Wednesday, October 10, 2012

Watts in a Kilojoule?

Peering into the drafts folder, I found this nearly completed post I started about a year ago. I don't have any races, trips or epic rides to talk about right now, so fill your coffee mug and see if you can follow along here.

When I started the Hill Junkie blog, I promised readers they would find no political ranting here. Life is too short to get worked up over debates in ideology. It all boils down to opinion anyway, and we all know what opinions are worth. This post is about energy, where it comes from, and how it gets used. As such, it may touch on issues of national policy and cultural awareness's  Some quantitative technical content will be presented with references.

I have been an electronics tinkerer since the age of 12. Back then I built a crystal radio that used no batteries yet could receive AM radio stations hundreds of miles away. I found this fascinating  It seemed like magic, as we could not sense this energy that apparently traveled through the very air we breathe. I would later go to school in the field of electronics and learn much more. After a brief stint working as a tech in a product development lab, I landed an engineering position with a robotics company in Michigan. I worked there 11 years, designing controls and all sorts of articulating devices for guided vehicles. I developed a thorough understanding of battery storage capacities, electric motor efficiencies, losses in drivetrains, and power required to perform specific tasks. I was not a cyclist at the time. Later I would pursue an advanced degree in engineering and move to New England. My work progressed into the world of microelectronics, an extreme shift from industrial electronics. Megajoules became microjoules and centimeters became nanometers. Although I didn't work with motive power anymore, my increasing interest in cycling gave me new ways to think about motive systems - human powered systems.

All avid cyclists have an appreciation for how hard it is to ride 20 miles or to climb a 30 minute hill. But how many cyclists know the power consumption of other systems in terms of cycling power? Those with power meters may have some inkling  But do you know how many gallon's worth of gas a whole year of riding is worth? Or how many cyclists can be sustained by the energy produced from one acre of corn? You may be surprised by some of the comparisons presented here. Presumably you are reading this blog because you ride. Let's delve deeply into this topic by relating diverse sources of energy to that of a typical cyclist.

For purposes of analysis that follows, let's assume that our standard cyclist can produce 250W of power for one hour. This is about 900 food Calories per hour, or over 20mph on flat terrain. Most competitive cyclists will have no trouble producing this much power. You may recall the ESPN commercial with Lance Armstrong on his trainer in the basement. He stopped for the night and the whole ESPN building went dark. If we put one or more standard cyclists on bike generators, how many cyclists would we need to power everyday things?
  • Streetlight: 250W - 1 cyclist
  • Microwave: 1kW - 4 cyclists
  • House: 25kW - 100 cyclists
  • SUV: 75kW - 300 cyclists
To be sure, I made a few assumptions here. Average house power over course of a day is much lower, but peak service to new houses is rated for at least double the 25kW used here. Estimated 75kW for SUV assumes 65mph on highway. So a cyclist is good only for a streetlamp or maybe a small TV or computer. Think about the SUV. If you drive one to work and back on the highway one hour round trip, 300 cyclists would have to work an hour to produce the energy you burned to transport one person. Of course, an SUV can get you to work faster (most of the time) or carry a few more people. But even if you drove the same speed that a cyclist could maintain at 250W, the SUV would consume many, many times the energy a cyclist would consume.

I think most people utterly fail to understand how much energy cars consume. My dad is a retired autoworker, and he's been keenly following the development of GM's concept car the Volt. But I don't think he fully comprehends that if everybody started driving electric cars that drew an appreciable portion of their energy from the electric grid, we'd have total grid failure. Here's why.

About 45% of the oil consumed in this country is put in auto gas tanks [1]. This is around 377M gallons per day of gas burned in cars [2]. Now here's the kicker. One gallon of gas contains 130,000,000 Joules of energy. That's 31,000 food Calories. A gallon of 1% milk has about 1600 Calories in contrast. Now if we multiply 377M gallons by 130MJ, we find that nearly 50 petajoules of energy are consumed in cars daily (that's 50 with 15 zeros behind it, as in 50,000,000,000,000,000 Joules). Stunning, eh?

Here's another way to look at things. I figure in a whole year's worth of riding, I may burn about 1.92 GigaJoules of energy. I figure this from 600 training hours with an average of 800 calories per hour. This would be upper limit. I likely burn much less over a year. 1.92GJ is less than 15 gallons of gas. A whole year of my riding (8000-10,000 miles on and off-road) can be powered by the energy contained in just 15 gallons of gas. Avid recreational cyclists will burn even fewer gallons worth of gas energy in a whole year. A one hour hammer ride for me might burn only four ounces of gas! I point this out because gasoline has incredibly high energy density. That is why it works so well for cars. Cars are energy hogs, and energy hogs need high density fuel, else the storage space or weight requirements would be far too great. We have not found a reasonably safe, denser way to power transportation. Our best batteries fall way short. Other chemicals, like ethanol, don't stack up well with gas. Much more will be discussed on ethanol shortly. We haven't exactly figured out cold fusion either. So we're stuck with gas in the interim.

