Monday, November 2, 2009

The Limits of Clean Energy


Last Wednesday, October 27, 2009, President Obama toured a solar facility in Florida where he announced certain investments in clean energy technologies as part of his stimulus package. I sincerely hope that, all the lofty rhetoric notwithstanding, Obama’s science advisors are suitably realistic about the limits of solar and other clean energy technologies. They may pin great hopes on our ability to engineer a solution to our energy dilemmas, but they must also understand the facts as they currently stand.

I have no such faith in the press, the blogosphere, or the common man. Lately, I have heard and read accounts of renewables’ promise which are so far removed from reality as to verge on the absurd.

I am a big fan of clean energies, but I also am painfully aware of their limitations. In particular, I am not hopeful that we may soon generate a significant percentage of our energy from clean or renewable sources. I am on the board of directors of a company which makes products for the solar industry, so I have looked fairly deeply into the subject and am not sanguine about it.

In working these issues out for myself, I have concluded that there are at least two difficulties which keep people from truly understanding the limits of clean energies.

The first is human beings’ inability to conceptualize, and therefore to contextualize, large numbers. This phenomenon affects the understanding of more than just clean technologies. For instance, there are plenty of people who don’t really know the difference between a billion and a trillion. To them, both are just really large numbers. Thinking so, however, makes it awfully difficult to understand the issues at the bottom of last year’s financial crisis, for instance. In fact, a trillion is a thousand billions. They are vastly different numbers. If one doesn’t conceive the difference between several orders of magnitude, it will be frustratingly difficult to understand much about macroeconomics, and it will be even harder to understand the science of energy. Unfortunately, most people don’t.

The second reason people have difficulty with the science of renewables is unfamiliarity with the metrics used in describing and measuring energy. For instance, the cost of manufactured solar silicon panels is measured in dollars per watt. Well, what the heck is that? Most people have no way to put that figure in context. Most people know that a watt is a very small amount of energy, but they have no idea how small. At the other end of the scale, our typical power plant in the US generates something like 1,000 megawatts of electricity. Again, what the heck is that? Normal people just have no way of understanding the scale of that number. That particular metric also combines both difficulties I’ve mentioned, insofar as it is a very large number (1,000 megawatts is 1,000 million watts of electricity) and it also mentions the frustratingly opaque “watt”.

To a certain extent, I’ve struggled with these difficulties too when thinking about energy. In such situations, I’ve always found it helpful to write it down – to do the math, do the conversions. In my case, I generally write these things down on an Excel spreadsheet. So several years ago, I started to dig into the science of renewables by putting it all in a spreadsheet. And I found out some interesting things. Furthermore, I found that by doing a few extra calculations, I could then explain the issues in terms that people could really understand.

So now I have taken it upon myself to remedy these difficulties for the faithful readers of Polartics. In blog posts over the next several weeks, I will put the physics and economics of clean energy into terms that people can understand. Here is what I will do:

• I will develop a metric of energy that people can understand because it is based on human activity. As an aside, at this time I will also perform a few calculations comparing this metric to our current use of energy so that we can see just how much energy the average American actually uses (and how much we take that energy for granted).

• Second, I will perform an energy audit of my own home. Many readers of this blog no doubt live in digs similar to my own, and can probably assume that the scale of their energy use is roughly similar to mine (it may be off by a percentage, but it will not be off by an order of magnitude!). Once done, this energy will be put into the context of the understandable energy metric which I devised in step one.

• Third, I will translate the capabilities of today’s solar technologies into my energy metric, and use the result to calculate the amount (and cost) of solar technology which would be necessary to take my house “off the grid” (not just for electricity, but for all of my energy uses, including oil heat and hot water, and propane cooking).

• Fourth, I will perform a similar analysis with wind energy.

• Finally, I will wrap it all up in a post which will, among other things, discuss the preceding two posts taking into account the economies of scale which may be achieved with very large green energy power plants. I will also discuss the limitations presented by the unpredictable nature (no pun intended) of the sun’s shining and the wind’s blowing, and I will come to some conclusions about the topic.

