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The Money Talk:Curtailment!

Updated: Sep 14, 2023

Let us talk about curtailment today.

When will my export be limited?

It depends!

  • Time of the day: flexible generators are less likely to be curtailed during “typical” peak demand hours e.g. dinner time or office hours (although this is changing because of electric vehicle and heat pumps!). Mid-day is normally bad for solar since it’s sunny and demand is low.

  • Weather: sunny and windy day is bad for flexible renewables! Especially when there is lots of wind and solar in the same area.

  • Network not available: same as road closure! When system operators (SO)or distribution netowrk operators (DNO) shut down a circuit to fix or do maintenance, less generation can go through the system. This can be a fault or a planned outage. SO/DNO don’t have a crystal ball, so they won’t be able to warn you for the former.

  • Seasons: summer demand is lower than winter and there is more sun so it’s bad for area with a lot of solar generation!

Why is this needed?

Electric power system usage is like road traffic, there are rush hours and quieter times. When the road is busy, traffic officers will divert the traffic to ease the congestion. Similarly, SO/DNO will have to stop a generator exporting to the network when it gets busy!

Why is there a congestion?

The short answer is there is more generation than demand. Power system is one of the most complex artificial system and needs to be managed carefully to maintain a balance. Too much generation (or load) breaks this balance!

What cause congestions?

  • Frequency: regulated by the system operator. Frequency will go up if there is too much generation

  • Voltage: Voltage will go up if there is too much generation

  • Equipment rating: conductors and transformers get too hot when there is too much electricity going through them

  • Protection: relays to protect equipment from getting damaged. Protection philosophy is designed for sending power from large plants to household so can limit how much you can send back.

What is Timed Connection?

A simple rule applied to your generator: you are not allowed to export during certain hours. Same as the Congestion Charges: you can drive into London for free after 10pm and before 7 am or you must pay!

Flexible connection?

This is also known as active network management (ANM) connection. SOs or DNOs monitors what is happening in the network and controls which generators are curtailed real time. This is typically based on a last in first out (LIFO) queue: the later the generator joins the queue, the more likely it will be curtailed!

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