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Comment by tomkinstinch | Hacker News Reader

And for a depiction of both how energy is generated and how it is used, see this flow chart from LLNL:

https://flowcharts.llnl.gov/content/assets/docs/2014_United-...

Petroleum is huge for transportation because of its energy density, but it seems like solar is poised take a chunk out of coal for electricity generation (at least during the day, or via what energy we can store).

It's amazing how much heat is rejected from electricity generation. Imagine if we could recapture that lost energy!

There are also state-specific charts on the main LLNL site, and ones depicting water use and carbon emissions. It's easy to see the influence of local resources (solar in HI, oil in TX), and of local industry (note the huge water use in CA compared to, say, NY).

https://flowcharts.llnl.gov/

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Since you brought up the Sankey diagrams I'll piggyback on you to mention that I spent a summer at LLNL and got to meet the team/person that produces these. I was also given the program they currently use (it's java, still have it somewhere. . .), and tasked to look into applying it to city flows. I have a couple of the results here[1] (my boxes are off in terms of size, but the flow widths should be correct). I still love those diagrams although I haven't touched them in 3 years. It's a fantastic way to visualize a ton of information. The trick is really just finding appropriate data.

[1] https://www.flickr.com/photos/23215983@N02/sets/721576342348...

>It's amazing how much heat is rejected from electricity generation. Imagine if we could recapture that lost energy!

Well there is combined cycle[1] which does this with steam and gas turbines.

https://en.wikipedia.org/wiki/Combined_cycle

Combined cycle is very important, but that still only gets you from maybe 35% to maybe 54%. That means that half is still "wasted". It's those pesky laws of thermodynamics. Who was that Carnot guy who's causing us all these problems?

What that link also discusses is that using the residual energy for community heating can get you "theoretical efficiency" of 95%. Now we're talking!

Looking at the first flowchart, a few things stick out to me greatly:

  * Transportation is wasting almost 80% of its input energy. 
  * Transportation rejected energy makes up 36% of rejected energy.

Electricity makes up a tiny fraction of the transportation input. How much will the rejected energy output decrease as we switch to electric cars, and even moreso electric buses and cargo trucks?

  * Electricity generation makes up 43% of rejected energy.

I haven't heard anything about more efficient electricity generation. Maybe that should be a focus of the Green Energy movement?

Have you heard the term "Smart grid?" Being able to postpone some types of usage (water heating, etc) and to quickly ramp down generation based on demand will reduce the amount of rejected energy.

Hawaii depends heavily on imported oil for electric generation (~70%).

Interesting. Unfortunately, it looks like only imported electricity is counted as a net import. It would be great to see diagrams that show all imports—many states lack coal mines but still burn coal for generation.

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