Power Green Alliance
Solar Power Components

The four primary components for producing electricity using solar power are:

  • Solar panels
  • Charge controller
  • Battery
  • Inverter

  • Solar panels charge the battery,
  • The charge controller or charge regulator insures proper charging of the
    battery,
  • The battery provides DC voltage to the inverter,
  • The inverter converts the DC voltage to normal household AC voltage.

Solar Panels:

The output of a solar panel is measured in watts.  Wattage is calculated by
multiplying the rated voltage by the rated amperage. The formula for wattage is
VOLTS times AMPS = WATTS.   For example, a 12 volt 60 watt
solar panel measuring 20 X 44 inches has a rated voltage of 17.1 and a rated 3.5
amperage.
V x A = W 17.1 volts times 3.5 amps equals 60 watts.  If an average of 6 hours of
peak sun per day is available in an area, then this solar panel can produce an
average 360 watt hours of power per day; 60w times 6 hrs = 360 watt-hours.

The intensity of sunlight varies throughout the day, therefore the term "peak sun
hours" is used to smooth out the variations. Early morning and late-in-the-day
sunlight produces less power than the mid-day sun.  Cloudy days produce less
power than bright sunny days.  Geographical areas are rated in average peak
sun hours per day based on yearly sun data.

Series or Parallel

Solar panels can be wired in series or in parallel to increase voltage or amperage.
Series wiring connects the positive terminal of one panel to the negative terminal
of another. The outer positive and negative terminals will produce voltage the sum
of the two panels, but the amperage remains the same as one panel. So two 12
volt/3.5 amp panels wired in series produce 24 volts at 3.5 amps. Four of these
wired in series produce 48 volts at 3.5 amps. Parallel wiring refers to connecting
positive terminals to positive terminals and negative to negative. The result is that
voltage stays the same, but amperage becomes the sum of the number of panels.
So two 12 volt/3.5 amp panels wired in parallel would produce 12 volts at 7 amps.
Four panels would produce 12 volts at 14 amps.  Series/parallel wiring refers to
doing both of the above - increasing volts and amps to achieve the desired
voltage as in 24 or 48 volt systems.

Charge Controller:

  • A charge controller monitors the battery's state-of-charge to ensure that
    when the battery needs charge-current it gets it, and also prevents
    overcharging.

  • Connecting a solar panel to a battery without a controller risks damage to the
    battery.  Charge controllers (or charge regulators) are rated on the amount of
    amperage they 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.

  • PWM - The most advanced charge controllers utilize Pulse-Width-Modulation
    (PWM) - which ensures the most efficient battery charging and extends the
    life of the battery.

  • MPPT - 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.

  • LVD - Many charge controllers also offer Low Voltage Disconnect (LVD) and
    Battery Temperature Compensation (BTC) as an optional feature. The LVD
    feature permits connecting loads to the LVD terminals which are then voltage
    sensitive. If the battery voltage drops too far the loads are disconnected -
    preventing potential damage to both the battery and the loads. BTC adjusts the
    charge rate based on the temperature of the battery since batteries are
    sensitive to temperature variations above and below about 75 F degrees.

Batteries:

Deep Cycle
batteries 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.  Amp hours refer to the amount of current
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.

Batteries can be wired in series and/or parallel to increase voltage and amp
hours.  The battery should have sufficient amp hour capacity to supply needed
power during the longest expected period "no sun" or extremely cloudy conditions.

Lead-Acid batteries are the most common in PV systems because of low cost
and availability.  The most important designation is that they are
Deep Cycle
batteries.  Lead-Acid batteries are available in
Wet-Cell, and sealed versions
such as
AGM and Gel-Cell.

A lead-acid battery should be sized at least 20% larger than this amount. If there
is a source of back-up power, such as a standby generator along with a battery
charger, the battery bank does not have to be sized for worst case weather
conditions.  The size of the battery bank required will depend on the storage
capacity required, the maximum discharge rate, the maximum charge rate, and the
minimum temperature at which the batteries will be used.

One of the biggest mistakes made by those just starting out is not understanding
the relationship between amps and amp-hour requirements of 120 volt AC items
versus the effects on their DC low voltage batteries.

For example, say you have a 24 volt nominal system and an inverter powering a
load of 3 amps, 120VAC, which has a duty cycle of 4 hours per day. You would
have a 12 amp hour load (3A X 4 hrs=12 ah). However, in order to determine the
true drain on your batteries you have to divide your nominal battery voltage (24v)
into the voltage of the load (120v), which is 5, and then multiply this times your
120vac amp hours (5 x 12 ah). So in this case the calculation would be 60 amp
hours drained from your batteries - not the 12 ah. Another simple way is to take
the total watt-hours of your 120VAC device and divide by nominal system voltage.
Using  the above example; 3 amps x 120 volts x 4 hours = 1440 watt-hours
divided by 24 DC volts = 60 amp hours.

