Tag Archives: Electricity

Other Alternatives

Posted on by
Reply

Here we will cover a few more electricity producing alternatives, specifically geothermal in its different flavors, and the waste of money that is tidal power. Before that, let's make a quick roadmap of what we have covered, where that is going, and what we haven't yet covered.

Pretty much, we have talked about electricity producing resources. We have only briefly touched on energy as a whole. In the US, for example, 35% of all energy use is petroleum for transportation. None of the stuff we have discussed is useful to replace that without better battery technology. Nonetheless, it is likely that at some point in the next century, much of our domestic energy needs, including transport, will be covered by electricity. And we will require a lot more of it. An upcoming post will assess all the different tech for producing energy we have discussed, and which ones can be potential solutions.

Geothermal

Geothermal energy exists because it gets hot underground. In general, the temperature of the Earth rises by 30 degrees C for every km you go underground. This temperature increase in depth is called the geothermal gradient. If you go 7km underground, you are pretty much guaranteed temperatures of higher than 200 degrees C. Which, as we all know, is hot enough to boil water. 7km underground is pretty deep, however. In some places, the underground is much hotter. The temperature rises much more rapidly. It could be due to volcanic activity in the area, or radioactive decay underground. Either way, when hot temperatures are closer to the surface, that heat can be harnessed to drive a turbine.

Map of the geothermal resources available in the US. In general, this represents areas of higher temperature gradients.

Geothermal comes in two main flavors. One directly harnesses the steam from the ground to produce electricity (called flash steam, cause the pressurized hot water comes out, flashes to steam at atmospheric pressure, and drives a turbine), the other uses a heat-transfer mechanism where pressurized hot water from the subsurface (it needs to be pressurized, because it is above the boiling point of water at atmospheric pressure) is run through a set of heat-exchanging pipes before being put back underground. There is a third type discussed later in the article called hot dry rock.

Surprisingly, the first mechanism of directly using steam, in practice, is unsustainable and produces pollution. This is because the used steam is often vented to the atmosphere. The steam produced underground has pollutants. Like CO2 and sulfur, amongst other things. If the steam is used directly in a turbine and then expelled to the atmosphere, these pollutants come with it. If the used steam is instead re-injected into the formation, this problem is avoided.

Reinjecting the steam is easier and more common in the heat-exchange mechanism. The super heated stream of steam from underground is already isolated, and re-injection is pretty simple.

And here comes the fun part. If the steam is used and then vented rather than reinjected, the formation will run out of water. Instead of being a renewable resource, the geothermal will be a depletable resource that will only last for 10 or 20 years. This is because the pressure of the formation will drop, and the steam will no longer be able to rise. Does this sound familiar? Oil and gas production need to do this all the time to get maximum recovery rates. Reinjection of fluids is rather easy, and has been pretty well developed by the oil and gas industry.

Hot Dry Rock

The next major innovation takes a cue from the oil and gas industry. Hot dry rock is exactly what it sounds like. The rock starts off hot and dry. It has plenty of heat in it, but there is no steam or water to produce and then make energy from. How is this dealt with? Hydrofracking and injection. A well is drilled, the drill hole goes horizontal, it is fracked to drastically increase the surface area that the well hole can be exposed to, and water is injected into the rock. The water heats up a lot, then it is produced via a separate well to make steam. It is fairly complicated, and costs a lot more.

EGS

EGS stands for enhanced geothermal systems. You will run across this term a lot these days. It more or less means that the heat in the field is managed by either fracking beforehand, injecting water afterwards to maintain pressure in the field and extend the life of the geothermal power plant, or a combination of both. It drastically increases the lifetime and viability of a geothermal site.

Cost

The capital costs of geothermal pretty much will dictate the average cost of electricity produced. It looks like flashed steam will cost the least. In reality, unless the steam is reinjected afterwards, the field won't last as long, and the capital investment costs will have to be paid out over a shorter period of time, resulting in higher costs. Hot dry rock will undoubtedly always remain more expensive because of the costs associated with fracking and reinjection.

Footprint and other

Most of our power plants produce heat above ground, and need storage for either spent nuclear fuel or a coal pile (except for gas plants. They just need pipelines). So geothermal power plants don't take up a ton of space

fun uses of geothermal: geothermal heat is produced and used in Iceland to melt snow on the roads and such.

Tidal

I tend to think that tidal power sucks. In part because it is very expensive, and in part because at best it could provide all of 1% of world electricity.

Tidal power has two main problems: it uses salt water and it has only a few areas that it will work. There needs to be tides of sufficient strength that it can produce electricity, and even then, salt water is corrosive, limiting the lifetime of these power plants and making the levelized capital cost very high.

Tidal power also comes in two main flavors. One is tidal impoundment. Think of it as creating a hydroelectric dam every time the tide goes out. The tide comes in, fills up the area behind the impoundment dam, and then as the tide goes out, the area behind the impoundment dam is filled, and as it flows out, it generates electricity. As you recall from the hydropower article, the energy produced from a hydro dam directly relates to its height. The height of a tidal impoundment dam is limited by the height of the tide. In most parts of the world, this is not very high, so it is not very efficient. Moreover, it kinda messes with natural habitats.

The other type of tidal power is more or less an underwater wind turbine. The problem is that all the moving parts are underwater in the ocean. Where decay and breakdown happens quickly. Moreover, looking at the equation of energy produced via such a turbine:

where A is area, and v is velocity,

we quickly realize that the area of the rotor for a tidal turbine is small (wind turbines have 40m blades, and we aren't gonna have 80m of water depth in most places to replicate that scale in tidal areas), and the speed is slower (water doesn't flow at 6-8m/s very often). Tidal power can't scale and produce as much energy as wind. And the environment is unfavorable. In short, this is not a viable resource for large-scale energy production. And it costs a lot.

Hokay, that is all for today! Thanks for reading!

-Jason Munster

 

Solar 2

Posted on by
Reply

Photovoltaic solar cells. Solar PV.

This is not an easy thing to describe. For some, you may want to just skip past the technical section, cause it is pretty technical.

Solar PV: they used to take as much electricity to make as they produced in their lifetime. Now they they produce about 5x as much energy as they take to make, and the time to break-even on emissions compared to our cleanest fossil fuel stations is about 6 years (see Kannan, 2005, Lifecycle Assessment Study of Solar PV). Of all the clean technologies (nuclear power excluded), this is the only one with the potential to supply world energy needs (that is the subject of a later post).

In other words, when you hear some fool saying that solar panels take as much energy to manufacture as they ever produce, they are referring to a specific type of solar cells called thin film. A type that was made in the 70s and 80s and only goes into things like calculators. Feel free to ask them to stop being foolish.

Some Math

The light we see is not a homogenous single color. In fact, the light we see is not even all the light that is coming from the sun. Infrared and UV rays are also light, but we cannot see them at all. All this light is just an electromagnetic wave. The waves have different wavelengths, but the same speed, and so all the different wavelengths travel together. What we see is a blend of a tiny part of the electromagnetic spectrum.

This is the electromagnetic spectrum. Visible light, what we can see, is only a small part of it.

This is the electromagnetic spectrum. Visible light, what we can see, is only a small part of it.

The amount of energy contained in a photon is equal to

where is the wavelength. h and c are Planck's constant and the speed of light, respectively.

Smaller (shorter) wavelengths give more energy. This is easily shown just by plugging a smaller number into the denominator. Stuff in the infrared is long wavelength, and stuff in UV, X-ray, Gamma ray, etc, are really short wavelength.

Technical Stuff

There is no easy way to do this. I am going to use some terminology that most of you all are unfamiliar with.

