Wind Farms Usually Involve Several Wind Turbines

On the other hand, the effect of wind on large structures is something that structural engineers need to analyze in order to ensure the safety of these structures. Some examples of structures that are heavily affected by wind are skyscrapers, towers, cable suspension bridges, and the wind turbines mentioned above. Here, wind is like a curse because structures can fail and collapse under heavy winds if precautions against wind effects are not taken when designing these structures.

For a wind turbine, winds cause a bending moment in the shaft of the turbine. This is because vertical wind speed profiles are not uniform (more so on land than over water), meaning the wind speeds at low elevations and high elevations are different. This difference in wind speed causes a difference in forces at the top and bottom of the wind turbine shaft, which makes the shaft want to bend. Too much bending moment will cause a wind turbine to break and collapse. Engineers have a variety of tools at hand to help them combat this challenge of wind loads, such as building material to use (different materials have different properties against failure), and geometry of the shaft (like the cross-sectional shape and area of the shaft).

For cable bridges, high winds can cause vibrations in the bridge. One famous historical example of a suspension bridge is the Tacoma Narrows Bridge (Wikipedia). Opened in 1940 to traffic in Washington state, it collapsed four months later due to high winds that caused large periodic motions of the bridge. Forces on the bridge from the wind combined with the natural frequency of the bridge to result in large-scale fluttering, which is a phenomenon known as aeroelastic flutter. You can see video footage of the Tacoma Narrows Bridge collapse here (YouTube).

The Tacoma Narrows Bridge collapse serves as a lesson learned in today’s world of engineering. Ways that engineers can safeguard against suspension bridge failure due to high winds include considering stiffness of the bridge and how the bridge deck is constructed, as well as studying the winds themselves (looking at historical wind speed data for a particular area).

Next time you walk outside and experience a heavy wind in your face, know that winds are a necessary evil. Sure, they are something that engineers need to consider when designing large buildings and bridges, but they also serve as a renewable source of energy.

Photo from Wikipedia.

Nuclear Plant in Michigan

This is Part 4 of our series on “Intro to Power”. If you haven’t checked out Part 1, Part 2, and Part 3 already, I recommend that you do. I talked about the fundamentals to electricity generation, steam turbine power plants, and efficiency.

Now that you have a better understand of how most of today’s power plants work, let’s go back to the big picture. Let’s look at the problems we face today with global warming and the need for new sources of energy.

Greenhouse gases have only recently entered the public’s eye. Carbon dioxide (CO₂) is by far the most well known of these, and for good reason. According to Energy Information Administration of the US, CO₂ makes up about 80% of these gases. Methane (CH₄), the bulk of natural gas, makes up about 10%. Other gases make up the other 10%.

Please understand that carbon dioxide isn’t, and has never been, considered a pollutant. If it were, then every living person and animal on this earth is a polluter, and we would be bad for our own health (though we are, in a way). It just doesn’t work like that. Environmental and air pollution is the cause of smog, bad air, and black lungs. Carbon dioxide is none of these things. Our very lungs produce CO₂.

In order to save ourselves from ourselves, we set a new fundamental goal: Release less carbon dioxide into the atmosphere. Yes, this much we all already know. But how do we accomplish this?

The first idea is to turn to renewable energy, like solar and wind. Renewable energy has come a long way, but without a revolutionary way to integrate the world’s electric grid, it is far too unreliable. For the most part, power plants are needed to produce energy instantly, whenever it is demanded (where “instantly” requires a 5-6 hours lead time). The electricity that produced is not stored by any means. Many people tend to overlook this fact. All the same, solar and wind energy is not stored. They produce when there is sun light or wind, and they sit idle when there isn’t. However novel of an idea, it is far too unreliable as a source of energy without an integrated smart electric grid which can draw energy when the solar and wind farms fall quiet.

