Many people confuse the terms watt and volt, or what they mean. They may seem like two totally different things when they first meet. But understanding their relationship is essential to understanding electricity.
The volt-ampere (VA) is a unit of apparent power in an electrical circuit, equal to the product of the root mean square (RMS) voltage and the average current. In alternating current circuits, it is equivalent to the product of the RMS voltage times the average current.
What is the difference between a watt and a watt hour (Wh)?
What is the difference between a watt and a watt hour? The watt is a measure of the rate of energy transfer. One watt (W) is defined as the energy transfer of one joule (J) per second.
One joule is, by definition, the energy required to produce one watt of power for one second. A watt hour (Wh) is a unit of energy, not power.
A watt (W) and a watt hour (Wh) helps you understand the impact of your home’s energy use on your electric bill.
Although the watts and watt hour (Wh) They are related terms, they are not the same.
A watt hour (Wh) is a unit of energy, not power.
A watt-hour (Wh) is a unit of energy, not power. It may seem like a bit of a strange distinction, but it’s important to know why we say it.
One watt can be thought of as the rate of energy transfer over time. In other words, it tells you how much work your device is doing in a given period of time, and not just how much power is available at any given time. A kilowatt hour (kWh) is simply 1,000 watts operating for one hour.
What is a watt-hour (Wh)?
watt hour (Wh) (Whes a unit of power, and power is the rate at which energy is produced or consumed.
Think of watts as a measure of electrical flow. Does an electrical device need a large flow or a small flow to work?
For example, a 100 W bulb consumes more energy than a 60 W bulb; this means that the 100W bulb needs a higher «flow» to work.
Similarly, the rate at which your solar power system «flows» energy into your home is measured in watts.
So what is a watt hour (Wh)?
A watt hour (Wh) is a unit of energy; It is a way of measuring the amount of work done or generated.
Appliances and other electrical devices perform «work» and this requires energy in the form of electricity.
Utility companies typically charge you for electrical energy per kilowatt-hour (kWh), which is equal to 1,000 watt-hours.
Depending on your interconnection agreement, your utility company may credit you for excess generation that will also be measured in kilowatt-hours.
For example, a microinverter system can generate 400 kWh (quantity) in the month of September (time period).
One kilowatt hour (kWh) is 1,000 Wh, so 400 kWh is 400,000 Wh. In some cases, it will show energy as megawatt hours (MWh), which is one million watt-hours.
What is the difference?
Simply put, watt hours (Wh) measure amounts of energy over a specific period of time, and watts measure rates of power at any given time.
A common analogy for watts and watt hours (Wh) is speed and distance. Speed is the speed at which you drive in an instant (watts).
Distance is the length or amount driven in a period of time (watt-hours).
For example, if you drive at a constant speed of 60 miles per hour for one hour, then you will have traveled 60 miles.
Similarly, if a 60 W bulb is on for one hour, then that bulb will have consumed 60 Wh of energy.
If left on for two hours, the 60W bulb will have consumed 120Wh of energy.
watts
Knowing about watts and watt hours (Wh) can give you a greater appreciation of the energy savings on your utility bills.
Please note that your utility company will only bill and credit you for energy that goes through your electric meter.
Watt hour vs. ampere hour
Electricity carries energy that can be measured in several different ways. Power, the rate at which equipment uses energy, is expressed in units called watts.
The total amount of energy used over time is in watt hours (Wh). Amps, or amps, measure current, the flow of electrical charge.
Volts measure its strength. Ampere-hours measure the electrical storage capacity of a battery, assuming that its voltage remains constant.
Watts and watt-hours
Virtually all equipment and appliances have power consumption ratings in terms of watts.
A 15-watt fluorescent lamp, for example, consumes electrical energy at a slower rate than a toaster with a 1,000-watt capacity.
Watts multiplied by hours gives watt-hours, a measure of the total energy consumed over time.
If you run the 1,000-watt toaster for five minutes, that’s one-twelfth of an hour for 1,000 watts, or 83.33 watt-hours.
If you leave the 15-watt fluorescent lamp on for six hours, that’s a total of 90 watt-hours, that’s more total energy consumed.
Your electric meter measures kilowatt hours, or units of 1,000 watt hours. To advance the meter by one unit, the appliances, lights, and electronics in your home used 1,000 watt-hours of energy.
Ampere-hours
Alkaline batteries size AA, AAA, C, and D produce the same voltage straight out of the package: approximately 1.5 volts.
Batteries differ not only by their size, but also by their capacity: the bigger the battery, the higher its current capacity.
For large batteries, it is measured in amp-hours; for small batteries, it is measured in milliampere-hours.
