Just finished reading through Mike's extensive post regarding the "clean and green" lie that is solar and wind. It inspired me to write this post. This post is more for educational purposes and I thought it would be kinda fun to write.
So, here is my understanding on how many of the more prevalent electrical generation sources work based on my knowledge and education as a Mechanical Engineer. Keep in mind 2 of the key laws of thermodynamics:
1 - You CANNOT produce more energy from a system than was put into it. Sorry, no perpetual motion devices.
2 - You CANNOT produce as much energy from a system than was put in. Every system has parasitic loses.
To put these to laws another way (the way my dad and I like to say them): You can't produce more energy then you started with and you can't break even.
If one was to truly try to calculate the energy production of a power generation technology, they really should try to account for the energy that went into PRODUCING or CONSTRUCTING the technology in the first place.
Solar - An electrical engineer would have a better understanding on how this works, but the gist is that an electrochemical interaction occurs when solar energy (photons) hit a solar panel (photovoltaic plate). Photons are in fact electrons, a photovoltaic plate takes the energy from a photon (moving basically at the speed of light) and uses that energy to excite electrons in the photovoltaic. Newer panels are ~20% efficient at this conversion and the panels are only operating during daylight hours and at best when the panels are CLEAN (minimal dust/dirt on the panels) and there is little to no cloud cover. As Mike also mentioned, there is going to be an upcoming problem with toxic waste from solar panels that have reached the end of their useful life. Solar is also the only technology that I know of that does not use any 'moving parts', which makes it unique. (unique does not mean something is better.)
Before I get into the next technologies I want to explain the basics of 'mechanical' electricity generation. When I took my basic electronics courses as well as 2nd semester physics (the physics of electricity and magnetism), we were taught and shown through simple demonstration that in order to generate electricity you need 3 ingredients: A conductor (typically copper), A magnetic field (typically some form of rare earth or permanent magnet) and you need movement (the magnetic field needs to be moving in relation to the conductor). The simple demonstration for this was a coil of copper wire connected to a dial voltage meter. The instructor would then take a bar magnet and physically move/pass it through the center of the copper coil and the needle on the meter would move. An electrical current had been produced.
Wind - The second 'green energy' poster child. These work by wind spinning turbine blades (basically fancy, complex geometry versions of propeller blades you would find on a propeller driven aircraft). The turbine blades convert wind energy into rotational mechanical/kinetic energy. The turbine shaft is often connected to a gearbox/transmission to regulate the speed of the generator shaft. The generator shaft has magnets on it that spin with the shaft. The generator shaft spins inside of a housing that has copper coils along the walls of the housing. So, a physically spinning magnet is moving in relation to stationary copper coils and electricity is produced. Remember this setup and it's going to become a regular design theme.
Hydroelectric (dams) - This works pretty much like Wind but instead of harnessing wind energy, we use the power of falling/moving water. First, find a river and build a dam to create an artificial lake (a reservoir). Inside the dam there are turbines. Water is directed from the reservoir into the dam and the water encounters essentially a paddle wheel. The paddle wheel is connected to a drive shaft, the drive shaft is connected to the turbine. After that, the process is the same as wind. Magnets spin on a shaft in relation to copper coils and electricity is generated.
Coal/fossil fuel (but NOT natural gas) - Another variation on the common theme here but with another element added. Coal/fossil fuel is burned to create heat. The heat from burner fossil fuels is used to heat water until it turns into steam. The steam is directed into a turbine. Turbine spins, electricity is generated. generally speaking, there will be steam 'left over' after going through the turbine, this steam is vented to the atmosphere and is the white discharge seen in many photos of coal power plants. This steam (essentially man made clouds if you will) are what the media claim are CO2 emissions, which is wrong. CO2 is invisible, no color and is odorless. Also, when Greta Thunberg claims she can see CO2 emissions from coal power plants she is either referring to the STEAM discharge or she is hallucinating. The need to generate steam is also why you will often see coal plants built near rivers or lakes, otherwise water has to be sourced from somewhere and pumped to the plant.
Natural Gas - This technology has more in common with turbojet engines found on commercial airplanes. Natural gas (either from a natural gas pocket in the earth or as methane produced from landfills) is combusted in a turbine that very much resembles a turbojet aircraft engine. The turbine spins a shaft, magnets spin, electricity is generated. CO2 is produced as a product of combustion.
