Tag Archives: Energy Use

Tesla's Powerwall - Not Economical

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Tesla Powerwall

I'm gonna open by saying that I really like Tesla's powerpack. Technology isn't pushed past the bleeding edge without loss-leaders pioneering. That being said, the numbers, as usual, don't lie. On a per-unit-energy cost basis, these things aren't economic in most of the US. Once you consider the externalities, however, the overall benefit does make them "profitable." Likely you will see subsidies to internalize these externalities, thus making the powerpack work.

Unless the inverter costs too much. More on that later.

One major implication I haven't seen anyone talk about? Utility companies currently have to pay people with solar panels who produce excess electricity at market rates. They've been trying to get rid of this for years. This technology gives utilities every reason to demand they no longer pay people for their excess produced solar power. This has enormous implications. It's now indefensible to force utilities to buy at market rates the extra power produced by homes with solar. Read more near the bottom.

It's in my weight class!

Tesla's Powerwall next to a car. Small-ish and sleek. 7 inches deep, weighing 220 lbs

What is this Powerwall?

Powerwall is a power pack that you hang on your wall. It costs $3,000 for a 7kwh pack designed for a daily cycle, meaning it's charged and used once per day. This is the cost without installation. Also, this is the cost if you already have solar cells and an inverter. If you want to work with the grid alone, you have to buy an inverter*. Even if you already have solar cells and don't need an inverter, this seems like it's a product designed for the wealthy. Let's look at the math (my favorite part!)

*Inverters. Batteries and solar panels produce DC current, or Direct Current. This means it doesn't change phase. What we use in our homes is Alternating Current or AC. The alternating current means that the positive and negative terminals switch sides of the power plug. In the US, they switch sides 60 times per second. DC means that the terminals do not switch sides. Hence batteries having a + and - terminal, and all your non-battery electronics not having these.

The Maths!

We are going to make some of the rosiest assumptions in the world. First, though, let's get some solid data lines up. Take a peak at NPR's cost of electricity infos.

1. On average, people pay 12 cents per kwh of electricity

2. In Hawaii, they pay 33 cents. We'll use this as a case study.

3. The Northeast and California, two other case studies, pay about 16 cents.

4. The average American uses 900kwh of electricity per month in their home (from eia.gov).

Really rosy assumptions

1. The sun shines for 300 days a year and provides enough electricity to power your house during shining and to fully charge the battery

2. The electricity grid doesn't buy back your excess solar*. If they do have to buy it back, then the economics discussed here don't play out

3. You've already paid for all of your solar installation and you aren't concerned about those costs of that electricity going into this powerpack

4. These things don't degrade over time (extremely rosy assumption)

Hokay!

300 days per year of 7kwh of electricity provided by this beast is:

So 2100 kwh/year. What's that get you in most of the US?

So $252 per year. For a $3000 battery pack. In most of the US, if your solar panels worked perfectly for 300 days a year, it'd take you 12 years to pay back your investment. This is a 6% annualized ROI (Return On Investment). In other words, you'd make more money in the stock market, so it's a bad investment, not even accounting for installation costs and with impractically rosy assumptions, in most of the US.

What about in the Northeast and California, where electricity is $0.16?

Or payback in 9 years. This is an 8% ROI, making it a decent investment.

Let's be realistic, though. In the Northeast, we have storms and winter. Solar panels don't work so great here. We aren't getting 300 cycles per year out of this. We'd be lucky to get 150, making it an 18 year payback, or about a 3% ROI. What about California? They actually might get 300 days of viable sun a year. So in California, you could be break-even.

Now what's the problem here? Normal people don't look for 8% ROI on their home upgrades. They look for 15%. Pretty much they want 3-5 year payback periods. So pretty much, someone has to have a very green outlook on life to buy one of these. Or there have to be subsidies (more later)

Hawaii

Hawaii has sunshine and electricity costs 33 cents. Let's say you've paid off your solar panels in Hawaii.

In Hawaii, with our rosy assumptions and no installation cost, the powerpack will pay for itself in 4.25 years, for a whopping 18% return on investment, without any subsidies. There is a viable business model here.

Seriously, someone go start a powerpack/solar panel installation company in Hawaii.

Anywhere else, and these things will need hefty subsidies.

