An Engineer Comments on "Renewable Energy and Basic Physics"

My friend Geoffrey Nicholson comments my post “Renewable Energy and Basic Physics”:

Craig, I couldn’t agree more.

 Other than geothermal energy, all the other sources of energy available to us originally came from solar energy and with a rather lossy process. Petrochemical from solar growing primordial goo. Hydrokenetic from solar driven convection. Wind from solar convection with a bit of coriolis effect. Water from lightning from solar convection. Wood and alcohol from solar energized green growy things.

Gas turbines can be around 50% efficient burning fuel but, again, how efficient is the production and transportation of the fuel?

Steam turbines a bit more efficient.

Gasoline engines about half as efficient as turbines with Diesels a bit more efficient that gasoline.

Stirling engines are quite efficient but pound for pound don’t produce much work.

Interestingly, hydrogen fueled aircraft could be more efficient than kerosine since the specific weight of hydrogen is less than gas but the design of the aircraft would have to change dramatically since the specific volume of hydrogen is greater. Fat planes would result that would probably fly slower than today’s aircraft. Again, how would the hydrogen be produced?

The idea of collecting solar energy from the upper surfaces of already constructed buildings seems like the least intrusive and most efficient method to utilized light, in my opinion. It doesn’t shade the natural ecosystem and collects/distributes the energy where humans need it.

What do you think?”

To which I respond:

Thanks, Geoff.  Everything you write here is true, as far as I understand.  PV on rooftops makes a great deal of sense.  The costs and coming down, the efficiencies are going up, and the overall engineering is getting increasing clever.  See my post on California-based Solyndra as an example.

The only piece you’re missing, I feel, is solar thermal / concentrated solar power (CSP) as described at the bottom of the post.

Thanks for writing!