General
Safety Precautions and Installation Tips:
- Place the inverter on a reasonably flat surface,
either horizontally or vertically.
- The inverter should not be installed in the
engine compartment, due to possible water/oil/acid contamination, and
excessive heat under the hood, as well as potential danger from gasoline
fumes and the spark that an inverter can occasionally produce. It's best
to run battery cables to a dry, cool inverter mounting location.
- Keep the inverter dry. Do not expose it to rain or
moisture. DO NOT operate the inverter if you, the inverter, the device
being operated, or any other surfaces that may come in contact with any
power source are wet. Water and many other liquids can conduct electricity
which may lead to serious injury or death.
- Avoid placing the inverter on or near heating vents,
radiators or other sources of heat. Do not place the inverter in direct
sunlight. Ideal air temperature is between 50° and 80° F.
- In order to properly disperse heat generated while
the inverter is in operation, keep it well ventilated. While in use,
maintain several inches of clearance around the top and sides of the
inverter.
- Do not use the inverter near flammable materials. Do
not place the inverter in areas such as battery compartments where fumes
or gases may accumulate.
Call Today
(1-866-786-6979)
We can help you determine your
needs.