Don’t forget the vast amount of space required to support solar and wind farms, too. Isn’t it funny that most of the electric power goes to big cities and metropolises and the electricity comes from small, remote towns? Unfortunately the amount of energy generated on even a good, sunny day by solar cells cannot match the robustness of a plain, old steam turbine power plant. And the latter takes up far, far, far less room to function. These renewable energy sources are good when they work. Unfortunately, most of the time, they are inadequate to meet people’s ever-growing demand for more.

Another idea we have is to build upon what we have today. Let’s try sticking with the steam turbine power plant template for a while longer. After all, it is the most efficient and cost-effective means of energy today. Consider that greenhouse gases are merely the by-product of the heat we need to convert water to steam. It comes from only the fire we build in the boiler. We have two options: A) get a heat source that is free of carbon dioxide in the first place; or B) capture the carbon dioxide before it hits the atmosphere.

Today, Option A gives us nuclear power. It produces no greenhouse gases and no pollutants. It is robust and its operating schedule is not determined by the weather (the style we’re used to today with our fossil plants). There’s just this little problem of radioactive waste and the possibility of a meltdown. To this day, this nuclear waste waits in high-security containers in the ground, until we figure out what we’re going to do with it “later”. This doesn’t sit well with many people. Geothermal is another clean type of energy that follows the steam turbine model.

Let’s look at Option B. Today, we have a process called carbon sequestering or carbon capture. Basically, it’s the capturing of carbon dioxide through chemical or physical means. The problem is what to do with this stored carbon. Some have proposed to store it underground. My question is this, why should we be okay to stick carbon dioxide in the ground when we are weary of putting nuclear waste in the ground? they both do not belong there, and they both pose problems to the environment should they leak.

Other people say we are already too far gone, that any measure to reduce greenhouse gases is futile. They say we needed to stop emitting over 10 years ago. Unfortunately, and of course, no one wants accept this fact.

As President Carter said in a speech, “Conservation is the quickest, cheapest, most practical source of energy.”

This ends our really long series on “Intro to Power”. There remains a lot of unanswered questions and a lot of missing details. I intend to address them in future posts, in more bite-sized bits.

Feel free to leave a message below if you have any questions or comments.

(Nuclear plant image from Flickr.)

Efficiency is the hot word of the news today, but the science and engineering of it is actually pretty dry, I’ll admit. Consumers worry about fuel efficient cars and trucks, but do they think about fuel efficient power plants? Power plants generate about 20% of the world’s greenhouse gases, while all modes of transportation weigh in at around 15%.

What is efficiency anyway? In thermodynamics, efficiency is a ratio of the work extracted from a system to the heat or energy put into the system. Output over input.

Still with me? To increase efficiency, we want to essentially use less energy in for a certain amount of work done by the system. Makes sense, doesn’t it? If we look at the formula above, the math holds true to common sense.

Efficiency Leads to Complex Plants

In a power plant, overall efficiency can range from 20-50%. There are efficiency-ratings of every component in a power plant. For example, a boiler may be 80% efficient, while the generator might be up to 95% efficient. Why is the overall efficiency so low? There are many factors. Whenever energy is converted from one for to another (in this case, chemical to thermal to kinetic to electrical), energy is lost in the actual conversion. In addition, there can be leaks and insulation problems. Nothing is 100% efficient; it is an unattainable goal.

There are a lot of things power plants do to make the overall system more efficient. In fact, this is the what people in the field of power engineering do. They develop systems and processes to make the basic teakettle example run more efficiently.

I will mention just one type of idea, that is reheating and preheating the water and air via heat exchangers. Let’s assume a two-stage turbine system. (There is usually more than one co-axial turbine to get more energy from the boiled steam.) The steam that leaves the boiler and enters the first turbine is called the “main steam”. Instead of releasing the left-over steam to the atmosphere, we capture it and reuse it. It is still plenty hot and it returns to the boiler for a second run, bringing it back to the optimal max temperature. It is then called “reheat steam” and then enters the second turbine. The warm exhuasted steam is collected and reheated with stage heaters before returning into the boiler to eventually become “main steam” again. After all, less energy is required to boil hot water than is required to boil cold water!

