# Solar 2

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.

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.

-Jason Munster

# Some dams

Dams. They provide clean electricity. Sometimes they cause earthquakes that kills thousands of people.

As I mentioned before, hydro is a tapped resource in all places except Asia, Africa, and South America. In other words, it works great in developing countries. It is not an option for developed countries.

Despite that I provide references where I can, this post is pretty unprofessional. Also, since I didn't post last week, this will be a mid-week post. It is as close as I will get to a blog rather than a collection of science-based articles.

Hydro Plants Causing Earthquakes

Three gorges dam represents the domination of Man over Environment like nothing else on the planet.

Remember that earthquake in Sichuan earthquake in 2008 that killed 60,000 people? This earthquake was likely caused by the three gorges dam.

three gorges dam! "I cause Earthquakes" says Three Gorges.

How do earthquakes happen in general? Stress builds up in the Earth, usually from shifting tectonic plates. Loading a massive amount of water in an area increases the stress by huge amounts. Dams load billions of tons of water into an area. Dams are not the only way to do load the environment to prime it for an earthquake. Downtowns of cities with skyscrapers also do a pretty good job of it. But dams are way better at it.

Pros and Cons of a hydro plant

Let's look at more information on Three Gorges. I've recommended y'all read When A Billion Chinese People Jump. In that book, we find that the past several presidents of China have been hydrological engineers. The most recent one didn't show up at the opening of Three Gorges because, because in some ways, it is very controversial. It has very strong benefits and issues. Despite negative effects, it produces 22.5GW of electricity. In other words, it replaces 22 very large coal fired power plants. And in China, that means 50 years of 22 unfiltered powerplants not belching harmful pollutants into the atmosphere. In case you haven't heard, China in general and Beijing have some of the worst air pollution in the world. Before you start judging, remember all those jobs that are being outsourced to places like China? This is the result of that. We are exporting our trash and our pollution to poor countries, where environmental regulations are more lax. Getting back to the point, those 22 coal fired power plants that are being replaced would probably have caused more long-term deaths than the earthquake. Moreover, China is a very dry country. Like most dry countries, it is prone to flooding without controls. Containing the river behind the three gorges prevents the downstream from ever being flooded again. So they saves the homes and such of millions of people, but had to move millions behind the dam, and it also flooded historic areas. How's that for controversial? Serious positive and negative implications. No dam embodies the pros and cons of building a dam more than Three Gorges.

Other uses of dams

It turns out that producing electricity is only a small part of what dams do. Many are used for irrigation, for flood control, for reservoirs, and to protect the environment. We are mostly an energy blog, so we don't give a damn about all that stuff. Except one major point: electricity is less than 10% of the economic benefit from dams. A huge amount is in flood control, irrigation, and recreation.

FEMA says these are the benefits of dams. Notice that hydroelectric is tiny.

Hoover Dam

Hoover "meh" Dam

When you think of a huge American dam, you think Hoover. This is silly. It is a 2.5GW dam. It is 10% the size of Three Gorges. It is like comparing Bangor ME, to Boston, MA. One is just tiny. Why do people care about Hoover? I dunno. Maybe after spending too much time in Vegas they decide they want to see something natural? Hoover dam is tiny. It only replaces 2 or so coal plants. Hoover Dam, you are not worth wasting words on.

Grand Coulee Dam

Grand Cooulee Dam is one of the largest dams in the world. Notice the size of the houses for scale.

You know which dam is an American dam? Coulee Dam. This dam produces 7GW. Fully 3x of Hoover, and near 1/3 of Three Gorges. It is also in Washington state, which, compared to Nevada, is better in every way except for gambling and prostitution. Which shouldn't be family activities. Why don't more people visit Grand Coulee instead of Hoover? This is not a rhetorical question. Someone please tell me.

Grand Coulee has this other sweet feature I already discussed. They have pumped hydro storage. In other words, they pump from the area behind the dam to another dam that is far higher up. This is a great way to make a giant battery. It recovers about 60% of the electricity that is put into it.

Interesting note: While scouting around the interwebs looking for information on the pumped hydro storage at Grand Coulee (it is really difficult to find), I stumbled across a blog that already has written posts that are way more in-depth maths about many of the things that I write about. If you are one of my sciencier readers, you might want to check his page out. I will poke around there some and give you more info on it later.

Dams produce clean power. They are environmentally friendly! Or not.