A Photo Voltaic (PV) solar panel is a sandwich of two materials. The materials are largely the same, with a few key differences. Both are likely made of silicon (processed sand). But each one has very specific impurities put into them, in a process called doping (not the same type that Lance Armstrong does). This doping is incredibly technical, and very skilled chemists are paid a ton of money to figure out how to do it.

Doping

I won't get into specific materials. Some elements cause there to be a shortage of electrons, or a electron hole, in the whole material (p-type semiconductor). Other elements cause an excess of electrons (n-type semiconductor). So you have one material that can accept electrons, and another material that can give electrons. Putting them together (literally stacking them together) makes magic happen. And by magic, I mean quantum mechanics. Which to most people, including many who study it, is no different than magic.

Just because one has more electrons doesn't mean it wants to be nice and share them. The electron in the n-type literally needs to be excited to be shared. And in PVs, what turns the n-type material on is sunlight. More specifically, photons. Photons are particles of light. ("But Jason!" you say, "Isn't light, like, a wave?" to which I say, "It is both a wave and a particle! Please don't ask me why, just accept it.") Photons contain energy based on their wavelength. Shorter wavelength, more energy (see above).

Here's the fun part. It takes energy to make the n-type semiconductor want to party with the p-type semiconductor. There is a threshold level of energy that needs to be met to kick that electron up from the n-type to the p-type. Too little energy, and the photon doesn't get excited enough to go to the electricity-production party. If there is enough energy from the particular wavelength of light to make that electron jump, then is does jump.

But what if there is more than enough? This threshold level is pretty much determined. Any extra energy will be wasted. This is why PV cells are not particularly efficient. There is a huge amount of light that is too low-energy (all of infrared) for the cell to gather any energy from. There is a lot of light that has much higher energy than required to meet the threshold energy as well. The excess energy is wasted as heat. This can be solved by having a multiple junction cell (multiple junctions just means it has a bunch of different width absorption gaps, so it can harness tons of different energy levels in light). It is capable of absorbing more wavelengths of light, increasing efficiency. And since it has multiple junctions, it is also more expensive and complicated to produce.

Hokay, so, what happens next? You have an electron that has jumped the gap. Then you close the circuit by connecting them with a wire. The electron will go home, back to the n-type, and create an electric charge on its way down. That's about it.

New Methods 

Transistors are expensive. Normal glass optics are relatively cheap. The transistors absorb about 20% of the light that hits them. So it would make sense to use cheap optics to focus more light on the transistors and make the transistors small, yes?

One problem with these cells is how warm they get. If they warm up too much, they begin to lose efficiency. Here we see that we have a tradeoff. We want more optics and fewer cells, but if we do this, they get too warm. They stop being efficient. Some scientists and engineers are working on increasing the efficiency of the cells instead, to get more electricity from light. Otherwise, there are clever ways that some mechanical engineers are trying to get around these issues. One new design uses focusing mirrors and liquid cooling to get around this issue.

The pertinent stuff

Everything pertinent, like insolation and weather, was in the last solar article.

Next post: rounding up some of the stray power sources: tidal, geothermal, wave, and then I am pretty much done.

Thanks for reading.

-Jason Munster

Power Grid

Posted on by
Reply

I was struggling to write a post about PV solar panels (the struggling part came in while trying to describe the quantum mechanics that take place), and realized that I need to describe how our power grid works in far greater detail than I had before. What follows is the gory details about how power is transmitted to your home. This is important because while solar power costs 5x as much as coal on the wholesale market, it only costs about 2x as much as coal at your house. Sometimes less. This is because coal-powered electricity is wheeled and dealed through several players as it reaches you, and is marked up every time. Solar power dumps straight into your home. Some of you are gonna love this article, others have already closed it.

power_grid_300

On a logistical note, I haven't posted in the last two weeks cause I am too busy with life things to write both the blog and play computer games. Computer games sometimes win out. Thanks, X-Com: Enemy Unknown.

Generators, LSEs, Home Energy

Generators are all the different types of power plants we have discussed. They produce power, and in a deregulated market, sell the power to the grid. They are given a price based on demand. We have discussed how each power plant will "bid in" a day ahead and say how much power they can produce at which prices. As more power is demanded, the price will rise to bring more expensive power online. No matter what the power plant bids in, if they are online, they will get the per-MWh payment of the most expensive plant to come online. In other words, the marginal cost of energy production is what each power plant gets paid per MWh. If an expensive power plant is brought on-line for $1000/MWh, for instance, every single plant that is operating will receive that.

Okay, we have also seen the cost to produce power in several posts. It makes sense to repeat it here.

U.S. AVERAGE LEVELIZED COSTS (2011 $/MEGAWATTHOUR) FOR PLANTS ENTERING SERVICE IN 2018
PLANT TYPE CAPACITY FACTOR (%) LEVELIZED CAPITAL COST FIXED O&M VARIABLE O&M (INCLUDING FUEL) TRANSMISSION INVESTMENT TOTAL SYSTEM LEVELIZED COST
Dispatchable Technologies
Conventional Coal 85 65.7 4.1 29.2 1.2 100.1
Advanced Coal 85 84.4 6.8 30.7 1.2 123.0
Advanced Coal with CCS 85 88.4 8.8 37.2 1.2 135.5
Natural Gas-fired
Conventional Combined Cycle 87 15.8 1.7 48.4 1.2 67.1
Advanced Combined Cycle 87 17.4 2.0 45.0 1.2 65.6
Advanced CC with CCS 87 34.0 4.1 54.1 1.2 93.4
Conventional Combustion Turbine 30 44.2 2.7 80.0 3.4 130.3
Advanced Combustion Turbine 30 30.4 2.6 68.2 3.4 104.6
Advanced Nuclear 90 83.4 11.6 12.3 1.1 108.4
Geothermal 92 76.2 12.0 0.0 1.4 89.6
Biomass 83 53.2 14.3 42.3 1.2 111.0
Non-Dispatchable Technologies
Wind 34 70.3 13.1 0.0 3.2 86.6
Wind-Offshore 37 193.4 22.4 0.0 5.7 221.5
Solar PV1 25 130.4 9.9 0.0 4.0 144.3
Solar Thermal 20 214.2 41.4 0.0 5.9 261.5
Hydro2 52 78.1 4.1 6.1 2.0 90.3

So the cost to produce is the total system levelized cost (and now you should realize that producing power for $1000/MWh is ridiculously high. Except it has happened recently and momentarily in New England).

People at home don't see the price that a generator gets. Do you notice that you pay about 20 cents per KWh in MA (I use MA cause apparently all my readers are here), it is $200 per MWh. What gives? All these power plants are producing power for way less than that. Except for solar thermal and offshore wind, which both suck and are expensive.

The reason for this is that home/commercial retailers do not buy from the generators and from the wholesale market. Things called Load Serving Entities (LSEs) buy from the wholesale market. Often they will just be your utility company. They then distribute it to end-users or to other complicated things that we don't care about. The end users are your households and commercial things like shopping malls and stores and offices.

Sidebar: One important thing to note is that industry usually buys directly from generators. So while we pay $200/MWh for electricity, a Ford power plant might pay $60/MWh. This has implications that we will discuss later.

So, the LSE buys electricity off the wholesale market. And then marks it up and sells it to consumers. That is why you pay $200/MWh.

RTOs, system management

This section is getting specific, some of you may want to skip to the end of the article, the implications part.

Who tells generators when to come online and manages the wholesale market? Regional Transmission Operators. In New England, our RTO is called ISO-NE, for Independent System Operator of New England. They take bids and determine which power plants produce. They have important things to consider, like making sure a regional power line isn't too congested.

Line Losses

Nearly all power lines lose a percentage of their power as heat. Transmitting long distances loses around 8% of power. This is because there is always some resistance to the flow of electricity. It is like friction for the flowing of electrons. Power lines also have a limit to how much power can flow through them. If you try to go past the limit, they heat up rapidly and lose a ton of power.