But say we did make a sudden breakthrough in battery technology. Say we could drive 400 miles on one charge, just like we do with a 30 gallon tank in a SUV today. I'm not talking hybrid here, but 100% pure electric vehicle. Then all we'd have to do is come home from our evening commute and charge the car in the garage, right? Um, there's that pesky detail that nationally our cars burn 50PJ per day. Where is this going to come from? Our grid system is already strained in most parts of the country. We haven't built a new nuclear plant in decades, and the number of operational plants peaked almost 20 years ago. There are about 104 units in operation today. Coal powered plants are coming under increasing environmental pressure and will likely become less attractive as they are forced to use increasing percentages of net output to reduce emissions [3].

Cars use 50PJ per day. That's 18,250PJ, or 1.825x10^19 Joules per year. Total nuclear plant electricity production last year was about 800,000MkWhrs (leave it to Dept. of Energy to use million kilowatt hours) [4]. This is 2.88x10^18 Joules. These are staggeringly big numbers, and some of you will probably already be looking for the conclusion of this number crunching fest. But you should be able to see that cars consume more energy than the total nuclear power output in this country, which provides about 20% of our electricity. Now here's the next kicker. Suppose we converted all of our cars to pure electric vehicles that derive all their energy from the grid. Also suppose that nuclear electricity production was the only currently viable way to meet this huge demand. We'd have to build over 600 new nuclear power plants. That's 12 per state on average. Think the public is ready for this? Personally, I would favor a revival in nuclear plant construction. New plants could be vastly safer than plants of 30 years ago. We have to start weaning ourselves from oil for so many reasons. We can do this now.

Some say ethanol is the renewable energy of the future. In theory, it is supposed to have low net greenhouse gas impact. It goes something like this. Corn grows using energy from the sun to capture carbon from the atmosphere in its carbohydrates. A fermentation process converts the sugars to alcohol  This in turn is burned cleanly in cars, releasing the carbon back into the atmosphere where the corn can grab it again. Sounds very clever, eh? It's not. The whole ethanol production system is rife with dirty politics, twisted science, and a duped public.

First off, corn is a very expensive crop to grow. I mean this in many ways. Growing up in farm country Michigan, I saw first hand what my friends had to do to harvest a bushel of corn. You plow and disk the field. You plant the seed corn. You apply herbicides. You apply anhydrous ammonia (fertilizer). Then you must harvest the corn. It gets trucked to an ethanol production facility. Every one of these steps use diesel fuel. It also takes a lot of energy to produce the herbicides and fertilizers. Large scale corn production simply cannot be performed without these. Fermentation and distillation take more energy. Ironically, some ethanol plants burn coal to produce ethanol, a huge environmental impact. Once ethanol is produced, it cannot be piped in the same lines used for gas. It is too corrosive. So it must be trucked again to destination cities. The bottom line is producing a gallon of ethanol burns almost a gallon of oil. It is just a little better than a break even proposition on a energy analysis basis. Forget about net greenhouse impact. It is very negative.

Our government knows this. The professional society I'm a member of has rallied against ethanol production for years [5]. Yet many Americans think it's a good idea due to clever ads and an over eagerness to jump on the "green" bandwagon. Subsidies go to farmers in key election states. Ethanol mandates from congress ensure demand for corn. It keeps the US agricultural system going, which for years was too efficient and suffered from price weakness. What is sad is ethanol production promotes non-sustainable farming methods. Corn is hard on land. We are putting increasing amounts of world food supply in our gas tanks. This is already causing food shortages and is rapidly getting worse. World food prices are going up.

Lets get back to how much energy an acre of corn can really produce. One report estimates an acre of corn can produce 362 gallons of ethanol. That's a one shot deal, that is one crop per year. Ethanol has only 2/3 the energy density of gasoline. Thus you must burn 1.5gal of ethanol to go the same distance on 1gal of gas. The US burns about 377 million gallons of gas per day. If we all switched over to ethanol, we'd use 206,407 million gallons of ethanol per year. This would require about 570 million acres of corn to produce. Guess what? Based on latest available numbers, we only harvest about 300 million acres of cropland in this country [6]. In other words, we could put 100% of our crop land output into our gas tanks, have nothing to put in our stomachs, and still get only half way to work in our SUV's. Factor in how much external energy (fossil fuel) it takes to produce this ethanol, it just doesn't make any sense. Ethanol is not an alternative fuel, and the bigger picture shows it is not low emission. Ethanol production should stop.

