Green Building Bible, Fourth Edition |
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Posted By: philedgeCant seem to be able to quote from the previous page
Power flowSo, yeah, it's basically all one grid (and has been since about 1938) but losses and capacity limitations mean it's close to, but not quite, uniform and needs tweaking as generation and demand move around. Adding a 2.2 GW link is a significant tweak but doesn't change the basic situation all that much.
In 2009–10 there was an average power flow of about 11 GW from the north of the UK, particularly from Scotland and northern England, to the south of the UK across the grid. This flow was anticipated to grow to about 12 GW by 2014.[33] Completion of the Western HVDC Link in 2018 added capacity for a flow of 2.2 GW between Western Scotland and North Wales.[34]
Because of the power loss associated with this north to south flow, the effectiveness and efficiency of new generation capacity is significantly affected by its location. For example, new generating capacity on the south coast has about 12% greater effectiveness due to reduced transmission system power losses compared to new generating capacity in north England, and about 20% greater effectiveness than in northern Scotland.
Posted By: me on the previous pageDiagram here:If John had opened the link, he'd have found that his area is supplied by a major east-west connection running from the Scottish HVDC wind turbine link in N Wales, via Birmingham across to Humberside, with a second connection to/from the NW London area.
https://data.nationalgrideso.com/backend/dataset/cf3cbc92-2d5d-4c2b-bd29-e11a21070b26/resource/bb6d6ec6-16d9-4be5-b32c-1a70c09fd871/download/network-diagram-ew.png
Posted By: Ed DaviesFrom the departments of “what if everybody did that?” and “grandmothers need egg-sucking advice” could I suggest it would be good manners not to start and stop electricity use nicely NTP synchronised to the half hours but rather to add some sort of (pseudo-)random offset?
Posted By: WillInAberdeenThe problem they have in N Scotland region, is that there is usually more intermittent wind and hydro power than the inhabitants can use, so their method almost always says that our intensity is zero. But we rely on the English gas and coal stations for grid frequency stability and calm weather backup. So is it fair to say that the neighbours of those English gas/coal stations have high intensity, while ours is always nil? In that case, I can run fan heaters in the garden at whenever time I like. Or is it actually the case that we all share the grid and so our intensity is the same - I think so.I think so, too, almost. Every kW used in the north of Scotland is one less kW available to send south to displace higher-intensity generation there unless all the lines south are running at capacity (which I understand doesn't happen most of the time).
Posted By: Ed DaviesThere are transmission losses (as noted in the Wikipedia text I quoted above) but still a spare kW of wind in the north is worth something like 800 W on the south coast so should be counted at maybe 80% of the south's intensity, not the tiny fraction that it seems come from that National Grid regional intensity AP
It is then possible to calculate the carbon intensity of electricity in each region. If the region is exportingIt's as if they think there are different coloured electrons, green through black, and it actually matters which particular ones you're using.
power, then that region consumes electricity equal to its carbon intensity of generation. If the region is importing power, then the carbon intensity of the power that it consumes is equal to the weighted sum of its regional generation plus the power flow from the lines it is importing from.
Posted By: Ed DaviesYes, but it's this bit which doesn't seem to make much sense:
Posted By: John WalshIn Figure 2 of the report's pdf what do the horizontal lines represent?They represent a bus (in the electrical sense of the word) standing for that part of the grid which is in a region.
For example, is this where balancing happens?Yes, basically the sum of generation - demand + flow in - flow out has to be zero. (Note, they get the formula back-to-front in Step 3 vs the text description above it.)
Is it that the flow of electricity into a 'region' for consumption in that region is one control and the flow of electricity through the region and onto another region is another control?Once they've predicted the generation and demand in each region they then solve for the flows into and out of the regions along each of the lines between them in step 4, so they aren't really controls as such, more like outputs of the model.
In the absence of that, I would tend to take the authors' opinion.That's up to you, of course, but if it's giving obviously nonsensical results others can be a bit more sceptical.
Posted By: Ed DaviesThat's up to you, of course,
Posted By: Ed DaviesE.g., at least late this afternoon it was giving an intensity of 0 g/kWh for northern Scotland. I ran my washing machine during the afternoon (because it was windy). Do you really think total emissions for Great Britain were not at all affected by that? I think emissions were increased but not quite as much as they would have been if I'd run it in my old house in High Wycombe.
Posted By: John WalshPeople on here are very sure that it isn't possible/viable/reliable to forecast *regional* carbon intensity.I, for one, said nothing about the reliability of the *forecasting*. I don't think WiA did, either. All my criticism applies equally to the values they give after the fact.
Posted By: JontiIsn't it the overall carbon intensity that counts??
Posted By: John WalshEurope has the world's largest electricity grid - the Continental Synchronous Area - with 400 million customers in 24 countries, and with detailed carbon intensity data for each country. For example, average intensity for consumed electricity is almost double in Germany what it is in neighbouring Austria.Given the longer distances and presumably limited inter-country transmission (WiA: “I can't find 2020 figures, but earlier years' figures for Germany/Austria were similarly very low.”) a 2:1 ratio seems quite plausible. This doesn't support the idea that a 307:0 ratio within a well-connected area makes much sense.
I'm not going to even read what the likes of WillInAberdeen and Ed Davies have written because it has tended towards personal insults.For anybody else still reading, then, I've just re-read all my own posts on this thread and don't think I've written anything which can be described as personal insults. I've described the outputs of that model as “nonsensical” and “bonkers” but I think that's legitimate kick-the-ball-not-the-player comment.
Posted By: WillInAberdeenIt would be interesting to consider: when exactly would that time come, such that a single intensity figure applies across Europe? Possibilities are:
A) when 'significant' electricity flows across frontiers - in 2020 GB imported 3% of electricity supply from France and 1% each from Belgium and NL. I can't find 2020 figures, but earlier years' figures for Germany/Austria were similarly very low. So Europe-wide interconnection is still quite limited.
B) when the UK/European transmission system becomes managed as a single grid with shared dispatching decision-making, rather than a system of independent national grids with limited cross border interconnections (as it is at present in GB, Ir/NI and the independent national grids within the CSA)
Posted By: John WalshPosted By: JontiIsn't it the overall carbon intensity that counts??
That would depend on what your purpose was:
Posted By: John Walshthreshold concept or 'troublesome knowledge', where students are confronted with a seemingly counter-intuitive concept. Once over the hump of understanding the concept though, students see the world differently and are able to take on board further new knowledge.See