17-05-2013, 02:49 PM
The Basics of Solar Power for Producing Electricity
The Basics of Solar Power.pdf (Size: 67.15 KB / Downloads: 168)
An excellent place to start for those just beginning.
Solar power works well for most items except large electric appliances that use an
electric heat element such as a water heater, clothes dryer and electric stove - for
example - or total electric home heating systems. It is not cost effective to use solar
power for these items. Conversion to natural gas, propane or other alternatives is
usually recommended. Solar power can be used to operate a gas clothes dryer
(Maytag, etc) because the electrical requirement is limited to the drum-motor and/or
ignito-lighter, but not a HEAT element for drying the clothes, for example.
The basics of solar power:
Using solar power to produce electricity is not the same as using solar to produce
heat. Solar thermal principles are applied to produce hot fluids or air. Photovoltaic
principles are used to produce electricity. A solar panel (PV panel) is made of the
natural element, silicon, which becomes charged electrically when subjected to sun
light.
Solar panels are directed at solar south in the northern hemisphere and solar north
in the southern hemisphere (these are slightly different than magnetic compass
north-south directions) at an angle dictated by the geographic location and latitude
of where they are to be installed. Typically, the angle of the solar array is set within
a range of between site-latitude-plus 15 degrees and site-latitude-minus 15 degrees,
depending on whether a slight winter or summer bias is desirable in the system.
Many solar arrays are placed at an angle equal to the site latitude with no bias for
seasonal periods.
This electrical charge is consolidated in the PV panel and directed to the output
terminals to produce low voltage (Direct Current) - usually 6 to 24 volts. The most
common output is intended for nominal 12 volts, with an effective output usually up
to 17 volts. A 12 volt nominal output is the reference voltage, but the operating
voltage can be 17 volts or higher much like your car alternator charges your 12 volt
battery at well over 12 volts. So there's a difference between the reference voltage
and the actual operating voltage.
The intensity of the Sun's radiation changes with the hour of the day, time of the
year and weather conditions. To be able to make calculations in planning a system,
the total amount of solar radiation energy is expressed in hours of full sunlight per
m², or Peak Sun Hours. This term, Peak Sun Hours, represents the average amount
of sun available per day throughout the year.
Components used to provide solar power:
The four primary components for producing electricity using solar power, which
provides common 110-120 volt AC power for daily use are: Solar panels, charge
controller, battery and inverter. Solar panels charge the battery, and the charge
regulator insures proper charging of the battery. The battery provides DC voltage to
the inverter, and the inverter converts the DC voltage to normal AC voltage. If 220-
240 volts AC is needed, then either a transformer is added or two identical inverters
are series-stacked to produce the 240 volts.
Solar Panels:
The output of a solar panel is usually stated in watts, and the wattage is determined
by multiplying the rated voltage by the rated amperage. The formula for wattage is
VOLTS times AMPS equals WATTS. So for example, a 12 volt 60 watt solar panel
measuring about 20 X 44 inches has a rated voltage of 17.1 and a rated 3.5
amperage.
Charge Controller:
A charge controller monitors the battery's state-of-charge to insure that when the
battery needs charge-current it gets it, and also insures the battery isn't overcharged.
Connecting a solar panel to a battery without a regulator seriously risks
damaging the battery and potentially causing a safety concern.
Charge controllers (or often called charge regulator) are rated based on the amount
of amperage they can process from a solar array. If a controller is rated at 20 amps
it means that you can connect up to 20 amps of solar panel output current to this
one controller. The most advanced charge controllers utilize a charging principal
referred to as Pulse-Width-Modulation (PWM) - which insures the most efficient
battery charging and extends the life of the battery. Even more advanced controllers
also include Maximum Power Point Tracking (MPPT) which maximizes the amount of
current going into the battery from the solar array by lowering the panel's output
voltage, which increases the charging amps to the battery - because if a panel can
produce 60 watts with 17.2 volts and 3.5 amps, then if the voltage is lowered to say
14 volts then the amperage increases to 4.28 (14v X 4.28 amps = 60 watts)
resulting in a 19% increase in charging amps for this example.
Battery:
The Deep Cycle batteries used are designed to be discharged and then re-charged
hundreds or thousands of times. These batteries are rated in Amp Hours (ah) -
usually at 20 hours and 100 hours. Simply stated, amp hours refers to the amount of
current - in amps - which can be supplied by the battery over the period of hours.
For example, a 350ah battery could supply 17.5 continuous amps over 20 hours or
35 continuous amps for 10 hours. To quickly express the total watts potentially
available in a 6 volt 360ah battery; 360ah times the nominal 6 volts equals 2160
watts or 2.16kWh (kilowatt-hours). Like solar panels, batteries are wired in series
and/or parallel to increase voltage to the desired level and increase amp hours.
Using an Inverter:
An inverter is a device which changes DC power stored in a battery to standard
120/240 VAC electricity (also referred to as 110/220). Most solar power systems
generate DC current which is stored in batteries. Nearly all lighting, appliances,
motors, etc., are designed to use ac power, so it takes an inverter to make the
switch from battery-stored DC to standard power (120 VAC, 60 Hz).
In an inverter, direct current (DC) is switched back and forth to produce alternating
current (AC). Then it is transformed, filtered, stepped, etc. to get it to an acceptable
output waveform. The more processing, the cleaner and quieter the output, but the
lower the efficiency of the conversion. The goal becomes to produce a waveform that
is acceptable to all loads without sacrificing too much power into the conversion
process.
Inverters come in two basic output designs - sine wave and modified sine wave. Most
120VAC devices can use the modified sine wave, but there are some notable
exceptions. Devices such as laser printers which use triacs and/or silicon controlled
rectifiers are damaged when provided mod-sine wave power. Motors and power
supplies usually run warmer and less efficiently on mod-sine wave power. Some
things, like fans, amplifiers, and cheap fluorescent lights, give off an audible buzz on
modified sine wave power. However, modified sine wave inverters make the
conversion from DC to AC very efficiently. They are relatively inexpensive, and many
of the electrical devices we use every day work fine on them.
Efficiency Losses:
In all systems there are losses due to such things as voltage losses as the electricity is
carried across the wires, batteries and inverters not being 100 percent efficient, and other
factors. These efficiency losses vary from component to component, and from system to
system and can be as high as 25 percent.