Subsidies

Why would you subsidize these things? Easy. There are only two reliable power sources that can compensate for variability in solar power: hydro and natural gas. Every other power plant takes far too long to spin up to be useful. In other words, nuclear power doesn't stop producing pretty much ever. Coal power takes about a day to get to capacity, so it can't cycle well.
Hydro power is a limited resource. We are pretty much tapped out in the US, and what we have is already being used, so it can't ramp. We'd have to replace what's currently being used with coal, natural gas, or nuclear to use hydro for solar-grid reliability, so that entirely defeats the point.
Natural gas ramps quickly, and we have excess capacity in the US. Natural gas still produces CO2 that spreads globally, and NO2 that spreads locally. NO2 becomes a strong acid when you breath it in, so we have healthcare reasons to reduce it. Thus it might make sense to subsidize these powerpacks to make people more likely to buy them.
Second, this is good tech. It's pretty much where it needs to be in order to make sense to buy in many parts of the country, if you already have solar. Subsidizing it will cause further advancement in battery tech, making it that much more viable in a wider array of applications. Battery tech is one of the things holding us back from so many viable technology applications, so if there is something to subsidize that will more than pay for itself, it is battery tech that is nearly cost-even now.
Some Extra Thoughts on my Rosy Assumptions
*If Solar Companies don't need to buy back Electricity
In most places, if you produce excess electricity that you don't use, the solar company has to buy it back at market rates. So buying this powerpack and storing energy for commercial purposes is useless. All of the economic discussion above is bunk if the grid needs to buy your excess power. In other words, only greenies would buy it.
One important thing to consider. This product makes storing electricity from solar into a break-even cost in any sunny part of the country. Utilities have always hated paying for this. They lose money on it. They've fought legal battles to get it repealed. And now they have the ammunition they need to repeal it, because it's now no longer a burden to consumers to store their excess electricity for later use themselves.
Maybe consider buying utility stocks if you find a company that is over-exposed to paying for home-solar-produced power? I'd tell you to look towards California here.
Inverter Costs
If you don't have solar already, you have to pay for the inverter to make this thing convert DC back to AC for your home. I can't see any reason to do this. The cost differential between peak power and non-peak is about 4-6 cents in most places. Far too little to justify the expense of both an inverter and a powerpack. A gas generator is a better bet if you need reliable power.
Large Scale Efficacy
I'm betting the large-scale systems are more cost-effective. They don't need to be as small and as sleek. And you can have one large inverter for all of the daisy-chained power packs. Who would buy these? Commercial electricity buyers, like stores.
Who wouldn't buy these? Industrial complexes. They make deals directly with electricity companies and pay $0.07 to $0.10 per kwh.
Thanks for reading!
 - Jason Munster

Solar Roadways: Full of Crap and Bad at Math

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First of all, sorry it has been over a month since I've posted. I've decided to get together a few people to start addressing some of the things I write about, and that has taken my time up til now. I'll be posting once per month from here on out, on the first Sunday of every month. Today's post is a long one, but one of the most interesting I've written by far.

This is the one time where I will say the following: if you are short of time, skip directly to the math section. It shows a serious glaring deficiency of either forethought or disclosure on the part of the founders of Solar Roadways. Moreover, it shows they can't do basic math. Never trust an engineer who can't do basic math. It's a very crackpot idea.

Here We Go!

I've heard a lot of talk about Solar Roadways recently. I'm going to use it as an example of how to analyze some "science." After you follow the very basic math below, you will see that the team at Solar Roadways does not know what numbers to run*. A much larger problem: they suggest that solar roads can replace fossil fuel power, while simultaneously and surreptitiously admitting that they need a ton of grid power to make this work. So pretty much they are either dumb or straight up liars.

First, let's talk about why these roads might be good, from their point of view. Being a by-the-numbers type of guy, the first thing I did was check the "numbers" section of their website. While their assumptions are dubious at best (more on that later) They say that their roads could provide 3x the energy that the US needs, in kilowatt hours (kWh is a useless measurement here, cause it will be intermittent power. In other words, it produces no energy at night, and will need to be supplemented by fossil fuel power. More on that later). Also, the roads look a lot cooler, with light-up sections, and ability to melt snow so that road maintenance is reduced.

So the thing is wired to the grid so that if it snows, it can use heating elements to melt the snow instead of plowing it. But doesn't snow take a lot of energy to melt? Would it take less energy just to push it with a plow? Time for the math!

Math of Melting vs Pushing Snow

Plow trucks to be replaced by Solar Roads? Not happening.

Plow trucks to be replaced by Solar Roads? Not happening.

Okay. Let's assume middle-case scenario of 8 inches of snowfall, being removed with one sweep by plow trucks, and that this is between powder and heavy snow in consistency, which means 1" of water equivalent. A DOT snowplow clears 10' width of snow, or 120 inches. In one foot of movement forward and plowing 8" of snow it moves the water-weight of 1"x120"x12" or

Now we have to figure out how much energy cost this took in fuel, so we will later relate this to the mileage efficiency of a DOT truck. First, let's figure out how much energy it takes to melt this much snow into water. Do do this we need the latent heat of fusion, or the energy it takes to transition from ice to snow. It's 334 Joules/gram. How do we convert from cubic inches of water to grams? Easy. Because the metric system makes sense, one of water = 1 gram. There are 2.54 cm per inch, so:

Okay, we have grams, now let's calculate the energy to melt as much snow as a plow moves from driving 1':

Or ~7.8MJ. Per foot. Or, for a mile:

to melt 8 inches of snow.

Okay, so, a plowtruck uses diesel. Each gallon of diesel has 136.6MJ. Very conservatively assuming a plowtruck gets ~5 miles to a gallon (I'm guessing it's more like 10, someone who has driven one, correct me and I will correct these #'s), it would take 27.3 MJ to plow one mile of snow. Compared to 41,184MJ to melt it. It literally takes 1500x as much energy to melt is as it would to move it.

