Grid Capacity

[Energetic]

I had an interesting conversation with my local DNO planner a few weeks ago after i made an inquiry for a 30kWp barn system for a local farmer. It seems there's no export capacity left on the 11kV lines for a few miles around due to a solar farm not too far away, the most my client can have is 3.86kw.

We are WPD and this is a rural area but we've seen a handful of solar farms spring up on our 'patch' but never had anything close by them. The planner said something along the lines of: 'get used to it, there's loads more in planning and Cornwall is full. The big onshore turbine developers are moving to Wales as the grid infrastructure is better from the mining days, without significant increase in consumption locally or billions in grid upgrades that's large PV and wind finished in Cornwall.'

We as a company are moving more into commercial but looks as if even big commercial could be a problem if most of the energy is being exported and the grid is already so tight. Doubt this will affect you guys near big population centers for a while yet but a real concern for rural areas.

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[Worcester]

We're seeing it even in populated areas as at weekends the daytime (sun up ) overall power consumption drops and the commercial systems are now trying to export as the power isn't being used on site, so we are seeing a requirement to limit export more and more frequently. Even had a 5kw wind turbine restricted the other day.

 

[TedM]

Of course when the big boys have their export restricted they get compensation payments. It would be interesting to see what happened if that sort of 'level playing field' applied to everyone.

 

[Worcester]

That's an interesting one - there anything in the 'FiT' legislation or Ofgem's guidelines to generators about that ...?

 

[Worcester]

Just checked and the answer is no. - They are called 'Constraint Payments', currently paid to wind operators, as well as other generators, the difference is in the scale.. Coal fired power stations bid a -ve payment (saves them fuel) were as wind have been getting up to 4 x the FiT / RO payment! The comments are that they will have to be introduced if Barking is to get his 20GW of solar power by 2020 (p.s. the grid can;t take it and will fall apart before then... see
Notes on Wind Farm Constraint Payments

and for solar:
Solar Photovoltaic Generation in the United Kingdom
paragraphs 24 to 26 are the killer ones there!

 

[Gavin A]

what's needed is the sort of ripple control the germans have set up - baffles me why this hasn't been implemented, although I got a good clue to the reason when discussing this with ofgem while discussing the G83 revisions... ie they had little clue what we were talking about, and it seems it just hasn't been discussed with the DNOs.

I think we're all going to have to be a little proactive here in terms of looking at options for onsite consumption / export limiting, and getting DNO approval for these methods - I think some DNO's have already approved the emma device for this, I'm hoping the new elios unit will also be capable of being approved, but some sizable heat dumps (or storage mechanisms) could well be needed on commercial systems.

 

[Gavin A]

perhaps those interested could look at forming a little working group to investigate the potential, get test sites installed and monitored, and gain DNO approval for different methods of output limiting?

 

[Worcester]

We've got a 200kW system that has restricted export - never a problem for about 40 weeks of the year, the problem is the summer 12 weeks and only then when they factory is closed at weekends (ironically the same 12 weeks when wind is the least productive...)

It's ridiculous that we are looking at heat / dump loads for excess power so that the client can still get the generation tariff.

This site doesn't get paid for export since as mentioned above there is so little of it, however it COULD theoretically peak up to 200kW export on those summer days

Fortunately this site has 14 SMA STP's on it, so at this scale the solution is quite simple though crude, we monitor the export and using contactors disconnect the grid from the inverters one by one to ensure the export power isn't overstepped. Crude but effective. DNO Happy.

We're working to see if ther is any way the we can use the SMA Power control module instead (if we can get the DNO to approve it)

 

[Worcester]

Here's the German requirement:

The Renewable Energy Sources Act (EEG) as amended mid-2011 and in force since the beginning of 2012 also includes new requirements regarding the grid integration of PV plants. It stipulates that PV plants with more than 100kW peak power must participate in feed-in management and, at the same time, extends this requirement to smaller PV plants, albeit in somewhat less stringent form: for instance, there is no longer any obligation to let the distribution network operator retrieve the current actual power of the plant. For PV plants with less than 30 kWp, plant operators may moreover skip installing a device for remote power limitation, providing that they accept a general limitation of feed-in capacity to 70% of the installed generator power.
PV plants between 30kWp and 100kWp must be retrofitted by the end of 2013 if they were commissioned after 31 December 2008. For plants with less than 30 kWp, no mandatory retrofitting applies.