“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),
Don’t have an hour to spare? Okay, I’ll give a little synopsis of the book here.
Dr. MacKay
begins with three reasons why we must cut our addiction to fossil fuels:
- fossil fuels are a finite resource;
- CO2 emission is a very likely culprit in global climate change; and
- 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.)
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% 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.
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% 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% efficient. Electric vehicles are 85-90% 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% improvement. A gas
furnace is 90% efficient. Air-source heat pumps are 300% efficient or
better. (Okay, nothing is more than 100% 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% 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% - 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 US 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.
Images: Dr. David MacKay
Video: Harvard University
Video: Harvard University
source: engineering.com
Great post about renewable energy but Solar Savings Estimator is best for using solar panle.
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