Inverters

  • An inverter is a device which changes DC power stored in a battery to
    standard 120/240 VAC electricity (or 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 switch from DC to 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  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 in the conversion process.

Sine Wave and Modified Sine Wave Inverters

  • Inverters come in two basic output designs - Sine Wave and Modified Sine
    Wave.  Most 120VAC devices use modified sine wave.  Exceptions are
    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 devices, like fans, amplifiers, and cheap fluorescent lights, give
    off an audible buzz on modified sine wave power.

  • Modified sine wave inverters make the conversion from DC to AC very
    efficiently. They are relatively inexpensive, and work for most household
    appliances.

  • Sine wave inverters can virtually operate anything. Your utility company
    provides sine wave power, so a sine wave inverter is equal to or even better
    than utility supplied power. A sine wave inverter can "clean up" utility or
    generator supplied power because of its internal processing.  Inverters are
    made with various internal features and many permit external equipment
    interface

  • Common internal features are internal battery chargers which can rapidly
    charge batteries when an AC source such as a generator or utility power is
    connected to the inverter's INPUT terminals.

  • Auto-transfer switching is also a common internal feature which enables
    switching from either one AC source to another and/or from utility power to
    inverter power for designated loads.

  • Battery temperature compensation, internal relays to control loads, automatic
    remote generator starting/stopping and many other programmable features
    are available.

  • Most inverters produce 120VAC, but can be equipped with a step-up
    transformer to produce 120/240VAC. Some inverters can be series or
    parallel "stacked-interfaced" to produce 120/240VAC or to increase the
    available amperage.

Efficiency Losses:

In all systems there are voltage losses as  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.

Power Consumption

2.5KWh Inverter, 480Wh Solar array, will produce on average approximately 1.4
kWh per day. Power is defined as the rate at which work is done or energy is
consumed.  The formula for average power is acquired by dividing work by the
time needed to perform work: P = W/t. Power has units of newton-meters per
second or joules per second or watts.

Power Plants

Electric power for residential use comes from power plants via a power
distribution
grid. The power derives from a power site within the power plant,
consisting of a central mover like a turbine that is then pushed by water or steam
to run a system of generators.

Household Power Consumption

The amount of power that a household consumes depends on how many
appliances there are and the amount of time they are in use. Some appliances take
a lot of energy to operate, so it will result in more use of power.

"A kilowatt-hour is the electrical energy consumed in one hour at the constant rate
of one kilowatt. The average household 8,900 kilowatt-hours of electricity each
year."

Typical Power Consumption
Air Conditioners WATTS ANNUAL kW
One ton 1,900 3,078  
Three-and-one-half-ton 6,500 10,530  
Five-ton 9,200 14,904  
Major & General Appliances
CD Player 85 85  
Clock 2 17  
Clothes Dryer 2,790 900  
Computers 240 1,248  
Dishwasher 1,201 363  
Electric Blanket 177 147  
Fan (Attic) 370 291  
Fan (Ceiling or    Circulating) 88 43  
Fan (Furnace) 500 660  
Fan (Rollaway) 171 138  
Fan (Window) 200 170  
Fish Tank 4 35  
Floor Polisher 305 15  
Freezer-Upright (18 cu. ft.) 380  1450
Manual Defrost 540 1,250  
Automatic Defrost 700 1,830  
Hair Blow dryer 1,000 15.6  
Hand Iron 1,100 60  
Heat Lamp 250 13  
Heating Pad 65 10  
Humidifier 177 163  
Jacuzzi/Spa Pump 1,300 2,100  
Kiln 5,760 1,659  
Lighting (Avg. Resd. Use)   1,200  
Radio (Solid State) 15 18  
Radio/Recorder (Solid State) 26 26  
Range (with Oven) 12,200 750  
Range (with self-cleaning) 12,200 775  
Refrigerator-Freezer      
16 cu. ft. 380 1,450  
20 cu. ft. 420 1,950  
Refrigerator-Freezer (frostless)      
16 cu. ft. 600 2,150  
20 cu. ft. 800 2,700  
Sewing Machine 75 11  
Shaver (none rechargeable) 15 0.5  
Sun Lamp 279 16  
Swimming Pool Pump Motor 2,000 8,780  
Television Cable (TV) Box 23 50  
Television, Color (Tube) 286 600  
Television, Color (Solid state) 175 350  
Television, Screen (45") 147 329  
Television, Video Games 45 100  
Video Tape Rec. 175 350  
Washing Machine 512 103  
Water Heater 2,475 4,219  
water Heater (Quick-Recovery) 4,474 4,811  
Waterbed Heater 450 1,460  
Well Pump 2,238 1,894  
Kitchen Appliances
Broiler 1,140 85  
Coffee Maker 1,200 140  
Deep Fat Fryer 1,448 83  
Food Blender 300 1  
Food Mixer 127 2  
Frying Pan 1,196 100  
Hot Plate 1,200 90  
Microwave Oven 1,450 190  
Roaster 1,333 60  
Slow/Rice Cooker 200 144  
Toaster 1,146 39  