So then, without further ado, let us begin!

Chapter One - The Energy Metric

Ever since I busted up my knee playing soccer three years ago, this is how I get my exercise during the winter:

I generally max out at about an hour. It’s hard to ride on rollers such as these, because you can’t stop pedaling or you’ll fall down. I’ve done that a few times, and it’s not pleasant.

In an hour, I generally burn just under 1,000 calories. I know this because I wear a heart monitor. These monitors are not perfect, but they’re close enough for our purposes. Since calories and watts are both simply different measurements of energy, it’s very easy to convert from one to another if you know the conversion factor. It turns out that if I ride on my rollers for an hour and burn slightly less than 1,000 calories, then I am generating just over 100 watts of energy the whole time. It’s pretty darn hard work. I don’t know if you could see it, but there was a lot of sweat dropping off my face in that video.

To put 100 watts in perspective, an elderly person out for a leisurely stroll might generate about 5 watts of energy. Conversely, a professional bike racer may generate over 400 watts while climbing up the steepest climbs in the Tour de France, but he can’t sustain it for very long – maybe 30 minutes to an hour.

So, that’s it. The metric I will use to explain the physics and economics of energy is the amount of energy that I generate while riding on my rollers. I’m going to call this unit of energy a Matt. Once again, a Matt equals 100 watts. If I were to generate this amount of energy for an hour, I would call this energy a Matt-hour. If I were to ride my bike like this (I couldn’t, but just imagine I could), for an entire day, it would be called a Matt-day. For a month, it would be a Matt-month; for a year, a Matt-year, etc. Essentially, it is a way to put energy into human terms. A Matt-month is approximately the amount of energy that I could produce, working really hard, in a month. Similarly, a Matt-hour is that amount of energy that I could produce in an hour.

OK, so now that we have this energy metric, let’s determine how many Matt units are in some other sources of energy that people often talk about. For instance, how many equivalent Matt-units are in a barrel of oil? How long would it take me, working hard enough to have sweat dripping off my face, to generate the energy which is contained in a barrel of oil?

Why don’t you take a guess.

Two days?

Five days? In five days of furious work, could I generate the energy in a barrel of oil?

Well, not quite...

Ten days?... Fifteen days?... A month?

In order to make this analysis really visceral, really understandable, let’s make a Matt-day only that amount of work that I could do in a real work-day, meaning eight hours, from nine to five. Furthermore, let’s assume that I would get my weekends off, and I’d get some holidays and a vacation. There would therefore be eight work hours in a day, 20 work days in a month, and 250 work days in a year. These would all be translated into Matt equivalents, which is that amount of energy which I could generate while riding my rollers (i.e. 100 watts).

Under these definitions, how much Matt work is in a barrel of oil?

Keep guessing.

The answer, ladies and gentlemen, is 8.5 years. (The math is not all that complicated. You can skip to the end of this blog post to see the calculations.)

There are 8.5 years of my hard, sweat inducing, thirst generating labor in a single barrel of oil.

Wow. A barrel of oil today costs just under $80. Compare that to the actual cost of human labor. Let’s say my landscaping guy pays his workers $20/hour. By the time those workers have toiled for 8.5 years, he would have paid them $340,000. And yet I can buy the equivalent amount of energy in a barrel of oil for $80. Are you starting to see why I said we take our energy for granted? Oil is ridiculously cheap.

Those numbers sound almost absurd, so let’s do a quick sanity check to make sure that we’re not screwing something up. Let’s compare those calculations to some other ones which you might be familiar with.

There are 42 gallons in a barrel. My car weighs about 3,000 pounds. It gets about 25 miles per gallon. That means that a barrel of gasoline (let’s ignore the difference in energy between crude and gasoline for the moment) would propel my car 42 * 25, or 1,050 miles.

How long would it take me, with my bare hands, to carry or push 3,000 pounds 1,050 miles? Let’s ignore the practical difficulty of that question (I’d have to break the car up into small pieces in order to do it), but let’s only consider the scale. I’ve got to move 3,000 pounds 1,050 miles. How long would it take? That’s from Far Hills, NJ to about Des Moines, Iowa. If I could push 300 pounds at once, that would take me ten trips walking back and forth. How long would that take? 8,5 years? Certainly sounds reasonable.

