OT: Gas turbine generators

Yes. Otherwise they'd melt at low load. Thermodynamics.

No. If the load on the turbine increases, its governor (which probably isn't two spinning balls these days) must increase the fuel supply in order to maintain the same speed. For electricity generation for the grid, it has to be *exactly* the same speed, and it requires more fuel to maintain that speed as the load gets heavier.

No. Of course not. But they are (designed to be) most efficient at full load

-- If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State.

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No Otherwise they'd melt at low load. Thermodynamics.

-- If you tell a lie big enough and keep repeating it, people will eventually come to believe it. The lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie. It thus becomes vitally important for the State to use all of its powers to repress dissent, for the truth is the mortal enemy of the lie, and thus by extension, the truth is the greatest enemy of the State.

Joseph Goebbels

So can they 'tick over' with no load using little fuel? Like when the wind suddenly drops, or clouds suddenly appear?

This is an innocent question.

I mean, that was nonsense. I'll try again.

I am not sure that the oft repeated claim that "there are no stupid questions" is entirely true

Fair enough - I expect I got the question the wrong way round.

'spinning reserve'

I don't think it works either way, from first principles, because the turbines also output energy as waste heat, in addition to electrical energy. Under low load they could just expel more waste heat.

From previous reading, I'm pretty sure they do increase fuel when load increases. Which is what most of us would expect.

The clouds do not afrect gas turbines

They are jet engines with a steam turbine on the back.

You would be surprised how much fuel is burnt taxi-ing onto the runway and waiting for clearance, but full power it is not

yes. up to a point. They still have to overcome frictional losses etc.

Yes, that's sort of part of the question. When taxiing and waiting, of course the engines aren't at full power, but they're spinning more slowly.

I thought a gas turbine generator would have to run at a constant speed, but it seems there are different types.

The RB211s that are used to pressurise the gas grid at various points can consume as much fuel as a large town when they run.

Hence there is a very string incentive to minimse compressor usahe and strategically order gas from a complex matrix of suppliers, rigs, contracts and demand.

That was where I cut my IT teeth in the real world ....

That's the point. They must be designed to dissipate the waste heat at full output due to less than 100 percent efficiency but it would be very difficult to actually get rid of ten times as much heat if they burnt just as much fuel at lower output.

Can be. But the difference us less than you think. They need to be spolled up a bit to work at all.

Actually, most UK gas power plants are slightly modified Rolls Royce Trents.

Obviously once synched to the mains they are constant sped, and power is varied by adding or subtracting gas.

Like most fixed speed heat engines they tend to be designed to be best efficiency at maximum power,

No - the rate of fuel usage is a function of the power being generated, but it's not linear. Gas turbing engines are only efficient within a very limited range of speed/load operating conditions. Outside of that range they use more fuel per unit if electricity generated.

That's why they're good for turbo-prop aircraft which spend most of their time in a defined cruise condition - but useless for road vehicles because road vehicles rarely use anything like their maximum power.

In the 1950s, 60s and 70s, Rover put a lot of effort into developing gas turbine-powered cars and, after their acquisition by Leyland, went on to develop gas turbine-powered trucks - but this all had to be abandoned after varies fuel crises and the escalating price of fuel because they were nothing like efficient enough under normal operating conditions.

Even with a multi-spool gas turbine the efficiency at low loads or idle is atrocious, where fuel consumption is often a significant fraction of full load.

This is not about overcoming "frictional losses".

IIRC in the 1950's there was a prototype gas turbine car in the Science Museum made by Rover. See