The latter is something that the RTOs manage, to make sure that there won't be problems. The former has massive implications for renewable energy. Most of our renewable energy is wind and solar. Like wind in the sparsely populated midwest. And solar in completely unpopulated deserts. Transmitting this power to cities incurs huge line losses. With current capabilities, transmitting power from Iowa wind farms to NYC would make power more expensive than just building the wind farm near NYC, despite that wind in NY sucks (heh, punny). I don't have a source for this, I just saw it at a talk at Harvard.

Implications for installing renewables at home, commercially, and in industry

boa_photo1

We pay $200 per MWh of power as residents in Boston. Solar PV in the best cases is $144. This will be in deserts. In MA, we don't get as much sunlight. But for the sake of argument, lets say that the average cost of solar in MA comes out to be $200-$250. With subsidies, it will be less. So would you pay $200 per MWh from your utility, or $200 per MWh to produce your own energy and stick it to the man? Also your own power would be clean, with far less CO2. With subsidies available in places like MA and NJ, solar comes out to less than $200/MWh at home.

Next lets consider commercial places. They also buy from LSEs. This is why you see a ton of them building solar panels. It makes sense economically and gives them a good vibe that the public likes.

Finally, let's consider industry. They buy directly from the wholesale market. So they pay closer to $100/MWh. They won't give two shits about renewables. Because they won't save money by installing renewables on their sites.

And this, my friends, is the trend we see. On-site renewables are adopted by commercial real estate and by residents, and industry is highly unlikely to ever embrace it. Interesting, eh?

Thanks for reading!

-Jason Munster

Solar Power

Posted on by
1

Solar power. It comes in two primary flavors: photovoltaics (PV) and concentrated solar power (CSP). The latter is easy. I decided to do solar power this week, and go back to the dams next week. Big picture: CSP is a bridge technology at best; an investment in most places is little more than a show that the investor is serious about green tech. Moreover, not all places are created equal to invest in solar power. Many of the places that offer the best incentives to have solar power (NJ, MA, Germany) are far from the best places to have solar power.

So this time: insolation, what it means, where it happens. And CSP. PV comes later. Cause it involves quantum mechanics.

So, first, solar insolation map, AKA "Where is the sun shining all the time" map.

Solar power resources in the US. Darker colors indicate better regions for solar power.

Solar power resources in the US. Darker colors indicate better regions for solar power.

Who is not surprised that Alaska is awful for solar power? But check out MA and NJ. Why are they giving tax breaks to install solar cells? Easy answer. To drive the technology forward. Solar panels are really useful in places without any other power source. Like small villages in Africa and other depopulated places. California also has big incentives to build solar, and at least that makes sense, yes?

What determines how much insolation a place gets? Well, you need sun to have solar power. The sun doesn't come out to party at night, so no solar power. A huge one is how much atmosphere the sunlight has to pass through on the way to the the solar panel. More atmosphere means more absorption and dispersing of sunlight (the atmosphere reflects, absorbs, and spreads out sunlight). So higher elevation, like mountains, helps. Less atmosphere. On a related note, the latitude is also very important. Far northern places don't get as much sun annually (Canada, Alaska). Finally cloud and moisture make a huge difference. If there are clouds or moisture in general, sunlight is blocked. This explains most of the east coast of the US, as well as why Nevada, a giant desert, has great insolation. It has a high elevation, and no moisture to make clouds or block sunlight.

The equivalent amount of sunlight hitting the earth at a high latitude spills out over a larger area. In other words, there amount of energy per area is lower. link

The equivalent amount of sunlight hitting the earth at a high latitude spills out over a larger area. In other words, there amount of energy per area is lower. link

CSP is easy. There are a bunch of mirrors, either flat or parabolic (to focus the light even more intensely), and they reflect light to a single point. It produces heat and and then that heat is used to make steam and drive a turbine, just like the basic thermal power plants we have discussed. The heat is typically stored in molten salt, cause it can store a whole lot of energy before it rises a degree in temperature (kind of like water). The heat from this molten salt is slowly released to make that steam for the thermal part.

CSP in action. Lots of light reflected to a single point that then gets very hot. link.

Given that some places on Earth receive upwards of 500W/m directly to the surface (assuming no clouds, no pollution, and daytime), a CSP plant that is 500m*500m could produce 125MW of power. Sounds great, right? 'Cept we know from basic thermodynamics that a thermal power plant that this thing is likely going to be 30% efficient. So something with a quarter of a square kilometer footprint might produce 40MW of power.

So why don't we use this? First, the depiction above is too rosy a picture. CSP is not all that efficient, because if you look at the picture above, you see that not all the area is used for gathering light. There are plenty of empty spaces. Moreover, the transfer of heat from the salt to water is not very efficient. Cause the high temperature and low temperature of the Carnot cycle are closer together (review the thermal power plant post for a review of Carnot efficiencies for all heat engines). Finally, this stuff is expensive. It is easily 2x as expensive as almost any other power technology (other than PV). It requires water to clean the mirrors and has other maintenance costs, the mirrors themselves are quite expensive, and the entire design is expensive. And, if you want to harness the power of the sun, there are better alternatives. Like PV.

As you can tell, I don't have a very high opinion of CSP. Why is that? Take a look at this guy again:

U.S. average levelized costs (2011 $/megawatthour) for plants entering service in 2018
Plant type Capacity factor (%) Levelized capital cost Fixed O&M Variable O&M (including fuel) Transmission investment Total system levelized cost
Dispatchable Technologies
Conventional Coal 85 65.7 4.1 29.2 1.2 100.1
Advanced Coal 85 84.4 6.8 30.7 1.2 123.0
Advanced Coal with CCS 85 88.4 8.8 37.2 1.2 135.5
Natural Gas-fired
Conventional Combined Cycle 87 15.8 1.7 48.4 1.2 67.1
Advanced Combined Cycle 87 17.4 2.0 45.0 1.2 65.6
Advanced CC with CCS 87 34.0 4.1 54.1 1.2 93.4
Conventional Combustion Turbine 30 44.2 2.7 80.0 3.4 130.3
Advanced Combustion Turbine 30 30.4 2.6 68.2 3.4 104.6
Advanced Nuclear 90 83.4 11.6 12.3 1.1 108.4
Geothermal 92 76.2 12.0 0.0 1.4 89.6
Biomass 83 53.2 14.3 42.3 1.2 111.0
Non-Dispatchable Technologies
Wind 34 70.3 13.1 0.0 3.2 86.6
Wind-Offshore 37 193.4 22.4 0.0 5.7 221.5
Solar PV1 25 130.4 9.9 0.0 4.0 144.3
Solar Thermal 20 214.2 41.4 0.0 5.9 261.5
Hydro2 52 78.1 4.1 6.1 2.0 90.3
Solar thermal is expensive. And the capacity factor is junk. There are places for it, but those are so few that it is not worth further exploring this technology.
That's it for now. Thanks for reading!
-Jason Munster

Hydro Power

Posted on by
1

Hydroelectric Power is pretty simple, yes? Build a dam, run water through turbines, get energy out. Turns out that it is a bit more complicated that that. But not by much, actually. So I am going to do a quick summary of how hydropower works, the environmental disaster that it can be (always with the tradeoffs, eh?). I was going to profile three major power plants: Hoover, Grand Coulee, and Three Gorges. But I ran out of space. Next week we will discuss pumped hydro to make the biggest batteries on the planet, and also these three dams in details.

DSC01732

Hey! Finally! A picture I took myself! I was at the three gorges dam as they were just completing it. Also, China has air pollution issues.

