SRI Blog

Let’s Get Real about Our Future Energy Supply

Energy supply is perhaps the largest global problem facing us today, yet the public is largely unaware of the scale of the problem.

Meeting the future global demand for energy is a daunting challenge and will affect the lives of billions of people. Therefore, the public must engage in making decisions to determine how we address this challenge. In other words, we need a shared working understanding of our energy problem—how much energy we use and how much we will need—before we can fix it.

To begin to explain the magnitude of the problem and the nuances to the solutions, my colleagues and I co-authored the book A Cubic Mile of Oil. In it, we discuss how energy is derived from many different sources: oil, coal, natural gas, nuclear power, wind, and so on. However, energy production and consumption are measured differently for each source: oil in barrels, coal in tons, gas in cubic feet, and nuclear and wind in kilowatt-hours. Using a standard scientific measure of energy use, a number close to about 570 exajoules of energy is derived. That sounds like a lot (and it is), but it doesn’t mean much to the public.

Thus, my co-author Hew Crane developed the cubic mile of oil (CMO) as an understandable and visual standard metric that scales to global use.

A CMO is a good measure to use for global energy consumption. The approximately 80 million barrels of oil the world uses each day adds up to 1 CMO over a year. In addition, we use the equivalent of 0.8 CMO from coal, 0.6 CMO from natural gas, and about 0.2 CMO from each of hydroelectric power, nuclear power, and wood-burning for a total of 3.0 CMO of energy per year.

In 50 years, global energy need is projected to be between six and 9 CMO of energy per year.

Think of it this way: until now we have been spending our inheritance of coal, oil, gas, and nuclear energy (our finite resources). However, we know our endowment won’t last forever, so we need to transition to our renewable energy sources, which constitute our income: wind, solar, and biomass. These renewable sources represent a steady flow of energy we can depend on in the future.

The transition to alternative and renewable energy will take a long time and must be done carefully. We are not yet efficient enough at capturing renewable energy to replace our inherited energy sources in the near term.

Adding capacity to produce just 1 CMO per year is harder than you think. For example:

  • It takes 2,500 nuclear plants of 1-GW capacity to generate 1 CMO in a year. That equates to building one nuclear plant per week for 50 years.
  • It would take about 3 million 2-MW wind turbines spread over approximately 600,000 square miles to produce 1 CMO per year.
  • The sun gives us 23,000 CMO every year, but currently we can capture only a small fraction of this energy (we convert about 15-20% of the sunlight that falls on our photovoltaic materials into usable energy). It would take 4.5 billion residential rooftop photovoltaic systems (2kW each) to produce the equivalent of 1 CMO per year. In other words, we would need to install a quarter of a million rooftop systems every day for 50 years!
  • The scale of these replacement projects is almost unimaginable. Improvements in efficiency, along with a reduction in the huge cost of associated support structures, won’t happen overnight.

To meet our energy challenges, we need all-out commitment and perseverance to develop all our energy sources. Yes, we need to move toward developing more income (not inheritance) resources, but calls to turn off the fossil fuels that we use today and quickly power ourselves with renewable energy sources are irresponsible. We need to move carefully and gradually from dependence on coal, oil, and gas to better and better ways of harnessing renewable sources.


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Robert Yawn

The most underutilized is geothermal based energy. How would this be measured in CMOs?

Ripudaman Malhotra

Total energy being dissipated by the cooling core of the Earth is estimated at 7 CMO/yr. We currently use only about 0.005 CMO/yr for heating and power production. We tap into this energy at locations where the magma is close to the surface of the Earth and there is underground water table to help transfer that heat to the surface. Not all geothermal resources are equal; some can provide only low grade heat, while others can provide high temperature steam suitable for power production. Estimates of technically usable geothermal resources vary from a low of 0.06 CMO/yr to 0.78 CMO/yr. There are also geothermal resources where there is no natural water table nearby. In such cases, surface water must be injected deep into hot dry rocks (HDR) to extract heat. HDR resources are more widely located, and represent a larger resource base, but so far it has not been economical to extract power from this resource.

Samuel French

Having studied thermal flat plate solar collectors for a few years in the 70's and 80's we had much higher efficiencies than photovoltaic conversion is, even today. Should there be a study to determine the relatively simple conversion from heat to storage or heat to motor power? Given the simplicity of thermal systems, and the possible gain in output, wouldn't that be worth some tests?

Ripudaman Malhotra

Absolutely. Solar heat collectors offer a cost effective approach for reducing heating requirements. Solar water heater units currently cost about $300 in emerging economies like India and China, and less than $2,000 in the U.S. At that price many homeowners can afford to have both a water heater plus a gas water heater as a backup. Widespread adoption of solar thermal systems has a low economic barrier, well suited for places like China and India where we are likely to see the greatest growth in energy use in the coming decades.