What is a Watt And Why Should I Care?

As a business owner, you need to know some basic electrical concepts to understand how electricity is measured and stored, and why you are paying so much for electricity, and so you learn to save money.

Volts, Amperes, and Watts

A common analogy used to describe electricity is water flowing through a garden hose.

Volts (V) is analogous to water pressure. The more volts you have the more electrical "pressure" is being placed on pushing electricity through the battery, wire and electrical device.

In the US and Canada, electricity in a home is 120V. In other countries 240V is commonly used. The difference is that the 240volt system is pushing electricity twice as hard than 120V system.

Amperes or Amps (A)  is  analogous to how fast the water is flowing through the garden hose.  The larger number of amps the greater the flow speed of electricity.

Watts (W) are a measurement of power.

Electrical devices have a label  (usually on the back or bottom) that details these Voltage and the Amps used. For example an office document shredder will be 120Volts with 3.5Amps. To calculate the amount of power it uses the calculation is:

Volts X Amps = Watts

So a 120Volts X 3.5Amps = 420 Watts

420 Watts is used to make the motor work. If the shredder was used for a full hour, then it would be 420 Watts/hour. Utilities charge for how much power you use over a period of time,  expressed in Kilowatt hours. This is increments of 1000 watts per hour. This is part of your electric bill - the KWHs used.

Instead of an office shredder, if you may have lathes, conveyor belts or drills in your business. Each of these have electric motors will add up to the watts that are used in your business. This is what you pay in electricity usage  rates. Usage is italicized because on your electricity bill you are usually charged an additional connection or delivery fee, which usually pays for the physical electrical equipment infrastructure to deliver the power to your business. (We discuss usage and delivery fees in more detail under **How to Save)

Knowing your total KWH usage, and when it is used, and how it is used, is an important information to be graphed to get a picture of how to electricity reduce or possibly eliminate power company monthly bills.


A Watt is a Measurement of Power

All this Volt, Amp, and Watts numbers are kind of hard to understand from a personal experience point of view.

Let's use a example that may make sense.

Pretend that your on a special bicycle that has a small electric generator which has replaced the rear wheel.  The bicycle chain now powers the generator instead of turning the wheel.

For the following examples the generator outputs a constant 1.5Amps. The number of volts is variable determined by how fast the bicycle is peddled to turn the generator.

When you peddle the generator spins sending electricity (electrons) down the wire to a light socket.

You put in the 15 Watt LED light bulb in the socket. When you start peddling the LED light starts to slowly shine until it gets fully illuminated by a leisurely peddling pace.  What is happening is physical energy (power) from your legs is being converted into electrical power of electrons moving at 10V at 1.5A = 15 watts to the LED light bulb.


Volts x Amps = Watts

10V x 1.5A = 15Watts

But how did we know the voltage being generated is 10 volts? We know the generator outputs 1.5Amps no matter how fast the bicycle is peddled. We know that turn on the LED light takes 15W. Dividing the watts by the amps will give us volts

15W / 1.5Amps = 10Volts

Watt is the amount of power equal to how fast the electrons are zooming down the wire to the light socket that converts the electricity to light by the LED light bulb.

You replace the LED light bulb with the 60 Watt incandescent light bulb, and start peddling. You have to peddle 4 times harder to illuminate the 60 Watt incandescent light bulb than the LED light, because you are sending 4 times amount of energy (power)  down the wire. In this example you are peddling to generate 40V at 1.5Amps = 60Watts. This kind of light bulb generates a lot of waste heat, and some light. (And sore legs from peddling).

Watts indicate power. Power can exist in very short or very long periods of time. Watt-hour is a measure of how much power was generated and you used over time.

What is a Watt-Hour?

A watt-hour is a measurement of how much power is generated or consumed over time.

You put in the 15 watt light bulb, and hop on your stationary electricity generator bicycle, and peddle for 1 hour at a leisurely pace. You have generated and consumed 15 watt-hours. If you did this with LED light off, you would still be generating the 15 watts, but none of it is being used so you are literally "spinning your wheels" for no outcome other than improving your physical health.

Kilowatt-Hour  - Payment Measurement

So to attribute a value to energy, it is measured and paid for over the amount of time you use it. Electrical power plants attribute their fuel costs, and infrastructure  in increments of 1000 watts used over 1 hour. Since Kilo represents number 1000, then 1000 watt-hour  = 1 Kilowatt-Hour. It is also written 1 KWH.

For example most American and Canadian homes use about 30 Kilowatt-hours per day.

Using our stationary electrical generator bike at 15W output would take you 2000 hours over 24 hours of peddling to equal 30,000 watt-hours or 30KWH of bike generated power peddling to power your home for 1 day.

A single person  with one generator bike will never be able to generate 30KWHs in 24 hours. You would need many people with many generator bicycles to achieve this. In fact, it would be possible - but impractical.

If you were to peddle 4 times harder at 60 Watts it would take 500 hours of peddling to generate 30KWH.

So the question arises how can a house consume 30KWHours in a 24 hour day? 30 Hours is greater than 24 hours.

The answer is that different electrical equipment from refrigerators, lights, furnaces, air conditioning, electronics, washers, dryers, and dishwashers concurrently use a lot more energy than a 15Watt light bulb. This quickly adds up to about 30KWH per day within 24 hours.

A light industrial business can use 75 KWHs per day, and a school can use 350 KWhs/day or more per day.

Of course we don't use all this energy in a constant way through 24 hours. Most homes in Canada and the US demand a lot a power in the morning, and again at night. When line graphed it looks like the outline of the back of a duck. In the power industry it's called the "duck power curve".

