Issue #154, April / May 2013

Beginner

- Beginner

If you’re new to the world of renewable energy—like PV, wind, or hydro— some of the industry terminology and jargon may feel beyond your reach. But never fear, just keep reading *Home Power* and soon the basic concepts will become clear. In the meantime, here are some brief explanations of basic terms you will often see describing electricity, including from renewable sources.

**Alternating current** (AC) is a flow of electrical current, which repeatedly reverses direction in an electrical circuit. It is the type of electrical current provided by utility companies, and results from the rotating magnetic fields in alternators.

**Amperage** (current, A) is the rate of the flow of electrons through a conductor—the amount of electrical charge that passes a particular point in a circuit. Current is measured in amps—1 amp = 6.24 × 1018 electrons per second.

An **amp-hour** (Ah) is 1 amp of current flowing for 1 hour. Amp-hours are the most common unit of measurement for a battery’s capacity.

**Direct current** (DC) is the one-way flow of current—electrons move in the same direction. PV modules produce DC current, which can be stored in batteries.

**Energy** is the amount of power either consumed or produced during a quantity of time. It is commonly measured in watt-hours (Wh) or kilowatt-hours (kWh).

**Hertz** count the number of alternating cycles per second (frequency) when describing alternating current (AC). North American AC electrical systems are 60 Hertz, meaning they have 60 cycles per second.

**Kilowatt-hour** (kWh) is a unit of measurement for energy. One kWh is the equivalent of using 1,000 watts of power (or 1 kilowatt) for 1 hour, or 100 watts for 10 hours.

**Ohm** is the unit of measurement of resistance to the flow of electrons in an electrical circuit or wire. Resistance is often discussed during wire sizing, and is determined by factors such as conductor gauge (size of the wire’s cross section), length, and temperature.

**Ohm’s law** defines the relationship between voltage (V), current (A), and resistance (Ω, or Ohms), V = A × Ω. The same formula rearranged can calculate any of the values, so long as the other two are known: A = V ÷ Ω; and Ω = V ÷ A.

**Parallel** connections are electrical connections made with the same polarity (positive to positive; negative to negative). For example, a PV array with PV modules wired “in parallel” results in current being additive while voltage remains the same. (See “Series” for comparison.)

**Polarity** is either positive or negative, and determines the direction of electron flow in a circuit. A point in a circuit with negative polarity has more electrons than a point with positive polarity, causing those electrons to flow toward the positive side of the circuit.

**Power** (watts or W; kilowatts or kW) is the instantaneous rate at which electricity is transferred by an electric circuit. Power is calculated using the power formula, P = V × A.

**Series** connections are electrical connections made one after the other. Commonly, those made between the positive wire of one PV module or battery and the negative wire of another. In a PV system wired “in series,” voltage is additive, while current remains the same. (See “Parallel” for comparison.)

**Voltage** (V) is the unit of electrical pressure—the potential for pushing current through an electrical circuit.

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