This is what you would call a very very bad idea. Engineers as cofounders should know better than to let this slide as a potential solution.

End of Math Section

Okay, so now that we've completely dismantled the case of using these things to melt snow, lets move on to some other issues. We'll skip the minor issues, because that's just nitpicking, and move straight to the parts where they just don't know what they are talking about, and finish with things they clearly know about, but are purposefully misleading people with in order to get more money. Finally, we will close with me realizing that Nathan Fillion is a fool.

Okay, to the problems with this solar roadways project:

Dubious assumptions:

Things they don't understand: the supply lines of a very basic input.

REE mining in China is not a clean thing. Nor was it great in the US. Right now there is not enough world production to make enough of these solar roadway tiles. Look at this article to see more pictures of REE production in China.

They assume an 18.5% efficiency of the solar panels. These are panels that use Rare Earth Elements (REEs). On their FAQ, when someone asks if they are using REEs, they state (paraphrased), "Our electronics don't use silver or gold" (neither of which are REEs, so they are either changing the topic or don't know what question they are answering) "but we can use any solar cell." Good that they can use any solar cell, because there is not enough REE production in the world to produce solar at the scale they need to even replace one major highway with these. Bad they they use 18.5% as their assumed efficiency, because solar cells in this range of efficiency use REEs.

REEs are pretty much only produced in China, because producing them make a massive amount of pollution. Decades ago every other major country quit producing REEs because of the pollution they cause, and because China didn't care about pollution or health hazards, so the world was happy to let them pollute themselves and take their REEs. It's been so long since the US produced REEs that we literally don't know how. Solar Roadway's answer is "let's leave this to the government." They aren't addressing the problem at all. While other countries are looking to have their own production, it will take a very long time for this to come to fruition, and the production rate still won't be enough for a second-rate harvesting design (flat roads with bad optics vs. tilted panels with great optics to concentrate light perfectly).

At best, they can go with non-REE solar cells, which have about an 5-10% efficiency. That means that each of their hexagonal panels will produce half the power anticipated, and thus will make half as much money toward recuperating their costs. In other words, these non-REE solar panels need more basic raw materials (in terms of roadway) per kwh produced, and thus will cost more per unit energy, in an already material-intensive design for a solar cell. This shows that the project is lacking in any real expertise or understanding of the core problem they are trying to solve. Keep in mind that these are not dealbreakers. The team could hire an expert, or consulting, to fill in their knowledge gaps (likely the former, consultants are expensive, and they really need long-term help to bring this to fruition). Also, it doesn't negate all the other benefits of the solar roadways. Finally, non-REE solar panels are a hot topic in research. If the rest of the solar roadways tech is developed, and they are just waiting for good solar cells, it will rapidly enhance future deployment.

In short, the solar cells are a slight additional benefit to whatever holds them in this case of mass-distribution and inefficient use of cells. So if this new road itself doesn't compare favorably to asphalt, the project is sunk in the water.

Things they are just completely wrong/misleading about: melting snow, shutdown of fossil fuel, price of energy

We discussed the melting of snow. They suggest it replace snowplows. Bad idea. It's clearly not going to work, energetically speaking.

They keep talking about how 50% of US electricity use is from fossil fuels, and how these roads are going to replace it. This is so wrong that it is hard to debunk in one post. But here goes: First, only 40% of US primary energy (my link, please read it for background if you feel a bit lost, it is far briefer than this post) is for electricity. Second, only 66% electricity of this comes from fossil fuels. In other words, 26.4% of US electricity comes from fossil fuels (if we change all our transportation over to electric, these numbers will change, but that would require these roads to have induction power installed - AKA roads that provide the car with energy for driving so they don't have range issues). This is the total amount of emissions that could be replaced by solar roads in their current design.

Primary energy in the US. As detailed by the math above, only 25% of primary energy in the US can currently be replaced.

 

So, pretty much they are off to a bad/misleading start there. But this is nitpicking. The real issue comes in when they talk about replacing fossil fuels. First, they talk about heating the roads. This means they will have to put energy into the roads. Where will this energy come from? Power plants. So much for shutting down fossil fuel. But wait, there's more! Solar power is intermittent. It doesn't even work at night, so power plants also have to be on then. So pretty much, their idea of shutting down power plants is completely shot out of the water by these two things. Can solar roadways still be part of a larger energy solution? Well, not if they are heating roads to melt snow. That just takes far too much energy. If they scrap the melting snow idea and go to just producing energy? Yeah, it might help some. But let's get to one last funny part, the one that shows they know that they won't be shutting down fossil fuel power any time soon.

Energy storage. From their FAQ, they mention that there will be "virtual storage" in that during the day they will add power to the grid, and at night they will take power from the grid. This is double-speak to mean: during the day we will provide power that can offset coal and natural gas power plants. At night when we aren't producing, natural gas powerplants (again, my link) will fire up to power our roads (nuclear is not an option for power phasing like this, nuclear powerplants don't spin up or wind down on half-day timescales). In other words, they fully well understand that they aren't going to do away with the rest of the power grid, and that they aren't going to replace all those fossil fuel emissions. So pretty much, saying that these can replace our power grid is double-speak sales points.

