The Energy Future

8 June 2007

We hear a lot about global warming, technology, and energy in the news, but it's hard to get an overall picture of our energy situation. So, I decided it was time to do some research, and I've collected below some information about the present and projected future of energy production and usage by the world's people. But before I present the supporting facts, let me present my conclusions:

  • Over the next few decades, if we do not drastically change our energy usage habits, we will need to find a way to generate large amounts of energy from sources other than fossil fuels, because the fossil fuels are not an infinite resource, and because using fossil fuels contributes to global warming.
  • Taking into account capacity and the energy cost of producing more energy, the best potential for developing significant new energy sources lies in solar and wind power. Biofuels such as ethanol, in spite of current hype, have essentially zero potential for contributing in a positive way; other mechanisms, such as nuclear and hydropower, can contribute some, but are unlikely to make much of a difference.
  • I think we need to give some serious thought to making drastic changes to our energy usage habits, especially given that the world's population is increasing, and that as the developing world develops, the people there will tend to catch up to our levels of energy use. The transportation sector has a lot of potential for efficiency increases, which could include trip reduction, trip consolidation (mass transit for people as well as goods transport), and more efficient vehicles. The main potential for efficiency in the industrial sector is probably for people to consume and purchase less, which would also lead to a decreased need for commercial transportation. Pursuing home and commercial building efficiency is worthwhile, but since these sectors are smaller parts of the world's energy consumption, efficiency increases in these areas are less likely to make a huge difference.
  • Although technology can certainly help, major reductions in energy use in the transportation and industrial sectors will require lifestyle changes, which are difficult to promote. And while no one likes to think about it much, population control is probably one of the best means for limiting growth in energy consumption.
  • Public policy can provide incentives for needed changes in both production and consumption of energy. One thing we could do is shift the focus of our energy policies: add funding for solar and wind technology, stop funding subsidies and research for biofuels, and abandon the legal hassles of trying to build more nuclear and hydroelectric plants. We could also change our tax structures to add economic costs to activities that consume energy, produce greenhouse gases, and add to the world's population; or conversely, we could give economic benefits, through our tax structure, to energy conservation activities. And we could also replace subsidies for inefficient transportation modes (such as highways) in our government budgets with subsidies for more efficient modes (such as railroads).

So, here are the facts and reasoning behind the above conclusions. A quick note on units: In this article, energy consumption and generation are given in terms of instantaneous rate (power), in watts (W) -- by "power" I don't mean just electric power, but energy use/production in any form. 1 kW (kilowatt) = 1,000 watts. 1 MW (megawatt) = 1,000,000 watts. 1 GW (gigawatt) = 1,000,000,000 watts. 1 TW (terawatt) = 1,000,000,000,000 watts.

World Energy Usage and Projections

  • According to a recent article I read in Science News ("Reaching For Rays", only available with subscription), and the Wikipedia article "World Energy Resources and Consumption" global energy consumption happens at a rate (i.e. power) of about 13-15 TW.
  • Given a world population of something over 6 gigapeople, the average person on earth is consuming roughly 2.2 kW, either directly or indirectly. However, the distribution is not equal: the United States consumes about 11 kW per person, while in the developing world, consumption is about 0.5 kW per person, according to the Wikipedia energy article cited above. China is currently using about 2.2 kW per person, but I imagine a significant fraction of that amount is used by industry that makes goods for other nations.
  • The Science News article cited above projects that world energy use will double by 2050, due to population growth and development. The world's population is expected to approximately double by that time.
  • We use energy for many purposes. The US Department of Energy divides energy consumption into four sectors, and according to its Energy Outlook 2007 report, worldwide:
    • 37% of the energy we produce is for industrial uses, including agriculture, mining, manufacturing, and construction.
    • 20% is for transportation uses, including personal and commercial transportation.
    • 11% is for residential uses, including home heating, lighting, and appliances.
    • 5% is for commercial uses, including lighting, heating and cooling of commercial buildings, and water and sewer services.
    • The remaining 27% (wow!) of the energy the world produces is lost in the generation, transmission, and distribution of electricity.

