One of the most common sources of confusion we encounter when discussing photovoltaic energy is the meaning of the abbreviations W, kW, and kWh. The difference between W and kWh, and the conversion from W to kWh, also often generate many questions, such as how many watts in 1 kilowatt

It may seem trivial and somewhat obvious to professionals who work with more alternative types of energy, but these are the most common questions among people who are thinking about buying a photovoltaic power generator for their homes or businesses.

With that in mind, SolarLab created this content that explains what W, kW, and kWh are, the difference between kW and kWh, and how to convert kW to kWh – watts to kilowatts

What is W?

W, or Watt, is a unit of power whose symbol is W, corresponding to one joule per second. Basically, it’s a measure of power in terms of the capacity to perform work. The Watt is characterized by the amount of energy converted into joules, whether used or simply dissipated in one second.

In solar energy, the Watt would be the unit of energy for a system with a current of one ampere under a voltage of one volt, as the product of voltage and current.

What is kW?

kW, or kilowatt, is a unit of power equivalent to 10³ watts, meaning 7

kilowatts (7 kW) is equivalent to 7000 watts (7000 W). Furthermore, kW represents the size of a solar power system. This means that the larger the kW rating of a system, the greater its capacity to produce energy on sunny days.

What is kWh?

kWh stands for kilowatt-hour, which refers to the amount of energy produced or consumed. This unit indicates the volume of energy that can be generated by a solar power system within one hour. Therefore, if your panels produce 1 kW in a 60-minute period, 1,000 W of energy are produced every hour.

What is the application of W, Kw, and kWh?

Here are the applications for each one:

• W (Watt): Used to measure the power of small electrical devices, such as light bulbs, cell phone chargers, etc.
• kW (Kilowatt): Used in contexts where the power of larger appliances or systems is relevant, such as motors, air conditioners, and energy systems.

kWh (Kilowatt-hour): Used to measure electricity consumption over time, such as on a home or business electricity bill.

What is the difference between kW and kWh?

Here we will explain in a really simple way what the difference is between kW and kWh, so that there will be no more doubts.

Let’s first explain what each letter represents:

• k stands for kilo, which means “thousand”.
• W stands for Watt, which is a measure of power.
• h stands for hour, which is, obviously, a measure of time.

So kW means kilowatt, which is the same as 1000 watts. We are talking about a measure of power; note that the correct way to write it is always with a lowercase kW and an uppercase W.

The size of a solar system is defined by its power output. For example, a 1kW system can produce 1 kW of power on truly sunny days.

kWh stands for kilowatt-hour. A kWh is a measure of energy (not power). If your photovoltaic solar panels, for example, continuously produce a total of 1 kW for a period of 60 minutes, then you will have produced 1 kWh of energy.

The amount of electrical energy you use (or generate) is defined in kWh. For example: “My solar energy system produced 4 kWh of electricity today!”

So, in summary: kW measures the generator’s power, and kWh measures the energy produced by the photovoltaic generator.

How do I convert kW to kWh?

The formula for converting kW to kWh is: Consumption (kWh) = Power (kW) x time (h), therefore a power of 10 kW (or 10,000 W) generated for 6 hours will be equivalent to 60 kWh. Therefore, it will be necessary to multiply the power generated by the number of hours used.

However, it is essential to analyze aspects such as standardized conditions and the usage time of the photovoltaic module in question. For example, the power of a solar panel that generates 0.5 kW and is used for a period of 200 hours will be calculated by power x time, in this way:

• Power = 0.5 kW x 200h
• Power = 100 kW

Why is the difference between energy and power important?

It is very common for people to use the terms “energy” and “power” incorrectly. For example, when someone is talking about their electricity usage and says, “I consumed 8kW yesterday.”

This information becomes really important if you intend to install photovoltaic energy in your home or business. If someone says they need a solar energy system to produce 8kW, they may end up receiving a quote for an 8kW solar system, which will cost around Php 500,000 reais at today’s prices and produces about 32 kWh per day, on average.

However, if what he really meant was that he needs a system to cover an energy consumption of 8 kWh per day, then what this person really needs is a 2kW system. So, don’t confuse kW and kWh. If you do, you might end up buying the wrong size solar power system!

For this, we use some specific units of measurement:

• kW (kilowatt): Indicates the power of the inverters.
• kWp (kilowatt-peak): Refers to the power output of photovoltaic modules.
• kWh (kilowatt-hour): Measures the energy generation of a system or energy consumption.

These acronyms help consumers better understand the capacity and performance of solar energy systems.

TIP: To identify good solar energy companies, ask the salespeople what the difference is between kW and kWh; if they get it wrong, how can they truly understand your needs and quote the correct photovoltaic system?

What else do you need to know about watts and kWh?

• Meaning of kWh/month: you pay your electricity bill monthly, therefore you will find the total energy you consumed in a month, shown in kWh/month.
• The Watt unit was named in honor of James Watt for his contributions to the development of the steam engine, and was adopted by the second congress of the British association in 1889.
• Energy is a term derived from the Greek word “ergos,” whose original meaning is work. In physics, energy is associated with the capacity of any body to produce work, action, or movement.
• Power: This is the rate at which energy is used. Power is measured in Watts.
• 1 Watt is an energy consumption rate of one Joule per second.
• The power rating listed on each electrical appliance indicates its power consumption over a period of 1 hour. For example, an oil heater with a power rating of 1500 W (Watts) will consume that power in one hour.

1 Wh is equivalent to 3,600 joules (a unit of energy). Other multiples of watt-hour are:

• Megawatt-hour (MWh), which is equivalent to 1,000 kWh
• Gigawatt-hour (GWh), which is equivalent to 1,000 MWh
• Terawatt-hour (TWh), which is equivalent to 1,000 GWh