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Conservation
Conservation plays an important role in keeping down the cost
of a photovoltaic system. The use of energy efficient appliances
and lighting, as well as non-electric alternatives wherever possible,
can make solar electricity a cost competitive alternative to
gasoline generators and, in some cases, utility power.
Cooking, Heating,
& Cooling
Conventional electric cooking, space heating and water heating
equipment use a prohibitive amount of electricity. Electric ranges
use 1500 watts or more per burner, so bottled propane or natural
gas is a popular alternative to electricity for cooking. A microwave
oven has about the same power draw, but since food cooks more
quickly, the amount of kilowatt hours used may not be large.
Propane and wood are better alternatives for space heating. Good
passive solar design and proper insulation can reduce the need
for winter heating. Evaporative cooling is a more reasonable
load than air conditioning and in locations with low humidity,
the results are almost as good. One plus for cooling-the largest
amount of solar energy is usually available when the temperature
is the highest.
Lighting
Lighting requires the most study since many options exist in
type, size, voltage and placement. The type of lighting that
is best for one system may not be right for another. The first
decision is whether your lights will be run on low voltage direct
current (DC) or conventional 110 volt alternating current (AC).
In a small home, an RV, or a boat, low voltage DC lighting is
often the best choice. DC wiring runs can be kept short, allowing
the use of fairly small gauge wire. Since an inverter is not
required, the system cost is lower. When an inverter is part
of the system, a home will not be dark if the inverter fails
and the lights are powered directly by the battery. In addition
to conventional-size medium-base low voltage bulbs, the user
can choose from a large selection of DC fluorescent lights, which
have 3 to 4 times the light output per watt of power used compared
with incandescent types. Halogen bulbs are 30% more efficient
and actually seem almost twice as bright as similar wattage incandescents
given the spectrum of light they produce. High quality fluorescent
lights are available for 12 and 24 volt systems. In a large installation
or one with many lights, the use of an inverter to supply AC
power for conventional lighting is cost effective. AC compact
fluorescent lights will save a tremendous amount of energy. It
is a good idea to have a DC-powered light in the room where the
inverter and batteries are in case there is a problem. AC light
dimmers will only function properly on AC power from inverters
that have pure sine wave output.
Refrigeration
Gas powered absorption refrigerators are a good choice in small
systems if bottled gas is available. Modern absorption refrigerators
consume 5-10 gallons of LP gas/month. If an electric refrigerator
will be used in a stand-alone system, it should be a high-efficiency
type. Some high-efficiency conventional AC refrigerators use
as little as 1200 watt-hours of electricity/day at a 70º
average air temperature. A comparably sized Sun Frost refrigerator/freezer
uses half that amount of energy and a Sundanzer refrigerator
(without a freezer) uses less than 100 watt-hours per day. The
higher cost of good quality DC refrigerators is made up by savings
in the number of solar modules and batteries required.
Major Appliances
Standard AC electric motors in washing machines, larger shop
machinery and tools, swamp coolers, pumps, etc. (usually 1/4
to 3/4 horsepower) require a large inverter. Often, a 2000 watt
or larger inverter will be required. These electric motors are
sometimes hard to start on inverter power, they consume relatively
large amounts of electricity, and they are very wasteful compared
to high-efficiency motors, which use 50% to 75% less electricity.
A standard washing machine uses between 300 and 500 watt-hours
per load, but new front-loading models use less than 1/2 as much
power. If the appliance is used more than a few hours per week,
it is often cheaper to pay more for a high-efficiency appliance
rather than make your electrical system larger to support a low-efficiency
load. Vacuum cleaners usually consume 600 to 1,000 watts, depending
on how powerful they are, about twice what a washer uses, but
most vacuum cleaners will operate on inverters larger than 1,000
watts since they have low-surge motors.
Small Appliances
Many small appliances such as irons, toasters and hair dryers
consume a very large amount of power when they are used but by
their nature require very short or infrequent use periods. If
the system inverter and batteries are large enough, they will
be usable. Electronic equipment, such as stereos, televisions,
VCR's and computers have a fairly small power draw. Many of these
are available in low voltage DC as well as conventional AC versions.
In general, DC models use less power than their AC counterparts.
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Information courtesy
of Alternative
Energy Engineering.
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