Solar PV Feed In Tariffs - Good or Bad?

zeupater

John_Pierpoint wrote: »

For the ordinary reader, who is having trouble keeping up with all these engineers; this bit of the discussion was sparked by this link:
http://www.germanenergyblog.de/?p=7313
It seems that Germany will be having problems with PV capacity switching on in the summer sunshine faster than the grid controllers can turn off fossil fuels, especially so as the PV generation is dispersed into all sorts of nooks and crannies in the lower voltage out lying grid.
As these outlying areas of the grid get over provided with electricity the frequency increases from 50 to 50.3 Hz (Cycles per second - I can see why this would happen with a conventional mechanical turbine revolving faster but I'm not sure why a PV inverter would follow suite) The only obvious solution is to turn off one of the local large PV sites, thus stopping its FiT payment on a really sunny day..

Have I got that right?

Hi

As I understand it, the issue isn't directly related to the pv installations because they measure and match the grid frequency anyway. When there is less demand the load on turbines reduces and they spin faster, so the frequency increases (the opposite happening as load increases) and decisions need to be taken to adjust generation at various sites to compensate .... the issue is that in Germany the installed pv capacity is now large enough for the entire grid to see fluctuations, either from massive pv-farms or just the combined effect of a large populated area with pv, and of course, when this happens the grid controllers have absolutely no direct control over the pv which can result in rapid variations in supply frequency which can cause inverters to see 'out of specification' power conditions and shut down, which of course places more load on the generators and causes them to slow which reduces the frequency .... then the inverters all see the power conditions improve and switch on, which causes ...... well let's just call it an 'infinite loop' condition ... so the Germans are looking at preventing this happening ....

... Anyway, that's my understanding ... perhaps someone like Graham, being an actual expert in this area, could comment - that's if he's still prepared to assist after all of the recent childish abuse ....

HTH
Z

John_Pierpoint

Yes I can see that the whole thing could become inherently unstable - sort of reminds me of the baby boom that happened in New York 9 months after a relatively "minor problem" on the network.

PV stuffs too much electricity into the network, the traditional capacity speeds up having to work less hard, the PV inverters "panic" and close down, possibly so fast that they don't switch back on again as it now looks like the network is trying to brown out, somewhere else a load of safety switches rush to protect generators and large compressors from damage and total confusion reigns - now program that safely away from manual intervention.

Could end up on the rocks - to be topical.

albyota

However, if this were a problem with PV overload, rather than the grid frequency rising, surely there would be facilities for dumping, either to earth or in to large scale electrical immersion heater driven underground storage for district heating systems.

ed110220

Given that the Brazilians have had no problems building 2500km HVDC lines to carry hydroelectricity from dams in the far corners of Amazonia to the populated south east of the country (and there are similar systems in China and other places), the challenge of connecting Scotland and England is trifling in comparison.

In South Africa until the 1950s-60s electricity was generally generated in small (by today's standards) power stations near where it was consumed, and the coal was brought to the power stations. After that, they found it much more economical given advances in electricity transmission to simply shovel the coal straight out of the ground at the coal fields into very large power plants and send the electricity from there all over the country via the grid. Again, the distances involved are much larger.

Martyn1981

zeupater wrote: »

Hi

... Anyway, that's my understanding ... perhaps someone like Graham, being an actual expert in this area, could comment - that's if he's still prepared to assist after all of the recent childish abuse ....

HTH
Z

Your point is taken, well taken.

But I must say that I've always found people on forums and threads like these to be funny, polite and pleasant. You've corrected me on numerous occasions, always politely, and I've found all such posts very interesting and informative. I genuinely enjoy learning new stuff, and squirrelling it away in my odd brain.

If you scan through posts on threads like this one you'll find loads of intelligent and dare I say humorous individuals (smiley faces - got to love em). Roger, John, Zenoka, HJ, Don, Blossom, Sally, Penny, James, Ed, Albyota (and everyone else who knows me, as they say on Pop Master).

But I have to say regarding both Cardew's and Graham's posts, 'if you sow the wind, you reap the whirlwind'. People will respond in kind to the way they are treated. It is simple human nature. Or for another analogy, Rottweilers are one of the most friendly and placid breeds of dog there are. They share one of the lowest rates of attack, and make great companions to any age. But if you mistreat them enough, then you must be willing to accept the consequences.

I do however hope you are correct, and some friendly debates on PV can be restored. the way these discussions naturally branch off into renewables, nuclear, efficiencies, awareness and so on can make for fascinating reading. And please keep the numbers coming, you're better than google!

Mart

zeupater

albyota wrote: »

However, if this were a problem with PV overload, rather than the grid frequency rising, surely there would be facilities for dumping, either to earth or in to large scale electrical immersion heater driven underground storage for district heating systems.

Hi

That's where the variability of pv generation and microgeneration comes in to play. When pv installations reach a certain saturation level then control measures need to be implemented, the problem seems to be that all of the required control measures don't really exist on the inverters, so the only option currently available is to increase the control over major plant to compensate and keep the frequency stable. Ultimately it's likely that inverters will be instructed to shut down or divert power to an internal load such as batteries or immersion heating but that technology doesn't seem to exist 'in the field' yet. This could be done via commands transmitted over the grid itself .... anyway, with the current level of pv penetration in the UK we don't really need to worry (well I'm not going to, even if others do ), so let's just see how it's handled in Germany, as it seems to be the testbed, and then follow their lead ....

HTH
Z

Martyn1981

zeupater wrote: »

Hi

That's where the variability of pv generation and microgeneration comes in to play. When pv installations reach a certain saturation level then control measures need to be implemented, the problem seems to be that all of the required control measures don't really exist on the inverters, so the only option currently available is to increase the control over major plant to compensate and keep the frequency stable. Ultimately it's likely that inverters will be instructed to shut down or divert power to an internal load such as batteries or immersion heating but that technology doesn't seem to exist 'in the field' yet. This could be done via commands transmitted over the grid itself .... anyway, with the current level of pv penetration in the UK we don't really need to worry (well I'm not going to, even if others do ), so let's just see how it's handled in Germany, as it seems to be the testbed, and then follow their lead ....

HTH
Z

Am I misguided to think that Germany are well ahead of us in inverter technology, or is it just an assumption based on the percentage of the market they have?

M.

zeupater

Martyn1981 wrote: »

Am I misguided to think that Germany are well ahead of us in inverter technology, or is it just an assumption based on the percentage of the market they have?

M.

Hi

In reality it's the fact that the installation saturation in Germany is so high that the issue exists and it will take the UK years to catch up to where they are right now, so any problems will be found and solved there well before we see any real issues with pv.

Inverters themselves aren't really an 'advanced technology' product, it's just that the German (& Austrian ) companies have developed a lead, both in economy of scale and association with quality/reliability which natually links to product brand leadership ....

HTH
Z

Martyn1981

Cheers Z. Yeah, market share and 'German engineering reputation', make for a tricky business fight.

M.

Martyn1981

Looks like the 3rd March is the next deadline for subsidy cuts, unless the govt goes to the supreme court.

http://www.clickgreen.org.uk/news/national-news/123081-government-lose-appeal-bid-over-unlawful-feed-in-tariffs.html

http://www.bbc.co.uk/news/business-16721328

I guess it'll really only be after 1/4/12 that all of this settles back down, and new PV'ers will know where they stand.

Mart.