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    How Much Energy Do We Really Use?
    By Thor Russell | January 6th 2012 11:37 PM | 11 comments | Print | E-mail | Track Comments
    About Thor

    My background is in science, maths, engineering and psychology. My work in artificial intelligence and pattern recognition gives me some unique insights...

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    It is said that Mankind uses about 15TW of energy continuously, with most of that coming from fossil fuels. However I think there is another just as valid way of looking at how much energy we use that gives a very different answer. This is relevant when people say in a discussion about reducing fossil fuel use “But what we really have is an energy problem” as if it is somehow a more profound assessment of our situation. I consider it misleading for the following reasons:

    Consider heating your house on a cold but sunny day. You could heat it with electricity from the grid, by having large windows letting the sun in, by having solar panels power a heat pump, or by burning some dried out weeds that you have lying around. All of these would work but they would get counted very differently. Using the grid gets counted as energy in the 15 TW figure, so might solar panels (who knows if they are not connected to the grid). But compare solar panels connected to a heat pump, to having the sun stream in through glass windows. This is pretty much the same thing, however one may get counted as using energy, the other definitely will not.

    Now compare solar panels to the weeds. Solar panels take energy from the sun, convert it to electricity which then heats the house. So does growing weedy plants, chopping them down and burning them, but with the energy stored chemically rather than electrically. The amount of sunlight hitting the weeds over their lifetime would be huge, of which only a small fraction is made use off when you cut them down and burn them. So how much energy do you “use” when you heat your house this way?

    1. Nothing because it wasn’t electricity
    2. The amount of heat that was given off in the fire, or 
    3. The total amount of energy hitting those plants that came from the sun over their lifetime, even though only a small %, say 1% actually ending up as heat in your house.

    I would argue that #3 makes the most sense, because If you then go and replace that land with weeds on them with solar panels, you are still using all that energy one way or another, as electricity rather than chemically. (Ecologically of course it is different, but not necessarily even better to have plants if they are intensively farmed and you consider the ocean dead zones etc from fertilizer runoff.) So, where does this lead? 

    It is said that about 50% of all land based photosynthesis has been co-opted by humans in some way, this includes land directly to make crops, indirectly to make grass that is eaten by cows to make milk, meat, and land used to grow cotton etc. As I am going to make a rough estimate, lets go with the 50% figure. Now world energy consumption is quoted as 15 TW average. (wikipedia) This figure includes sources of energy such as fossil fuels, nuclear, and renewables, but does not include the energy needed to power those plants the support humanity. So what is that energy? The land surface area of earth is 148,940,000 km^2 or 1.514 m^2. Assuming plants cover 1/2 the land as a very rough guess (deserts, high mountains excluded etc) and humans use half of this, then we use 3.7513 m^2 of land. So what is our real energy usage that we would need if the sun went out? The average insolation of the sun in space is about 1366 W/m^2, but about 1000 W/m^2 at sea level when you take into account losses through the atmosphere. The average through all the day/night is ¼ of this because of geometry. (The surface area of a sphere is 4*pi*r^2, the radius facing the sun is pi*r^2). So without clouds the average would be 250W/m^2. As a rough estimate taking cloud cover to be 50% we get 125W/m^2 continuously. This is approximately the average amount of energy hitting the land that we use day and night. 

    So how much energy do we get if we use this figure, and the land area calculated before?
    125 W/m^2 *3.7513m = 4.715W or 4700 TW

    Compared to 15 TW this is over 300* the amount of energy in the widely quoted 15 TW figure. Now this is deliberately not accurate because I have not even included any of the sea. How do you calculate the energy needed for our fishing? If you had to include the sun that powered the plankton at the bottom of the food chain that has to exist for fish to survive it would make the 4700TW significantly larger.

    That troubling 1%

    To me this means that mankind is already over 99% solar powered, we just don't realize it. To me that also means that 15 TW is not large at all, but small and when people talk about mankind's supposedly large energy and unsustainable energy usage, I don't agree at all as they are generally not talking about the energy needed to grow our food/cotton/fish etc. If 4700TW is large, then 15 TW is not. We definitely are using a large amount of the land area of the planet, but I’m not sure our direct energy usage of 15 TW or so is a problem, or even a meaningful number. The technology and resources (fossil fuels) we use to provide this energy definitely causes problems but this is not the same thing. Pointing out that it will be difficult to replace the source of the 15 TW is also valid, but saying the 15 TW itself is too large is not so valid without making some pretty sweeping judgments about what will be or is already technologically possible. If someone says that we really have an energy problem then what energy are they talking about? The 15 TW or the 4700 TW? Saying that 4700 TW is too much is just a roundabout way of saying that our current land usage is too much or is being used unsustainably.

    Comments

    You said "We definitely are using a large amount of the land area of the planet, but I’m not sure our direct energy usage of 15 TW or so is a problem, or even a meaningful number."

    Guess you missed all the data that shows the correlation between the Industrial Revolution and global warming. And the associated pollution, environmental destruction and long-term effects on human health and the biosphere.

    Of course the 15TW is "a problem", certainly this is a meaningful number in the context of your article. It's the "how" we generate that 15 TW that matters. Either use more land, or continue with the business-as-usual (exploit energy sources). Either way, it's very significant.

    In any case, you utterly ignored what 15TW actually means to human habitation, and what it means for the planet at large (to include the biosphere of course). Is it too much? What yardstick do you want to use? Pre-Industrial civilization? American living standards? Truth be told, humans do not "need" that 15TW, so anything above that is "elevated" usage.

