4 ms·

I believe that figure is electric efficiency only. For combined heat and power plants, the efficiency routinely goes over 80%, and for heat-only plants, 95+%

I believe that figure is electric efficiency only. For combined heat and power plants, the efficiency routinely goes over 80%, and for heat-only plants, 95+% is common. However, there is still sleight of hand. The efficiency quoted is when the equipment is new and clean. Fouling and wear both take single digit percentages off. Also, they use the lower-heating-value for the gas energy supply. That, in my view, is dishonest - the correct energy measure for gas is the higher-heating-value, which is 10.7% more. The difference comes from how you account for the heat in the steam produced by burning gas. In my view, the energy from that steam should be accounted for when considering efficiency - in GE's view, it shouldn't.

AtlasBarfed 3y ago
And of course carbon removal from burning the natural gas is totally out of the equation.
- lazide 3y ago
  Since no one is requiring it at scale, and since there is no commonly accepted way of doing it - pretty hard to add it to an equation no?
- est31 3y ago
  > And of course carbon removal from burning the natural gas is totally out of the equation. Sorry for being nitpicky, but burning natural gas does not remove carbon, it adds new CO2 to the atmosphere (if you release the burn products which is usually done). You probably mean that if you released that natural gas directly into the atmosphere instead, it would have a larger greenhouse effect than the CO2 released by the burning process. This is true, and one should absolutely choose "burn it" when given the choice of releasing only vs burning and then releasing. But expressing it in the way of carbon removal is misleading. The number of carbon atoms in the atmosphere is the same in both scenarios, they are just bound in a less greenhouse-y form (also, natural gas decays into CO2 plus water eventually, but it's a very slow process). The number of CO2 equivalents goes up in both scenarios as well, just way less if you burn it before. Maybe some people refer to those through "carbon", idk.
  - AtlasBarfed 3y ago
    Ah, hacker news is out in force defending petroleum companies right to pollute the world. As always to economics, if you can't measure it well, it doesn't exist!
  - philwelch 3y ago
    > if you release the burn products which is usually done It’s also possible to capture the CO2 rather than releasing it into the atmosphere.
adrian_b 3y ago
I do not think that using the lower heating value is really dishonest, especially in the context of this discussion. The lower heating value corresponds to the heat actually produced during burning. The higher value is based on the fact that the exhaust gases contain water as a gas, and if that water were condensed into liquid water, an additional quantity of heat would be produced, the latent heat. Due to the low temperature of condensation, that latent heat cannot be easily recovered, except if it is used for hot water production or for home heating or for home cooling (e.g. with absorption chillers). If instead of using combustion gases, the same heat engine would use heat from an external source, like also the thermophotovoltaic devices discussed here, the heat engine would function in the same way and with the same efficiency, when receiving the amount of heat corresponding to the lower heating value (assuming no heat losses during heat transfer).

AtlasBarfed 3y ago

And of course carbon removal from burning the natural gas is totally out of the equation.

lazide 3y ago
Since no one is requiring it at scale, and since there is no commonly accepted way of doing it - pretty hard to add it to an equation no?
est31 3y ago
> And of course carbon removal from burning the natural gas is totally out of the equation. Sorry for being nitpicky, but burning natural gas does not remove carbon, it adds new CO2 to the atmosphere (if you release the burn products which is usually done). You probably mean that if you released that natural gas directly into the atmosphere instead, it would have a larger greenhouse effect than the CO2 released by the burning process. This is true, and one should absolutely choose "burn it" when given the choice of releasing only vs burning and then releasing. But expressing it in the way of carbon removal is misleading. The number of carbon atoms in the atmosphere is the same in both scenarios, they are just bound in a less greenhouse-y form (also, natural gas decays into CO2 plus water eventually, but it's a very slow process). The number of CO2 equivalents goes up in both scenarios as well, just way less if you burn it before. Maybe some people refer to those through "carbon", idk.
- AtlasBarfed 3y ago
  Ah, hacker news is out in force defending petroleum companies right to pollute the world. As always to economics, if you can't measure it well, it doesn't exist!
- philwelch 3y ago
  > if you release the burn products which is usually done It’s also possible to capture the CO2 rather than releasing it into the atmosphere.

adrian_b 3y ago

I do not think that using the lower heating value is really dishonest, especially in the context of this discussion. The lower heating value corresponds to the heat actually produced during burning. The higher value is based on the fact that the exhaust gases contain water as a gas, and if that water were condensed into liquid water, an additional quantity of heat would be produced, the latent heat. Due to the low temperature of condensation, that latent heat cannot be easily recovered, except if it is used for hot water production or for home heating or for home cooling (e.g. with absorption chillers). If instead of using combustion gases, the same heat engine would use heat from an external source, like also the thermophotovoltaic devices discussed here, the heat engine would function in the same way and with the same efficiency, when receiving the amount of heat corresponding to the lower heating value (assuming no heat losses during heat transfer).