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0 pointsRetric3y ago0 comments

Every hour in operation 2GW of natural gas emit the same CO2 as 1GW of coal. In terms of how quickly we hit 2.5C of global warming that makes a big difference on its own.

However, large steam turbines simply take a lot of energy to warm up to operating temperature. This means simply turning coal power plants on and off releases lots of CO2.

This makes a huge difference as we add wind and solar because you can turn natural gas off and on multiple times a day with minimal cost. Which enables you to dramatically scale just how much wind and solar is connected to the grid.

Nobody wants to turn off a wind farm in favor of a coal power plant but it happens. Eventually we want to swap to energy storage, but for now getting off of coal is a huge deal in both directly and because it allows the grid to be more flexible.

> Electric cars are an expensive distraction from the problem.

As long as people live outside of cities they need personal transportation. Electrifying roads is a viable option, but it’s much easier when cars carry a big battery so you get similar results with 1% of the infrastructure.

*Actual efficiency varies somewhat, but it’s still big gap.

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timr3y ago

> However, large steam turbines simply take a lot of energy to warm up to operating temperature.

Boilers, not turbines. The boilers at a coal plant are gigantic -- 5+ story hunks of metal the size of city buildings. They don't turn on/off on demand. The whole system is complex, of course, but the boilers are giant boxes of fireball that flash-vaporize water using pulverized coal at ~500C and 200+ bar of pressure [1].

My father was a control systems engineer for coal plants (and later, gas) for a major utility. When I was a child, he'd be away for weeks at a time when plants were spun up or down for maintenance.

One of the more memorable events in my life was when I was allowed to take a tour of a big coal plant when it was down for maintenance. Those boilers were terrifying, even when "off". The gates of hell.

[1] https://www.sciencedirect.com/topics/engineering/pulverized-...

RetricOP3y ago

I was referring to a nuance that’s easy to overlook. As you say the coal power plant needs to heat up a boiler to operating temperatures before it’s turbine can generate power. Yet, that’s still not enough for maximum efficiency.

Cold pipes and turbine blades steal energy from the steam. Similarly the boiler is less efficient when fed cold water vs hot water from the condenser. Thus the startup process is more involved than just how long it takes to start generating power.

The most efficient coal power plants are actually double-reheat which takes even long to get up to optimal conditions. https://www.sciencedirect.com/science/article/abs/pii/S03605...

timr3y ago

Yes, definitely. Not disagreeing with you, just adding color and an anecdote.

The broader point that we can't just turn these things on and off is 100% correct, and one of the (many) things that people don't understand when talking about the power system and emissions.

I don't know the details of wind and solar, but any system that deals with hundreds-to-thousands of megawatts can't just be spun up on a dime. Make a mistake, and things blow up.

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0 pointsRetric3y ago0 comments

Every hour in operation 2GW of natural gas emit the same CO2 as 1GW of coal. In terms of how quickly we hit 2.5C of global warming that makes a big difference on its own.

However, large steam turbines simply take a lot of energy to warm up to operating temperature. This means simply turning coal power plants on and off releases lots of CO2.

> Electric cars are an expensive distraction from the problem.

*Actual efficiency varies somewhat, but it’s still big gap.

0 comments

timr3y ago

> However, large steam turbines simply take a lot of energy to warm up to operating temperature.

My father was a control systems engineer for coal plants (and later, gas) for a major utility. When I was a child, he'd be away for weeks at a time when plants were spun up or down for maintenance.

[1] https://www.sciencedirect.com/topics/engineering/pulverized-...

RetricOP3y ago

The most efficient coal power plants are actually double-reheat which takes even long to get up to optimal conditions. https://www.sciencedirect.com/science/article/abs/pii/S03605...

timr3y ago

Yes, definitely. Not disagreeing with you, just adding color and an anecdote.

The broader point that we can't just turn these things on and off is 100% correct, and one of the (many) things that people don't understand when talking about the power system and emissions.

I don't know the details of wind and solar, but any system that deals with hundreds-to-thousands of megawatts can't just be spun up on a dime. Make a mistake, and things blow up.

j / k navigate · click thread line to collapse