Electricity Basics

Power is Voltage Multiplied by Amperage

Electrical power (the ability to do work) is a function of pressure (voltage) and current (amperage). Double either one and you double the power the current is carrying through the circuit. The actual formula for calculating power is quite basic - simply multiply the voltage by the amperage.

Power = Volts x Amps

This formula is known as Ohm's Law. The watt (W) is the measure of the power of electricity and will be our basic unit of measure for determining the size of our electrical loads.

A 1 watt load that is powered for one hour will consume one watt-hour (Wh) of power. A 100 watt load powered for 2 hours will consumer 200 watt-hours. And so on.

A 100-watt load could consist of a 12-volt appliance drawing 8.3 amperes or it might consist of a 120-volt appliance drawing .82 amperes (120V x 0.83A = 100W). And so on.

Another unit of measure that you will come across is the kilowatt (Kw). A kilowatt is 1000 watts. A kilowatt-hour could result from a 100-watt load being power for 10 hours or a 1000-watt load being powered for just 1 hour.

What Is the Difference Between AC and DC Electricity?

Electricity flows in two ways: either in alternating current or AC and in direct current or DC. The difference between AC and DC has to do with the direction in which the electrons flow. In DC, the electrons flow steadily in a single direction, or "forward." In AC, electrons keep switching (alternating) directions, sometimes going "forwards" and then going "backwards."

The power that comes from our wall outlets is AC, the more common type of electricity. However, homes which are completely disconnected from the electrical utility company frequently have outlets which provide DC electricity. This is because most alternative energy systems store their energy in batteries which use DC electricity. To convert this electricity into AC electricity requires the use of a inverter, which inherently isn't 100% efficient at converting the DC to AC electricity (usually between 70 and 95% efficient). To not lose more valuable power to electrical inefficiencies, people living off grid will often use only appliances and devices which can run directly off of the DC electricity a battery bank can provide. The downside is that most common appliances only work with 120 or 220 volts AC.