The final problem? They don't understand energy distribution. Electricity is produced at about $0.03 to $0.08 per kwh at a power plant. By the time it arrives to us, we pay $0.13 to $0.25 (or $0.50 in Hawaii), because distribution costs a lot of money. Solar panels on our roofs produce power that costs about $0.15 to $0.20 cents per kwh, give or take. So the end-user cost of grid power is the same as that of house solar. But if you run that solar power through the distribution channels and add that price, suddenly you're talking $0.25 to $0.40 power. So, unless they are giving this power away for free, it's probably not gonna be a great solution.

Some Solutions

I've softened my usual tone quite a bit for this writeup, cause I don't want to be a complete naysayer of something who is trying to do something positive (sorry, I know how much you all know and love my biting sarcasm and scathing reviews).Outside of their false solution of trying to solve the energy/climate issue, this idea has some potential. On that note, rather than pointing out problems, I've come up with some great solutions.

My suggestions:

1: Nix the whole melting of snow concept to replace plow trucks. Energetically, it doesn't work. Plow trucks should still exist. Instead of replacing them, replace the salt and sand they need to spread. Make it so plowtrucks plow all but the last 1/8" of snow, then melt that (note, this is still a tremendous amount of energy, but stay with me). This will have a few benefits:

  • No more salt and sand on roads means less salt and sand damage to vehicles, making vehicles last longer
  • No more salt and sand on roads means that DOTs can save money buy not buying these things
  • ... no salt and sand runoff, which pollutes local waterways
  • ... animals that go to roadways in the spring to lick off accumulated salt won't do that, reducing traffic accidents from moose and deer, etc.

2: Get a bit more cognizant or REEs and their limitations. Don't use bad assumptions that are easy to poke holes in.

3: Stop selling people on false promises of doing away with fossil fuels. It makes the whole green movement look bad when prominent people are lying or severely misinformed.

4: Focus on the real potential of making these have inductive energy for electric cars. This could eliminate range anxiety (people fearing their electric cars will run out of energy and leave them stranded). Electric car sales will move a lot faster if people can drive from LA to SF, or between Boston/NYC/DC. The potential partnerships include every major car company that markets in the US. Also, this could reduce oil use, and drastically reduce air pollution from cars in these busy areas by further replacing combustion engines with electric ones (even if we power them with electricity from coal, a well-scrubbed coal plant produces fewer bad things than a car). Moreover, since people won't need fuel, they could be assessed a charge per mile driven instead. By whoever owns the roads. Here is your real money-maker for the roads, fellas. It will be far more lucrative than producing tiny amounts of electricity. Please get on this. It will lead to more electric car research, and more rapidly drive forward battery development, and it turns out that cars make a bunch of really bad pollution that causes harmful side effects like death.

This last bit, changing your startup's tack when a better model comes along, is important. And solar roadways needs to do that for a viable product, because their core solution faces a lot of headwinds (yay, sailing puns!) in break-even with their current model.

So, overall, these roads could be an excellent idea. The solar part, their main selling point, is BS because of cost, efficacy, and the need for gas-fired power plants to supplement them. The shutting down most fossil power plants is a lot of nonsense for the same reason. Making the environment better by reducing salt and sand use? Decent. Potentially by making most cars electric? Game-changer, but they are barely looking at that aspect right now. Probably cause they are too busy counting the piles of cash that indiegogo just threw at them (or, more likely, answering the insane number of emails that comes from this sort of campaign).

Hokay, that's my piece. Thanks for reading this long one.

- Jason Munster

Extra stuff!

Some background about Solar Roadways initial funding: They were funded by government SBIR. This stands for Small Business Innovative Research. It's for high-risk, high-reward research. In other words, this was considered high-risk from the start. They got a phase II, which means they did well. It's clear they still have issues and are still high-risk. But I'm glad someone is paying for research and innovation like this, especially because if it pays off, it could result in more jobs and more taxpayer base. That being said, they haven't received more funding or any grants to build this out further. Possibly cause it's a big, crazy idea. Elon Musk can pull off big, crazy ideas, because he is a brilliant manager and has a very strong personality. These guys are going to need some bigger guns on their team if they are going to make something of this project.

Second, Nathan Fillion is a bit of a fool. In touting Solar Roadways, he displays why pop culture heroes shouldn't get involved in matters outside their field of expertise (mainly, looking good in front of a camera, and pretending to be someone who they aren't in front of a camera). His adoration of something he doesn't understand falls deep within the territory of religious fervor. Nerds: just cause one of your heroes likes something doesn't mean it actually is plausible.

One final-final note: I know that this post is 3x longer than my rest. I assure you, it's far shorter than I wanted it to be. I don't believe in two-part posts very often, though. If you have read this far. please leave a comment so I can appreciate you forever 🙂

*Engineers who don't know what numbers to run are a bad investment. For my own company, all business types are skeptical of how much I know (or want to take advantage of me fully) until they find out that I used to be in finance and have a really good idea of the big picture of most things. In short, this company has a lot of potential once they take on broader experts.

