Massive changes to G83 rules for solar PV installations needing advance permission

[mdovey]

Re: Massive changes to G83 rules for solar PV installations needing advance permissio

5 - Suggestions made about investigating / adopting the German solution of inverters that reduce their output to limit localised voltage spikes or overall high frequency issues, instead of the inverters being either 100% on, or 100% off. As virtually all inverters have this capability built in anyway it should be relatively simple to adopt this approach, which would then fully solve most of the concerns the DNOs have around localised over voltage issues. Ofgem seemed interested in this, but it's too late for it to make it into G83/2.

From a technical viewpoint this may be simple - from a FIT perspective, this looks like a minefield.

The current FIT is based on how much is generated, not how much is actually fed into the grid. If the panels of a system are generating at 3KW but the inverter is limiting the output to 1KW due to local grid issues, then the FIT should be based on 3KW not 1KW, i.e. on existing installations any limiting should be done between the generation meter and the grid, not at the inverter. Otherwise I can see some nasty court cases against OFGEM/DECC that this was a retrospective change to the FIT contract or with solar installers for mis-selling for not taking this into accounts in their financial forecasts.

This could be introduced for new installations. However, it will make the financial projections even harder to produce, and could even further impact sales - how many would install solar knowing that there is a risk that payback period if one of their neighbours installed a generation facility which resulted in the inverter throttling the output!

Matthew

 

[Gavin A]

Re: Massive changes to G83 rules for solar PV installations needing advance permissio

From a technical viewpoint this may be simple - from a FIT perspective, this looks like a minefield.

The current FIT is based on how much is generated, not how much is actually fed into the grid. If the panels of a system are generating at 3KW but the inverter is limiting the output to 1KW due to local grid issues, then the FIT should be based on 3KW not 1KW, i.e. on existing installations any limiting should be done between the generation meter and the grid, not at the inverter. Otherwise I can see some nasty court cases against OFGEM/DECC that this was a retrospective change to the FIT contract or with solar installers for mis-selling for not taking this into accounts in their financial forecasts.

This could be introduced for new installations. However, it will make the financial projections even harder to produce, and could even further impact sales - how many would install solar knowing that there is a risk that payback period if one of their neighbours installed a generation facility which resulted in the inverter throttling the output!

Matthew

I take your point, however if the alternative is for the system not to be allowed at all, or for only a smaller system to be allowed, I think this option is generally preferable.

Your suggestion on the point at which this should be applied is a complete technical non-starter IMO, and possibly a dangerous one at that. If throttled at the inverter, it uses the MPPT system of the inverter to throttle the output entirely safely by adjusting the voltage point it's drawing power from the panels at to a less efficient point. If throttled on the AC side of the inverter then the only method of throttling the system is via a heat dump or similar, which while technically possible, is going to add significantly to the costs and complexity of the systems, and lead to the potential for 2kW+ heat dumping for long periods in peak summer which is unlikely to be a desirable situation, and if mounted in the wrong place could pose a fire risk (I know of someone who's house burnt down due to a similar heat dump unit used in an offgrid system).

Possibly you could look at allowing the use of immersun / emma style load management as an alternative option, but the problem with these units would be that they're only capable of storing a certain volume of excess energy in the hot water tank before they stop working, at which point the full generation would be sent back to the grid. I'd therefore see them as being supplementary measures that we as installers could recommend to customers to minimise the levels of reduced output, rather than actually being an alternative method of safeguarding the grid in the way that the inverters can do. Apart from anything else, the inverters already have to be g83 compliant, whereas these units don't, and I don't see that it's going to be an advantage to have to pay the additional costs involved in getting them type tested.

I'd be very surprised in most cases if this led to more than a 1-2% reduction in output through the year, and it's a simple enough matter to factor such reductions into your calculations, especially if it's mitigated with the use of an Immersun. It's certainly worthwhile if it allows for a 4kW system to be installed instead of a 2kW system, or no system at all, or is an alternative to not being allowed to install for 28 days which means missing a FIT cut deadline.

Put simply though, if we're going to get anything close to the 20GWp of solar PV installations being discussed, then we will have to adopt these measures at some point to prevent severe localised grid problems, or there simply not being enough capacity on the grid to take that level of uncontrolled SSEG connection. It's far far better to implement this measure before it becomes a significant problem, as the more widespread the implementation of the measure, the less severe the restrictions need to be on each individual sseg.

 

[mdovey]

Re: Massive changes to G83 rules for solar PV installations needing advance permissio

Yes, it did occur to me that a limiter after the generation meter wouldn't be a great idea, due to the need to dump the energy somewhere.

If the impact really is only 1-2% then there is unlikely to be an issue but if it is much higher it would have impact, and it would only need a few well reported cases of examples of higher limiting to further damage sales (even if these cases were abnormal).

I'd also be concerned that the DNOs would just use this as an excuse not to invest in the infrastructure needed to make the best use of micro-generation.

I do take your points the alternatives aren't great either.