The same can be done with air. Regardless of the fuel that is being used, the burning of it (called combustion) requires oxygen. Lots of it. Of course, the cool air is taken from the surroundings. When it’s used in the boiler, where it’s hot, a noticeable portion of the boiler’s energy goes into heating the air before it’s being used. In order to combat this, the dirty and hot exhaust air is used to preheat the fresh incoming air so that less energy from the boiler is needed.

What all this reheating and preheating does is to lower the amount of energy required for electricity (or work). Remember that the efficiency formula is energy out divided by energy in. If we can lower the amount of energy we need, we can drastically increase the overall efficiency of the plant! Different fuels have different amount of energy and the power plant’s overall efficiency is a direct result of how “good” the fuel actually is.

That’s it! Remember that these ideas refer to steam turbine plants. Renewable energy like solar and wind and hydrodams don’t follow steam turbine system.

And finally, for the last installment of “Intro to Power”, I promise we’ll talk about something more interesting. Promise!

(Plant image from my Flickr.)

The simplest form of a steam turbine power plant consists of a boiler and a turbine driving an electric generator. Typically, the axis of the turbine and the axis of the generator (i.e. the spinning magnet) shares a common shaft. So, if the turbine spins, then the magnet spins, and then we generate the power we need. Still quite simple, huh?

GE's LM6000 Turbine

At this point, we have switched over from the invisible magnetic field stuff and electric currents to something we can physically deal with. In fact, if we can get someone to run really, really fast in a circle and turn the generator’s shaft, we can also generate electricity. Unfortunately, we can never run quite fast enough. Instead, we let steam do it for us.

Why steam, anyway? Why not ammonia or some special hydrocarbon? Well, water is rather nonvolatile, meaning it doesn’t react with other components so easily, and if there happens to be a leak somewhere, it wouldn’t be too problematic. Most importantly, though, water’s properties are just too good to pass up. It has the chemical properties of vaporizing at just the right temperatures and pressures we need. Plus, it’s “pure,” right? You wouldn’t clean your kitchen counter with orange juice’s citric acid, for example.

What the hot and pressurized steam does is turn the turbine. You can think about wind mills, where the wind turns blades on a shaft to do kinetic work. It’s also like a jet engine in reverse: instead of using gas to turn the blades and cut the air, it’s analogous to having high-pressured air turn the blades to generate electricity. Sort of … 

Turbine-Generator Assembly

Now the trick is getting the steam. Anyone who drinks tea would know that we can get steam from heating up water. We use fire as a heat source and the teakettle as the boiler. The steam that’s produced turns the turbine, which turns the generator, which produces electricity.

That’s the fundamental process of a power plant. It’s fairly straight-forward.

The question you might ask is: If a power plant is so basic and simple as the teakettle example, why do we have these complex monstrosities full of dirty piping, smoke stacks, and tanks? The answer is simple too: Efficiency. The amount of electricity a teakettle can produce in this system is practically none; the efficiency is essentially zero.

The different kinds of plants differ primarilly in the kind of fuel that’s used. Coal, natural gas, fuel oil, and nuclear sources are the more popular ones. They all use the same steam system of heating up water and turning the turbine! The difference is the kind of boiler that’s used; in other words, how we are getting from water to steam. Of course, there are inherent trade-offs. Now, it’s just a question of which kind of fuel. Of the fossil fuels (coal, natural gas, and petroleum), coal offers the most energy per pound. It is a relatively dense solid and is made up of complex chemical bonds which is broken up to release energy. Petroleum (fuel oil) is a thick liquid, and natural gas, is, well, a gas (made mostly of methane). Certain fuels release more energy than others when they are burned.