China's Water Shortage and Power Plants (their power plants definitely have a drinking problem)

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In the previous post, I described how thermal power plants use a massive amount of water. This time we are going to explore a specific case. As usual, it's China.

Power plant water use can be a problem in a water-stricken area. Let's look at a case-study. China is a water-stricken area, and has a lot of thermal power plants. In fact, China uses more primary energy than any other country in the world. Unfortunately, their power plants are far less efficient than they should be. So they are wasting water, and this is unsustainable. Moreover, China has 1,350 million people. The US has 314 million.

First, let's look at the rainfall of China, compared to the US:

Rainfall in China, in inches

Rainfall in China, in inches

Rainfall in the US, in Inches

Rainfall in the US, in Inches

Looks pretty similar, right? Now recall that the US has 1/4 the population of China. And pretty much the exact same amount of area. Keep that in mind while we look at China's powerplant locations:

 

China's water stressed areas, compared to where power plants are planned. Source,

China's water stressed areas, compared to where power plants are planned. Source,

So. The places that have the most people and need the most power are the same as the dry places. In other words, China is building the bulk of its thermal power plants in the area that can't provide sufficient water to cool the power plants.

Before coming to the complete picture, let's check out the water use:

Fresh Water Use in the US. source

Fresh Water Use in the US.
source

In the US, 80% of water use is to grow food and to make electricity.

Finally, where is all this water coming from? Rain alone isn't enough, it comes from the ground. Fresh water from the ground is not unlimited, and we are running out of it. It's called Fossil Water, and here is what the situation looks like in the US:

Water withdrawals in the US

In other words, a huge chunk of our country is relying on water that will not exist in a few decades.

And looking at China:

China's groundwater depletion rate

In the US, the scale of groundwater depletion tops out around 400 cubic kilometers. In china, it tops out at 3,000 in regions. That's not to say that the US won't run out. It just says that China is in serious trouble.

Again, 80% of water use is for electricity and agriculture. And China has 4x the people of the US. There is not sufficient water. Would you rather run out of electricity, or run out of food? It's not an easy choice, but food can be imported. That being said, someone has to grow the food, and that country better have a robust water supply. Moreover, food growth is a low income industry. A country that marries itself to being a food supplier, unless it charges gouging levels of prices, is marrying itself to never being a high-income country. But charging price-gouging levels is a bad idea.

While this mental exercise was fun, let's look at some examples.

First, while Californians probably shouldn't have been growing water-intensive almonds in a dessert in the first place, running out of water has imperilled the world supply of all sorts of nuts and things. They are tearing up their farms because of lack of water.

That's only the start. Drought in Syria helped bring about war there. Syria is a tiny country that doesn't matter on the world scheme. India, China, and Pakistan face water shortages. Combined, they have 1/3 the world population. They also happen to hate each other. As climate change progresses, and some countries face droughts, people may not want to choose between food and electricity. They may try to divert water supplies, sparking tensions and even war.

So. Does your power plant have a drinking problem? If you live in China, it definitely does, and it's causing all sorts of strife.

Wrapping it all together: Yes, a country can import food. But you know how much of the world relies on the middle east for oil, and we talk about energy security? That's just stuff that makes your cars move. Remember how Russia threatens to shut off natural gas to Europe if they don't get in line with Russia's plans, and so much of Europe is cowed? That stuff keeps homes warm, but it isn't as important as food. Imagine a powerful country that is mostly reliant on other countries for food to stay alive. That's a really bad situation. The country in this situation has to either take dictations from whoever feeds them (not really a problem if you are getting your food from non-powerful nations, but still irksome), or has to take over a food-producing country.

One potential solution: Chinese power plants are notoriously inefficient. If you have a 25% thermodynamically efficient powerplant, it uses 30% more water than a 37.5% efficient power plant. China should either shut down inefficient plants and require new construction that is efficient, or require retrofits of old plants. It would be very expensive, but less expensive than the social and political cost of running out of water too soon. What about the US? Most of our plants are pretty efficient already. Especially our Natural Gas plants that much of the country runs on. We probably spend too much water on watering desserts to make food, but that's another story.

An almost-final note. While solar power and wind power use water in construction, their water use is minimal compared to that of thermal power plants. Barring solar-thermal (it's thermal, it uses water), these renewable resources are the only answer to the reducing the choice between electricity and food. In other words, expansion of wind power and solar PV is the only cheat code we have to deal with this impending water shortage.

One last thing. Why did I single out China? Only because I know a lot about China. Pakistan will have water shortage issues, but they already don't have electricity. In the summer, they have blackouts for up to 20 hours a day cause they can't produce enough electricity. This is a country of 180 million people, bordering India, and sharing a strong mutual resentment with India. More on this later, though.

Thanks for reading,

- Jason Munster

Why Giant Houses Always Use More Energy

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Big houses use more energy to heat and cool, for reasons you might not suspect. Houses lose heat to the outside. Nearly all houses are drafty in some form or another, and they need to be somewhat drafty, as we will soon find out.