So what about wind? These have huge potential. China is actually developing wind farms so rapidly their grid system can't keep up with it. My New England neighbor state, Vermont, has opposed wind farm projects for years, and only recently has begun construction of wind farms [7]. Vermont projects an image of being a progressive "green" state, home of Ben and Jerry's and all. But when it comes down to actually doing something green, well, not in my backyard pops up. It is well known that northern parts of New England are very windy. The jet stream here dips south and low. The summit of Mt Washington many days of the year actually pokes into the jet stream. The highest non-tornadic wind speed recorded on Earth was recorded there. I enjoy pristine views a well as the next guy, but I value clean air and energy to do other things I like too. I've seen large scale wind farms in Scotland, and my first reaction was how cool. And this was in an area where there was nothing but rolling hills, not expecting to see a massive wind farm over the next ridge. Wind power is still in it's infancy but rapidly growing all over the world. There's not enough easy data out there to see where wind is going. I really doubt, however, it will supply a significant portion of transportation energy here anytime soon.

There's also photovotaic. This I understand a little more about. Einstein won a Nobel prize not for relativity, but the photoelectric effect. This is where light energy stimulates electrons in a semiconductor structure to produce a current. Raw sunlight contains upwards of 1000W per square meter at best, but more like 600W average over 8hr day per square meter in northern latitudes. Best solar cells today are >30% efficient, but are cost prohibitive. Crystalline production cells may be more like 15% efficient, but still take many, many years to pay for themselves. The cheapest cells in development still, are only about 3-5% efficient, but dirt cheap and may have short payback period despite poor efficiency (you need lots more of them for given output). Say you tile your roof with the 15% efficient cells. That's about 90W per square meter. You might be able to tile 72 square meters, or 6480 Watts worth in bright sunlight. You could harvest about 187 megajoules per day. This would be about enough to power a car for a one hour round trip commute. This system would cost somewhere in the range of $50,000 to $100,000. At today's grid rates, this would take a very long time to pay for itself. You would need a much bigger system if you wanted to power your house and a second car. It is only viable where it is sunny most of the time. New England is questionable. As electricity rates go up and photovotaic cell costs continue to come down, solar PV systems will soon be a viable solution for average homeowners.

This "back of the envelope" analysis shows solar has huge potential. Most homeowners own enough roof area or land to capture all their energy needs from the sun. Huge solar farms could be set up in the desert too. Electricity is cheap and zero emission to generate and transport, unlike ethanol. Once a solar panel is fabricated and installed, it can potentially operate for decades without recurring use of fossil fuels and chemicals likes crops require.  There is a lot of private investment going into solar power. Driving the cost down is crucial for large scale deployment. More government investment would help here.

There's this thinking that we have to do something to save the planet. There's a sense of urgency that has been instilled in us. This makes us vulnerable. We buy more expensive products because they are "green." Yet how green are they? Like ethanol  many products or services labelled as green are far from it when the total life cycle is analyzed. Then there's the whole sham of carbon credits. I've commented on this before and won't go into it again. It allows individuals to appease their souls from driving to a bike race or creates loopholes for corporations to produce CO2. Some people are provoked to the point of eco terrorism. Don't like McMansions going up in the mountains? Burn 'em down. Don't like  Hummers being sold? Burn them too. That's gotta be really good for the environment, all those toxins being released, and those symbols of excess will no doubt be replaced anyway.

One of the best ways to reduce your environmental footprint today is by living below your means. Our culture is all about conspicuous consumption, which pushes us to live beyond our means. This drives us to buy bigger vehicles and homes than we need, pushing our energy needs way up.  My frugal Dutch heritage has made living modestly come pretty naturally. Beside reduced environmental impact, a modest lifestyle has many other rewards. Contentment, reduced stress and being free of debt are just a few.

Thanks for reading.
-HJ

    12 comments:

    Bill said...

    Interesting stuff!

    Colin R said...

    Wow, good read.

    CB2 said...

    In want to see wind-powered-hybrid plug-in electrics, with auxiliary solar cells to power a single serving espresso maker. Until then maybe I'll just ride my bike.

    Ari said...

