DC Loads
Inverter
AC Loads
The Basics of Solar Electricity Are Simple
The basics of how solar systems work can be seen in the diagram at right. The sun
shines on solar modules that produce DC current. The current goes through a
controller that regulates the amount of power that goes into the batteries. The
batteries store DC power for use when needed. DC appliances run off energy
straight from the batteries. You can choose to use AC appliances instead of
DC—or in addition to DC—but the energy from the batteries must first be changed
to AC voltage by an
inverter
.
Solar system design is not just about using the sun for electricity. It is
about using this energy efficiently. Things as simple as window
placement and flooring and window covering materials can affect how
well your design will function. The ability to understand how energy is
created, stored and used in your home is important. Many books are
available on passive solar home design, and various statewide solar
energy associations can be found on the Web along with the national
solar energy association. Our New Mexico Solar Energy Association is
located at: http://www.nmsea.org.
Energy conservation is the first area to consider. You will now be the
power company as well as the power consumer. Your choices in
appliances, lighting, cooking and heating will greatly affect the cost of
your power plant. Use less power and you can buy a smaller power
plant.
It really is simple.
Developing an overall strategy for energy independence is the most important first
step. Many people want to purchase equipment based on a budget. That is only
part of the equation. It is better to make a plan of where you want to go with the
money that you have to spend….and the money that you will want to spend later.
The most economical step in going off-grid is to lower the amount of energy you
use. You may be better off to start out with a new energy efficient stove,
refrigerator and computer than to buy a small solar system that won’t be able to
run the inefficient appliances that you use now. Even if you purchase a grid-tied
system to reduce your electric bill, you will realize a great savings with
energy
efficiency,
even before you buy any solar equipmen
A Short Lesson in Electricity
Amps x Volts = Watts
Watts / Volts = Amps
Watts / Amps = Volts
Kw = 1,000 Watts
Electricity is the flow of electrons through a conductor like a wire. It’s like the
flow of water through a pipe.
To increase the flow of water through a pipe you need either a larger pipe or
more pressure. The pressure in an electrical system is called voltage and is
measured in volts. The higher the voltage in a system the more force behind it.
In a water pipe the size of the pipe also determines the rate of flow. The bigger
the pipe the greater the flow. The amount of flow in electricity is called
amperage, measured as amps or current.
Electrical “power” is a combination of the pressure, or
VOLTAGE
times the
flow, or
AMPERAGE
. This combination is called the
WATT
or
WATTS
. This
is generally the unit of power that we use in assessing electrical systems. It
functions as a common denominator for different voltages and amperages. For
example:
5 amps at 24 Volts = 120 Watts (Amps x Volts = Watts)
or
1,500 watts / 120 Volts = 12.5 amps (Watts/ Volts = Amps)
One watt that is powered for one hour is called one
WATT HOUR.
1,000 watts
use for one hour is a
KILOWATT HOUR.
These formulas help us figure out how much solar power it will take to run our
loads:
A 4 amp motor running for 1/2 hr. at 120 volts uses 240 watts.
4(amps) x 120(volts)=480 watts / 2 (1/2 hr.) = 240 Watt hrs.
A 100 watt solar panel produces 100 watt hours per full solar hour. It would take
about 2 1/2 hours for that solar panel to run the motor for 1/2 hour. This is a
simplistic example because there are various inefficiencies in solar electric
systems, but this is a good “rule of thumb”.
Phantom Loads
Don’t pay for electricity that you aren’t using. Phantom loads are the
electricity that appliances use when they are turned OFF! That’s right… The
light on your stereo or TV that shines when they are off means that as much
as 50% of their “on” power is being used while they are “off” so that they
can come on “instantly”. I tested my stereo, TV and VCR when they were off
and found that they were using 42 watts per hour! That’s 1,008 watts per day
to be “off”!
Common phantom loads are: TV, VCR, clocks on appliances, computer
systems. Plug these loads into “power strips” and turn the strips off when the
appliances are not being used. If you are building a new house, get your
electrician to put in a wall switch that turns power on and off to these
appliances. It’s a simple and inexpensive way to conserve electricity, even if
you are ON the grid.
The numbers 110 volts, 117 volts and 120 volts
AC all refer to household current in the USA.
We use the number 120 to do the math.
Should you wire your electrical system for
AC or DC?
To design your system you need to decide what voltage you will use. Most off-
grid homes use a combination. In our home most loads, including lighting, are
AC and run off the inverter. This catalog is published on a MacIntosh computer
powered by the sun. Only our phone system and our pumps are 12 VDC. In the
event of an inverter failure we still have phone and water.
If you have a small system, then DC is a simpler and less expensive way to go
because there is no need for an inverter. But if you plan to use appliances that
you already own (stereo, TV, tools etc.) you will need an inverter. Since AC
appliances, light bulbs and tools are more readily available and generally less
expensive you may want to run most things AC. Just remember that if your
inverter goes down so does everything that relies on it. Fortunately, inverters
are very sturdy and long lasting.
Some people are concerned about the magnetic field that AC wiring creates in
their homes. There are possible health hazards related to this phenomenon. If
you are concerned, then don’t put AC wires in the walls by your bed where you
spend the most time in your house.
Broadcasting Solution 