When energy prices skyrocketed in the 70s due to price gouging and market manipulation of oil (thanks, OPEC), there was a big movement to make it so houses didn't leak air (and leak their heat energy in the process). The idea is that for every bit of air you heat and then let out into the environment, you have just wasted energy. So the process of sealing houses began.

OPEC oil embargoes of '73 and '79. The prices of energy spiked worldwide.

Some groups bragged that they could build houses that only exchanged 1% of their air per hour with the outside. In other words, it would take 4 full days to lose all the heat or AC energy of a house to the outdoors. Excellent, right?

It was excellent in terms of energy savings. But anyone with a flatulent spouse/significant other can tell you that being stuck in a place that is producing unhealthy fumes is dangerous if you don't vent it. It turns out that a lot of basic human activity, like cooking and heating, produce things that are bad for humans and need to be vented.

Much more importantly for advanced cultures*, cooking (it boils water, yo) and breathing and sweating make the air inside a house humid. Humidity in a house causes mold that can make you ill or, in extreme cases, kill you. One of the most effective ways to remove all this humidity is to let the air exchange with the outside.

So here we have a problem. We need to seal our houses well in order to save energy on heating and cooling, yet we also need to allow loss of all this heated and cooled air so we don't sweat ourselves out and cause bad mold to grow.

And we arrive to the crux of the matter. A good exchange rate is .6, or that 60% of a houses air is exchanges per hour. Sounds like a lot? It kind of is. But it's what is healthy for normal technology (we aren't all going to install CO and CO2 scrubbers and dehumidifiers in our houses). So in 24 hours, we have

hours exchanges per day. Of your entire house volume.

So. You have to exchange air in your house. About 15 times per day. Otherwise you might start falling ill. If you have a gigantic house that is 2x larger than you need, then you will use 2x as much energy to keep the place heated and cooled as you need to. So, in short, living in a giant house is a bad thing for energy conservation (take notice, Al Gore**)

Next week we will suspend our assumption that all houses have decent exchange rates, and discuss why this is a huuuuge policy gap.

You don't really need to live in a place like this, do you?

Thanks for reading!

- Jason Munster

*Developing countries still use coal. By 2020 there will be up to an estimated 400,000 deaths per year in China from indoor air pollution associated with burning coal for heat and cooking in poor rural homes (160,000 median estimate). Obviously this is more pressing than mold.

**I was going to rip Al Gore a new one for having had a huge electricity bill just after making An Inconvenient Truth, but it turns out that in 2007, before it was cheaper or easier, he elected to power his home, in TN, with solar and wind power almost exclusively, jacking up the price to a level higher than most Americans pay. So yeah, he did have a much higher electricity bill than the average American, but he only used about 4x the electricity, apparently. Which is still a lot. Except that he and Tipper both also work out of their houses. And now they have solar panels all over it. So it's not that bad. Though it is still huge.

 

Is Nuclear Power Really the Most Expensive Technology?

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No. It isn't.

Let's explore this more. In a country that already has a well-developed electrical grid / electricity distribution system (sorry, much of Africa), doesn't have ideas based on fear about how dangerous nuclear power is (European and North American countries, +Japan), and doesn't have a terrorism issue (proliferation), nuclear power is the cheapest and least polluting type.

Okay, so where can we find a country that meets this description? How bout Croatia, where some scientists did some probabilistic modeling on this?

From the results of the simulations it can be concluded that the distribution of levelized bus bar costs for the combined cycle gas plant is in the range 4.5–8 US cents/kWh, with a most probable value of about 5.8 US cents/kWh; for coal-fired plants the corresponding values are 4.5–6.3 US cents/kWh and 5.2 US cents/kWh and for the nuclear power plant the corresponding values are in the range 4.2–5.8 US cents/kWh and a most probable value of about 4.8 US cents/kWh.

Let me sum this up. In Croatia, nuclear power is likely going to be the cheapest source. Plus is doesn't pollute and kill people like gas or coal.

Admit it, you needed this.

Why do we face a different situation in the US and Europe? Easy. I've mentioned it before. There is so much concern about the safety of nuclear power that each construction gets mired in legal battles. The legal battles themselves don't cost much. What costs a ton is that these power plants took out $8 billion in loans, meant to be paid back over 10 years. Those loans accrue interest. If legal hurtles slow the construction of the plant down and it takes 15 years instead, those extra 5 years of loans are gonna have several extra billions in interest to pay. Suddenly the cost of power produced goes up.

These costs need to be paid back. The only way to pay back higher than anticipated costs would be to charge more for nuclear power.

So it's safe to say that stalling the construction of a nuclear power plant can effectively prevent it from ever getting built. Now we are in a situation where no one wants to fund a power plant, because the chance of it being slowed and made unprofitable is a bit higher.

Sometimes there are just plain time overruns. The US hasn't build nuclear power plants in years. Our companies barely know how to do it. Our people haven't been trained in colleges and universities to build nuclear power plants. We just don't have the nuclear engineers we would need to make a nuclear renaissance happen, and we'd need several nuclear power plants built before we finally get the hang of it. So there will be a learning curve. Would you want to fund that learning curve? Probably not when natural gas is so cheap in the US.

