[From the last episode: We looked at an IoTThe Internet of Things. A broad term covering many different applications where "things" are interconnected through the internet. example involving fleets of semi-trailers.]
We’re now going to look at energy and how electronics fit into the overall global energy story. Whether it’s about saving money on electricity at home, making data centersA collection of computers that are interconnected so that they can share and distribute work. For our purposes, it’s the same as a computer farm, but the focus is on its application for processing data. more efficient, using fewer batteries (or charging them less often), or the bigger climate-change story, energy is an important consideration.
What is Energy?
First of all, what is energy? I’m going to give you a definition in my own words, although there are probably a million different ways to describe it.
“Energy is something that allows us to do work.”
That works in both the literal and figurative sense, such as when you say, “I just don’t have the energy to do that.” It’s something one can be store, convert, and move around, but, importantly, one can’t create or destroy it. In other words, energy is “conserved.”
Anytime you have something going on that involves energy, the energy can be changed from one form or another – it can even be turned into mass, thanks to Einstein. So it’s really mass/energy that’s conserved*. So, when you run the energy bookkeeping numbers in any process, you should end up with the same energy that you started with. If not, it means that more energy joined from elsewhere or energy escaped and went elsewhere. But none was created outright, and none simple disappeared altogether.
Here’s an example of conversion: a bowling ball that you’re holding at the top of a children’s slide. It’s not doing any “work,” since you’re holding it. But it could do work, so it acts as storage of potential energy. If we release the ball, then it starts to roll, and that potential energy has been converted into kinetic energy – the energy of motion.
The same thing holds for electricity, only here, instead of gravity creating a potential, it’s electric fields (or electro-magnetic fields, since the two are interlinked) that create the potential. That potential is literally called voltageVoltage is what gets electrons to flow. It's analogous to water pressure, which gets water to flow. Voltage is measured in units of "volts.". And voltage is what makes electronsA fundamental particle found outside atoms. It carries a negative charge. It can move easily in a conducting material, which gives rise to electrical current. move, and moving electrons are called currentThe amount of electrical flow. Measured in amperes or amps (A).. We talked about these before by analogy to flowing water.
Energy Is Not Power
A battery stores energy. A wall plug provides energy through a cord. Of course, we often talk about this as “powerThe rate of energy consumption. For electricity, it’s measured in watts (W).” instead of energy – we say, “The power is out,” not “The energy is out.” But, technically speaking, the second odd-sounding one is more accurate. Because energy is the thing that you may have or not have. And it’s what is consumed when we do work – mechanical or electrical.
You will hear people talk about “power consumption.” You hear that a lot, even in the engineering world. That’s because it’s a familiar phrase, and people don’t think about it. But in reality, it makes no sense.
Power is the rate at which you use energy. One measure of energy is the joule (pronounced “jewel”); a measure of power would then be joules per second – also known as watts.
This, then, means that:
In your home, the power meter is measuring how fast you’re using energy – that is, the power. When you want to know how much energy was used, they express it in “kilowatt-hours.” That means “kilowatts (1000 watts) times hours” – power times time, which gives energy. (One can easily convert kW-hrs into joules.)
Comparing it to a car, energy is like the amount of gas in the tank, measured in gallons. Power is… well, technically, it’s how fast you use those gallons (gallons per hour, for example). We tend to think of it more in terms of miles per gallon, but that gets all mixed up with how fast you’re going and what kind of wind you’re heading into and how often you stop and… and… and… In the end, power boils down to how long it takes you to empty the tank.
Lower Power Might Mean Higher Energy
So it makes no sense to talk about “power consumption” since power isn’t a substance that can be consumed. That’s what energy is, and energy consumption (and conservation) makes perfect sense. You might say that, by reducing power, you also reduce the amount of energy you use (because you sip it more slowly). And that can be true, but it isn’t always so.
Let’s make up some arbitrary numbers here and say that at a power level of 4, you can do a job in 2 minutes. So the amount of energy you used was the rate (i.e., power) multiplied by the time it took, which gives 8. Now let’s say you cut the rate at which a circuit used energy from 4 to 2. But now the question is, how long does the task take now?
Just because the power is cut in half doesn’t mean the job will simply take twice as long to do. If it does, you’re good. But what if it now takes 4 times as long, or 8 minutes? Now the energy you used was 2 (half of the 4) times 8, giving 16. So even though the power went down, the energy consumed went up – in fact, with these made-up numbers, it doubled.
So it’s important to understand the difference between energy and power. And if you hear someone talk about power consumption, know in your mind that it’s really energy consumption.
* If you want to be technical about it, replace most of the uses of “energy” in this post with “energy/mass.”
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