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Discussion Starter · #1 ·
Anyone else noticed the unusual Agile tariff profile for today (Easter Sunday)? Any thoughts on possible reasons?

142970
 

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What, a sunny afternoon so good for PV and low demand for power from office and retail? :unsure:
 

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Same as always: supply and demand.
Wind is building so we should get good prices overnight.
Take a look at Carbon Intensity and you'll see predicted CO2 dropping all the way to 4pm then flattish through to 6am Monday. Basically means expecting lots of cheap renewables and less of the expensive Gas.
 

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142977

It’s breezy and sunny and Sunday of a bank holiday weekend. The ovens running don’t compare with industry running. Right now has the lowest carbon intensity I’ve seen in quite a while.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #6 ·
Thanks for all the interesting answers. I've learnt a lot today about UK power generation carbon impacts that I did not know before.

But I suppose what I was really interested in was the implication from the tariff that between 1pm and 4pm today, there was perhaps an acute excess of electricity being generated chasing consumption. Is that because we have a sunny day with not much industrial consumption sandwiched between two cold nights, so they have to keep the expensive gas generators lit up going and then along comes a load of solar? Or is it that they were artificially trying to incentivise transfer of load from another time of day? It's an interesting insight into the problems that the grid have to manage when so much of the generating capacity is neither directly controllable nor storable I suppose. I just had not seen such an extreme example of both no real reduction in the the early hours rate and then this big plummet in the afternoon.
 

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It’s hugely complicated and I wish I understood it better. My, probably flawed, understanding is that we do have periods of excess because we can’t just turn off nuclear and some of the gas plants, so when the wind blows and the sun shines and usage is low, due to the way contracts are organised we end up paying generators to shut down. That often ends up being the renewables, as they’re more variable. What’s actually being paid for is balancing of the grid. So we pay generators to stop but could just as easily pay for balancing through increased consumption. That’s what Octopus are doing here, providing a balancing mechanism by encouraging increased use. It’s also what the battery storage folk do. They effectively trade energy by buying in when its cheap, and help balance the grid in doing so, and output when it’s expensive, likewise providing a useful support to the grid.
 

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Electron Summit White NK13...107k 91.5 and rising
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Discussion Starter · #8 ·
That’s what Octopus are doing here, providing a balancing mechanism by encouraging increased use
Well, it worked for me. I plugged the car in @ 1pm and we shifted washing forward from Monday and our Sunday lunch back to 4pm ! I see its back to a cheap rate tonight so I'll pop out later for a burn round in Sport mode so I can help out again :D
 

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agile isnt been worth it for half a year now.
Consecutive days where the lowest rate doesn't go under 10p, unless some folks are getting some export figures out of it (and exporting a LOT) I dont see the point of that tariff anymore. I can average 9p/kwh on GO faster without even trying.
 

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It’s hugely complicated and I wish I understood it better. My, probably flawed, understanding is that we do have periods of excess because we can’t just turn off nuclear and some of the gas plants, so when the wind blows and the sun shines and usage is low, due to the way contracts are organised we end up paying generators to shut down. That often ends up being the renewables, as they’re more variable. What’s actually being paid for is balancing of the grid. So we pay generators to stop but could just as easily pay for balancing through increased consumption. That’s what Octopus are doing here, providing a balancing mechanism by encouraging increased use. It’s also what the battery storage folk do. They effectively trade energy by buying in when its cheap, and help balance the grid in doing so, and output when it’s expensive, likewise providing a useful support to the grid.
Yeah, pretty close. I used to work in the gas fired part of the grid doing data analysis so this is what drives my following few lines.

Renewables can't be turned off (well you can limit the output significantly but the fuel is free so why would you?). Nuclear can be turned off but the excess amount of electricity it produces for its fuel input means that you will tend to leave generation going flat out and sell it at what ever rate you can as it costs more to take it off line. That in effect means that you don't turn off nuclear either.

Coal and gas can be turned off but the problem being that the vast majority of the gas fired power stations (which make around 50% of the grid total capacity) lack black start capability.

Black start capability is the ability to start up the power station in the event that it is isolated from the grid through component failure. You need to draw on the grid to get you going again apposed to starting by yourself and then asking to join. This in effect means that gas won't be shut down either apart from the few black start sites.

You can of course start the site back up if you have a grid connection but you then rely on there being a surplus of energy on you corner of the grid to get these huge generators back online. There is a lot of rotating mass in these systems to get back up to speed. There is also the fact that these guys get paid to put electricity into the grid and not for taking it out of the grid to start their own generators. They pay for that as well.

Most gas fired power stations actually have 2 generators per gas turbine. One that is driven by the compressor end of the gas turbine and one that is driven by the steam created by passing the exhaust gases through a massive heat exchanger. This method drives up efficiency hugely.