We have discussed how dams get backed up and leave heavy metals in the sediment, and more or less create environmental issues. And how they block fish from swimming upstream. I wanted to touch on one thing again. In China, many places that built clean hydro plants attracted industry, cause industry loves inexpensive power. And hydro power is amongst the cheapest. So the skies and waters became quickly polluted with industrial wastes. Like, red polluted.

Image from the link above. It looks like the Earth is bleeding. I don't think this is healthy. And all my Boston readers are afraid of the Charles.

Outsourcing manufacturing seems even a bit crappier than it used to, doesn't it? Sure, we lose jobs, but they lose lives and the environment.

Alright, that's about it for my quite unprofessional rant. Thanks for reading.

-Jason Munster

# Power Grid

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.

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 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 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. 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 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

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.

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

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# Wind Power

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.

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.

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.

-jason munster

# Oil Refining

Today's post is about something important that I entirely took for granted that most people don't know about. Oil refining.

Oil refinery, pic from eia.

For those five of you that read last week's post and wondered where I got all that from, a lot of that information came from books on geopolitics and a course called Geopolitics of energy. More or less, geopolitics goes far beyond your government course to include geographic/geologic/demographic constraints.

Anyways. Refining. No equations here. Sorry if you like those.

Basically, refineries buy crude oil and distill it to usable products based on the fact that crude oil is a mix of a bunch of different products. Your typical barrel of low-grade crude from Venezuela will have 40% of a substance that can be only used as road tar. This is called residuum. Chemically speaking, it is chains of long, heavy molecules, not useful for much. More chemically speaking, the Van Der Waal's forces, which are based on molecular mass, attract these to each other, so they are sticky and have high boiling points.

Distillation temperatures (and a rock block diagram of a refining tower) of different crude oil components. from EIA.gov

How do these get separated? By their different boiling points! Refineries are towers. Everything at the bottom is very hot, so just about everything boils. Farther up the heaviest stuff with the highest boiling points will condense out to liquid phase, while stuff with lower boiling points will stay in the gas phase. This pattern continues all the way up, until the different products are fully taken out.

A schematic of a refining tower. Nearly everything in the bottom is volatile (gas phase). As you move up in the tower, temperature drops, and the heaviest items condensate out in liquid form, collect in trays, and are removed. source: chevron Pascagoula

Gasoline is amongst the most valuable commodity pulled out of a barrel of crude. Diesel in the US is more valuable if it can make its way to the east coast, where it can be shipped to Europe. Why does Europe use more diesel than the US? Cause the gasoline tax there is much higher than the diesel tax. So the price for gasoline is artificially raised very high, and then the price for diesel (which can be substituted for gasoline in most applications) rises to something underneath gasoline. Since petroleum products are a globally traded good, the price of diesel in the US is directly affected.

Barrels of oil are not created equal. Stuff coming out of Saudi Arabia can produce a lot of gasoline (we are talking nearly 70 or 80%). Stuff coming out of the Canadian tar sands might produce closer to 20%, and have a ton of residuum. A barrel of Canadian tar sand oil is thus worth much less than a barrel of Saudi crude. Note: the Bakken produces a barrel that is even better than Saudi. It is some of the best in the world. It is worth less at the well head (where it comes from the ground) than other barrels. Cause the Bakken developed so rapidly that there is not enough transport capacity. This elucidates another important point. Refineries buy crude oil.

Hokay, next stop on refineries: different types. The crude that comes from Venezuela and the Canadian tar sands is incredibly low quality. It is filled with heavy stuff. In order to distill it, it needs to go to special refineries. It turns out that Texas and the American South are one of the few places that can handle this super thick sludge. So Venezuela can complain all they want about the US, but their only buyer for their product is currently the US. No one else has the ability to process it. What about Canadian tar sands and Keystone XL? Most of us have heard that China is willing to buy that stuff, and they will if Keystone does not go in. It would be pretty easy for that stuff to be shipped to the coast, and if China could have a guaranteed supply of it for years, it would be worth it for them to build refining capacity for that thick sludge. So if we don't build Keystone or develop rail capacity to buy that junk from Canada, then China will.

How much money does refining oil make? A couple of dollars per barrel. Compared to Saudi Arabia making nearly $100 a barrel, this doesn't seem like much. But given there are 80 million barrels of oil used a day in the world, that means there is somewhere between$100 and \$150 million per day to be made in the world by refining oil. If you are Exxon and don't have all that much access to produce in a Saudi oil field, this could be a great option.