Are we gonna get there any time soon? Not without a major policy shift. Let's look at planned nuclear power plants worldwide:

Planned nuclear power plants. Image mine, constructed from data available at

Planned nuclear power plants. Image mine, constructed from data available  here

So um... Good job, China. US? Not so much. 32 of the 72 nuclear power plants scheduled to come on-line in the next 5 years are in China. 4 are in the US.

Nuclear power will be more expensive than gas (and coal) power in the US unless 3 things happen:

1. We account for the annual loss of life and increase in asthma and heart disease associated with gas power plants.

2. We start building nuclear power plants now, training a cadre of engineers and speciality construction personnel to finish power plants quickly, safely, properly, and on time (the first few will be finished slowly, behind schedule, but still safe and properly complete, cause lots of eyes will be on them)

3. We continue to build enough of them so that the future ones are build on time and for less expense, driving down the cost of nuclear power to competitive levels (especially when accounting for the external costs of pollution and CO2 from gas and coal).

Thanks for reading!

- Jason Munster

 

Natural Gas Price Drop, and Natural Gas Electricity!

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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

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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

Energy Requirements of Disposable Cups vs. Reusable, and Required # of Reuses to Break-even

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Most people assume that using disposable cups is universally bad for the environment. In truth, it depends on how they are disposed of and what else would be used in the place of disposable cups. In this post, I focus solely on the energy necessary to create each type of cup, to clean them, and how many re-uses are needed for a reusable cup to have a per-use energy cost lower than a disposable cup. The lifecycle energy use for disposable cups vs. ceramic and plastic cups have a surprising result: a restaurant will need to use a cup nearly 300 times to have break-even energy use*. Home use can be much better**, thanks to our much more lax health standards at home.

The scope of this post is limited to energy, which fails to provide a whole picture view. The next post will discuss other aspects, including pollution and greenhouse gases made during production, disposal, the intrinsic value of having a recycling mindset, and details about how the differing sources of energy used for production make a huge impact on these other factors.

The first part of this post will be pretty boring for most of you, containing basic explanation of units and dimensions that you will already know. If this is old hat to you, skip past the “basic background” section. It is meant for people who are unfamiliar with the basic physics behind energy who might be rusty calculating energy requirements for heating something.

If you know basic physics, skip down to the part beginning with "lifecycle energy assessment"

Basic Background – Energy, Joules, Heat, and Power

The really basic stuff: heat (most people should skip to next section, unless you know zero physics)

This section briefly goes over the basic units of energy. The unit of energy is a joule. It takes 4.2 joules per gram of water to raise it one degree Celcius (or about 2 degrees Fahrenheit). This number, 4.2 is called the specific heat of water.

This brings up another important concept: heat vs temperature. Everyone knows what temperature is. Not everyone knows what heat is. Heat is a measure of how much energy you have to dump into one gram of a substance to raise it one degree. Water, as we said, takes 4.2 joules. Iron take about one tenth of that, or .45 joules. Think about it this way: if you have a quarter of cup of nearly boiling 90°C water, and it falls on you, you are going to the hospital for some burn treatment. If you have a similar mass of 90°C iron fall on you, the heat of it won’t do much damage (although if it falls from high enough, it might hurt). So, roughly, for a given temperature, something with a higher specific heat has a lot more energy.

How much heat energy does it take to heat a large amount of water? To do this, we take the mass, multiply by the specific heat (represented by c), and then multiply by temperature change: m*c* ΔT, where the Δ means change, and Δt means change in temperature.

Less basic stuff

A cup of water is about 250 milliliters, or 250 grams. Raising a cup of coffee to 40° Celsius (about 100° F) from 10° Celsius would take:

Notice that the units of degrees Celsius and grams cancel out, with 1/(gC) from specific heat being multiplied by g and C from the weight and temperature parts of the equation, leaving only Joules. Sweet.

Anyways, 31,500 J is also written as 31.5 kJ (31.5x103 J). Let’s take a moment to convert this to kwh, or kilowatt hour, the standard unit of energy you pay for in your house. A watt is using one joule per second. If we took the coffee cup above, and wanted to heat it in 30 seconds, we would expend 1050 watts for 30 seconds (31.5kJ/30s). How many kwh is this? 31,500J/3600s = 8.75 watt-hours, or .00875 kwh.

Another point of reference for energy is the amount contained in one gallon of typical gasoline in your car. This is 120MJ (120x106 J). 120x106 J/3600s is 33.4x103 watts, or 33.4kwh. You could heat nearly 3800 cups of water to this tepid temperature with only one gallon of gasoline! Or you could drive 20 miles in a car. Or you could heat 3 baths with it (70 gallons of water per bath, water at 40°C, 16 cups in a gallon).

Alright, we are done discussing background energy for now. Onto the real stuff!

Lifecycle energy assessment of disposable extruded polystyrene (Styrofoam) cups vs. plastic and ceramic cups

In 1994, a professor named Hockins analyzed the energy use of disposable vs. ceramic cups. It includes the energy required to extract the components used to create the cups, the process used to form the compounds into cups, and for ceramic cups, the energy required to wash them.

