Inverters

  • An inverter changes the DC power stored in a battery to 120/240 VAC electricity (or 110/220).
  • Most solar power systems generate DC current which is stored in batteries for later use.
  • Most 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 is to produce a waveform that works for
    all loads without sacrificing power in the conversion process.

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

  • 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 1.4kWh 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 uses 8,900
kilowatt-hours of electricity each year.

Measuring Electricity

Watts
describe the rate at which electricity is being used at a specific moment. The amount of electricity that a 100-watt
light bulb draws at any particular moment is of course 100W.

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 constantly
draws 100 watts, uses 100 watt-hours of electricity in one hour.

Kilowatts and kilowatt-hours are useful for measuring amounts of electricity used by large appliances.  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.  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 X Appliance Watts = Daily Watt Hours Used
1 Microwave .5600300
2 Lights (x4) 640240
3 Hair Dryer .75750563
4 Television 4100400
5 Washing Machine 1375375
Total Daily Watt Hrs. Used = 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.
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
Inverter/Battery cables
$39.00 - $139.00
RG15852
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.
    Utility companies provide sine wave power, so a sine
    wave inverter is equal to or better than utility supplied
    power. A sine wave inverter can "clean up" utility or
    generator supplied power because of its internal
    processing.  
  • Most Solar Power Systems generate DC current which is stored in batteries.
  • An inverter changes DC power stored in a battery to standard AC power -- 120/240 VAC
  • Most standard household appliances, lighting, motors, etc. use AC power, so it takes an inverter to switch from DC to AC.  
  • 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.
Inverter Features

  • 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.
Inverters
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