Batteries Are Measured in Amp Hour Capacity

A battery energy storage system capacity is calculated by using the amount of volts (pressure) and amps to calculate the watts it can discharge or store over a given period of time. The phrase "given period of time" is italicized because batteries are measured in ampere hours (AH). The faster you discharge a battery the greater the number of amps are used.

For large capacity batteries they can have 2000AH or greater and are rated by the manufacture to a specific maximum amount of time such as 20 hours or 8 hour discharge times.  A and smaller typical solar systems use a 48V design because. To calculate how many kilowatt hours a battery system could produce

Watts x Amp Hours = Kilowatt Hours

Batteries can be daisy chained together to increase the total number of watts.

For example,  in a flashlight you have 2 x 1.5V AA alkaline batteries. Because the way the batteries are connected  (in series) the volts are added. So this means that flashlight will operate at 3V. (There is another way to wire batteries together to increase amperage, and keep the volts the same, which  is called parallel wiring.)

Typically, household to small business solar systems use 48volts.  Depending on the battery type each cell can have different voltages. If each battery in the storage system has 2V, then there will be 24 batteries in series. This will add up to 48 Volts.

2V x 24 batteries = 48Volts

So if you had a 2000AH batteries, then the total power availability of the batteries would be:

48V X 2000AH = 96,000 watt/hours or 96KWH.

This looks like 3 times the amount of power needed for a Canadian or US home. But there are limitations which are:

  1. They can only discharge for a limited amount of time (i.e. 8 hours)
  2. Depending on the type of batteries, (i.e. lead-acid, or Lithium-Ion), the depth of discharge (DOD), important factor in determining the long term health of a battery.
  3. Batteries are electrochemical. With each discharge, and recharge cycle, the metals, and chemicals (electrolyte) that enable the the battery to work make become slightly degraded, because of physical changes that are made to the chemicals and metals. Eventually, after many cycles the chemistry is no longer able to work.

So to allow the batteries to last as long as possible, the Depth of Discharge can be limited to a certain percentage, and the number of times the batteries are "cycled" will allow the battery to last longer.

So if your 96KWH energy storage system's total capacity was limited to 30%, then there would be 28.8KWH of battery energy just shy of a 30KWH capacity for a Canadian or US home. If the battery was rated for 8 hour use, then you would be using 3.6KW/Hour - if the same amount of power was every hour. (This is rarely the case).

A battery energy storage system would not be very useful, if it stopped working in just 8 hours. This means that the power has to be replaced on an ongoing basis.

Using a solar, or a fossil fuel generator, or even utility power, these can replace the energy in the batteries as they are being used, and that the total Depth of Discharge is really not used up in the 8 hour period. It can be stretched into the night and be useful. The more batteries, and more replacement energy being used, can allow the batteries to still produce power when needed.

Direct Current and Alternate Current

Electricity from batteries are direct current (DC). This means the electrons are moving in one direction along the wires from positive terminal to a negative terminal. Solar panels are DC devices. There are also DC motors and devices, such as flashlights, TV remotes, and other electronics use DC power.

In early days of the power industry, DC power transmission required thicker cables, and frequent regeneration.

Alternate Current (AC) has the electrons moving back and forth along the wires between positive and negative terminals. In US and Canada this is done 60 times per second. So a light bulb powered by AC power is being powered off and on at 60 times a second. It happens so fast, that we see it as steady stream of light.

The advantage of AC power is that you can use thinner cables, and be able to use transformers to increase voltages, and be able to transmit the electricity over greater distances without having to regenerate the power. This was invented by Nikola Tesla. Westinghouse used this technology, and the first AC power transmission lines were installed at Niagara Falls, NY USA and terminated in Buffalo NY. The Westinghouse generators used water from the Niagara river to fall down the gorge to turn the generators. This was replicated in Niagara Falls, Ontario, Canada.

This became the predominate means of power transmission. Therefore all the devices in homes and businesses had to be designed to accept and use that power.

This means that batteries, and solar, and wind power direct current sources need to convert their Direct Current to Alternating Current to to power existing AC equipment. (It is possible to buy DC equipment, such as a DC refrigerator, or DC motors, and use only DC power, but AC equipment cannot be used.)

A device called an Inverter is used to convert DC power to AC power. They are often used in recreational vehicles, to take a 12VDC source (i.e. power socket), and power small devices such as a TV etc.

Energy Storage systems for solar applications typically use 48V(DC) to 120V(AC) inverters.

For much larger systems, where the AC voltage is 240V, 480, 800V+, then it is sometimes better to pay extra for an Inverter that can handle equivalent DC power sources.

If you have a 48V(DC) system, and 120V(AC) system such as the office paper shredder the batteries will have to be drained faster to match the demand. This is measured in amp discharge.

Recall the paper shredder uses 120V(AC) at 3.5 Amps to give 440Watts.

120V x 3.5A = 440W

If you have 48V(DC) battery energy storage system being inverted to 120V shredder at 3.5Amps draw, then this would occur

Watts / Volts = Amps

440W /48V(DC) = 8.75 Amps

The batteries will be discharging 2.5 times faster using a 48V(DC) to 120V(AC) inverter.

Why not use a a 120V(DC) battery system to 120V(AC) Inverter to ensure the batteries are not discharged so fast?

The reason is cost:

  1. Batteries are expensive - so configuring them into 120V(DC) or higher voltages means more batteries, and more cost.
  2. Higher powered Inverters are also expensive as well.

2ndLife Batteries® provides large DC voltage systems at much lower value.

Through Knowledge: Less Cost and More Energy

We purposefully rearranged our homepage tag of More Energy for Less Cost Through Knowledge to this heading Through Knowledge:  Less Cost and More Energy.

Granted this has been a lot to learn in a short amount of time. But understanding how electricity is generated, and consumed, and how to measure it's use means that you have the knowledge to lower costs and use more energy, and wisely use energy you receive.