Can We Live on Sustainable Energy Alone?

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handsearth“Every 40 minutes, enough solar energy reaches the Earth’s surface to power the entire planet for a year.”

“There simply isn’t enough renewable energy to replace fossil fuels.”

I’ve read both statements over and over again. Which one is correct?

To help answer that question, Dr. David MacKay, professor of physics at Cambridge University, wrote a book called “Sustainable Energy – Without the Hot Air,” in which he gives a thorough and critical analysis of the feasibility of a post-fossil fuel world. Is there, using today’s technology, enough renewable energy available to eliminate fossil fuels altogether? 

You like math? This book is loaded with calculations. You could read the book (it’s free in electronic form), but if you don’t have time, you can watch his presentation in a video at the bottom of this article. But if you don’t have an hour to spare, I give a little synopsis of the book after the jump.

Dr. MacKay begins with three reasons why we must cut our addiction to fossil fuels: 1) fossil fuels are a finite resource; 2) CO2 emission is a very likely culprit in global climate change; and 3) a lack of energy security is a threat to all nations. (MacKay is specifically addressing the United Kingdom, but he also expands his discussion to the world in general.)

One of the confusing things about the energy discussion is the multitude of units that are used. Heat can be expressed in BTUs or calories, electricity in kilowatt-hours, energy in general is expressed in Joules, so Dr. MacKay uses a standard unit of energy throughout the book: the kilowatt-hour (kWh). He also uses kWh per day as the standard unit of power. For those who don’t know, power is the rate at which energy is converted from one form to another. In layman’s terms we might say that it’s the rate at which energy is produced or used.

He uses easy to remember “round” numbers to simplify calculations. In his discussion of energy production and consumption, he includes the energy in our food, since biofuels are one form of renewable energy and because some types of renewable energy (e.g. large solar farms) take up potential farmland.

After going through some basic assumptions and definitions, MacKay starts to build a two column bar graph: Energy consumption and energy production. Each bar is built piece by piece, starting with consumption. For example, he calculates that the average car uses 40 kWh of energy per day. (All calculations are in the book; I won’t repeat them here.)

Credit: Dr. David MacKay.

Credit: Dr. David MacKay.

Here are some of the highlights of the video with approximate time stamps:

7:00 Dr. MacKay dispels the significance of “vampire power.” A cell phone charger plugged in all day uses as much energy as driving a car for 1 second. We won’t save the planet just by unplugging all of our chargers. That’s not to say that we should leave them on all day, but that solving the energy crisis will take a lot more effort than that.

10:00 Renewables take up space. He discusses power density (generation and consumption) in watts per square meter and compares that with population density (people per square meter) and energy consumption per person.

14:00 Wind power generates 2.5 W/m2 in a windy area. That’s twice the power consumption of all of Britain, so if half of Britain were covered with wind turbines, wind power alone would provide all the energy needed. (Of course that’s not feasible – we know that.) The same numbers apply to Massachusetts. (His source: data from existing wind farms in Britain.)

16:00 Energy crops deliver about 0.5W/m2. This is not sufficient for Britain, but more than enough for Brazil, since they have more land.

18:00 Solar delivers 20W/m2 in Britain, where it’s not very sunny. Rooftop solar on every UK house would provide less than 5 percent of its energy needs. Solar farms are better; in the UK, they’re twice as good as wind farms.

19:00: Average tide pools produce about 2.7 W/m2. In Britain, the North Sea provides a large tide pool that could provide 8 W/m2.

21:00 Concentrated Solar Power (CSP) in deserts provides between 5W and 20W per m2. While this is not an option in the UK, it is feasible in many other countries.

24:00 Nuclear produces 1000 W/m2. While nuclear power isn’t exactly renewable, he includes it in his plan (later) as a stopgap solution.

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25:00 Professor MacKay talks about the opposition to wind and solar farms based on aesthetics and perceived property value. He jokes that nobody wants wind farms in their backyard, so we’ll put them far away. But wait – nobody wants to disturb pristine land, so we can’t put them there either. (On that note, a recent study showed no decrease in property value due to wind farms nearby.)

27:00 In Britain, renewables could reasonably take care of about 25 percent of the current energy needs. How can this improve? Reduce demand or increase production through population reduction, lifestyle changes, and improved technology. He looks first at plans that don’t affect lifestyles. Keep lifestyle changes on the table, but off to the side for now.

