When you have a hammer…

“When you have a hammer, everything looks like a nail”

What a wonderfully simple way to describe much of our world.  I am reminded of this whenever I see people working on the “energy” problem.  Software people clearly know, that if only we wired everything up and monitored our energy use, the rest of the problem would be trivial.  Economists clearly have the upper hand, because they can describe carbon trading as the sure fire method to reduce carbon output,  increase energy efficiency, and still have economic growth.  Photovoltaic manufacturers, electric car builders, and wind farm developers are among the many queuing up at the public feeding trough.

Nothing wrong with any of those solutions.  Just bear in mind the aphorism.

By the way, our hammer is a whole house fan.

Sustainable or Self Contained?

The concept of sustainable living, or sustainability has wide appeal. It’s hard to argue with the idea that if you think of natural resources and energy as a bank account,  we should not be overdrawn.

If you do it right, and it’s a tall order, you could model the “real” costs of resource extraction.  Our simplistic economic models increase the Gross Domestic Product when a tree is cut down, or oil is burnt.  Basic accounting practices would at least require us to decrease the amount in our natural resource account.

Let’s table that thought. Onto the rant du jour.  Our local food co-op has the following announcement:

——————————local Co-op announcement——————————————–

FRIDAY also means PORT ORFORD Hook and Line Caught Fish are here.Port Orford fisherman also dropped off some sea water! We’re going to make our own “Port Orford Sea Salt” for Eat Local Week!


Isn’t that great?  Well, of course not! Otherwise this would not be a rant.

How do you make your own salt?  Evaporate the water.  Great. With what energy?  Electricity as it turns out.

Let’s do some calculations …

Percent salt in seawater (by mass) 3.50%

Energy to evaporate 1 kg water 2,257,000 joules
Efficiency of Evaporation* 60.00%

Energy to recover 1 kg salt=> 107,476,190 joules
Convert to=> 29.85 kWh
pounds of CO2 per kWh 1.35 source: DOE
pounds of CO2 produced per 1 kg salt=> 40.3

* Engineering Estimate

Salt Evaporation Using Solar Energy
Salt Evaporation Using Solar Energy

Bottom line. You made your own salt. If you had purchased standard packaged salt, it would most likely have been harvested using solar energy, and energy efficient vacuum evaporation process (see http://www.cargill.com/static/sb/tour.htm).

Perhaps this adventure falls into the self-contained, but not sustainable category.

Can we grow our own energy ?

farmer-plowingSo you think we can grow our own energy?  My first thought was “why not”, but the inner engineer said “do the math”.  OK, inner engineers always win.
Now what facts and numbers are we interested in.  I thought that it would be interesting to take the average American, put him and his average family on a piece of land.  This piece of land would have to provide him with all the direct energy the family uses.  I’ll define direct energy as the energy used for heating, cooling, electricity, and automobile transportation.  For this scenario, we’ll assume that each factory, office, etc. has its own “energy farm”.

The best source for energy statistics is the US department of energy website (http://eia.doe.gov/).

I thought this was going to be hard. In fact the data is all right on this one table: http://www.eia.doe.gov/emeu/recs/recs2005/hc2005_tables/c&e/excel/tableus1part1.xls

It seems that the average US household consumes 95,000,000 BTU (equivalent) for electricity, natural gas, and heating oil.The average daily consumption of gasoline for the U.S. is about 9,000,000 barrels (42 gallons.)  I’ll assume that half of that consumption is for individuals (tell me if I’m wrong). There are 127,000,000  dwelling units.

The total energy growing requirements calculate out to about 157,000,000 BTU per year.

On the supply side…How much solar energy do plants absorb ?  According to http://bioenergy.ornl.gov/main.aspx it’s possible to obtain 10 tons of dry plant material per acre per year.  At an average of 19GigaJoules per ton, this would yield (assuming 50% conversion to useful energy) 45,000,000 BTU per acre.  Doing the division 157,000,000/45,000,000 gives us 3.5 acres.

In reality, you’ll need much more area. Because you have to eat, the horses (or tractors) have to eat, you may have to irrigate your energy crops, and you need manufactured products.

Assuming very little “home grown energy”, we would need: 127,000,000 households x 3.5 acres = 445,000,000 acres of additional cultivation. The US has about 407,000,000 acres of arable land.


Well, maybe this efficiency thing isn’t such a bad idea after all..

Other sources:

  • http://www.eia.doe.gov/kids/energyfacts/science/energy_calculator.html has conversions from different energy sources and units.
  • http://www.eia.doe.gov/kids/energyfacts/science/energy_calculator.html

“I have been so happy as by accident to hit upon a method of restoring air which has been injured by the burning of candles and to have discovered at least one of the restoratives which Nature employs for this purpose. It is vegetation.”
Joseph Priestley 1771