How does water power work? Put simply, water falls from a height and the energy of it is harnessed by spinning a turbine. More complicated, it is mass*gravity*height:

Schematic cross-section / block diagram of a hydropower plant. link.

Now we also need to round down for efficiency. Our thermal power plants are limited by carnot efficiency, yes? And even the best don't really break 50% efficiency all that easily. What would you guess the efficiency of a hydro plant turbine is, then?

That depends on the type of turbine used. It turns out that turbines are some of the most efficient parts of any generating facility. In short, expect these guys to have 90%+ efficiency, probably closer to 95%. Different styles are used depending on the height of water drop (water moving really fast from a half-kilometer drop will have very different dynamics than water moving from a 20m drop).

The general design of a hydropower turbine. Water flows through the blades and the generator is, in turn, spun quickly. link

So let's figure out how much water we need to move to make 100MWh of electricity from a 200m drop! Now 1 MWh is  , so 100MWh

of water needs to be moved. In other words, it takes 18 thousand kilotons of water movement to produce 100MWh. Or, looked at another way, 18,000 cubic meters of water. Still not following? It's about 8 olympic sized swimming pools worth of water. Dropping 200m. Or 1/8 a mile, for you Americans out there that don't play in Metric.

Hokay, enough maths for now. This sounds great, right? Why don't we build these things everywhere? When I take courses on how to fix the environment, there are always a majority of people that assume we can build more hydro power plants. But we can't in the US. Why not?

Well, it turns out that you need to have a large height drop to make this work. You also need a lot of water flowing into whatever reservoir is behind the dam, a ton of land behind that dam to flood, and you also need enough high terrain behind it so the water doesn't spill out everywhere. Moreover, you need a massive height difference between the upper reservoir and lower reservoir to make it work. Example: the Amazon river has a huge % of total world river flow, but we can't get electricity out of it, cause the elevation drop of it is so tiny. In short, there aren't a ton of places where where hydro works well. And imagine if a few people live there. Most aren't gonna take to kindly to their homes being put under tons of water. But you know where this can happen? China! They moved 1.3 million people to build Three Gorges. More on that later. Also, Africa has a ton of places that are building dams. Turns out that China is funding a lot of these. Cause China is starting to do humanitarian things internationally to make allies with the countries that will be the source of most world growth over the next 50 years. Upsides and downsides of a command economy, right?

Hokay, I got distracted there. Environmentalists don't like dams because they mess up fish migrations, destroy natural habitats, destroy the landscape in general, and in many countries, since hydro power is so cheap, heavy industry moves in next to them to get the cheap electricity. China is a great example (sorry I keep using you as an example, China, but I haven't read about other countries much). Along many rivers, supposedly clean hydro power goes in, only to be followed by very polluting industries. Rivers turn funny colors, the water is terrible to drink, and you can't see the sun through pollution on several days. This is getting better, cause China is making the middle-income transition, and citizens are demanding safer living environments.

I got distracted again. Other problems with dams? They tend to be on rivers. Rivers carry sediment. Much like wind can pick up grains of sand and throw then around, rivers do the exact same thing. They carry a lot of sand in them. But when they hit a damn, the river stops. The sediment load drops to the ground. After several decades, sufficient sand has dropped to clog the dam. Adding to this problem is that these sediments have a bunch of heavy metals that have been leached from the local environment. In short, a hydro dam leaves behind a mess that is quite hazardous. Cleaning it up can be difficult. Still, hydropower doesn't cause many deaths, unlike coal-fired power plants.

Focusing on that last point, what does hydro power not produce? CO2. Mercury. SO2. NOx. It produces none of the nasty things that coal fired power does (even gas-fired plants produce NOx and CO2). It tends to be very inexpensive. It is much prettier to look at a hydro plant than a coal, gas, or nuclear plant (Except on a polluted day in China, look at that picture again!).

We are running out of space in this article (I am calling them articles cause I am pretending they are articles on a web page instead of a blog post, cause I am pretentious). To summarize, hydro power is cleaner than other power supplies. It is cheaper than most. It does have its drawbacks, including displacing people and destroying land, but these are smaller than the drawbacks of coal and natural gas. It is also a nearly completely tapped resource in the US.

-Jason Munster

End-note: if you have a lot of interest in this sort of thing discussed here, I would highly suggest the book When A Billion Chinese People Jump by Jonathan Watts. It is an amazing book

.

Wind Power

Posted on by
Reply

I haven't posted anything in a while because I am teaching this semester (Earth Resources and the Environment), which has made me incredibly busy, and also I was playing a computer game for the past month. Anyways, some friends told me they actually read this, so I am gonna start up again.

Today we discuss how wind power works, how a wind turbine works, and limitations on placement of wind turbines.

Block diagram of a wind turbine. Wind spins the blades, which in turn goes through a transmission to spin a turbine to produce electricity.

Block diagram of a wind turbine. Wind spins the blades, which in turn goes through a transmission to spin a turbine to produce electricity.

Wind power harnesses the power of wind to turn a turbine. Unlike every other power plant we have discussed, this is not a thermal plant. How does wind even happen? As we all know, the sun shines more directly near the equator than it does the poles. And so the equator is heated more than the poles. The Earth doesn't like having one part heated and another not, so the major prevalent winds are the way the Earth redistributes this uneven heating from the equator to the poles. Smaller winds are local manifestations of this phenomenon. In short, wind power is extracting the energy deposited by the sun.

Next: the design

The mechanical design of a wind turbine. Link

The rotors of a wind turbine catch the wind, and thanks to Bernoulli's principle, the wind forces the turbine to spin. Think of it as creating an area of low pressure behind the blade, so the blade is getting sucked, or pulled, rather than pushed in a circle. These blades are attached to a hub, which spins with it. The entire box behind the turbines is called the Nacelle, and contains all the parts that produce power. The hub itself spins somewhat slowly, but thanks to a gearbox, the shaft that goes to the generator spins much more rapidly. The windvane senses the wind direction, and a motor beneath the hub rotates the entire turbine to face directly into the wind.

Wind power plants face four primary limitations. First, they don't work when wind isn't blowing. So you aren't placing these things in windless or low-wind locations. Second, depending on the design of the turbine, each has a maximum wind speed where it most efficiently extract energy. In fact, during high winds, they have to shut down to prevent damage. Third, there is a factor called the Betz limit that indicates that the most energy you can extract from wind is about 60%. In reality, the best might be 45% efficient. A corollary fourth limit is that you cannot place wind farms too closely, because they become far less efficient if you place them nearby. They literally suck out the power from the wind. In the end, availability of location is the most important

This photo from NOAA uses LIDAR to track the turbulence produced in the wake of wind turbines. It visually depicts the limitations of putting turbines in the same place. The turbulence behind the turbines can damage the props on the next turbine, requiring further replacement. It also reduces the efficacy of the next turbine. link to NOAA.

Ultimately, the largest problem is where to site wind farms. You can't put them in places without wind, or you spend a ton of money on them and they don't return the payment.

This map indicates regions and their use for wind farms. It shows that many areas are not great for wind farms. Click the link for a more detailed image.

There are two closely linked issues associated with wind power. In most places, wind does not always blow. When the wind is not blowing, power cannot be extracted. This is called intermittency. It means that wind power cannot provide baseload power. In some places, like California, the intermittency is dealt with by power up peaking gas-powered power plants. In other places, the intermittency is seen as an insurmountable issue (California surmounted it. Those other places are foolish.) Other methods of dealing with it are compressed air storage (more on that later), batteries, and pumped hydro (more on that later).

