@mk4  - perhaps I should clear up some of those 'unknowns':

1: There is a mechanism called Active Network Management (ANM) which is used to curtail/reduce the amount of generation which may be exported to the grid by commercial sites. Prior to the site being constructed, the Applicants can be provided with a forecast, showing the expect level of constraint for hours of the day and days of the year.

The ANM forecast can vary substantially, depending on what existing generation sites are already connected to the grid in the vicinity.

The Shutdown Order given to Derril Solar and other regional generators is not the same as ANM.

The Order is for a complete cessation of export to the grid, rather than a quantity of curtailment which will vary by the hour.

2: There is a priority mechanism in place for connections to the Distribution Grid.

Each generation site is allocated a number corresponding to the date when they obtained a grid connection.
Earlier sites are therefore less likely to be adversely affected by curtailment.

The table below shows 22 sites which have "Offer to Connect" status for a particular location on the grid.

The Position column is their number in the priority list.

Most of these will physically be connected at lower-voltages on the grid, rather than directly at this location.

However, the cumulative total shows the potential maximum power which this location might be presented with.

Some details are deliberately omitted for security and confidentiality reasons.

3: The Guardian article states that National Grid (NGET) have been told by NESO to take a supergrid transformer out of use during summer 2026.

That isn't an action instigated as a response to over-supply. Exporting more to overseas wouldn't alleviate the situation.

The problem in the West Country is lack of Reactive Power support.

Almost all the generation sites in Cornwall and Devon are connected to the grid using inverters. At the time they were ordered and installed there was no requirement for these to be "grid forming". Therefore they do not provide the necessary Reactive Power handling.

Reactive Power forms part of the mechanism by which NESO controls supply and demand on the grid. When there is insufficient Reactive Power capability, the grid becomes unstable in that region. It can suffer rapid Rate of Change of Frequency (RoCoF), which is a parameter measured by the grid operations room.

Reactive Power is usually provided to the grid by rotating turbines and flywheels.

There is such a concept of 'having too much solar' in a region. The West Country is now experiencing that.

DESNZ have continued to encourage more solar farms to be constructed, regardless of the potential for having too little Reactive Power support. NESO may not reject further applications for solar farm connections in the region.

On Thursday (16th July) Cornwall Council Planning Committee will discuss application PA24/05312 from EDF Energy for another 49.9MVA solar farm at Trelion. It would be competing with Derril Water for access to Route-K of the grid.

Posted by: @old_scientist

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Are planners able to mandate co-location of BESS for new solar sites, and would that help solve the GRID issues by effectively turning them into a steady 24h predictable supply.

No.

Neither a Council Planning Committee, nor the grid operator may instruct an Applicant what power mechanism they wish to install.

In any case, BESS also uses inverters to connect to the grid.
That doesn't provide a solution to the lack of Reactive Power support.

Posted by: @toodles

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@jamespa You may or may not be aware but: Ripple Energy were the architects of the individual co-ops for the four energy projects; two wind farms were set up and are still running. The third co-op is Derril Water Solar Farm and the fourth (another wind farm) project collapsed and Ripple Energy went into receivership. As an aside, I recouped my investment in the fourth project via Section 75. DWSP was in take-off mode at the time but was delayed on the runway. As a co-op, it is independent of the parent company; however, at that stage there was very little if any management and it fell to co-op members to volunteer as managers. Other than to say that various mishaps occurred after this stage had been reached, I will say no more at present. Regards, Toodles.

My experience of green energy investing isn't great. I invested in Secured Energy Bonds, another solar scheme, one of the many mini bond failures generally.

After years of complaints via the FOS and FSCS we got all our money back with interest (due to issues with the original promotional material approved by a FCA regulated company) 

I now stay clear of green generation investments..