29:00 One way to get off of fossil fuels is to improve efficiency in transportation. Internal Combustion Engines (ICEs) are only 25 percent efficient. Electric vehicles are 85 to 90 percent efficient. Public transportation and electric cars are a part of the solution. I realize that EVs have limited range, but a large percentage of daily driving is short-range and improvements in battery technology are increasing the ranges and decreasing the recharge times. In ten years or less, I expect range to no longer be an issue.

33:00 A lot of energy goes into heating buildings. Turning a thermostat down a few degrees cuts your energy consumption significantly. Better insulation can give a 25 percent improvement. A gas furnace is 90 percent efficient. Air-source heat pumps are 300 percent efficient or better. (Okay, nothing is more than 100 percent efficient. A heat pump is extracting heat from the air. That energy is “free,” so the energy input in the efficiency calculation refers to the electricity required to run the pump. Let’s call the 300 percent figure “apparent efficiency.”) Ground source heat pumps (i.e. geothermal heating/cooling) are even better, but more expensive up front. Mackay suggests that we all switch to heat pumps instead of burning natural gas or other fossil fuels. This does increase electrical demand, which he also addresses in his plan.

37:00 Read your electric meter. Monitoring the electric meter makes people use less electricity. He says it’s like playing a video game. On a related note, cars that show instantaneous MPG – or miles per kWh if we go electric – cause drivers to drive more efficiently. (That’s been experimentally verified.) Smart meters with in-home displays can show how your power usage spikes when the air conditioner turns on. Have it translate that into money and maybe people will adjust their thermostats. Programmable thermostats can help reduce energy consumption if they’re used properly.

39:00 Unplugging unused appliances reduces electrical consumption by about 1 percent — a small part of the equation, but waste is waste, no matter how small.

40:00 Switching to renewables increases the need for storage and demand management. Heat is one way to store energy. He describes a Canadian community that uses solar water heating to heat more water than needed in the summer; they store the heat underground and recover it in the winter. This is similar in principle to old-fashioned ice houses. Side note: the utility industry is exploring many potential grid-level storage solutions. Even the industry sees the inevitability of renewable energy sources on the grid.

42:00 Make a plan. On the demand side: Electrify transportation, heat with heat pumps, insulate buildings, and monitor consumption (read your meters). This will roughly triple electricity demand because we’re electrifying transportation and heating. (MacKay is talking about Britain, so he acknowledges the fact that other countries have less population density and more renewable potential, so buying energy from other countries is an option.) He includes nuclear power as a stopgap solution.

46:00  Is there enough solar? To provide all of the energy needs (not just electricity) in all of North America, at levels comparable to current U.S. consumption, you’d need a solar farm slightly smaller than Texas. Of course, that’s at current consumption levels with current technology. (A recent NREL report says that a 32 acre solar farm would provide enough electrical energy to power 1000 homes. Extrapolating that to all of North America, and taking into account that electricity is only a small part of our total energy needs, I verified MacKay’s estimate.)

MacKay’s conclusion: it’s possible to live without fossil fuels, but the conversion won’t be easy. My take on that: when faced with adversity, human beings have demonstrated the willingness to adjust their behaviors and the ingenuity to create solutions. (In fact, the word “engineering” is derived from the same word as “ingenuity.”) Case in point: World War II. Industries were retooled to support the war effort. People conserved fuel and recycled materials. New technologies were created.

MacKay focuses on energy rather than economics, but near the end of the book he mentions the fact that developed nations spend a lot of money on “questionable” programs. He suggests, and I agree, that the money is there; it’s just a matter of priorities. I’ll add that the real cost of fossil fuels is much higher than the cost of switching to renewables. How much money do we spend “stabilizing” our oil supplies in foreign countries? How much does it cost to clean up and rebuild after superstorms that are likely caused by climate change? How much do we spend on health issues caused by breathing the remnants of oil, coal, and gas?

He concludes the book by showing five potential plans for changing to renewable energy. Keep in mind that this is only for Great Britain’s situation. MacKay includes appendices showing all of his calculations and assumptions, so the reader can perform the calculations for his/her own location. One of my colleagues did that for our community college district. I’ll share those results in a future article.

Credit: Dr. David MacKay.

Credit: Dr. David MacKay.

This article was originally published on and is reprinted in its entirety with permission.  For more stories like this please visit


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  • Ivan Quinchia
    October 8, 2013

    In Reference to wind, it’s ironic that all of the studies done by Lawrence Berkley Lab are done on technologies that are highly subsidized through tax incentives and tax credits.
    Drill down on the facts before quoting studies.

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