Another important feature of wind turbines is size. To get more power from a single turbine and reap larger economies of scale, you build a taller turbine. Also, taller turbines reach farther up into the part of sky where wind it a bit more constant. But those huge turbines, that can produce up to 5MW each (recall a larger power plant is 1000MW), are relatively new. We are not sure how long they last in the wild. Maybe 50 years (like a normal power plant) or maybe 20. This is important, because per MW, wind power used more resources to build than almost anything else.

Now, offshore wind is a different beast entirely.

Offshore wind turbines become progressively more expensive as you move to deeper waters.

Offshore wind turbines become progressively more expensive as you move to deeper waters.

These things need to be moored to the ocean floor, or have very expensive floats. It can increase production cost by a factor of three. Ameliorating this fact is that wind is often more consistent offshore. But these things face waves, corrosive ocean water, severe storms, etc., and need to be built very strong, increasing costs. Moreover, they need a way to connect them together, and then very powerful regional lines to transfer the power to mainland. Expensive. If you remember my post comparing the cost of nuclear power to other types, offshore wind is mad expensive.

Another interesting point about wind power (and solar): they produce DC power. This is direct current, like a battery. The power we get from the wall is AC power. It alternates. Anything with a motor likes AC power a lot. Many electronics prefer DC power, hence needing AC adapters for all your electronics. Batteries use DC. Another fun fact about AC vs DC? Electricity make your muscles constrict. If you grab something with AC, since it alternates you let go. You grab something with DC, like a car battery or a taser while being arrested, that stuff causes constriction and you can't let go. Point is, stay away from DC electricity.

Back to the point: Somewhere in the process, whether at the turbine or at a collection station, this electricity needs to be converted to AC to use on the electrical grid. More expenses. In short, offshore wind is incredibly expensive, and only for countries that are afraid of nuclear power. In a later article, I hope to compare the resource costs per MW of constructing each of these types of power plants.

Thanks for reading again!

-jason munster

 

Nuclear Reactors Final

Posted on by
1

I am getting bored of this topic, and I want to get to wind-solar-hydro so I can finish up with the energy technology stuff and write varied stuff. So I am going to compress it a lot. If anyone wants to see it expanded, let me know and I will take care of it later.

This post is about breeder reactors, thorium reactors, preventing nuclear proliferation, how the electricity costs stack up to other power plants, and why nuclear power is so expensive.

Nuclear power is expensive because the up-front costs are massive. The cleanest and most efficient coal fired power plants might cost a billion dollars to build. It might take 5 years to build it. Nuclear power plants seem to cost about $8 billion to build with all the safety features they use to prevent nuclear meltdowns (seriously, the new tech is very safe, and it shows in the cost). And they seem to take 8-15 years to build, depending on how much Greenpeace or pretty much every other group tries to stop construction via litigation. In other words, they take out an $8B loan and accrue interest for 8-15 years before they can start paying it back. Stuff costs a lot. Why do it? Cause nuclear waste can be contained, unlike the NOx and CO2 from natural gas and coal plants. Also, South Korea thinks it can build a nuclear plant a nuclear power plant in a short amount of time for only $5 billion. United Arab Emirates decided this was a good idea, and is buying four South Korean nuclear reactors to desalinate water.

Schematic of the South Korean nuclear power plant to be built in the United Arab Emirates, from link above.

The US Energy Administration Administration agrees that nuclear power is now less expensive than it used to be. I have ripped a table straight off their web page that shows it (see, I really am getting lazy in this post).

Table 1. Estimated levelized cost of new generation resources, 2018 
U.S. average levelized costs (2011 $/megawatthour) for plants entering service in 2018
Plant type Capacity factor (%) Levelized capital cost Fixed O&M Variable O&M (including fuel) Transmission investment Total system levelized cost
Dispatchable Technologies
Conventional Coal 85 65.7 4.1 29.2 1.2 100.1
Advanced Coal 85 84.4 6.8 30.7 1.2 123.0
Advanced Coal with CCS 85 88.4 8.8 37.2 1.2 135.5
Natural Gas-fired
Conventional Combined Cycle 87 15.8 1.7 48.4 1.2 67.1
Advanced Combined Cycle 87 17.4 2.0 45.0 1.2 65.6
Advanced CC with CCS 87 34.0 4.1 54.1 1.2 93.4
Conventional Combustion Turbine 30 44.2 2.7 80.0 3.4 130.3
Advanced Combustion Turbine 30 30.4 2.6 68.2 3.4 104.6
Advanced Nuclear 90 83.4 11.6 12.3 1.1 108.4
Geothermal 92 76.2 12.0 0.0 1.4 89.6
Biomass 83 53.2 14.3 42.3 1.2 111.0
Non-Dispatchable Technologies
Wind 34 70.3 13.1 0.0 3.2 86.6
Wind-Offshore 37 193.4 22.4 0.0 5.7 221.5
Solar PV1 25 130.4 9.9 0.0 4.0 144.3
Solar Thermal 20 214.2 41.4 0.0 5.9 261.5
Hydro2 52 78.1 4.1 6.1 2.0 90.3

 

Note that last column is $ per megawatt hour. It is the bottom line cost of producing power from that plant. First, what is dispatchable vs non-dispatchable? Dispatchable means you get it whenever you want it. You can ramp it up or down however you please. Non-dispatchable means that you depend on external factors, like the fickle winds of.. well.. winds?

Tangent! Winds are really just redistribution of energy from the equator to the poles. The sun shines more at the equator, heating it up, and then energy likes to move from areas of high energy to areas of low energy, so it does it using wind. And sometimes hurricanes. So really, wind power is just really inefficient solar power. You know what else is really inefficient (and slow) solar power? Hydrocarbons and coal. Cause they are really just buried plant and algae matter and such. That is tens to hundreds of millions of years old. So, coal and oil are really just really old, slow, and dirty solar power. Tangent done!

Tangent picture? This shows how the equator heats more than the rest of the earth. These extra heat has to redistribute to be more even. Hurricanes start near the equator cause of the heat there, then move away from it. from: http://oceanworld.tamu.edu/resources/oceanography-book/oceansandclimate.htm

Nuclear power is almost as cheap as coal power, and cheaper than clean coal (note, clean coal still produces a ton of CO and NO)! What gives? How is nuclear so inexpensive? Well, we haven't built a nuclear power plant in the US in years. We don't know what it will actually cost. Those are just estimates. Also, people are quite scared of nuclear power. The cost of building nuclear power rises when you have environmentalists and NIMBY folks suing the pants off nuclear power developers. But let's make one thing clear: if the new generation of nuclear power plants are as inexpensive as they are supposed to be, the power is less expensive that all other power plants other than natural gas (note: the US does not have capacity to build more hydro power), and less expensive than even that if you account for NO produced by and methane leaks associated with natural gas power (methane production and transport will always have leaks, and it is 23x as powerful a greenhouse agent as CO2).

Let's look at a few more things on the chart above. Remember when I said natural gas got cheap? Look at how cheap it is to produce power from natural gas on the chart above. Think anyone is building nuclear, solar, or offshore wind when you can build and deploy reliable natural gas power? Somehow, the answer to this is yes. Yes, people are building all these things, despite being expensive. Which is kind of cool.

Before moving away from costs, look at the variable costs. The variable costs are high for everything except renewables and nuclear. Why is this? Cause renewables and nuclear don't really use fuel. Yes, a nuclear plant uses fuel, but it costs almost nothing relative to the labor and the capital costs. All the cost of these is upfront CAPEX (capital expense), and then you get free power.

Finally, lets take a really close look at the variable costs. This link is pretty sweet for those of you interested. It contains variable costs for each power source. You can see that fuel is the bulk of cost of fossil steam plants, but less than a quarter of the total cost of nuclear, and nuclear fuel is 1/4 the price per energy unit than even dirt cheap natural gas.