    Super interesting. One thing is that while solar energy is carbon-free to transport, there is significant loss over long distances. That and the sun only shining at certain times. But old technologies and new (pumped storage, compressed air) can help to mitigate these shortcomings.

    I (so far) have never lived off the grid, but have visions of a trainer set-up tied in to a battery system so I could conceivably pedal a few hundred watts of power a day and run some small appliances (laptop, etc.) off of it. Shouldn't be too hard to set up, right?

    gewilli said...

    http://www.youtube.com/watch?v=vX0G9F42puY that's good

    also - biodiesel is chemically stored solar energy with an [nearly] indefinite shelf life.

    Doug, you know me and my bias/preference for BioDiesel so I'll refrain from getting a bit evangelical about it.

    Steve S said...

    Good read. I'm particularly in agreement with your last statment

    That said, I wish you had figured some estimate of efficiency into your comparison of gas vs. electric cars.

    from http://www.fueleconomy.gov/feg/evtech.shtml

    Energy efficient. Electric vehicles convert about 59–62% of the electrical energy from the grid to power at the wheels—conventional gasoline vehicles only convert about 17–21% of the energy stored in gasoline to power at the wheels

    So, your not really comparing apples to apples in your analysis.

    As for ethanol, I wish you could site some current data on the efficiency of its production. The best I could find is from 2008 (and uses data from 2005) http://www.usda.gov/oce/reports/energy/2008Ethanol_June_final.pdf
    I'll admit I glazed over a bit trying to read it (multi tasking on a conf call right now) and this is way out of my area of expertise, so I jumped to the conclusion. Hopefully their analysis isn't total BS.

    Conclusion
    A dry grind ethanol plant that produces and sells dry distiller’s grains and uses conventional fossil
    fuel power for thermal energy and electricity produces nearly two times more energy in the form
    of ethanol delivered to customers than it uses for corn, processing, and transportation.
    ....
    Overall then, ethanol has made the transition from an energy sink, to a moderate net energy gain
    in the 1990s, to a substantial net energy gain in the present.

    Brian B said...

    http://www.ted.com/talks/lang/en/donald_sadoway_the_missing_link_to_renewable_energy.html

    Dr. Donald Sadoway of MIT TED presentation.
    Well worth the 5 minutes.

    Unknown said...

    Doug, great read.

    Would be curious how substitution for oil with NG (fracked) changes the whole picture

    Hill Junkie said...

    Great feedback everybody. I may have to do follow-up post to address a few comments via email and PM.

    Ari - Your idea might be quite doable. There are many types of RV battery/inverter systems on the market. The tricky part would be how to configure a trainer to charge a battery. There are things out there, like this. A car battery may have a capacity of 100 Amp-Hours. At 12 Volts, this holds 1200 Watt-hours, or 4.32 mega-joules. A hard century ride might produce this much energy, so a car battery could hold multiple 1hr trainer workouts depending on generator efficiency. Most magnetic trainers don't generate usable electricity, but rather directly convert currents into heat.

    Steve - agreed. I was a little reckless in glossing over engine efficiencies. If we step further back and compare energy in sunlight to propulsion via all electric process to a biofuel process, the all-electric process is up to 600x more efficient. Photosynthesis to biofuel, it turns out, is a horribly inefficient way to harvest solar energy. I may post more on this later.

    Scott said...

    Growing corn is also very water-intensive.

    Some additional topical reading (slightly dated):

    Hill, J.; Polasky, S.; Nelson, E.; Tilman, D.; Huo, H.; Ludwig, L.; Neumann, J. Climate change and health costs of air emissions from biofuels and gasoline. Proc. Natl. Acad. Sci. USA, 2009, 106, 2077-2082.

    Campbell, J. E., Lobell, D. B., and Field, C. B. (2009). Greater transportation energy and GHG offsets from bioelectricity than ethanol. Science, 324 (5930), 1055-1057.

    Gerbens-Leenes, W., Hoekstra, A. Y., and van der Meer, T. H. (2009). The water footprint of bioenergy Proceedings of the National Academy of Sciences, 106 (25), 10219-10223.

    Mark said...

    I loved this! I did a similar set of "back of the envelope" calculations and came up with the same end - the need to reduce consumption. I've had a blog post on this top on the back burner for a long time but oriented more specificially around the un-greenness of racing. You may have prompted me to finish that article.

    Have you ever read Ivan Illich's paper on "Energy and Equity"? You can google it pretty easily. It's a good read although it primarily focus is on transportation and social implications. It does hit on some of the efficiency issues you brought up.

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