Solar ... In the news

Martyn1981

spgsc531 wrote: »

Funny how not so long ago, some people were complaining that PV is ineffective and can't make any significant contribution to our electricity consumption, and now they say it's so powerful it'll blow the grid!!

Germany seem to have solved that problem, using inverters that monitor grid frequency and shut down if necessary. Early days here, but nice to know we can copy the Germans homework.

Mart.

spgsc531

Martyn1981 wrote: »

Germany seem to have solved that problem, using inverters that monitor grid frequency and shut down if necessary. Early days here, but nice to know we can copy the Germans homework.

Mart.

Just requires something beyond 'Dinosaur' thinking. Brave new world and all that..

EricMears

spgsc531 wrote: »

Funny how not so long ago, some people were complaining that PV is ineffective and can't make any significant contribution to our electricity consumption, and now they say it's so powerful it'll blow the grid!!

It's generally much the same whenever anybody tries to make a forecast without some really good evidence !

Take the 'imminent' Ice Age we were going to have about now (according to the best statistical data in the 1960s).

Or watch any game of snooker on telly : "X will get this easy black then he should clear the table; Oh dear, he's missed !"

I'll refrain from my usual rant about weather forecasters (but strongly suspect I might mention that in the 'talking about my generation' topic later today).

rogerblack

Martyn1981 wrote: »

Germany seem to have solved that problem, using inverters that monitor grid frequency and shut down if necessary.

That works for national 'overloads' - not really for local.
Remotely disableable solar becomes needed, if the solar mix goes high enough that it can make small districts have too high a net outflow of power, leading to local overvoltage or overcurrent on lines.

zeupater

rogerblack wrote: »

That works for national 'overloads' - not really for local.
Remotely disableable solar becomes needed, if the solar mix goes high enough that it can make small districts have too high a net outflow of power, leading to local overvoltage or overcurrent on lines.

Hi

Inverters should already disconnect if they are presented with an out-of-specification voltage or frequency. I agree that for local conditions it's much more likely that overvoltage would be the issue, so disconnecting would already take place, this starting with the installations which would be closest to the substation/transformer, these nodes having experienced the lowest voltage drop.

HTH
Z

Martyn1981

zeupater wrote: »

Hi

Inverters should already disconnect if they are presented with an out-of-specification voltage or frequency. I agree that for local conditions it's much more likely that overvoltage would be the issue, so disconnecting would already take place, this starting with the installations which would be closest to the substation/transformer, these nodes having experienced the lowest voltage drop.

HTH
Z

Here's the technical bit:

http://www.vde.com/en/fnn/pages/50-2-hz.aspx

and here's some thoughts I found on what is now happening:

"In a nutshell the problem they have is that with so much PV generation, if there is too much power available and the frequency rises above 50.2Hz, then all the PV inverters shut-off at the same time creating a massive sudden shortfall. Then they all reconnect again 5 minutes later, in a yoyo effect.

Their new standard for GTIs requires that they support a form of frequency shift power control, so that they vary their output based on grid frequency between 50.2 Hz and 51.5 Hz."

Please don't ask me to explain any of it!

Mart.

grahamc2003

zeupater wrote: »

Hi

Inverters should already disconnect if they are presented with an out-of-specification voltage or frequency. I agree that for local conditions it's much more likely that overvoltage would be the issue, so disconnecting would already take place, this starting with the installations which would be closest to the substation/transformer, these nodes having experienced the lowest voltage drop.

HTH
Z

Inverters have to match exactly the grid frequency (they can't do anything else!), which is why connecting to the grid is called 'synchronising'. It's extremely unlikely that grid frequency will be outside the legal limits, and I expect all solar inverters can invert the dc to every frequency within the legal limit. While the frequerncy is the resonsibility of national grid and is the same for everyone connected to the grid, the voltage is the responsility of the dno (iirc, local grids aren't my expertise) and is unique for all of us. So the frequency is completely independent of the voltage. You can, and do, get any combination of high and low voltage and high and low frequency. Higher frequencies arise when generation exceeds demand and the excess manifests itself as additional angular momentum, and vv.

Desynching solar installations on some preset higher frequency looks sensible - it means the automatic frequency response of the grid has probably exceeded it's capacity to store any excess energy, so a precarious situation. I might as well add the obvious, that the more intermittent generation connected to the grid, the more probability of frequency parameters reaching and exceeding their limits.

It would be 'interesting' beinga grid engineer if the solar penetration were high, and several hundred MW dropped out due to a high frequency situation (sigh of relief), but then all kicked back in 5 minutes later (hair pulled out).

To ensure clocks and other frequency locked equipment maintain accuracy, the frequency integral is monitored constantly, and usually around midnight, grid engineers try to run the grid at a frequency such that the average frequency for the day is very close to 50Hz.

spgsc531

grahamc2003 wrote: »

It would be 'interesting' beinga grid engineer if the solar penetration were high, and several MW dropped out due to a high frequency situation (sigh of relief), but then all kicked back in 5 minutes later (hair pulled out).

That's some Grid engineer affected by that small amount

zeupater

grahamc2003 wrote: »

Inverters have to match exactly the grid frequency (they can't do anything else!), which is why connecting to the grid is called 'synchronising'. It's extremely unlikely that grid frequency will be outside the legal limits, and I expect all solar inverters can invert the dc to every frequency within the legal limit. While the frequerncy is the resonsibility of national grid and is the same for everyone connected to the grid, the voltage is the responsility of the dno (iirc, local grids aren't my expertise) and is unique for all of us. So the frequency is completely independent of the voltage. You can, and do, get any combination of high and low voltage and high and low frequency. Higher frequencies arise when generation exceeds demand and the excess manifests itself as additional angular momentum, and vv.

Desynching solar installations on some preset higher frequency looks sensible - it means the automatic frequency response of the grid has probably exceeded it's capacity to store any excess energy, so a precarious situation. I might as well add the obvious, that the more intermittent generation connected to the grid, the more probability of frequency parameters reaching and exceeding their limits.

It would be 'interesting' beinga grid engineer if the solar penetration were high, and several MW dropped out due to a high frequency situation (sigh of relief), but then all kicked back in 5 minutes later (hair pulled out).

To ensure clocks and other frequency locked equipment maintain accuracy, the frequency integral is monitored constantly, and usually around midnight, grid engineers try to run the grid at a frequency such that the average frequency for the day is very close to 50Hz.

Hi Graham

Our inverter is G83/1-1 certified and as such designed to match grid frequency, however, in compliance with the G83/1-1 specification, if the grid frequency moves to an out-of-specification condition for a set period of time, the inverter simply switches off ... I understand that the grid frequency is unlikely to be an issue, that's why the referenced post concentrated on overvoltage, which is a possible local issue.

Our voltage varies throughout the day .... it was 243.8V at the time that the reference post was written (sad though it may be - I looked !), but it's a Sunday and (almost) everyone's at home consuming energy, but during weekdays it's usually between 2V & 4V higher .... What I was attempting to convey was that a substantial increase in the number of local installations could feasibly push the voltage up a little more, but even in that event, before (/if) the voltage goes out of spec, the inverter would simply switch off ..... this would not necessarily mean that all other inverters in the area would also do the same as one further away from the transformer/substation would not be experiencing the same voltage.

Z

Martyn1981

Electricity production from solar and wind in Germany in 2012:

http://www.ise.fraunhofer.de/en/downloads-englisch/pdf-files-englisch/news/electricity-production-from-solar-and-wind-in-germany-in-2012.pdf

Lots of data. Pages 13, 14 and 16 are interesting, showing a nice correlation between wind and solar.

Mart.