Enough about costs! Onto breeder reactors!

In the first post I mentioned that one part of nuclear reactions is to give off neutrons. Sometimes instead of a neutron splitting an atom, the atom absorbs it. U-235 is the uranium we use in nuclear reactors. U-238 doesn't produce as much heat, cause it doesn't like to decay as fast, so it isn't viable nuclear fuel. Or is it?! U-238 is like a catcher in baseball. Except it catches neutrons. And then it incorporates them into its nucleus to become U-239. In other words, it really isn't like a catcher in baseball.

The breeder reaction series. From: http://nuclearpowertraining.tpub.com/h1019v1/css/h1019v1_76.htm

What's special about U-239? It decays rapidly through a special type of decay to become neptunium-239 and eventually plutonium 239! This process can extract up to 100x the energy from nuclear fuel. You know what's magic about that? Less nuclear waste produced. Also, you produce a ton of nuclear fuel this way. You can also use thorium-232, which then becomes uranium-233 after absorbing a neutron, which can in turn be used for nuclear fuel. Thorium is very cheap and very abundant. So the plutonium and uranium that is magically created through awesomely manipulating nuclear forces is then used in nuclear thermal reactors to produce power.

Nuclear proliferation!

Having a nuclear power plant does not mean you can make nuclear bombs. Nuclear bombs required U-235 enriched to a very high level. What exactly is enrichment? Natural uranium is less than a few percent U-235, the rest is U-238. The uranium comes as a solid, and is processed by making it dance with a bunch of flourine. UF is produced, which is gasified uranium. The U-238 is slightly heavier than U-235, so it very very slowly settles to the "bottom" if you spin it very fast in centrifuges. Once you have enriched it to somewhere between 5 and 8%, U-235, it is good to go into a reactor and make energy. To make a bomb, you have to enrich it to around 90%. Enriching it further gets exponentionally more difficult. Getting from 50% to 70% is much more difficult than getting it from 10% to 50%. So making bombs is hard.

What about plutonium? Seems like any fool can make plutonium. And in fact, they can! All you have to do it get some U-235, wrap it in U-238, and you have make a breeder reactor in your back yard! This seriously happened. Someone made a breeder reactor in their garage at 17. And this wasn't one of those kids that comes from a brilliant family with a ton of money that goes to work in a world famous lab and 'discovers' a new technique under the watchful eye of one of the most brilliant researchers in the world. This was your every day kid who was just really interested in something.

Except that building a nuclear weapon from plutonium is even more difficult than from uranium. Cause when you make the plutonium, you always get a large amount of another plutonium isotope. The other isotope loves to go critical much earlier than Pu-239. Remember what happens to a potentially critical nuclear reaction when the fuel gets split up? No? Remember what happened to Chernobyl when a small gas explosion spread the core out everywhere? It completely shuts down the critical reaction. In other words, plutonium loves to accidentally blow up to early and just spread itself around without going critical. Not much of a weapon there. How do we have plutonium bombs then? Really smart people made special triggering mechanisms to make this happen. How do they do this? I dunno. If I did, I wouldn't be out in public writing a blog, I'd be doing super secret awesome research somewhere.

Turns out that only the US and a handful of other countries have figured this one out. So while any old fool can make a breeder reactor, the combined science of most nations is not good enough to figure out how to do it.

One last thing. If nuclear power is so difficult, how did so many countries get it? Well, US and Russia developed it. The US gave it to China at some point to balance some power issues with the Soviet Union. The US gave it to several other allies as well. The Soviet union gave it out some, too. China then distributed to crazies like North Korea years later, and Pakistan and India were given it through similar pathways. In other words, it is still pretty difficult to develop.

Hey, I just covered 4 whole things in one post, and managed to get more terrible jokes in. Awesome.

Aww darn, I forgot to include the small amount of original research I did on this topic. Next article

Thanks for reading

-Jason

Natural Gas Power Plants

Posted on by
5

Excellent news! No math today. Bad news! There are some confusing terms here. Every thermal power plant drives a turbine to produce power. There is a special type of turbine called a gas turbine that directly burns natural gas inside of it to produce power. There are a few places where I use gas turbine and turbine in the same sentence. Sorry about that.

Natural gas fired power plants come in two primary flavors: standard thermal plants, and fancy jet turbines. The former has the same internals as a coal power plant and can provide baseload power, the latter is for peak power. Both produce less pollution than coal, simply because natural gas is cleaner than coal and produces more energy per unit CO2 emitted. Natural gas plants contribute to GHG emissions and PM2.5 (PM 2.5 can form from emissions of NOx, which occurs from any combustion). With hydrofracking causing a glut in natural gas in the US, producing power via gas is cost-competitive with coal in the US, and recently has been replacing coal to produce electricity. This has caused the US to decrease its annual CO2 emissions by nearly 10%.

Conceptual drawing of a natural gas turbine

Let’s get down into the meat of how these plants work. We have discussed how standard thermal plants work in a prior post. The jet turbine power plant is pretty simple. It is very similar to the turbines found on airplanes. The fuel is injected and burnt. It expands and drives a turbine to generate electricity. These systems get incredibly hot. They have thermal efficiencies approaching 30%. Unlike thermal plants, these gas turbines can fully ramp up power in about 20 minutes. These turbines also need to shut down frequently for repairs. Continuous operation for days at a time is not possible, or they will become very damaged. For these reasons, these turbines are typically used only for peak power production. One final difference is that a gas turbine has more like a 20 year life time, whereas a thermal power plant has a 50 year lifetime.

A natural gas turbine via DOE

Gas turbines can be combined with standard thermal plants often use what is called a combined cycle format. Before getting into that, let’s briefly revisit how a normal thermal plant has higher efficiencies. In a normal thermal power plant, the steam coming out of the first turbine has lost some heat and pressure. It is then more or less directed to a subsequent turbines that are designed to be efficient at lower temperatures, and even with wet steam. This series of turbines extracts much more heat, and thus much more efficiency, than a single-cycle turbine.

This combined cycle power plant has two sections: the thermal section and the gas turbine section. Typically the thermal section stays on. When peak electricity production is needed, the gas can go into the gas turbine instead of the thermal section. Our gas turbines discussed above produce temperatures in excess of 900 C. This waste heat can then be shunted to boil water in a more traditional thermal plant. Combining these processes together can result in a 60% thermally efficient plant. This is very efficient. If you recall from our previous article, thermal plants take a long time to ramp up power production. These combined cycle plants require the thermal section to almost always be on. The thermal section of the plant will provide baseload power, and the gas turbine part will spin up to provide peak power. These combined cycle plants are incredible versatile. They make money every day by operating in baseload configuration, and then make extra money as soon as demand requires more power.

This brings up a quick question. The thermal section of the plant is not as efficient as using both the gas turbine and the thermal section together. In other words, burning the natural gas in the gas turbine first extracts more energy from it. Why do these gas turbines not always run, then? Well, as we mentioned, the gas turbines are more fragile. They can’t always run, and they need frequent repairs. The economics of it works out so that even though they extract more energy from the gas, it is only worthwhile when electricity prices are high.

Conceptual image of a combined cycle natural gas power plant

Conceptual image of a combined cycle natural gas power plant

What are the downsides of these NG plants? They produce less pollution than coal plants by a good margin. They require less mitigation of pollutants, so they are much easier to build than coal plants, and are built more rapidly at a lower expense. They produce less GHG than coal plants, both because the combined cycle system is more efficient and because NG is a more CO2 efficient fuel than coal. They produce more pollutants than nuclear power plants or wind turbines or solar power, however. And outside of the US, the fuel is much more expensive than coal.