Nuclear - My personal favorite and the technology I personally believe the world needs to GET OVER it's fear of! Radioactive material (typically uranium or plutonium) is manufactured into fuel pellets or rods. The nuclear fuel is then immersed in a pool or liquid. As the nuclear reaction occurs, it generates heat. Nuclear reactors work on the steam turbine system just like coal/fossil fuel plants do but there is another step that has to be added to the process to keep the process safe for the environment. As the nuclear reaction occurs, it will irradiate the liquid bath, so this liquid cannot be safely used to generate steam, otherwise radioactive steam would be produced. So instead the heated liquid is pumped through a heat exchanger (picture the radiator in your car). Water is then passed across the heat exchanger to heat the water to boiling. Steam is produced, steam turbines spin, electricity is produced and waste steam is discharged to the atmosphere.
There are two more technologies I would like to discuss because they are interesting and are currently being researched and/or implemented on a small scale currently.
First is another green energy that I think actually has the potential to be green AND more reliable than wind or solar. This technology is wave or tidal energy. The best way I have to describe this technology is by using an analogy to a product you may very well have seen in your local hardware store. Recall those 'emergency flashlights' that were popular about 10 years ago where they didn't use batteries but instead you had to shake them? The way that works is by having a magnetic 'slug' inside of a cylinder wrapped in a copper wire coil. By shaking the flashlight, you are moving the magnetic slug within the copper wire coil to generate electricity. That's the basic principle of how wave/tidal energy generation works only scaled up. Picture a 50 gallon drum wrapped in copper wire coil with a magnet that is free to slide back and forth along the length of the drum. Place that drum into a bay where their is regular wave action and let the drum rock back and forth with the waves. The magnet slides back and forth and the system generates electricity. This system only relies on regular wave activity. Yes, wave activity changes throughout the day but in general there is always some wave action, even at night, so in that regard it is more 'reliable' than wind or solar.
The last technology is called a Molten Salt plant. These are very interesting and are (in a sense) a variation on 'solar energy' but it doesn't rely at all on photovoltaics. Instead these plants use a massive array of mirrors, all pointing at a central location at the top of a tower in the middle of the plant. At the focal point of the mirrors (on top of the tower) is a vat of salts (not necessarily your table salt but you can go ahead and visualize table salt for the purposes of this discussion). The thing that a lot of people don't know or realize is that given enough heat, salt can be melted and kept in a molten state. Naturally this takes a lot of heat energy to do, but the interesting property of molten salt is that it then retains that heat A LONG time. So, during the day, the mirrors 'collect' solar energy and 'transfer' it to the salt vat. This melts the salt, and molten salt can be pumped like a liquid. The molten salt is then pumped through a heat exchanger where it is used to heat water to boiling. Steam is produced and used to spin a steam turbine and produce electricity. The last interesting facet to this technology is that if you have a good day of sun shine, you can get the salt hot enough that it will pretty well maintain it's heat throughout the night. So this is the only solar energy plant I know of that can actually be used to generate electricity at night. There is one of these plants setup in Nevada and you can sometimes see it if you fly from Sacramento International Airport (California) to Denver, Colorado. Often that flight takes a path that will fly near enough the plant that you can see it from the plane window. The downside of this plant is the same as solar panels, you NEED a long period of direct sunshine for this to work. Too many clouds or not enough hours in the day and this plant still suffers.
This covers all the technologies that I am currently aware of. Notice how many of the technologies ultimately come back to steam generation? Just an interesting observation.
I hope you enjoyed reading this.
Thanks madmechanical engineer!
What a wonderful contribution.
That covered alot of ground with descriptions that have never been covered here before and I just learned from you......thanks!
I agree 100% on nuclear energy.
I note that you didn't mention geothermal.
Here's the thread that I think you were referring to that has tons of good info relevant to this discussion:
21 responses |
Started by metmike - May 6, 2021, 9:58 p.m.
Doh! Yes, I did totally forget about geothermal, which was daft of me as geothermal is a great technology for regions with a lot of natural hot spring activity.
We make a great authentic science and energy technology team and have the same initials MM (-:
Thanks MadMech. A great read for my Sunday morning.
I was at least vaguely familiar with all of these except the salt and you filled a lot of gaps for me Fascinating stuff that makes the forum a bit better :-)
Edit Note: In my youger naive days, I used to discuss the idea of perpetual motion with my step father, a chemical engineer out of MIT. He said, "I'm not going to say it can't be done, but you'll have to come up with something that current knowledge cannot support. The rule of thermodynamics is.. You can't win, you can only lose, and you can't get out of the game.".