    Thor Russell
    I believe in AGW and making a concerted global effort to avoid it so you have not understood my point.15TW is not the problem, fossil fuels are. At them moment they may seem like the same thing but as we de-carbonize they increasingly will not be.

    "You utterly ignored what 15TW actually does to human habitation ..."
    15TW powered by renewables such as solar has an immeasurably small affect on the climate, the planet, the biosphere, whatever you choose. Here is why:


    The total area of the earth including oceans is 5.1e14 m^2 from Wikipedia. So what is 15TW averaged over the entire earth’s area?

    It is 15e12/5.1e14 = 0.03 W/m^2. 

    That is 0.03 watts per square meter. The sun when overhead gives 1000 watts per square meter, or 
    over 30,000 times as much heat. The real figure to compare the 0.03 W/m^2 however is the extra energy trapped by greenhouse gasses etc which you can look up and is about 2 W/m^2.
    So, the greenhouse gasses cause over 60 times! more heating than the "large" 15TW figure. Also the sun intensity varies naturally, by about 0.1% during a solar cycle and more if you include changes between cycles. If you take 0.1% of the average 250W/m^2 figure you get 0.25W/m^2 natural variation, which is almost 10 times larger than what the 15TW gives. While we can clearly see the affect of the greenhouse gasses on climate, there is little change that we would ever detect any effect of the direct heating effect of the 15TW. If they are supplied by renewables then there is no problem. The yardstick I use is clearly the effect it has on the planet, that is what I am concerned about. Pre-industrial civilization is no guide. 

    Coming back to the land issue, I need to make clear an issue about energy "use". Our roof easily receives enough energy from the sun to power our electricity needs using solar panels. So if we covered 1/4 of our roof with solar panels would we use more energy? Well the roof already "uses" (converts sunlight into heat energy) energy just by being the color green. Now solar panels absorb more energy than a green colored roof, but if we painted the other part of our roof that was not covered by solar panels white, then the roof would absorb the same total amount of energy as before. From the planets point of view, we would not use any more energy at all, and the energy we did use would be irrelevant as far as climate was concerned. The energy I used from the solar panels would not be a meaningful number as it would have no effect on the global or even local climate. Once again powering the 15TW with solar would take far less land than we currently use for agriculture. I think you will find that if you replaced the corn used to grow ethanol for fuel (a terrible use of energy if there ever was one) then you could with a similar area of land power a large fraction of the whole world.

    I hope you see my point now.
    Thor Russell
    Gerhard Adam
    I'm not sure what you're trying to say here, because much of the discussion completely misses the point regarding the form the energy we need takes.  It's like talking about the benefits of nuclear energy and overlooking the fact that nuclear won't power my car.

    The overall "problem" of energy is due to the fact that we need to transform it or deliver in ways that aren't not intrinsic to the environment in which it will be used.  So, again .... I'm not clear on what your message is.
    Mundus vult decipi
    Thor Russell
    I didn't overlook the fact that at present you can't power your car with nuclear/wind/solar that's why I called it the troubling 1%. Many people I have spoken to don't think the problem is due to the fact that we need to transform the energy, but think the actual figure is too large. That's why I wrote the post. When talking about electric cars etc they insist that there isn't the electricity to power them, and it can't be generated by any method without a massive impact on the planet. As a consequence they oppose electric cars and would rather take a diesel powered bus! Sure at present etc enough of the electricity may come form fossil fuels but that is beside the point when discussing potential solutions to powering cars because of course the source of electricity can change and electricity is much easier to make sustainably than diesel. I think this attitude holds back progress.
    Furthermore I think many people if given the choice between using 2GW of renewables compared to 1GW of fossil fuel to power something would choose the 1GW of fossil fuels because they have the belief that 2GW is too large. That would also be pretty tragic as the 1GW would have much more impact than the renewables if they came from a sensible source. 
    Finally the connection between energy usage and CO2 could completely reverse if we properly develop the technology to use energy to suck CO2 out of the air. If there was a scheme to increase our energy usage by another 15TW (powered say by solar) and use that extra energy to suck CO2 out the air I would be all in favor, but I expect many people would oppose it because they would believe the 15TW is somehow too large. 
    Thor Russell
    vongehr
    Ohhh - now if you had written it like this. ;-) I was like Gerhard - where on earth is this going - what does he want? Midway started to expect you will tell us that the total energy in my morning egg is several atomic bombs according to E = m c2, and so 15TW is nothing. Allow me to suggest to explicitly state what precisely you want to express and perhaps even why. Then give your argument after that or wrap the text around it. I discovered people actually like that, rather than feeling insulted. Of course, it doesn't stop them from discussing totally off topic in the comments nevertheless.
    Thor Russell
    My comment about improving went in the wrong place, but I won't delete it ...
    Thor Russell
    MikeCrow
    Tell us what you want to tell us about, tell it to us, then summarize it.

    We shouldn't feel insulted by this. I want to know what the blog/article is going to be about. Digest the points of the article, and then confirm I understood the points. The more abstract/complicated the topic the more important the conclusion/summary is.
    Never is a long time.
    MikeCrow
    but think the actual figure is too large
    And IMO these people want us to live as if it was 100 years ago.
    Never is a long time.
    >> And IMO these people want us to live as if it was 100 years ago. <<

    Nah. They want YOU to live that way. They're plenty satisified with their life but you must change.

    MikeCrow
    Point taken Frank!

    This reminds me of the kinds of car that are driven by those well off (including the people who set the rules) in Europe vs what "normal" people drive.
    Never is a long time.
    Thor Russell
    OK I will keep that in mind for next time. still got some learning to do I expect :)
    Thor Russell