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Residential Load Calculations

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Last Updated
7th of October, 2018

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Electric Power Calculations (Basics):-

Electric power definition: P is the electric power in watt (W).

Electric power calculation: Electric power is the rate of energy consumption in an electrical circuit. The electric power is measured in units of watts.

The electric power P is equal to the energy consumption E divided by the consumption time t:
Example: P = E / t = 120J / 20s = 6W;
E is the energy consumption in joule (J),
t is the time in seconds (s),

Power of DC circuits: Electrical power is the “rate” at which energy is being consumed in a circuit.

The electrical power within an electrical circuit is only present when both the voltage and current are present, that is no open-circuit or closed-circuit conditions.

P = V · I;
P = I[2] * R;
P = V[2] / R;
V is the voltage in volts (V),
I is the current in amps (A),
R is the resistance in ohms (Ω),

Power of AC circuits: Electrical power follows the constant change of the current wave and has two components, an instant resisitive value and a reactive value.

P = Vrms*Irms = Irms[2]R,
Vrms and Irms are the direct resistive values components and they give the same heating effect as an equivalent DC power,
Vpk = Vrms × √2,
Vrms = Vpk * 0.7071,
Pavg = Vrms[2] / R,
Irms = Pavg / Vrms,
Vpk = Peak Voltage value,
Vrms, Irms are Voltage respective Current Root-Mean-Squared values,
Pavg is the average power value,

Power Factor: The power factor is equal to the real or true power P in watts (W) divided by the apparent power |S| in volt-ampere (VA):

The electrical power consumed by a resistance, (R) is called the true or real power and is simply obtained by multiplying the rms voltage with the rms current. The power stored by a reactance, (X) is called the reactive power and is obtained by multiplying the voltage, current, and the sine of the phase angle between them.

The symbol for phase angle is θ (Theta) and which represents the inefficiency of the AC circuit with regards to the total reactive impedance (Z) that opposes the flow of current in the circuit.

PF = P(W) / |S(VA)|;
PF - power factor,
P - real power in watts (W),
|S| - apparent power - the magnitude of the complex power in volt⋅amps (VA),
For sinusuidal current, the power factor PF is equal to the absolute value of the cosine of the apparent power phase angle φ (which is also is impedance phase angle),
PF = |cos φ|,
φ is the apprent power phase angle,

Residential Energy Calculator
Appliances Watts No. Of Appliances Average Usage Hrs/Day Approx. Units/Month
GLS Lamp
Tube Light
PL Lamp
Exhaust FAN (Domestic)
Exhaust FAN (Industrial)
Room Cooler
Air Cooler (Medium)
A/C Window Type
Electric Iron
Dhobi Iron
Toaster Oven
Electric Oven
Water Heater
Room Heater
Electric Stove
Water Geyser
Washing Machine
Pump Motor
Mixer Grinder
Hair Dryer
Sewing Machine Rexin
Vaccum Cleaner
Total Unit / Month

Number of Units = kilowatt-hour (kWh)
Total electricity cost per month = (Number of Units) * (kWh average price),
The kWh average price is based on utility provider contract value.
SO Cal. Edison Electric rates as 2018 are:
Tier 1: 0-356 kWh || $0.17/kWh,
Tier 2: 357-1424 kWh || $0.25/kWh,
Tier 3: 1425+ kWh || $0.33/kWh,
A household consuming 2500 units per month will pay:
Tier 1: $60.52 for first 356 units,
Tier 2: $266.75 for the next 1067 units,
Tier 3: $354.75 for the last 1075 units,
It comes to a totl of $681.75 for 2500 units of electric energy consumed in a month time.
At $8181.00 per year, it becomes an incentive to go for solar panel based power generation.

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