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Comment by dredmorbius | Hacker News Reader

Checking that out:

  You have: 40 MWh
  You want: tonoil
          * 3.4393809
          / 0.29075
  You have: 1 tonoil
  You want: barreloil
          * 6.8419323
          / 0.14615754
  You have: 6.84 barrel
  You want: liter
          * 1087.4731
          / 0.00091956298

So, roughly 1,100 litres of oil per 40 MWh(thermal).

The generator is likely ~30% efficient at converting heat to eletricity, so bump that up to 3,700 litres/hour.

Even allowing for other inefficiencies, 12,000 litre/hr seems high to me. Though as a practical measure it may be correct. It's within a factor of 4 of the actual demand though.

(Calculations using GNU units.)

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I think that's wrong. One liter of diesel contains about 10 kWh of energy [1], so you need 4000 liters at 100% efficiency to generate 40 MWh.

12k liters per hour for the datacenter sounds about right, after accounting for diesel engine efficiency.

[1] https://www.sustainabilityexchange.ac.uk/files/cambridge_reg...

Ramrodification caught my missing tonsoil -> barrels conversion.

https://news.ycombinator.com/item?id=31258490

No need to complicate things with obscure units.

  You have: 40 MW/30% / (10722.2 W*hr/L)
  You want: L/hr
   40 MW/30% / (10722.2 W*hr/L) = 12435.259 L/hr

GNU Units has builtins for some standard energy equivalent units, specifically "tonoil" and "barreloil". "litreoil" doesn't seem to be included by default (though it can be added via a local configuration file).

    literoil = 1 barreloil * liter/barrel

And the calculation gives me ...10.69 kWh/L

The barreloil value is for crude, diesel may have a slightly higher net energy density. But we're good to 3 sig figs.

I could have bypassed the tonoil step and calculated thermal energy in barreloil directly though saving another conversion.

Otherwise I'd have to remember energy density/L of diesel fuel.

I've added the definitions for litre, pound, and kg oil and can now run:

  $ units --terse '40 MWh/30%' literoil
  12470.969

The fun part though, at least for me, is showing how to do conversions with GNU units, and the equivalences which become apparent doing so.

I looked around a bit in "definitions.units" and there are actually energy densities in there for various fuel sources, including diesel.

  You have: 1 diesel
  You want: Wh/L
   1 diesel = 10103.465 Wh/L

Slightly different value than in Wikipedia, but close enough.

*blink*

TIL, there are!

Thanks.

(For the curious, the definitions file is ~7500 lines, there's a lot in there. GNU version. For those on MacOS, the stock BSD units offers far less.)

Aren't you missing x3.4393809 on those ~1100 litres?

Bingo, that's the error, thanks.

Corrected:

  You have: 40 MWh
  You want: tonoil
          * 3.4393809
          / 0.29075
  You have: 3.439 tonoil
  You want: barreloil
          * 23.529405
          / 0.042500012
  You have: 23.529 barrel
  You want: liter
          * 3740.8121
          / 0.00026732164
  You have: 3740/30%
  You want:
          Definition: 12466.667

Or a bit above 12,000 litres. Article was correct.

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