Let’s discuss that last point for a second. The low NG price in the US makes this very affordable. Other countries that care more about clean air than the US are not as concerned about the higher price of natural gas vs. coal electricity. They care more mitigating adverse health effects caused by coal power plant emissions. Japan is a great example. The largest importer of natural gas in the world, Japan is set to import a lot more of it. After the Fukushima Daiichi nuclear plant meltdown (future post on this and Chernobyl!), Japan is set to phase out nuclear power. They don’t want to build coal power plants, because they are dirty. They intend to import gas (they are even considering building an undersea pipeline from Russia to accomplish this!) and produce NG electricity to replace their retiring nuclear plants.

The technical section

The major emissions of these power plants are CO2, methane, and NOx. On a 100 year timescale, each molecule of methane and NOx is 21 and 310 (respectively) times more powerful than CO2. This scaling of potency is called the Greenhouse Warming Potential (GWP) of a compound. Methane is leaked from incomplete combustion and also from line leaks and delivery leaks, NOx is a byproduct of burning things in a nitrogen based atmosphere. Another way to put it: since our atmosphere is 78% nitrogen, burning anything, even a campfire, will produce NOx. In the graph below, excerpted from an NREL document , we see that while CO2 is the primary emission, multiplying these emissions by the GWP shows that methane is a significant % of total warming potential.

Nat Gas Emissions GWP

Relative to the other natural gas emissions, NOx is not important to greenhouse warming. Why would they want to control it? Because it is a precursor to PM2.5. The stuff that causes minor health issues, like heart attacks and death. NOx is mitigated by spraying ammonia (NH3) into the flu gas (flu gas is a fancy way of saying the stuff that comes out of the smokestack). The NH3 mixes with NOx to produce H2O and nitrogen. Some NOx is still is emitted after this scrubbing, and still leads to PM2.5, causing local pollution. But in much less quantity than a coal fired plant.

In review, natural gas power plants produce less pollution than coal fired power plants. There are some pretty neat technologies in these natural gas power systems. In the US, the electricity is nearly cost-competitive with coal. Other countries choose to produce power via natural gas because it is cleaner than coal, despite that it is 5x as expensive in those countries.

That’s all! Thanks for reading!

Natural Gas Price Drop, and Natural Gas Electricity!

Posted on by
5

Today’s post is about the shift in US primary energy use from coal to natural gas (AKA methane). Hydrofracking, the hydraulic fracturing of rock to subsequently produce natural gas, is a new favorite pass-time in the US. Natural gas prices used to track oil prices per unit of heat. They now roughly track coal prices per unit heat. As a result, it is now economical to produce electricity from methane rather than coal. As we discussed before, coal produces a whole bunch of dirty pollution, and methane does not. All good, right?

This is very important for both CO2 emissions reduction and for reduction of other pollutants. The math section is chemistry heavy. If you are going to skip a math section, this is the one.

The highest grades of coal have composition , and lower grade coal is All coal is tainted with mercury and other heavy metals. Lower quality coal has more pollutants per unit heat, and this produces more pollution for the same amount of electricity. From the last post, we learned burning coal has quite the array of negative health effects.

The chemical composition of natural gas is CH4. It contains almost no other pollutants. It doesn’t produce particulate matter. When it is burned to produce electricity, we do not have the direct adverse health effects associated with coal. What about the CO2 emissions? These are reduced. Cause of math.

The Math of Chemistry! This is bond enthalpy chemistry. (Feel free to skip ahead if you don’t like the math parts)

Let’s look more closely at the composition of these two things. When any substance burns, it produces heat by converting everything to H2O and CO2. The resulting H2O and CO2 have lower internal energy than the coal or methane that formed them. The difference in energy from the coal to the H2O and CO2 has to be given off as heat.

Before the math: First, what is a mol? It is short for mole. Pretty bad abbreviation, eh? A mol is the number of molecules it takes to make one g times the molecular weight of the molecule. It is molecules. This is confusing. Lets use examples to make it less confusing. Hydrogen has a molecular weight of 1. A single mole of it weighs 1 gram. CH4 has a weight of 16 (12 for the carbon, 4 for each hydrogen). A mole of it weighs 16g. CO2 has a molecular weight of 44, and a mol of it is 44g. Done.

The amount of energy used to hold atoms together to make molecules is the bond energy. Chemical reactions happen, chemical compositions are changed. If the overall energy of bonds are lower after the change, heat has to be released. This creates fire.
Bond energies: C-C bonds (aromatic, the ring-type found in coal) have 519 KJ/mol. C-H is 410. H-O is 460. C=O (double bond) is 799. O=O are 494 KJ/mol.

We simplify coal as aromatic bond chains of 4(-CH-) (this is generous in terms of calculating CO2 produced per unit coal, as all my prior calculations have been) (I stole this clever approach from my advisor, Jim Anderson, to simplify things). CH4 is pretty easy as CH4.

We can write these as:


The molecular weight of our coal is 4*(12+1) or 52. Methane: 12*1+1*4 = 16

Coal: We break four C=C aromatic bonds (only four cause we would be double counting if we did each side of (-CH-), four C-H bonds, and 5 O=O bonds. We form 8 C=O and 4 H-O bonds.
Methane: 4 C-H bonds are broken, as well as 2 O=O bonds (the two O=O bonds are from converting the 4 H bonds into H2O). 2 C=O, and 4 H-O bonds are formed.

Coal: 

Methane: 

Math done!

The changing landscape of energy production based on cheap NG

Back in the day (pre-2010 or so) natural gas was much more expensive per unit heat than coal was. If you were going to burn something to produce electricity, coal was much cheaper and so produced cheaper electricity. The fact that it was pretty dirty didn’t matter as much. Then hydrofracking happened. Natural gas got cheap. Its price once roughly tracked with but below oil. Now it tracks with coal. This makes it a viable alternative to coal in power production. This fundamentally alters the primary energy landscape in the US. Once more data is available, we will revisit this.

Hydrocarbon Prices 86-12

Historic hydrocarbon prices per million BTU. Natural gas roughly tracked with oil, until hydrofracking made a glut in the market

Hydrocarbon Prices 07-12

Zooming in on the recent few years, the divergence of oil and gas and convergence of coal and gas becomes evident

 

Let’s discuss policy and environmental implications. They are pretty huge.

The math shows that in energy per unit CO2 produced, methane is about 60% more efficient than coal. This means that if we have to burn either methane or coal, and we seek to limit CO2 production, methane is the natural choice. Historically pricing prevented this from happening.

Natural gas is now only slightly more expensive per unit heat than coal. It makes sense to make electricity from natural gas, cause it produces far less pollution per unit heat. Since 2008, the US has reduced the amount of CO2 is produces for the first time in a long time. The reduction of CO2 produced by the US is partially based on this change in natural gas price. We now produce more electricity from methane than we used to. Since methane is more efficient at producing energy per unit CO2 produced, we produce less CO2 as a country.

Many staunch environmentalists argue this is a bad thing. Natural gas is still a hydrocarbon and still produces greenhouse gases. It kills far fewer people directly than coal does. The deaths that came as a result of coal might have pushed us towards a much greener economy. Methane is the lesser of two evils. It produces energy like coal. It produces CO2. It is still a finite resource. It is much better than coal.

Coal: The great of two evils between coal and methane. A picture of anthracite coal to break up the monotony of a text well. From Wikipedia.

Barring legislation to prevent hydrofracking, this trend of cheap NG will continue for a long time in the US. We have massive reserves of natural gas in our shale, and hydrofracking can get it out. This is not limited to the US, but there are only a few countries in the world that will be able to do this.