Current Energy Sources and Future Potential

  • According to both the Science News and Wikipedia energy articles cited above, fossil fuels (coal, petroleum, and natural gas) currently provide 86% of the energy we consume, amounting to about 13 TW of power. The earth contains finite amounts of these fuels: according to the World Coal Institute, the world's coal reserves are equivalent to 155 years at current usage levels, our petroleum reserves are equivalent to 41 years of current usage, and our natural gas reserves are equivalent to 65 years of current usage. Using fossil fuels also leads to greenhouse gas production and global warming, so we will probably have to reduce their use in the future. In any case, if energy use grows as projected, or even if it stays at today's level, over the next several decades we will need to come up with other sources to replace fossil fuel energy.
  • We currently generate about 900 GW of nuclear power in 435 nuclear power plants, according to the Wikipedia energy article cited above. Building a new plant adds 1-2 GW of power production, which means we would have to build about 1000 new nuclear power plants worldwide to begin to generate power that would make a significant contribution to our future needs... and deal with the hassles of finding places to put them, and store the waste. The energy cost to build, operate, and de-commission a nuclear power plant (including costs to mine and dispose of the fuel) is about 1-5% of the energy the plant can expect to produce, according to this nuclear power web site, which appears to have done a fairly careful analysis, and this comparison of energy paybacks.
  • Biomass (including wood, ethanol, biodiesel, etc.) is currently supplying about 260 GW of the word's power, including fuel used for heating, but not including fuel used for cooking, according to the Wikipedia energy article. Consuming biofuels produces greenhouse gases -- actually, even more than generating the same amount of energy from fossil fuels, because biofuels have lower energy content. The potential for developing more biomass power production is limited, in spite of the current hype about biodiesel and ethanol. For instance, according to this editorial by Tad Patzek, if we converted all of the US annual corn production into ethanol, we could only replace about 6% of the US annual consumption of gasoline. Of course, it also costs a significant amount of energy to produce corn and refine it into ethanol (all the analysis I have seen indicates that producing ethanol from corn costs more energy than you get out, which means it is clearly a no-win proposition). Some biofuels may actually do slightly better than break-even on energy cost, but even this is not clear. Furthermore, as the world's population grows, we will need to use more land for food production, not convert agricultural land into biofuel production; converting more currently wild land into such uses is not an appealing possibility. So, the end result (see this video presentation for more details) is that the potential of future net biomass energy production in the world is minimal, compared to our future needs.
  • The Wikipedia energy article cited above states that we currently have about 826 GW of hydropower in production. According to the Science News article cited above, there is about 500 GW of new hydroelectric power that could be developed in the world. This is fairly insignificant compared to our future needs.
  • The Wikipedia energy article states that we are generating about 100 GW of geothermal power, including electric generation, direct heating, and more passive methods. I'm not sure what the future potential of geothermal power is.
  • We are currently generating about 93 GW of solar power, according to the Wikipedia energy article cited above, which is mostly solar heating, and a small amount of electricity generation. The potential is much larger: according to the Science News article cited above, the total power of sunlight hitting the earth is approximately 120,000 TW. Of course, we can't really expect to use all that energy. One reason is that solar cells are not 100% efficient at converting sunlight to usable energy (e.g. electricity) -- the Science News article says the best cells today are only about 20% efficient. Also, we cannot cover the entire surface of the earth in solar cells: 75% of the earth's surface is covered by water, and about 48% of the land area is currently being used for agricultural or forestry purposes (see this Nova web page), which we probably cannot afford to reduce, as discussed above. We probably also need to preserve some or most of the un-developed land on the planet (about half of the land total), and remote areas may not be practical locations for generating power either. So perhaps an area comparable to the 2-3% of the earth's land currently being used for housing, industry, and roads could be devoted to solar cells, and maybe the existing buildings could have solar cells on their roofs, giving a total of about 5% coverage. That would mean a potential of about 300 TW of power, taking into account efficiency, which is certainly significant. To generate 1 TW of power (i.e. to start making a difference when compared to our current energy usage), we would need about 3700 square kilometers of solar cells. According to this article on solar-cell "payback", with current technology, the cells have an up-front energy cost of about 20% of their eventual energy generation (which is spread over 20-40 years).
  • We currently have about 58 GW being generated by wind, according to the Wikipedia energy article. The worldwide potential for wind energy is about 72 TW, according to this analysis of wind power potential, which analyzes wind speeds in comparison to those needed to run actual, available wind turbines. A typical turbine generates about 1.5 MW of power, so it we're talking about roughly 1 million turbines before the generation becomes significant, when compared to our energy needs. The energy cost to build and operate a wind turbine is about 5% of the energy generated over its lifetime, according to this comparison of energy paybacks.