How many acres is your energy footprint?

How much land area would your state have to set aside for all its resident’s energy needs?  It all comes down to the type of energy you use. David MacKay does the math.

chat Posted Sep 17, 2014 by Rezwan | Category : Scoreboard Footprints
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The TED Talk

In what is sure to become a classic approach to the subject, MacKay breaks down the footprint calculation as follows: 

On one side, you have the area and how much energy the residents use.  This gives you the energy demand as Watts per unit of area. 
On the other side: you have the amount power supplied per unit of area for different energy types.

David MacKay TED Talk: Reality Check on Renewables

How much land mass would renewables need to power a nation like the UK? An entire country’s worth. In this pragmatic talk, David MacKay tours the basic mathematics that show worrying limitations on our sustainable energy options and explains why we should pursue them anyway. (Filmed at TEDxWarwick.)


Biomass is wildly inefficient

Compare energy consumption and production per m2

Energy consumption per m2

Energy production per m2 above and below the line.


Notes & Related:

By David MacKay:

New Jersey Example

Let’s take the Garden State, since that’s where I am now.

Calculating Energy Density:

Total Energy Consumption (per EIA): 2,272 trillion Btu, which is 665.8 TWh/year
Area: 8,729 sq miles or 22,608 km²

Divide Total Energy Consumption by area to get average energy consumption/m2: 3.36 W/m2 

This means that if your energy supply has a density of 3.36 W/m2, it would blanket the entire state. So…what is the density of your preferred energy supply?

Meeting the need with 100% Renewables

Looking at the Energy production chart, we see that solar PV parks have an energy production density of 5W/m2.  If you want to use solar PV alone to power New Jersey, you would have to cover 67% of the state with them. Concentrating Solar is denser at 20 W/m2, but only if the sun always shines, which is not the case in New Jersey.  Even if it did, if you choose this path 16.8% of the state area would be required to run it. 

Onshore wind is insufficient - 2.5W/m2 - you’d have to cover the entire state with wind turbines and add turbines to adjacent states.  If you plant biomass under the wind turbines, that could add a 0.5W/m2 of energy to the area, bringing you up to 3, still shy of the 3.36 demand. Everyone would live within earshot of a wind turbine, covered in biomass.

Offshore wind is better, but I don’t have the numbers on this.  If you know of an infographic that breaks down the energy density of various wind technologies, please let us know in the comments. 

You will notice that plans calling for 100% renewable energy require a substantial drop in demand.  For example, the SolutionsProject plan for New Jersey is based on a 47% reduction in demand, and 55% energy from offshore wind.

Meeting the need with 100% Nuclear

The energy density of Nuclear is 1000 W/m2, ~300 times the consumption density.  Thus, if New Jersey were to use 100% nuclear power to meet all its energy needs, it would need 1/300th of the state area, or 29 square miles, leaving the other 8,700 square miles free of energy supply clutter.  We’d still need the power lines of course.

But, as MacKay points out, nuclear has some popularity problems.

The Composite Choice

In the end, market and popularity forces will determine the mix of renewables, nuclear and conservation that prevail.  100% Renewables aficionados will start out with the intention of getting the state to drop 50% of its demand and cover half the surface area with energy supply clutter, but will face resistance to conservation (deprivation), and a NIMBY backlash as the wind turbines scale up.  Solar will have an easier time now that the panels come in different colors : ). 

Meanwhile, nuclear aficionados will try to tempt the populace with reliable power and no need for deprivation - but the cost is a bit high, and, oh yeah, NIMBY. 

Although, come to think of it the cost is not higher than renewables.

More fun facts

NJ Population: 8.865 million (2012) people. 
NJ Population density: (dividing population by area) 392 people per km2
If you divided New Jersey land equally among the residents, we’d each get 2250m2 or 0.63 Acres.  So much for 40 acres and a mule. That doesn’t give us much space to provide energy for our homes, let alone the energy overhead for our places of business, commerce, enjoyment. Because we use a lot of energy.

NJ Total Consumption per Capita ~75,000 kWh a year, which is 205 kWh/day
And I don’t think this number includes energy embedded into the products we import.  Research in progress.

Peak Washing Machine

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