Styrofoam cups (my word processor automatically capitalizes “Styrofoam” and I am too lazy to correct it) are a petroleum product called polystyrene. Styrofoam is the exact same material used in the disposable plastic silverware you use at picnics and other events, and also the cases that CDs come in. How does it get light and fluffy, then? In the manufacture of Styrofoam, gases are dissolved in the molten polystyrene under very high pressure. The Styrofoam is shaped into whatever shape they choose, then brought rapidly to low pressure (extruded, hence the name extruded polystyrene). The bubbles of gas dissolved in the polystyrene expand under low pressure, making Styrofoam mostly air (technically mostly a gas) with polystyrene holding it in place. They are typically disposed after one use. If disposed of properly, the polystyrene can end up at an incinerator where it produces mostly CO2 and H2O upon burning. In this way, part of the energy to make the cup can be reclaimed. If the Styrofoam is disposed of normally, it may be burnt to release black carbon and particulate matter, or end up in a landfill.

Ceramic cups are largely heated clay. The material needs to be mixed in the right proportions, shaped, and heated several times to dry and hold its form. The heating process requires a lot of energy. Moreover, washing the cups requires quite a bit of energy to heat the water for washing the cups.

Let’s get into the numbers.

Our reusable cups: A ceramic cup takes 14.1 MJ per cup to manufacture. A pyrex cup takes 5.5 MJ to manufacture, a reusable plastic cup takes 6.3 MJ. Our disposable cups: an uncoated paper cup is .5 MJ (500 kJ), and a Styrofoam cup is .2 MJ (200 kJ). The first thing we see is that manufacturing disposable cups requires between 4% (Styrofoam) and 10% (paper) of what it takes to make the most energy efficient reusable cups (glass and plastic). In other words, at very best, a plastic cup needs to be used 25 times to be as energy efficient as a Styrofoam cup, or 10 times to be as efficient as a paper cup. A ceramic coffee mug would require 75 uses before it would hit break-even energy as a Styrofoam cup, or 30 uses compared to a paper cup.

Now let’s account for the cost of washing. The same source indicates that a commercial washer requires between 80 and 120 kJ of energy to wash a single cup amongst an entire normal wash load. Compare this to the 31.5 kJ we calculated to heat coffee to a warm temperature. The differences arise in the amount of water necessary to wash and then rinse a cup in a commercial washer, and the higher temperature used in commercial washers compared to the temperature at which we drink in coffee or tea. A commercial washer has a wash cycle, a rinse cycle, and heats the water to a scalding 80 degrees C. Another important factor considered in this, which we will discuss in a later blog post, is the difference between energy used, and energy expended at a power plant to produce the energy used by the commercial washer. Power plants are not very efficient. The average power plant in the US will deliver only 35% of the energy from the fuel it burns. So we have to divide the wash energy by .35, getting a higher number of energy burnt to wash our cups.

Dividing the 80 kJ of energy of a dishwasher by a .35 efficiency results in nearly 230 kJ to wash a cup. This is more than it takes to produce a basic Styrofoam cup. In other words, in the US, no matter how many times you use a mug in a commercial setting, the total energy required will always exceed the energy used in a Styrofoam cup. Note that this is not the same as CO2 emissions (next post covers this!)

But hold on! Who uses a commercial dishwasher in their home? More importantly, who washes their cup every time they use it, besides my sister? Taking the former case and assuming we very efficiently wash the cups by hand, assuming it takes ½ a cup of warm water (heated up by 30°C) to wash a cup (both the temp and amount** of water use are highly optimistic!), and using ½ of what we calculated in the example section, it takes about 16kJ to wash a cup, or close to 45kJ accounting for the efficiency of electricity production. Now we are back to a break-even point closer to 100 uses for a ceramic mug, or around 35 for a glass! Not bad! And if you are like me, and you usually just rinse a mug with cold water and let it dry, or don’t wash it at all because you will be putting the same tea/water in next time, energy use is negligible, bringing us much closer to those 75 and 25 uses!

That’s enough for now. But there is so much left to discuss here! We need to consider many other factors. Pollution from production and disposal of disposable cups, energy sources used for electricity and how clean each is, recycling habits, landfill volume requirements etc.

What can we take away from this before we discuss all the other stuff? Be careful when you say that glasses and mugs are more energy efficient than Styrofoam or paper mugs. This takes many reuses. Another important implication: if you are throwing a party, you are better off buying paper cups (which can be recycled) and recycling them afterwards than you are buying glasses that will only be used during that party (or maybe one or two future parties).

This post is getting long, so I am going to sign off for now, and perhaps revisit this again later. Thanks for checking it out!

-Jason Munster

Edits (11-29):

* Lucas asked about a home dishwasher. A very efficient home dishwasher uses 3.6MJ of energy per wash (from EnergyStar). Assume you can cram 40 cups in there, you have 90kJ per cup, which would bring ceramic break-even re-uses to about 125, and glass to about 45.

** A lot of people are very wasteful when they wash dishes by hand, using a ton of hot water (as in running the water the entire time, probably using 8 cups of water to wash a cup). This is very inefficient and will never allow for break-even energy use.