Plugged In: A Look at Power Generation Methods
Many of us don’t leave the house without first checking to make sure we have our smart keys, watch, phone, tablet, headphones and/or laptop, and all of these devices are thirsty for electrical power. Every day, people around the world open a brand new shiny-shiny and bring it to life by connecting it to power, without a second’s thought given to where that magical life force originates. Today we are going to discuss the most common methods of power generation. We will be skipping over ‘Electricity 101’, as that will be covered in a different article. For now, know that power production can be simplified into two main types: mechanical and chemical.
Mechanical-to-electrical energy conversion is almost exclusive to Alternating Current or ‘AC’ power. This is the power you see on the massive high-voltage lines that run all across your state and connect to the overhead poles in your town, and finally the little wire making that last stretch from the pole-mounted transformer into your home. Those of you living in an area that does not utilize overhead distribution, have a look for the green box near the end of yours or someone else’s property. You likely live in an area that utilizes underground distribution, which we will explore in a later article. That green box is a transformer, similar to the pole-mounted ones used in overhead distribution.
Chemical conversion is almost exclusive to Direct Current or ‘DC’ power, predominantly used in batteries. We will first dive into the mechanically-generated, AC world as this flavor of power is most responsible for transforming our civilizations.
Mechanical
AC power can be generated en masse (utility-scale), or on-site depending on the application and circumstance. According to the U.S. Energy Information Administration (USEIA), around 60 percent of utility-scale energy is currently produced via fossil fuels, followed by 20 percent nuclear and the last 20 percent generated by renewables. 96.4 percent of these methods utilize mechanical-to-electrical energy conversion. 2.2 percent is solar generated, which harnesses the photovoltaic effect, and is both a chemical and physical conversion. Biomass accounts for just 1.4 percent; it can be burned directly or converted into another state for later use. (1) A future article will go more in-depth on alternative energy sources.
The USEIA does not include prime or back-up generation via internal combustion engine (ICE) driven, direct-coupled alternators. These can be as small as about one kilowatt (1,000 watts), all the way to one MegaWatt (1,000kW) and beyond. Examples of common uses for the smaller units are for camping, job site applications, cell phone tower applications and small home back-up. The larger generators are usually used for data centers and hospitals, as well as regional and military use. In recent years, though, our chemical romance with lithium-ion technology has seen a move away from ICE generation.
Both fossil fuel and nuclear applications boil water into steam in order to spin a turbine and create electricity (2), but it is the way in which the steam is created that causes all the hype and hubbub. Fossil fuels are burned to create the necessary heat — but in the nuclear world, the heat of nuclear material is harnessed instead. I was lucky enough to grow up in Albuquerque, New Mexico, and my first duty station in the military was just a stone’s throw away from the Trinity Site near Alamogordo, New Mexico. This is where the first atomic weapon was successfully detonated, on July 16th 1945. This event ushered humankind into a new era, for better or worse, as we experimented and developed methods to harness this new energy source. Like all emerging technologies, nuclear was shot-gunned at anything and everything from aircraft and submarines to food and medicine. Some of these saw success; others have gone down as historical disasters. The ultimate verdict on nuclear power remains unclear.
This geopolitically charged method (my one pun per article…) of electrical generation uses a fissile material, typically uranium in the form of a fuel rod, inside a chamber called a reactor. As the uranium decays and gives off neutrons, these cause a fission reaction when they hit the other surrounding fuel rods. These collisions release energy. Water is used as a moderator to slow down these neutrons and create sustained reactions. Control rods are inserted or retracted into the reactor core and absorb the released neutrons to further regulate the core’s reactivity. The heat created during these reactions is absorbed by the moderator (water), which is then pumped to a heat exchanger where a second body of water is heated and turned into high pressure steam to turn the turbine.
Turbines
A turbine uses blades in a radial configuration mounted to a central hub resembling a propeller. Just like a propeller, the blades interact with steam or in the case of a hydro-electric plant, the very water itself. As the steam or water is forced into the blades, they are then rotated. This spins the turbine, and with a little bit of regulation we get a steady 1800 revolutions per minute (RPM). The turbine is coupled to an alternator: a large device with, typically, three sets of copper windings mounted inside a round housing called the stator. Inside the stator is a rotating set of windings with, typically, two ‘north’ and two ‘south’ poles, aptly named the rotor. This is then energized to create a magnetic field.
