The Ergosphere
Monday, October 11, 2004
 

And now a word from the janitor

Clicking the "comments" link on a post should now take you to the first comment, rather than the top of the entire post.  If this doesn't work properly, e-mail me. 
Friday, October 08, 2004
 

The Oswalds get it partly right

The Oswald brothers of England (hat tip: PhysOrg.com) did something important and long overdue; they co-wrote a short analysis of the requirements for running Britain's transport systems on wind energy.  And they got a very large number, approximately 100,000 turbines of 3 MW capacity each, making a strip 10 km deep around the entire island nation.
Unfortunately (for them), they were not terribly clear in their assumptions; as a result, they have made several mistakes which call their conclusions into question.  I shall begin where they end, with their technical calculation.

It all comes down to the numbers

The Oswalds' calculation is stated in their paper thusly:
Annual consumption:  54 million tons of oil equivalent (MTOE)     (1)
Efficiency of electrolyzer/fuel cell chain:  50%     (2)
Annual renewable energy required:  108 MTOE     (3)
Converting units to average daily MW[1]:
108*1000*11.63[2]*1000/(365*24) = 143,000 MW   
  (4)

[1] The lack of units in the calculation is in the original.  This is an omission, not an error; if filled in, they would be:
108 MTOE/yr * 1000 kt/mt * 11.63 GWH/kt * 1000 MWH/GWH / (365 days/yr * 24 hr/day) = 143,000 MW
[2] The conversion factor 11.63 GWH/kt (equivalent to 11.63 KWH/kg) appears to be a bit high, but not unreasonably so.  They got it from a fact sheet available here.

What's wrong with that?

There are several minor errors and two major errors in this calculation.  The major errors dwarf the others into irrelevance:
  1. In (2), they assume that conversion to hydrogen is the best, or only, way to make renewable energy available to power transport.
  2. Throughout, they assume that the conversion of oil to work is 100% efficient.

The first assumption is debatable, the second is absurd.  The efficiency of typical diesel truck engines peaks out around 40% and averages considerably less; the efficiency of automobiles is much lower still, around 17% in the USA.

Trying to get it right

If we make an effort to correct their assumptions by: we get much more attractive numbers:
Annual consumption:  54 million tons of oil equivalent (MTOE)     (a)
Efficiency of current vehicles:  25%     (b)
Annual energy applied as motive power:  13.5 MTOE     (c)
Efficiency of battery storage:  70%     (d)
Annual renewable energy required:  19.3 MTOE     (e)
Converting units to average daily MW:
19.3*1000*11.63*1000/(365*24) = 25,600 MW   
  (f)

This reduces the requirements from a 10 km strip of wind plants around Britain to 2 km (assuming no improvements there either; the news just came of a 126-meter wind turbine capable of 5 MW peak, which would cut the number and depth still more) or 24 nuclear plants at 1100 MW each instead of 100.
That's still a hell of a lot.  Nobody said it was going to be a trivial job, but it's nowhere near as big as the Oswalds make it out to be.
There are better scenarios.  If you assume that rainy, foggy Britain gets 300 W/m^2 of sunlight for 6 hours on the average day and you've got solar panels at 15% efficiency, that 25,600 MW of average power could be met with a bit over 2,200 km2 of area; if you can get to 50% efficiency using ballistic-electron quantum dot cells, the requirement is a mere 683 km^2.  Do roofs and pavement on the island cover 3.4% of the area of Wales yet?  If they do, the impenetrable wall of wind turbines turns into faux slate tiles and the problem literally vanishes into the background.   Such are the tradeoffs.





 
Talk largely about energy and work, but also politics and other random thoughts


Mail Engineer-Poet

(If you're mailing a question, is it already in the FAQ?)

Important links

The FAQ
Glossary
The Reference Library

Blogchild of

Armed and Dangerous

Blogparent of

R-Squared




The best prospect for our energy future:
Flibe Energy

ARCHIVES
January 1990 / February 2004 / March 2004 / June 2004 / July 2004 / August 2004 / September 2004 / October 2004 / November 2004 / December 2004 / January 2005 / February 2005 / March 2005 / April 2005 / May 2005 / June 2005 / July 2005 / August 2005 / September 2005 / October 2005 / November 2005 / December 2005 / January 2006 / February 2006 / March 2006 / April 2006 / May 2006 / June 2006 / July 2006 / August 2006 / September 2006 / October 2006 / November 2006 / December 2006 / January 2007 / February 2007 / March 2007 / April 2007 / December 2007 / January 2008 / May 2008 / June 2008 / August 2008 / October 2008 / November 2008 / December 2008 / February 2009 / March 2009 / April 2009 / May 2009 / June 2009 / July 2009 / August 2009 / September 2009 / October 2009 / November 2009 / December 2009 / January 2010 / April 2010 / May 2010 / June 2010 / July 2010 / August 2010 / September 2010 / October 2010 / November 2010 / December 2010 / January 2011 / February 2011 / March 2011 / April 2011 / May 2011 / July 2011 / August 2011 / September 2011 / October 2011 / April 2013 / November 2013 / December 2013 / January 2014 / February 2014 / March 2014 / April 2014 / July 2014 / August 2014 / September 2014 / October 2014 / November 2014 / February 2015 / April 2015 / October 2015 / March 2016 / April 2016 / May 2016 / June 2016 / July 2016 / November 2016 / December 2016 / February 2017 / May 2017 / June 2017 / September 2017 / October 2017 / November 2017 / March 2018 / May 2018 / June 2018 / October 2018 / December 2018 / January 2019 / March 2019 / June 2019 / October 2019 / November 2019 / March 2020 / June 2020 / December 2020 / March 2021 / April 2021 / May 2021 / July 2021 / January 2022 / February 2022 /


Powered by Blogger

RSS feed

Visits since 2006/05/11: