> a holy grail of energy production

Since you're comparing it to nuclear, I'm assuming you mean electricity production here, not energy production?

It's always worth remembering that electricity only accounts for ~20% of global energy consumption (in the US it's closer to 33%).

I suspect people confuse these two because in a residential context electricity plays a huge part of our energy usage, but as a whole it's a smaller part of total energy usage than most people imagine.

But any serious discussion of renewable energy should be careful not to make this very significant error.

The Lawrence Livermore National Laboratory publishes a great diagram of US energy use: https://flowcharts.llnl.gov/sites/flowcharts/files/2024-12/e...

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jimbokun 9 hours ago | parent | next [-]

What does "Rejected Energy" mean in that graph?

Great chart, by the way.

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floatrock 9 hours ago | parent | next [-]

Only about 30% of the energy in gasoline is converted to useful work in a gasoline car (the 'make metal box go forward' part). The remaining 70% is Rejected Energy (the steam you see going out the tail pipe in winter).

Which (not sure if you did this intentionally or accidentally) brings up an interesting point on the parent comment and the LLNL sankey:

> It's always worth remembering that electricity only accounts for ~20% of global energy consumption (in the US it's closer to 33%).

That "global energy consumption" figure includes a lot of Rejected Energy going out tailpipes and smoke stacks turning burnables into electricity. A secret bonus of wind and solar is if you produce electricity without burning things, you actually decrease the energy demand! If you're not losing 70% of your energy consumption to the Rejected category, you suddenly need a lot less total energy.

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philipkglass 9 hours ago | parent | prev | next [-]

Rejected energy means energy that is lost as waste heat without performing any work first. For example, a coal fired power plant may generate 3 megajoules of thermal energy from coal combustion but only deliver 1 megajoule of it as electricity. The other 2 megajoules are lost as useless waste heat.

The 1 megajoule of useful electricity is also ultimately dissipated as low grade heat, but it can do work first (like generating light, or pumping water uphill).

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foota 7 hours ago | parent | prev | next [-]

It would be nice if before each box where rejected energy is an output, the inputs were split by rejected and non-rejected inputs.

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hluska 9 hours ago | parent | prev [-]

I live in a part of the world that is far below freezing for a significant portion of the year. Thus a large portion of my annual energy usage goes into not freezing to death.

When I drive my daughter to school when it’s -40 fucking degrees, a lot of the energy I use goes into heating my vehicle, swearing, moving and swearing. But this energy also leaks through my windshield, through my exhaust system and through my engine. This energy (heat) doesn’t provide any benefit to anyone and just leaks out into the atmosphere (which we’ve already established is trying to kill me).

That’s rejected energy. Or when it’s below -40, rejected motherfucking energy. :)

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mr_toad 8 hours ago | parent | next [-]

A IC car’s heating system normally taps into the engine’s cooling system, so that heat is mostly free. In a pinch you can actually turn the heater on full to help cool the radiator.

	▲	zdragnar 2 hours ago \| parent [-]
		I had to do that when my radiator sprang a leak on the freeway and the engine heat kept creeping up. Unfortunately it was late summer and not at all pleasant. I managed to get to a gas station with some stop leak in stock... If they didn't, I was ready to crack an egg in it.

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mcswell 3 hours ago | parent | prev | next [-]

"when it’s -40 fucking degrees" Celsius, or Fahrenheit? Oh yeah, it's the same either way :).

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ViscountPenguin 5 hours ago | parent | prev [-]

Do you live out in Siberia or something? Seems like a rough environment for most tech.

Sounds like a very unique experience :)

	▲	zdragnar 2 hours ago \| parent [-]
		Not OP, but upper Midwest US and Canada experience this every year, though where I'm at usually only hits -40 if you include the wind chill.

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iso1631 9 hours ago | parent | prev [-]

At home I use 15,000kWh of oil for heating each year (about 10kWh per litre, 1500 litres), and 8,000kWh of electricity (we use a lot more than the average household). For driving that's another 5000kWh a year if at 4 miles per kWh.

So even in a residential context, electricity is only about 1/4 of the demand. Across the whole country it's less than 300TWh out of 1500TWh, under 20%.

That excludes "imported energy" though, as in goods which used energy to make but were then imported.