Key Solar Electricity Concepts: What Is a Kilowatt-Hour?

You power your home with solar electricity, but if your PV system is connected to the grid, you still receive monthly energy bills from the utility company.

Take a look at your bills, and you’ll see that your power company charges you by the kilowatt-hour (kWh). But just to complicate matters, the operating power of your home appliances is expressed in watts. For example, your light bulbs are classified as emitting 40, 60 or 100 watts.

Kilowatt Hour

So if your home electronics use watts, why does the utility company bill by the kilowatt-hour? And what is a kilowatt-hour, anyway?

To illustrate this concept, let’s start with the watt.

What Is a Watt?

Expressed in the simplest terms, a watt is a measurement of power. For solar electricity, power is expressed as voltage times amperage. In other words, one watt = one volt × one ampere (amp).

To make this simpler, it may help to compare solar electricity to a garden hose. Think of voltage like water pressure, and imagine that amperage is how the water flows through the hose.

The amount of water that can fit through the hose depends on the hose’s diameter, or the number of amps. The pressure, or volts, is based on how far the spigot valve is opened. The watts (or water power) can be felt by putting a hand over the end of the hose.

Solar electricity flows through wires in much the same way. Voltage measures the force of the energy, while amperage measures the amount that flows through. Watts, then, are a measure of total electric power output.

What Is a Watt-Hour?

A watt is the amount of power or joules used per second. So every time you turn on that 100-watt lightbulb, you’re eating up 100 joules of energy every second you keep the light on.

As wattage is equal to joules per second, referring to watts per hour doesn’t exactly make sense. That’s like saying joules per second per hour, which is a bit awkward.

So when talking about the amount of solar electricity used, we use the term watt-hour instead. If we continue our water comparison, watts would indicate the power potential of the flow, while watt-hours would tell us how much of that power actually flowed through.

What Is a Kilowatt-Hour?

A single 100-watt light bulb, left on for an hour, uses 100 watt-hours. Turn it on for an hour every day, and you’re using about 3,000 watt-hours per month. When you think about the sheer numbers involved for all of your household electronics and appliances, it makes sense to convert to a larger measurement of power.

One kilowatt is equal to 1,000 watts. It follows, then, that a kilowatt-hour is the equivalent of 1,000 watt-hours. Your utility bill reflects this, as your total kilowatt-hours will be multiplied by your per-kWh rate to determine your amount due.

If you live in a state with net metering and your solar electricity system produces more energy than you need, you’ll see a credit instead of a charge for your kilowatt-hour usage.

Understanding the terminology and details that relate to photovoltaic solar energy can help you become a more informed consumer. To learn even more, contact Intermountain Wind & Solar today. As the region’s leading photovoltaic installer, our professional team can answer all of your questions about solar electricity.