Hello! Welcome to the third lesson in our module on System Inefficiencies.
In the previous lesson, we explored the technical and market-based reasons for renewable energy curtailment. We established that the primary driver is network congestion—physical bottlenecks in the grid that prevent electricity from being moved from where it's generated (like windy Scotland) to where it's needed (like London).
Today, we will analyze the direct financial consequences of this process. Our focus is on the economic inefficiencies that arise from curtailment. You will learn what "constraint payments" are, who receives them, how they are calculated, and why this mechanism results in a more expensive electricity system for everyone.
1. The Two-Sided Cost of Curtailment
When the National Energy System Operator (NESO) curtails a wind farm due to a transmission bottleneck, it triggers a two-part financial transaction to keep the grid balanced.
- "Turn Down" Action: NESO instructs the wind farm to reduce its output and pays it to do so. This is the "constraint payment" that you might see reported in the media.
- "Turn Up" Action: Since demand has not changed, the lost electricity must be replaced. NESO simultaneously pays another generator—typically a gas-fired power station—located on the other side of the bottleneck and closer to the centres of demand, to increase its output and fill the gap.
This short video provides an excellent summary of this two-sided process and its financial implications.
Wind Power: Why some wind farms are being paid to stop producing energy
This clip from Sky News, 'Wind Power: Why some wind farms are being paid to stop producing energy', clearly explains the dual cost of curtailment: paying wind farms to switch off and paying gas plants to switch on.
Please watch from 00:39 to 02:15. Pay close attention to the explanation of the bottleneck, the need to turn on gas power stations, and the breakdown of the associated costs.
As the video highlights, the total cost of managing a single constraint includes both the payment to the curtailed generator and the much larger payment to the replacement generator. This entire cost is ultimately passed on to consumers through their electricity bills.
2. Dissecting the Constraint Payments
It is a common misconception that the bulk of "constraint costs" are payments made to wind farms for not generating. In reality, the opposite is true. The largest portion of these costs is for paying fossil fuel generators to turn on.
Let's look at the data and the reasons for this disparity.
Toxic constraint coverage could damage Clean Power Plan
This article from Regen, 'Toxic constraint coverage could damage Clean Power Plan', provides a detailed and data-driven analysis of how constraint costs are distributed. It cuts through the misleading headlines to explain the real economics at play.
Please read the section titled 'Most constraint costs are not to compensate wind farms – they are to pay gas generators'. This section provides crucial statistics and explains the economic logic behind the payments.
The article reveals a critical point: in 2024, 76% of constraint costs were paid to gas generators to increase their output, while only 24% were paid to compensate curtailed wind farms.
Why is there such a huge difference? The answer lies in how the payments are regulated.
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Payments to Wind Farms (Turn Down): These payments are strictly controlled and are not a source of profit. They are designed as compensation for lost marginal revenue. A generator has a legal connection agreement with the grid operator, and when curtailed, they are essentially paying for a service (transmission) they are not receiving. The payment they receive covers losses from things like government subsidies (e.g., Contracts for Difference) and the value of Renewable Energy Generation Certificates (REGOs). It is compensation, not a bonus.
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Payments to Gas Generators (Turn Up): In contrast, when a gas power station is asked to turn up its output in the Balancing Mechanism, it can charge a market-driven price. During periods of high demand or grid stress, there may be few alternative generators available, giving the gas plant significant pricing power. This leads to much higher costs compared to the regulated compensation paid to wind farms.
This fundamental difference is the primary source of the economic inefficiency. We are forced to discard cheap, clean energy and pay a premium for expensive, carbon-intensive energy to replace it, all because of inadequate grid infrastructure.
3. The Rising Tide of Inefficiency
The problem of curtailment costs is not static; it is rapidly getting worse. As the UK builds more renewable generation (especially wind in Scotland) faster than it builds the transmission capacity to support it, the level of congestion and the resulting costs are soaring.
This chart illustrates the core economic problem: the gap between generation capacity and transmission capacity is widening, leading to an exponential increase in inefficient spending.
Test your understanding!
Imagine the System Operator needs to manage a constraint on the Scotland-England border.
- It pays a Scottish wind farm £2 million in compensation to curtail its output.
- It pays an English gas plant £9 million to increase its output to replace the lost power.
- What is the total constraint cost passed on to consumers?
- Why is this situation economically inefficient for the electricity system as a whole?
Show answer
- The total constraint cost is £11 million (£2 million + £9 million). This entire cost is socialized and recovered from all electricity bill payers.
- The situation is inefficient because the system is paying a premium of £11 million to manage a problem that exists only because of a physical bottleneck. If the grid had enough capacity, the cheap wind power could have flowed south, and this £11 million cost would have been avoided. The system is failing to use its cheapest resources, creating a deadweight loss for the economy.
4. Lost Revenue and Wasted Energy
Beyond the direct constraint payments, there is a more fundamental inefficiency: lost opportunity and wasted resources.
From the perspective of a renewable generator, curtailment represents lost revenue. While they receive compensation, their primary business is to generate and sell electricity. Frequent curtailment means their multi-million-pound asset is forced to sit idle, reducing its overall profitability and making future investments in clean energy riskier.
More broadly, for the UK as a whole, every megawatt-hour of curtailed wind or solar power is a lost opportunity. We have a source of energy that is free at the point of generation (the wind and sun cost nothing) and produces zero carbon emissions, yet we are unable to use it. This "wasted energy" represents a significant economic loss and slows our progress towards decarbonization.
Conclusion
In this lesson, we have moved from understanding the causes of curtailment to analyzing its costs. The economic inefficiencies are substantial and growing, stemming directly from the physical limitations of the electricity grid.
Key Takeaways:
- Renewable curtailment due to grid congestion creates a two-part cost: a smaller compensation payment to the curtailed renewable generator and a much larger payment to a replacement fossil fuel generator.
- The vast majority of constraint costs (over 75%) are for paying expensive gas power plants to turn on, not for paying wind farms to turn off.
- Payments to wind farms are regulated compensation for lost marginal revenue, not a source of profit.
- The total costs are ultimately paid by all consumers through their electricity bills, representing a major economic inefficiency where cheap, clean energy is replaced by expensive, polluting energy.
Preview of the next lesson:
The bottlenecks causing curtailment are a symptom of a wider problem. In our next lesson, we will explore another major inefficiency in the system: the grid connection queue. You will learn why there are long delays for new generation and storage projects to connect to the grid, creating a significant barrier to the UK's energy transition.