Let’s face it, driving a car uses an absurd amount of energy, and we take it for granted. In fact, if you do this math with virtually all of our uses of energy, you’ll find the same thing. Flying to Vail, heating your house, running your dishwasher, taking a hot shower, blow drying your hair. Compared to Matt-units, these things just suck energy away like it’s free. I read on some other blog page that it would take an elite athlete 30 minutes of vigorous work to heat a liter of water to 100 degrees Celsius to make a pot of tea.

We are hopelessly, hopelessly addicted to cheap energy. And that could be a problem.

In my next post I am going to calculate exactly how much of this cheap energy I use in my home, and then in subsequent posts, I am going to see how difficult it might be to generate that energy through clean technologies.

So, get your calculators all warmed up for next week’s blog post. Goodbye for now.

Calculation of Matt energy in a barrel of oil

How much energy in a barrel of oil? (from Wikipedia)
6.1178632 × 109 Joules

1 Joule = I watt/second

So, divide by 100 to get seconds of Matt energy in a barrel of oil = 6.1178632 x 107

Divide by 60 to get minutes of Matt energy = 1,019,644

Divide by 60 to get hours of Matt energy = 16,994

Divide by eight to get work days of Matt energy = 2,124

Divide by 250 to get work years of Matt energy = 8.5 Years!


Doug said...

Matt: Congrats on a nice explanation of energy. The low percentage of our population that can grasp the physics or the (simple) math behind the facts is dissappointing, but real.

I think I found one error in your analysis... Burning 1000 food calories an hour is the equivalent of 1163 Watts, which seems high. A local company sells cycling generators that they claim average about 150 Watts in output.

I look forward to more of your observations and anaylsis. We have been upgrading our house to solar hot water, a woodburning insert, and lots of insulation, trying to reduce oil consumption byu 25-30%. All projects have paybacks of less than 5 years. We'll see how it goes....

By the way, you almost answered your own question regarding heating water for tea. A calorie is by definition the amount of energy it takes to heat a litre of water by 1 degree C. So to heat water to boiling from 25C (room temp), you would exert 75 calories, assuming perfect conversion of energy from your muscles into heat. If you are burning 1000 calories an hour, you could boil a litre in about 5 minutes.

What I'm not sure of is how efficient the body is at translating calories burned into physical work done. You could rig up a power meter to the resistance unit on your trainer and figure it out. When you burn 1000 calories, some of it goes to heat your body, some goes to pull water from your cells and generate sweat (to cool the body thats getting hot), and I'd imagine you use some power to generate the daydreams of your impending victory in the Tour De France. What's left over goes to the pedals, and could then turn a generator to make power.

mfinlay said...

Ugh. Doug. You're going to force me to be very precise here.

The watts I was referring to while talking about my bike are the watts of power which are generated at the cranks of my bike. Most bike racers use a Powermeter to measure the actual power generated at the cranks while they train. Many of the guys I ride with actually use them while racing too, but there's a penalty, because the meter is heavy for a racing bike.

The difference between the 1,000 watts of power used by the body in exercise and the 100ish watts of power actually generated in the crank is due primarily to the inefficiency of the human body as an engine. As I mentioned in the post, I generated a lot of heat and thus sweat. Also, there are a lot of other uses of energy, such as a beating heart, muscles for balance, etc.

Bikers have some rules of thumb about how to calculate how many watts are being generated at the cranks while riding under various circumstances. It's easy to relate this to the number of calories which are presumed to be burned by the body while exercising, as measured by a heart meter. I don't actually ride with a powermeter, but I'm pretty sure that I'm generating about 100 watts at teh cranks while on the rollers.

All of that information, however, would have made my already too long blog post much, much longer, so I simply skipped that step.

From now on, I'll try to be more precise, and if any explanation would make the blog post too long, I'll put it in a footnote.

Glad to know someone's reading though!