Please keep in mind that none of these are considered “clean” fuel. There are always by-products and waste. Coal, is by far, the worst of them. (I will address “clean-coal” in the future.) Fuel oil is made up of the black, tar-like junk stuff that isn’t good enough to go into your car, and natural gas is the cleanest of the fossil fuels. But remember, coal is mined from the earth, petroleum is pumped from the earth, and natural gas is released from the earth. All of these are burned in the boiler to heat up water for steam. Even nuclear power plants just use radioactive material whose chemical energy becomes thermal energy to heat up the same water for steam. (There is only the added issue of radioactive waste.) Everything else can be more or less the same. Even biomass and corn ethanol are merely just fuels. The process outside of the boiler is the same.

Does all this make sense? Let me know if you have any questions in the comments.

For next time, the secret word is “efficiency”.

(LM6000 image from Aventi Technology. Assembly image from World Of Energy.)

Magnet Inside a Power Generator

I’d like to start off with something so important, but so invisible, in our everyday lives.  We all know by now that energy and power generation is the hot topic that’s moving us forward, with talk about global climate change, renewable energy, and “green” technology.

I’ll kick off the blog with a special 4-part series about energy and power generation. Let’s start with reintroducing the concept of energy and the basic ideas used by nearly all power stations today. It is at least a little bit scary that, with all the talk in the media about how we must reinvent the energy sector today, very few people actually know where we need to reinvent from. What are our current means of producing electricity? How do we make the energy we need to light today’s highly electrified infrastructure?

With the exception of photovoltaic cells (which atomically converts sunlight into electricity) and maybe batteries (even hydrogen fuel cells are essentially just chemical batteries), pretty much all the energy we use today is generated by something spinning or turning, from chemical to kinetic to electric energy conversion. It all starts with magnets and electric wire. Fundamentally, the electric generator consists of a bar magnet spinning inside a stationary coil of wire (called it the stator). As it spins, the magnetic field the wire experiences from the magnet changes, and this change induces an electric current in the wire. By winding a large number of turns of wire into a ring or doughnut, the end-result is a much more powerful current. It’s this single principle that’s what lights our homes and and power our computers. That’s it!

In actuality, however, a simple permanent magnet isn’t strong enough, at least in the past. Today’s permenant magnets have gotten strong enough to perform the way we need them to work. Otherwise, we need to beef it up by making it an electromagnet. (An electromagnet is magnetized by electricity flowing to another set of coil s of wire wound around the magnet itself.) This might be a sort of Catch-22. For the generator to function in any real capacity, this electromagnet needs to be powered. Otherwise, we can have all the kinetic and chemical energy we want with no way of converting it to usable, electrical energy. 

Basically, we need energy to make energy. (Keep in mind there are other components in the system that needs to be powered too, like motors, pumps, and lights. We’ll get to those things next time.) The simplest way to get this energy is to draw it from the energy from the plant itself. And surely enough, that’s what we do. But what happens if the plant is cold, i.e. completely offline? Well, then, we’ll need the help of the others connected to the “grid” or use an auxilary generator, which is smaller and whose sole purpose is to start up a power plant. Component by component, the plant comes online.

Here’s our goal: To get this magnet to spin really fast. Simple, isn’t it?

Wind Turbine in England

All the coal plants, natural gas plants, fuel oil plants, nuclear plants, biomass plants, geothermal plants, solar thermal plants, wind farms, hydroelectric dams, and tidal-powered systems are merely ways to get this magnet to spin. Remember, a spinning magnet relative to a stationary coil of wire creates electricity.

Now, it gets a little complicated. We all understand we need electricity. There is no way around it. Where the problems and controversy lies is how to do it. Believe it or not, all the types of power plants I listed above, except the last three, can be grouped together—they function essentially the same. We’ll refer to them as steam turbine power plants.

Next time, we’ll take a step-by-step look into how steam turbine power plants (the most popular “style” of power generation) get this magnet spinning.

If you have any questions so far, definitely leave a comment below.

(Power Generator image from Alternative Energy Blog. Wind Turbine image from Flickr.)