Before closing, we have one last thing. Many of you looked at the graphs of natural gas prices, saw that they were historically not much higher than coal for many years, and wondered why we didn't have natural gas electricity plants then. There are two answers. The first is that we did. It is why we have so many right now that can instantly go online. The second answer is that the EPA really only started getting strict on coal plants in 2004. The emissions from coal plants add many costs that go beyond the price of coal. Natural gas is pretty clean, so it doesn't face these costs, making it more competitive with coal.

Summary: Hydrofracking in the US has changed the natural gas price to be much lower and has made it a basic energy feedstock rather than a premium one. The US has natural gas power plant capacity, and has started shifting to electricity from natural gas. These power plants produce less harmful emissions as a result. CO2 emissions are reduced for the same amount of electricity. Harmful pollutants that cause heart attacks, asthma, and early death are also reduced. This is pretty huge.

Thanks for reading again, and sorry for the huge length

Jason Munster

* Will pointed out that I had Avogadro's # off by a factor of 10. Fixed

Coal Power Plants

Posted on by
8

Expect a lot of updates on this post. Thanks to Buck Farmer, who told me that I needed to learn LaTeX to make this prettier.

COAL FIRED POWER PLANTS

A coal fired power plant.

Coal fired power: it provides a lot of our energy, is less expensive than petroleum by far, makes cheap electricity, and causes all sorts of health ailments and pollution. Coal power plants produce particulate matter, sulfur pollution, and other pollution, resulting in deleterious health effects.

Coal fired power plants provide a huge chunk of the world’s energy. It provided almost 50% of US electricity in 2009. Today, the math section is a review of how much energy is in coal, how much coal we need to operate a single power plant, and how much coal we need to operate all the coal fired power plants in the US and China.

The topic of coal fired power plants used to be simple. Thanks to fracking, natural gas prices are now approaching coal prices. This post is written with 2009 information. It is largely relevant today, but this landscape may change in a few years as more power is produced via natural gas in the US. Suffice it to say that natural gas has become considerably cheaper in the US:

Oil be getting expensive, NG be getting cheap!

The price ratio per unit of heat in natural gas prices compared to oil in the US. The ratio used to be around 1. Now you get a lot more heat out of natural gas per dollar, thanks to the abundance from hydrofracking.

We will discuss this more in a future post.

Maths! Warning, this is pretty shocking!

High grade coal has an energy density of about 32MJ/kg (For our math, lets assume the best coal is used everywhere. In reality it is about 24, so my world with coal is 33% nicer than the real world). Compare this to a gallon of gasoline, from my very first post, at 120MJ. A gallon of gas weighs about 3kg, with an energy density of 40MJ/kg, slightly higher than coal, or nearly twice as high an energy density of a majority of coal.

A watt is a joule per second. A megawatt is a megajoule per second. A coal fired power plant can produce 1GW per second, which would be a gigajoule expended per second. But remember from our thermal efficiency post, these powerplants are not all that efficient! Let’s say a coal one averages 35% for thermal efficiency.

 

Coal_eqn1

31.25kg of coal used per second to produce 1GW of heat! But remember from the thermal plants post, thermal plants tend to only be about 35-40% efficient!

Coal_eqn2

A 1000MW coal fired power plant burns nearly 200 lbs of coal PER SECOND to provide power. That is my weight in coal for every second.

Let’s continue blowing your mind. There are 86,400 seconds in a day, yes? (yes).

Coal_eqn3

2.8 megatons of coal per year for a single coal-fired powerplant! Okay, 200 lbs. per second leaves a bigger impression. Here is another way to look at it. How much coal does it take to keep a 100W lightbulb lit for a year?

Coal_eqn4

 

280kg! Per year! This is about 2 lbs. of coal per day to power a 100W lightbulb. “But Jason,” you say, “We don’t get all our electricity from coal!” This is also true. We get almost ½ of our electricity from coal. But say ½ is from coal, the other ½ is from hydro power. If you turn off your light, we get back the ½ from coal, saving a pound of coal from being burnt. What about the ½ from hydro? Welp, that can go and power another light. The ½ of the light that would have been powered by coal. So yeah, even though ½ of our power comes from coal, the opportunity cost of using that light is the equivalent of getting all of it from coal.

Let me repeat that. If you have a 100W incandescent bulb, and you leave it on for a day, you just burnt 2 lbs. of coal. Good job. If turning off your lights to save on electricity is not enough to get you to shut em off, just picture that much coal burning to keep that light on. Your laptop computer uses about 2-3 pounds if it runs the entire day. Your TV, if left on, will burn more like 10 lbs. of coal a  day.

One last part. China provided 500GW of coal power provided in 2012. The US provided 200GW in 2009 (note: thanks to shale gas and fracking and using the gas to produce electricity, the amount provided by coal has dropped!). 200GW of coal power in the US means 600 megatons of coal per year in the US using our numbers, and 1500 megatons of coal in China. And remember, my numbers are rosier than the real world.

Turn off your lights.

The qualitative stuff!

Emissions from coal-fired power plants, and health trade-offs

Smog. Not fun to breath.

Burning coal emits sulfur (which can be mitigated through special filters, but often is not), CO2, NO and NO2, mercury (also can be mitigated, usually is in the US), other metals, and fine particles (called PM2.5 and PM10 for Particulate Matter of radius 2.5 microns and less, and radius 10 microns or less, respectively). Sulfur causes irritation and lung problems, smog, and acid rain. CO2 and NOx contribute to global warming, NOx also to smog. Mercury emissions are the reason we can no longer eat fish every day. PM2.5 causes cancer, asthma, and severe lung problems. Coal power plant emissions can lead to ozone at ground level, which causes smog and serious respiration issues.

Later we will discuss black carbon vs. sulfur here, since they have opposite effects on regional warming vs. cooling. Today we discuss the health effects of a coal fired power plant.

In the US, where coal-fired power is relatively clean, it causes tens of thousands of deaths per year. It causes hundreds of thousands of heart attacks, asthma attacks, ER visits, and hospital admissions per year. A compilation of EPA and heavily peer-reviewed articles estimates 13,200 deaths and 20,000 heart attacks were caused by coal-fired power plants in 2010. In 2004, before the EPA starting getting aggressive, these numbers looked like 24,000 deaths per year in the US.  The rate of asthma is drastically increased in the area of coal fired power plants. The US even then had relatively stringent requirements on power plants. When you factor in the population and lax controls of countries like China and India, I have heard estimates of premature deaths caused globally by coal fired power to be in the millions, and even larger numbers for asthma.These adverse effects are much more likely to be caused by the wealthy regions that use more electricity per capita than the poor regions that host the power plants and the adverse effects. In other words, the electricity used by large mansions in wealthy neighborhoods often comes from powerplants placed near poor neighborhoods.

The coal used by the US and China directly contribute to global warming on a huge scale. In a future post that describes the composition of the atmosphere and how greenhouse gases work, we’ll get directly into those numbers.

Satellite image of pollution in China. From: http://earthobservatory.nasa.gov/IOTD/view.php?id=76935

Beijing's got a bit of a particulates in the air in the winter. I was in an airplane in Beijing on this day. They announced "The fog is too thick to take off." Except it was below freezing and the air was dessicated, making fog unlikely.
A more clear day near Beijing

 

Let’s be pragmatic for a second.What’s worse than deaths and heart attacks caused by coal-fired power? Not having electricity to power your hospitals and other vital services. If you are a poor or developing country that can’t afford fancy nuclear or renewable electricity, and you don’t have access to hydro power, putting up a coal plant to power cities enough for basic services is a no-brainer.  Wealthier countries have a choice: suffer the pollution, or spend more money and avoid it by building more expensive yet cleaner electricity sources. The US as a whole can easily afford to do this. Pakistan and India? Not so much.

Take-aways: Turn your lights off, they require a lot of coal. Avoid breathing or raising children near coal-fired reactors.

-Jason Munster