What happens is that the exhaust heat can be diverted straight to atmosphere to take the steam generator offline and then you in effect idle the gas turbine to reduce the output from the other generator. If a site has multiple gas turbines you can take all but one offline to further reduce output but you really hope that the last one remains serviceable because if that goes, you risk taking the power station offline entirely. You can of course start up from the grid but that takes time. It's also very expensive to idle a gas turbine as the low amount of electricity provided doesn't bring in the same amount of cash as running it at a much higher output.

For information more than anything, it can take 10 to 15 minutes to get the gas turbine and it's generator up to speed and upto an hour to heat the water to produce steam in sufficient volumes to get the second generator back online. This is down to the shear mass of the rotating equipment, the need to start smoothly to avoid surging or stalling the gas turbine, the need to avoid thermal shocking the steam system and the requirement for the generator(s) to spin at 3000 rpm.

Why 3000 rpm? 3000rpm divided by 60 seconds gives 50 revs a second which for a generator providing an AC output just so happens to be the grid frequency in the UK. The large rotating mass of all the generators spinning at this speed is basically what keeps the grid at 50hz. On 60hz grids, you spin the gerators at 3600rpm.

This is obviously over simplified but you know, it's Easter...
 

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It’s just gone midnight and CCGT is producing less than 3 GWh nuclear just less than 5 wind 12 GWh metered another 3 GWh unmetered hydro .5 GWh and Belgium are sending us a bit and we are sending France a bit more. There will be a time when gas gets switched off at times just like coal, but as Mr sss jay states we need the inertia of the gas and nuclear power stations to smooth the frequency when demand spikes. Elsewhere we have a member works in a nuclear plant and has pointed out that all the cars starting to charge at 00:30 causes a dip in the frequency as the demand jumps. National Grid are on to this and call for extra power just before the great switch on. Fascinating!!
 

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I doubt "all the cars" currently on the road barely makes a dent compared with existing installed base of electric storage heaters, which will almost all switch on around midnight as the E7 rate kicks in...
 

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I doubt "all the cars" currently on the road barely makes a dent compared with existing installed base of electric storage heaters, which will almost all switch on around midnight as the E7 rate kicks in...
Apparently not, the spike in demand when Octopus Go kicks in at 12:30 caught the grid out a few weeks ago. With E7 there will be no surprise, the weather and past demand will make the load predictable and so gas turbines will be on standby to balance the load, but a wobble in the frequency set off alarms at one of the nuclear stations a few weeks ago. Presumably a warmer night with less spinning momentum.
 

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The problem with cars and the current lockdown restrictions is that you just don't know who wants to charge their car when, for how long and at what rate and that's where the smart chargers need to communicate any planned charging back to the grid. I have no doubt there is an element of this going on already.

I'd imagine when commuting becomes more and more stable it will become easier to forecast demand.
 

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The problem with cars and the current lockdown restrictions is that you just don't know who wants to charge their car when, for how long and at what rate and that's where the smart chargers need to communicate any planned charging back to the grid. I have no doubt there is an element of this going on already.

I'd imagine when commuting becomes more and more stable it will become easier to forecast demand.
That will be the case and so will delayed start to charging. I wondered why my Rolec starts 10 minutes after my projected set time and I guess it will be to prevent a surge in demand. Now Octopus will need to factor in different start times to their offerings, that is off the hour and half hour.... it can’t happen I suppose because of the metering, not yet anyway. What was interesting was the small jump in demand that caused the big flicker in frequency, it was less than .5 GWh. If the electric mountain was pushing water uphill, they could stop it just before the surge to compensate. The problem wouldn’t be so noticeable if we were still relying on fossil fuels and nuclear. Offshore wind doesn’t have heavy turbines to add inertia, particularly those with HVDC connectors which provide AC in tune with the grid. I saw Scottish Power had developed something which helped provide inertia up in the wilds of Scotland (not Tenants!) I guess it has some batteries attached to it.
 

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I doubt "all the cars" currently on the road barely makes a dent compared with existing installed base of electric storage heaters, which will almost all switch on around midnight as the E7 rate kicks in...
Oh I dunno, there’s about 150k BEV’s in the U.K. from what I understand and if all of them plug in and draw at least 7kw, the rough maths states that’s over 1GW in demand not including PHEV’s and other electric devices like storage heaters and this will be happening just when the grid is winding down for the evening.
 

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Oh I dunno, there’s about 150k BEV’s in the U.K. from what I understand and if all of them plug in and draw at least 7kw, ..
Except our good old friend 'diversity' steps in and not all of them will be charging, and of course some on Agile who only need a small charge or top up may not step in at (say) 4.5p but may be waiting for the 3.5p slots.

It maybe that SSE's planned new pump storage scheme will find a frequent use in these scenarios and, unlike wind, has the benefit of providing inertia and black start capabilities.
 
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