Electric boiler?

[JohnW2]

The incentive needs to be there, but nothing to actually prevent use at peal demand. Rather, I was suggesting there ought to be a system for high-demand appliances to switch themselves on at times of low demand, determined by the supplier. You set the appliance up, to wait until told to run by the supplier...

Indeed. That's what people would like. However, as I wrote, I think the time will eventually come (long into the future) when 'smart' appliances will be largely controlled 'remotely', outside of the control of the owner.

That is the individual's choice, and remains their choice.

At present it is - but, as above, that may not be the case 'for ever'. As for "it couldn't be done", if I understand correctly France has had some pretty draconian 'load limitation' (which can essentially trump the 'choice' of customers) operating for quite a long time?

 

[JohnW2]

I was not considering direct drive hydropower, my comment is about having inverters, which stop generators over loading even for a very short time.

I'm still rather confused. I still wonder what you did mean when you wrote ...

The big problem is lack of rotating mass. With an alternator connected to a large steam turbine, a sudden load will be taken up by the weight of the rotating mass ..... So we need both the fast reacting hydropower, and the plodding nuclear and other steam powered generators ....

I understand that hydropower can rapidly respond to increases in demand, since there is no need to 'get up steam' etc. but I cannot work out what "rotating mass" has got anything to do with this. What am I missing?

 

[Harry Bloomfield]

I understand that hydropower can rapidly respond to increases in demand, since there is no need to 'get up steam' etc. but I cannot work out what "rotating mass" has got anything to do with this. What am I missing?

I think what Eric has in mind was turbines and generators, cannot be suddenly powered up from cold, they have to be very gradually brought up to operating temperatures. That was what I learned, working in power stations.

Hydropower, they are designed to work cold, from cold water.

 

[plugwash]

I cannot work out what "rotating mass" has got anything to do with this. What am I missing?

Big heavy spinning things (including but not limited to turbines and generators) store energy in their rotational inertia. When those big heavy spinning things are coupled directly to the grid the grid as a whole effectively gains that inertia.

This inertia acts as the first line of defence against sudden changes in load on the grid, because no control system is involved, the reaction is essentially instant, a step-up in load causes frequency to start decreasing, releasing energy from the rotating mass. A step down in load causes frequency to start increasing, storing energy in the rotating mass.

Automatic control systems attatched to the generators can then respond to those changes in frequency by controlling fuel/steam/water going into the generator.

When conventional direct-coupled generators (and loads for that matter) are replaced by inverter-coupled generators (and loads) the inertia goes away. Sure, the physical device has it, but it's invisible to the grid. There are ways to simulate inertia electroncially with battery systems, but it still seems to be early days for that.

The combination of low inertia in the Iberian Peninsula, combined with high inertia in the core european grid was likely a large factor in the recent Iberian blackout.

 

[JohnW2]

I think what Eric has in mind was turbines and generators, cannot be suddenly powered up from cold, they have to be very gradually brought up to operating temperatures. That was what I learned, working in power stations.

Sure - in the case of ('hot') steam-driven turbines (gas, nuclear etc.)

Hydropower, they are designed to work cold, from cold water.

Indeed - as you say, it's cold water. My (only) problem has been in understanding what eric seemed to think that 'rotating mass' (and/or the lack of it) had got to do with this.

 

[JohnW2]

Big heavy spinning things (including but not limited to turbines and generators) store energy in their rotational inertia. When those big heavy spinning things are coupled directly to the grid the grid as a whole effectively gains that inertia. ... This inertia acts as the first line of defence against sudden changes in load on the grid, because no control system is involved, the reaction is essentially instant ...

Yes, I understand all that. What I didn't/don't understand is why eric seemed to be implying that hydroelectric generators are not 'coupled directly to the grid'.

 

[plugwash]

My understanding is that there are basically two sorts of hydro.

"Conventional hydro". Water is stored behind a dam and drives a turbine whose speed is coupled to grid frequency. Power is controlled by controlling how much water is released from the dam. This does have inertia, though perhaps not as much as a big gas or steam plant.

"Run of the river hydro". A turbine is placed in a flowing river, it's speed varies depending on river conditions and it is coupled to the grid through an inverter (similar to a wind turbine).

The main issues with conventional hydro are

1. building it is very destructive, both environmentally and to the lives of the people who live in the area. In the past, such things would just be forced through, but in the current political climate it's virtually impossible.
2. There are a very limited number of good sites.

So yes, hydro does contribute some inertia, but it's contribution to inertia is unlikely to increase significantly as other inertia sources go away.

Also if you are using your hydro for peak demand and you have a limited supply of water you probably don't want to be running it all the time.

 

[Harry Bloomfield]

Yes, I understand all that. What I didn't/don't understand is why eric seemed to be implying that hydroelectric generators are not 'coupled directly to the grid'.

Likely, Eric had in mind Dinorwig, which is only connected once the 'rotating mass', is up to speed. As you will know, it's only designed, to be able to support short runs, for satisfying peak demands.

 

[flameport]

Cannot government intervene?

They could, but they won't.

, bringing about a substantial reduction in energy costs would presumably be one of the most vote-catching things that any government could do?

Current and recent past governments do not care about votes. They care about themselves and nothing more.

 

[JohnW2]

My understanding is that there are basically two sorts of hydro.

Ah - maybe that's what I was 'missing'

"Conventional hydro". Water is stored behind a dam and drives a turbine whose speed is coupled to grid frequency. Power is controlled by controlling how much water is released from the dam. This does have inertia, though perhaps not as much as a big gas or steam plant.

That's the sort of hydroelectric generation I'm familiar with.

"Run of the river hydro". A turbine is placed in a flowing river, it's speed varies depending on river conditions and it is coupled to the grid through an inverter (similar to a wind turbine).

I've never heard of that, so it's perhaps it's what eric was thinking of?

 

[JohnW2]

They could, but they won't.

Seemingly not.

Current and recent past governments do not care about votes. They care about themselves and nothing more.

I don't really understand that. Doesn't "caring for themselves" include caring about whether or not they (the individuals) will have jobs the day after the next election?