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Author Topic: Major changes to G83 rules for solar PV installations needing advance permission  (Read 67871 times)
knighty
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« Reply #15 on: August 28, 2012, 07:48:43 PM »

does PV feeding back into the grid really make that much of a difference ?


you wouldn't expect a brown out if everyone in your street when and turned the kettle on at the same time or jumped into an electric heated shower... so why expect problems when you're feeding max. 4kw back in....

with the amount of pv we have now, it hardly makes a dint in put national power usage anyway ?

the electric company should get there act together and push as many installs through as they can... they pay out a lot less for PV that other generation types cost them, and because generation is so well distributed it cuts down on transition losses... which are about 10% iirc... they can earn a fortune for relativity little work?
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MikeD
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« Reply #16 on: August 29, 2012, 04:48:03 PM »

My thoughts exactly. My house can cheerfully pull 10kW out of the grid, and it handles that easily enough. So why the big deal if I wanted to push 10kW back in ?

And of course, in real life, there's 10 houses pulling current out of the grid for every house putting 2 or 3kW back, so in most cases the leccy generated on my roof would just go into next door's tumble dryer, thereby reducing the load on the grid.

Sure, if you're planning a 50kW solar or wind farm at the end of a very long bit of damp wire then I can see there might be an issue, but that's the exception, not the norm.
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brackwell
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« Reply #17 on: August 29, 2012, 05:00:34 PM »

I believe that transformer stations are configured as to not allow back feed presumably for safety reasons of working on the lines. Could be wrong.


Ken
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« Reply #18 on: August 29, 2012, 05:01:57 PM »

If I can be cheeky, maybe somebody who understands the grid could give us a quick lesson on the problems faced by the DNO's.

My basic understanding is that whilst our cables can easily carry the power, it's finding a use for it, when there are lots of installs on a sunny day. I've been told that the local sub-stations can't run backwards, so once it reaches them, there is a problem. More PV necessitates hardening these points, but again a quick lesson on what that entails would be greatly appreciated.

It occurred to me that mid-day, during the working week, my system putting out 4kW to 4.5kW could power 20 empty houses, running baseload only. So a 5% install level could under those circumstances cause local problems.

I was also told (not sure if this is true) that WPD's reputation for being tough is because in the early days they allowed too many self commissioned installs withing a small area and the local transformer burnt down one sunny lunch time, costing them a 6 figure repair bill.

Sorry for all the questions, but if anyone is in the know, I'd really like to learn more about 'the other side of the argument', if only to be made more aware of the work and costs that really need to be done to give us a more flexible energy future.

Cheers.

Mart.
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billt
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« Reply #19 on: August 29, 2012, 09:04:50 PM »

Substations are simple transformers; there is no mechanism which would allow them to work in one direction only, so local generation is fed to the grid at large, but at a level so low,relatively, that it is indistinguishable from noise.

There can be an issue with too much local generation, it can make the local mains voltage exceed the legally allowable levels, due to line impedance. How significant the effect is depends on local grid conditions, but it certainly cannot be ignored.

We are one of 3 properties at the end of an overhead line; looking at my logs shows that the local voltage goes up by about 6 volts when my system is at peak output. If the other 2 properties had 4kW systems the combined effect would be to raise the voltage to 255, which is above the maximum permissible. Our supply is actually quite good; in other areas I can imagine that the issue could be much worse.
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Gambot
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It's been very windy round here recently


« Reply #20 on: August 29, 2012, 10:41:57 PM »

My property is fed by overhead cables (newly replaced last year) and I have seen the output of my system go to 258V when the sun shines and then drop rapidly to 248V when a cloud passes by and then back up again a few seconds later. Rapid 10V swings like that are surely to be avoided.
There may also be safety concerns with over voltage and possibly fines for the DNO.
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knighty
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« Reply #21 on: August 29, 2012, 10:47:30 PM »

but... if your PV feeding in can cause that sort of swing... won't you be able to make it swing a shed load by turning things on and off anyway ?

my guess is, the voltage must be all over the place anyway ?



also.. for solar, highest output co-indices with highest demand too... when there's loads of shops/offices/factorys up and running
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marcus
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« Reply #22 on: August 30, 2012, 01:32:01 AM »

Coincidentally, i was talking about this the other day to the bloke who I bought my house off (who works for the local DNO).

He was saying in rural areas overvoltage from PV installs they hadn't been notified about were a problem and they do have to replace transformers to deal with it - he did say they were trying to make the regs such that if a new transformer would be required for a new install, the customer (getting the PV) would have to pay for it.

would make quite a dent in ones ROI methinks.
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regen
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« Reply #23 on: August 30, 2012, 07:37:06 AM »

I have always felt that, that same DNO generally does a good job.  However i was more than a little surpised that when i made an initial enquiry re generation they came on site and admitted that they did not know my house existed inspite of it being there for more than a hundred years and being one of two on the end of line with own transformer.

Who is not telling them about these mysterious installations? Surely there is a system in place re FITS which ensures they are told within 28 days of installation!  Why are they not investigating and closing down instalations which have not complied with the rules?

"he did say they were trying to make the regs such that if a new transformer would be required for a new install, the customer (getting the PV) would have to pay for it."

This is fine provided that the age of the existing transformer is taken into account!  That is its true written down value including cost of installation at their inflated prices is taken into account when a replacement is necessary and a percentage of the "fees" they receive anually is returned to the householder.

Regen
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Brian H
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« Reply #24 on: August 30, 2012, 10:10:03 AM »

I'm curious as to the "fix" from a new transformer. Would they generally propose as larger transformer to try to reduce variations due to its internal impedance, or an auto tap changing model (expensive). We notice the difference in the current rural location having our own pole mounted transformer and our previous urban property with a small substation a few hundred yards away, large loads always cause a lighting dip, before never saw it. Don't know if the difference is down to the small transformer or the miles of 11kV line, or a bit of both.  Not had any direct experience of local distribution, did some work at 275kV and up around 30 years ago.
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billt
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« Reply #25 on: August 30, 2012, 11:06:28 AM »

but... if your PV feeding in can cause that sort of swing... won't you be able to make it swing a shed load by turning things on and off anyway ?

my guess is, the voltage must be all over the place anyway ?

Yes it is, my local voltage for the last 24 hours should appear in the graph.

also.. for solar, highest output co-indices with highest demand too... when there's loads of shops/offices/factorys up and running

Not exactly. During the summer demand is quite flat between 08:00 and 20:00, PV has a large peak between about 11:00 and 17:00, depending on orientation, so it doesn't match demand at all well. In the winter it is worse, as the main peak is in the evening, when there will be no solar input, with a smaller morning peak.

The issue is one of diversity. Although each household will have a few appliances with high demand they are generally used briefly. We are fairly high users of electricity, our average usage is about 750W with a base of about 400W. Our peak for the last 24 hours was 6,000W. The highest that I've seen was about 12kW. AIUI the average household consumption is about 500W. When averaged over several consumers the delivered power drops towards the mean and peaks become suppressed. That allows the distribution system to be desigened with a lower capacity, hence using less resources and lowering costs, without impacting on the reliability of the service. Adding multiple generators upsets this averaging, as all the generators in any area will be generating at their peak at the same time for long periods. This introduces a large probability that the local distribution network may be overloaded if the number of generators increases above a low level.

« Last Edit: August 30, 2012, 11:10:19 AM by billt » Logged
MikeD
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« Reply #26 on: August 30, 2012, 03:29:11 PM »


The issue is one of diversity. Although each household will have a few appliances with high demand they are generally used briefly. We are fairly high users of electricity, our average usage is about 750W with a base of about 400W. Our peak for the last 24 hours was 6,000W. The highest that I've seen was about 12kW. AIUI the average household consumption is about 500W. When averaged over several consumers the delivered power drops towards the mean and peaks become suppressed. That allows the distribution system to be desigened with a lower capacity, hence using less resources and lowering costs, without impacting on the reliability of the service. Adding multiple generators upsets this averaging, as all the generators in any area will be generating at their peak at the same time for long periods. This introduces a large probability that the local distribution network may be overloaded if the number of generators increases above a low level.



Surely though, with a ratio of non-generating households to generating households of say 10:1, all that happens is that the (worst case) 4kW coming off my roof is hoovered up by the 10 non-generating households all consuming 500W each, and the load on the local grid is reduced. You don't get a problem until you get to a ratio of fewer than 3 non-generators to each generator, at which point there will be potentially more than 500W per household being exported rather than imported. Eg:

5 non-generators per one generating household producing 4kW:
6 houses in total each drawing an average of 500W = 3kW load
4kW generated - 3kW used = 1kW total export, = an average of 1/6th of a kW exported per household = reduced load on the grid.


3 non-generators per one generating household producing 4kW:
4 houses in total each drawing an average of 500W = 2kW load
4kW generated - 2kW used = 2kW total export, = an average of 500W exported per household = normal load on the grid, albeit exported rather than imported.

So for a standard 4kW installation, worst case, you'd still need one in every 3 houses to have solar panels (a ratio of 2:1 ng:g) before you hit any sort of loading issues.
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billt
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« Reply #27 on: August 30, 2012, 03:48:21 PM »

Yes, that's fairly reasonable and is probably why 16A was chosen as the level above which DNO permission was required. However, I'd guess that, as the installation numbers go up, you are starting to get quite dense clusters of installations, particularly in areas were the well heeled live. Also, some domestic installations comfortably exceed 4kW peak. Get the odd 10kW peak installation amongst all the 4kW ones and the problem quickly gets worse.
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« Reply #28 on: August 31, 2012, 12:53:33 PM »


also.. for solar, highest output co-indices with highest demand too... when there's loads of shops/offices/factorys up and running


Not exactly. During the summer demand is quite flat between 08:00 and 20:00, PV has a large peak between about 11:00 and 17:00, depending on orientation, so it doesn't match demand at all well. In the winter it is worse, as the main peak is in the evening, when there will be no solar input, with a smaller morning peak.

I've had similar arguments on MSE about PV supply and electrical demand. But I don't agree.

Yes, demand from 8am to 4pm is pretty flat, (then usually a slight drop before a higher peak 5pm to 7pm) but crucially is well above baseload, so PV is a perfect match for the heightened daytime electrical demand!

http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Demand/demand24.htm

In the winter, daytime demand is again well above baseload, so again PV supply matches heightened demand perfectly.

Perhaps I should clarify the word 'perfectly' - when PV is generating, demand is high. PV can't match all high demand, but high demand matches all PV.

The argument that PV can't help with the winter evening peak has always baffled me. The problem isn't caused, or worsened by PV, and PV has never been touted as a solution for winter evening peaks, so I always struggle to understand why it gets beaten with this particular bat?

In every report I've read (governmental, environmental or accountancy firm commissioned) PV is always praised for it's supply time benefits since it generates during 'the working day'.

Mart.
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ProDave
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« Reply #29 on: August 31, 2012, 02:12:15 PM »

I think the "problem" is a few years ago we "harmonised" on a mains supply voltage of 230V

But the DNO's never actually made any changes.

I have yet to find a property with this mythical 230V mains supply.  Virtually every time I measure the voltage anywhere up here it's between 240V and 245V

So almost everywhere is running at the high end of the acceptable voltage under the new harmonised rules, so can tolerate a LOT of voltage drop without issues, but that also means most installations can only tolerate a much smaller amount of voltage rise before it goes outside limits.

What's needed is the DNO's to actually make a change to get closer to the 230V target.  but at the moment they are just putting sticking plasters on a broken system, and discouraging too much microgeneration in one place as it shows up the weakness of their infrastructure.
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