Measuring Electricity

Watts
describe the rate at which electricity is being used at a
specific moment. For example, 100 watts describes the amount of electricity that a
100-watt light bulb draws at any particular moment.

Watt-hours measure the total amount of electricity used over time.  Watt-hours
are a combination of the how fast the electricity is used (watts) and the length of
time it is used (hours). For example, a 100-watt light bulb, which draws 100 watts
at any one moment, uses 100 watt-hours of electricity in the course of one hour.

Kilowatts and kilowatt-hours are useful for measuring amounts of electricity
used by large appliances, such as refrigerators, and by households. Kilowatt-
hours are what show up on your electricity bill. One kilowatt (kW) equals 1,000
watts, and one kilowatt-hour (kWh) is one hour of using electricity at a rate of
1,000 watts.  New, energy-efficient refrigerators use about 1.4 kilowatt-hours per
day, and about 500 kilowatt-hours per year.

Megawatts are used to measure the output of a power plant or the amount of
electricity required by an entire city. One megawatt (MW) = 1,000 kilowatts =
1,000,000 watts.

Gigawatts measure the capacity of large power plants or of many plants. One
gigawatt (GW) = 1,000 megawatts = 1 billion watts.

Step 1: Determine Daily Energy Needs
(Hours of use times watts equals daily watt hours used)
AC ApplianceHours of Daily Usage XAppliance Watts =Daily Watt Hours Used
1Microwave.5600300
2Lights (x4)640240
3Hair Dryer.75750563
4Television4100400
5Washing Machine1375375

Total Daily Watt Hrs. Used
Formula:Add Lines 1-5 >>>1,878

Step 2 Determine Rough Battery Estimate
Multiply total daily watt hours used by number of anticipated
days of autonomy (days between charging, usually beteen 1 to 5) to determine
your Rough Battery Estimate.
Rough Battery Estimate Formula:
Total Daily Watt Hrs. Used x days of autonomy >>>5,634

Step 3: Determine Safe Battery size in Watts Hours
Multiply Rough Battery Estimate x 2, to determine safe battery
size in watt hours. (This allows for 50% maximum battery
discharge in normal operation and an additional 50% in
emergency situations.)  Safe Battery Size in Watt Hrs.
Formula:Rough Battery Estimate x 2 >>>11,268

Step 4: Determine Safe Battery Size inAmp Hours
Convert safe battery size to amp hours by dividing the Safe
Battery Size in Watt Hours by DC system voltage (i.e. 12, 24,
48 volts DC)
Safe Battery Size in Amp Hrs. Formula: Safe Battery Size in Watt Hours / System
Voltage >>>470

Step 5: Determine Inverter Wattage
To properly determine inverter size add together the appliances that must/will run
at the same time, and add 25%. Then roundup to the next inverter wattage size.
Properly sized inverter wattage Formula: Add Total Appliance Watts + 25% >>>2,
500

Air Conditioners for residential homes, some countries set minimum requirements
for energy efficiency. The efficiency of air conditioners is often (but not always)
rated by the
Seasonal Energy Efficiency Ratio (SEER). The higher the SEER
rating, the more energy efficient is the air conditioner. The SEER rating is the BTU
of cooling output during its normal annual usage divided by the total electric
energy input in watt-hour (W·h) during the same period.

SEER = BTU ÷ W·h

For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, operating for a
total of 1000 hours during an annual cooling season (i.e., 8 hours per day for 125
days) would provide an annual total cooling output of: 5000 BTU/h × 1000 h
= 5,000,000 BTU which, for a SEER of 10, would be an annual electrical energy
usage of: 5,000,000 BTU ÷ 10 = 500,000 W·h and that is equivalent
to an average power usage during the cooling season of: 500,000 W·h
÷ 1000 h = 500 W

More Solar Energy information
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