Renewable Energy · Intermediate level · 3 min read ·
What is curtailment?
Curtailment is the forced reduction of the energy a system delivers to the grid, ordered by the grid operator when the grid cannot take any more at that moment. The system could produce more, but it is held back. In AGPE projects it is uncommon, though possible during hours of high generation.
In 30 seconds
- It is a limit ordered from outside: it is not a system fault.
- It happens when the local grid cannot take more energy at that moment.
- While the limit lasts, the system delivers less energy than it could.
Why should you care?
A generation projection assumes the grid takes all the energy the system can deliver. Curtailment is one of the reasons that doesn't always happen.
- You understand why real production can fall below what was possible.
- You tell a grid limit apart from an equipment problem.
- You read a solar project's risk section with more context.
Think of it as a highway at rush hour
Your car runs fine, but if the road is full, the traffic officer won't let you on until it clears. Solar energy is the car; the grid is the road. When it is congested, the operator asks the system to deliver less.
How does curtailment work?
- 1
The grid hits its limit
High generation, low local demand or a line under maintenance leave the grid with no room.
- 2
The operator gives the order
The Network Operator asks to reduce or pause the energy delivered, for a while.
- 3
The system holds back
The inverters lower the power they deliver, even with plenty of sun.
- 4
Lost energy is measured
The gap between what it could deliver and what it delivered is the curtailed energy.
The formula
Curtailment (%) = (Possible energy − Delivered energy) ÷ Possible energy
- Possible energy
- = what the system would have delivered without the limit
- Delivered energy
- = what the grid actually received
An example with numbers
Illustrative figures, unrelated to any project: a system would have delivered 2,000 kWh in a month, but received two curtailment orders on very sunny middays.
| Possible energy for the month | 2,000 kWh |
|---|---|
| Curtailed energy | 40 kWh |
| Delivered energy | 1,960 kWh |
| Curtailment for the month | 2% |
40 ÷ 2,000 = 0.02. A few short episodes weigh little; if they became frequent, the effect on the year's production would grow.
Where do you see it at Circular Urban?
Each solar project describes its risks and how they are mitigated, including those of connecting and delivering energy to the grid. Curtailment is among the risks you accept in the risk declaration: production and results are subject to the project's actual performance.
- Each solar project sheet, in Risks & Mitigants.
- Each solar project sheet, in Energy Production: Annual Production.
- The risk declaration you sign before subscribing.
What changes in your finances once you get it
You separate projection and reality
You know estimated production assumes the grid takes everything, and that this can vary.
You read the full risks
You check in Risks & Mitigants how each project handles its grid connection.
You look at the year, not a day
One curtailment episode weighs little; what matters is how much energy is curtailed over the whole year.
Common mistakes
- Myth
If the system produced less, something must have broken.
- In reality
Not always: with curtailment the equipment works fine, but the grid can't take all the energy.
- Myth
Curtailment only happens on cloudy days.
- In reality
It is the opposite: it tends to happen in very sunny hours, when there is more generation than the grid can take.
- Myth
Curtailed energy is stored to be sold later.
- In reality
Without batteries, that energy simply isn't produced: generation in those hours falls below what was possible.
Test yourself
A system could deliver 5,000 kWh in a month and the grid received 4,900 kWh because of curtailment orders. What was the curtailment?
Keep learning
This content is educational. Every participation carries risks inherent to the project, including the possibility of partial or total loss, and results are subject to each project's actual performance.
