Electricity 101: kW, kWhs, Watts, Amps, Volts and Ohms

If you’re a home owner, there are some terms you should know with regards to your electric power system. Understanding these units of measurement will make it easier to understand a solar photovoltaic (PV) system and grid, if and when you choose to make the switch to solar power. Below are definitions of some of the most important units of measurement.

Solar Energy, Power and Capacity

Although used interchangeably, energy and power have different meanings because they measure different things. Energy measures the volume of electricity in kilowatt-hours (kWh), while power measures the immediate output of electricity in kilowatts (kW). Thus, kWh represents cumulative energy (over time) and kW represents instantaneous energy (the energy output at any moment).

Capacity is the measure of a power system’s potential to generate power or a battery’s ability to store energy. All three of these terms are used in PV and conventional electricity systems, however, PV systems are usually measured in kWh. If you see a measurement of kW or kWp (kilowatt-peak), this typically refers to the peak output capacity.

Amps and Amperage

Amps or amperes measure the electromagnetic force between current-carrying conductors. Basically, it’s a current flowing through two parallel conductors of any length. Amperage is the strength of this current. Additionally, amps are the rate of flow of electricity in your PV system, which means they measure the strength and amount of electricity flowing through your solar panels.

Watts and Wattage

Watts (W) are simply a measure of power. A watt equals the rate at which work is performed when an amp flows through a volt. This is represented by the formula: W = V x A or watts equal volts times amperes. This and other formulas are used to calculate alternating current (AC) wattage when determining the size of the inverter for your solar panel system. You don’t need to know exactly how solar power works to know that the size of your inverter determines the efficiency of your system, or that all these units of measurement help determine the size and power of a solar array.

Volts and Voltage

Volts (V) represent a unit of electrical potential, or rather, the amount of potential energy that exists between two points on a circuit.


Ohms (R) and voltage are related, which can be explained by Ohm’s Law. The law basically states that an Ohm is the electrical resistance between two sections of a conducting wire when a volt applied to them produces an amp. So, ultimately, it’s a measure of resistance to a moving electrical current.

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