If a D-cell battery has a capacity of 12,000 milliamp-hours and is used in a 200-milliamp flashlight, the battery will last 60 hours.
Used in a smaller 50 milliliter flashlight, the battery lasts 240 hours.
Watt-hours for batteries
Battery manufacturers rate batteries in amp-hours as a convenience; they could easily classify them in watt-hours.
For example, a 12,000 milliamp-hour 1.5 volt D-cell battery stores a total of 18,000 milliwatt hours, or 18 watt-hours of energy.
Watt hours (Wh) recognize the voltage of a battery and amp-hours ignore it. As long as your units are consistent, either measure will work.
voltage change
Your electric meter measures kilowatt-hours instead of kiloampere-hours because appliances draw power at two voltages: 110 volts and 220 volts.
The kilowatt-hour takes into account both the voltage and the current used. Battery amp hour ratings work because the battery voltage remains fairly constant as the device draws its power.
How to Calculate Kilowatt Hour
A kilowatt hour is a basic unit of energy that applies especially to electricity. One watt is one volt times one ampere, and there are 1000 watts in one kilowatt.
A watt is a unit of power, which is the rate of energy used. When you multiply power by time, you get an amount of energy.
Energy is measured in many different unit systems and in many different applications.
Your electric company bills you for the kilowatt-hours you use. The energy content of batteries is given in amp-hours.
The energy density of liquid fuls is often given in British Thermal Units per gallon, or BTUs per gallon.
A home gas bill usually reports usage in cubic feet (of gas), or thermometers. A thermal is 100 cubic feet, and equivalent to 1000 BTUs.
Using the correct conversion ratios, the equivalent number of kilowatt-hours (KWH) can be calculated in any amount of energy measured in these other units. You can use the link in the Resources section to calculate conversion rates.
1 watt-hour = 1000 milliwatt-hours (mWh).
What exactly is a watt-hour? Let’s start with the most basic. A milliwatt (mW) is one thousandth of a watt. Therefore, one watt equals 1,000 milliwatts.
A kilowatt-hour (kWh) is the amount of energy consumed when 1 kilowatt is used for one hour, or put another way, it is the amount of energy it would take to power 10 100-watt light bulbs for one hour.
Convert milliwatts per second to watts:
You can convert any number of milliwatts per second to watts by multiplying it by 1000 (1 mW = 0.001 W). If your device uses 2 mW per second: multiply that number by 1000 and you get 0.002 W, or 2 W!
How to Convert Watt-Hours to Watts
How to convert energy in watt hours (Wh) to electrical energy in watts (W).
You can calculate watts from watt hours (Wh) and hours, but you cannot convert watt-hours to units of watts, since the units of watt-hours and watts represent different quantities.
Watt Hours to Watts Calculation Formula
The power P in watts (W) is equal to the energy E in watt-hours (Wh), divided by the time period t in hours (h):
P(W) = E(Wh) / t(h)
So
watts = watt-hours / hour
either
W = Wh / h
watt example
What is the power consumption in watts when the power consumption is 15 watt-hours for a duration of 3 hours?
P = 15Wh / 3h = 5W
Kilowatt-hour equivalents
Calculate kilowatt-hours in natural gas. To compare the amount you pay for natural gas versus electricity, you need to convert between kilowatt-hours and thermal. The conversion ratio is 0.0342 therms / 1 kilowatt-hour = 1.
Electricity and natural gas prices vary greatly from region to region, but typical prices are $0.10 per kilowatt-hour and $1 per thermal.
Calculate (1 dollar / term)*(0.0342 therm /1 kilowatt-hour) and cancel the therms to get 0.0342 dollars / kilowatt-hour.
In many places, natural gas is cheaper per unit of energy. That’s why, when it’s available, many homes use gas for heating and cooking instead of electricity.
Calculate the kilowatt-hours of a battery. Typically, a battery is labeled with the number of milliamp-hours it has.
Ampere-hours are not technically a unit of energy. But when you multiply amp-hours by volts, you get watt-hours.
There are 1000 watt-hours in a kilowatt-hour. A typical 1.5 volt AA alkaline battery supplies about 2000 milliampere-hours.
If you multiply 2000 milliampere-hours x 1.5 volts, you’ll find that an AA alkaline battery contains 3 watt-hours, or 0.003 kilowatt-hours of energy.
You can buy AA batteries for as little as fifty cents each, or $0.5. To find the cost per kilowatt-hour, calculate ($0.5 / 3 watt-hours) x (1000 watt-hours / kilowatt-hours) = $167/kilowatt-hour.
You can…