This magnetic field interacts with the stator windings to create a difference in potential (voltage) between each end of the windings. That 1800RPM mentioned earlier is how we obtain our 60 cycles per second, or 60 Hertz (Hz). The three sets of stator windings are how we obtain three-phase power in a four-pole generator. You can calculate this by multiplying the RPM by the number of poles, most often two or four, and dividing by the number of electrical degrees of separation. A three-phase generator has 120 degrees of separation: one revolution is 360 degrees, so dividing that by the number of phases (three) gives us 120 degrees. A 60Hz equation would look like this: 60=1800 X 4/120. Those of you who are in the UK, Europe, Asia, or half of Japan, you may be using 1500RPM or 50Hz (3).
If we were to plot this AC voltage on a graph it would show a sinusoidal waveform, or a sine wave: a 2D representation of the voltage changing as the alternator is rotated. That’s all the math in this article, I promise. To give your brain a rest, try this: take a corkscrew or spring, and look at it on its side — it will look something like a sine wave.
In a hydro-electric power plant, the turbine is in direct contact with the water flowing through it, whether it’s an arc gravity dam like the Hoover Dam, or a run-of-the-river dam like Chief Joseph Dam in Washington. Spillways and valves are used to control water flow and power output. The turbines used in wind power applications look the most like a propeller. Due to the transient nature of the wind, they are often coupled with variable speed generators along with power conversion equipment, to obtain a steady and reliable output for distribution and use.
This AC power is then transformed and distributed a number of times before reaching your home. On-site generation may go through some transformation and distribution as well before reaching the point of use, but typically not as much.
Chemical
Those shiny-shiny devices we spoke about earlier use both mechanically- and chemically-derived power. It may surprise you to learn that the average device is powered by chemical reactions rather than mechanical ones: your watch, phone, tablet, laptop — and now even your car can be powered by chemical reactions. We already mentioned the latest leap forward with lithium-ion, but humans have been using chemicals to produce power since well before today’s most powerful tools — even your fourth-grade science fair potato clock is powered by a chemical reaction.
In the chemical realm, we are most likely talking about Direct Current power, with the large majority of chemically-derived DC power being generated by batteries. For the longest time, larger lead-acid batteries were the main source of starting power for cars, motorcycles, aircraft and watercraft. Their relatively low cost also made them viable for use as energy storage in Uninterruptible Power Supplies (UPS) for hospitals and other ‘no fail’ facilities and applications. These are just like the small UPS you may have on your office or personal computer, but on a much larger scale. Meanwhile, on the more portable side of things, alkaline chemistry is a better choice than acid due to its higher energy density and sealed construction.
Batteries, regardless of chemistry, make use of differing electrodes and an electrolyte solution to facilitate electron flow from the charged electrode, to the discharge electrode depending on the state of the battery. These electrodes are divided into cells. In some batteries, multiple cells are stacked together to get the desired voltage. The most notable break from this convention is the solid state battery, which uses a solid electrolyte instead of a liquid. This mitigates many issues with liquid electrolyte solutions — most notably, the flammability of lithium batteries and the chemical burn hazards of lead-acid. You may have noticed that a unique characteristic of this chemical method of power production is its dual function as energy storage. (Some of you may also be familiar with capacitors and supercapacitors which are also energy storage devices, but they cannot produce a charge on their own.)
Our last stop in the realm of the chemical is the Photovoltaic cell. These utilize a semiconductor material to harness the Photovoltaic Effect. When light shines on the semiconductor material in the cell, its electrons are put into a high energy state and jump to a conductor material, creating an electrical current. These cells are assembled into a module to create what we refer to as a ‘solar panel’. These panels when wired together create the array, which is then plugged in to other power equipment to provide the desired power. The array provides DC power (4), which can be used to charge storage batteries, vehicle batteries, or end-use devices. If AC power is required, it can be run through an inverter.
Conclusion
As you now know, we are surrounded more and more by power generation sources in the world we live in today. We have just scratched the surface in this article, and as the calendar flips by there is potential for even more exciting developments to cover. We live in a world where many of us have easy access to power, but there are still many people in the world who live without it. There is a direct correlation between the availability of power and that of education. Even within our own borders here in the US, power is no longer guaranteed for many. Hopefully you are able to take away some ideas on power generation with this article, and maybe even create your own little power plant in the back yard or whatever space you have. This article was written during the COVID-19 pandemic, and I am currently planning on creating my own exercise-bike/generator to keep the weight off, and keep the battery-powered lawn mower running! Until next time, “Without Power, You’re Just Camping”.
- https://www.eia.gov/tools/faqs/faq.php?id=427&t=3
- Small, direct-coupled gas turbines account for such a small percentage that we are not considering them for the purpose of this article
- These RPMs are the most common, simplify the three-phase math, and will be used through the rest of the article
- There are currently AC PV panels being experimented with, but they’re still only found in labs at the time of writing
