I have an update on why Derrill Water Solar Farm isn't currently permitted to export.

There's more than one reason, and the zero-export decision originated from National Grid Electricity Transmission (NGET) rather than the DNO.

The information I'm prepared to post here on the open Forum is that South West England isn't stable because it has insufficient capability to handle Reactive Power demand.

Read NESO's description of the need for Reactive Power here, and a somewhat deeper explanation from Johnson Philips here.

Traditionally reactive power was supplied to the grid by the way in which electricity was generated using rotating turbines.

But when you scatter solar-farms and wind-farms across a large area then the electricity is being supplied by inverters, which use electronics. There's no rotating turbines and the magnetic flux which would be present in their coils of copper wire.

That's the situation in Devon and Cornwall, as you can see from the dots on this Barbour map of central Cornwall:

Yes, there are grid-forming inverters, and a DNO might insist that a generation site uses them.

And some commercial inverters can be configured to absorb reactive power.

But in South West England these technologies are not available at the scale required. NESO has been running an open consultation seeking more reactive power sources for 'medium term' use. That might be for a couple of years; perhaps when Hinkley-C starts operating in Somerset.

I don't know what inverters are used at the Derill water site.

Nor do I know how many other solar sites in the West Country are similarly effected by the order from NGET.

But we all ought to note that there are adverse consequences of allowing companies to build lots of solar farms in a sunny area just because it's "government policy".
Physics isn't going to change simply because the Secretary of State has a Net Zero timetable to meet!

@transparent I would imagine that DW’s inverters are not of the grid-forming type or the DNO would have welcomed that additional inertia I would have thought.

As to the Net Zero Timetable, it rather sounds as though, as a nation, we seem to have a need to increase our capability of murdering others under the badge of NATO and that the fossil fuel industry will continue to make billions for the foreseeable. Ho-Hum. Toodles. 

@toodles Just so that you know that you are not alone: over here it is nowadays common for the TSO to cut off the grid large PV parks during spring and autumn, when production is high (large enough daylight duration, moderate temperatures, no clouds) and demand is low (no heat demand, no cooling demand either).

During the summer energy demand is high for cooling (higher than during winter) and the PV parks work full time.

@mk4 And of course, the panels are less productive due to the ambient temperature of the panels. Regards, Toodles.

Posted by: @mk4

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over here it is nowadays common for the TSO to cut off the grid large PV parks during spring and autumn, when production is high

You have a different approach in Greece.

Here, Derril Solar is in a region where NGED is the licensed grid operator. They have two complementary rules to handle excess generation:

1: Generation Sites are given a number which reflects the date when they received an Offer to Connect. Later sites, with a higher number, will have their output curtailed first. The established sites are therefore not greatly disadvantaged when more generation comes on-stream.

2: NGED operates Active Network Management. ANM works across a dedicated radio system, and sends commands to generation and storage sites which govern how much export they are permitted. It is not an on/off switch, but an adjustable 'slider' which avoids surges and imbalances between supply and demand.

It is therefore very unusual to learn of a generation site in UK which has been instructed that it may not export anything at all for many months.

It's a decision with serious consequences. Most generation sites will be backed with investment funds from one or more commercial banks. Even if there's no income from selling electricity, then the contract with the bank would normally still require the same interest payments to be made, and possibly some of the capital too.

An instruction from an Ofgem-licensed grid operator to cease all export is therefore liable to cause the financial collapse of the business.

That has the potential to send a shock-wave through the energy sector, resulting in potential investors withdrawing from other forthcoming renewable energy projects. It's the exact opposite of Government policy, which is to encourage investment in renewables, and to facilitate more generation sites to come on-board.

Something has gone wrong in this instance.

You wouldn't expect Ofgem to allow a licence-holder to undermine Government strategy for Net Zero.

They will be entitled to constraint payments to cover their losses, but you are right that investment would evaporate overnight if the goalposts were moved.

@toodles @jeff

So I guess the question is: does someone, who has carefully constructed the Derril Water scheme in a way that protects themselves from risk, gain anyway, or is this just an unfortunate conjunction of unlikely circumstances?  The latter does, after all, occur although the former is not uncommon either.  

@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.

@transparent 

My statement about cutting large PV parks off was probably oversimplified. I do not know the details (duration, complete or partial cut off, who gets precedence over whom, etc). But I do read in energy press sites the complaints of the PV park investors about being cut off. And there is also talk about upgrading the interconnections with neighboring countries in order to increase the amounts of exported energy. 

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. If so, how could we incentivise upgrading existing problematic sites with BESS?

@old_scientist As Mahatma Gandhi is rumoured to have said: “It would be a very good idea”. (Not that I know anything about the ins and outs of energy politics, but, it makes sense to me anyway). Regards, Toodles.

I have just received an update from the Derril Water Solar Park Co-op: