Renewable Energy Curtailment

Renewable-energy curtailment is the deliberate reduction of a renewable plant's output below what the available wind, sunlight or other resource could produce. Transmission-related curtailment occurs when the grid lacks sufficient safe evacuation capacity to carry that electricity from the generating area to consumers.

How a transmission bottleneck causes curtailment

The grid must continuously balance electricity injection and withdrawal. Every line, transformer and substation has a finite transfer capability, governed by thermal loading, voltage, stability and contingency limits.

• When renewable generation in an area exceeds local demand and available export capacity, the surplus cannot safely enter the wider grid.
• If redispatch, storage or flexible demand cannot remove the congestion, the system operator instructs generators to reduce injection.
• Curtailment therefore protects grid security and equipment even though sunlight, wind or another renewable resource remains available.

Why renewable plants are exposed

Renewable projects are often concentrated where resources and land are favourable, while major demand centres may be distant. Their output can also rise simultaneously, causing evacuation lines to reach their limits during high-generation periods.

• Available renewable electricity means electricity the plant could produce from the prevailing resource, not electricity the network can necessarily carry.
• The must-run status of eligible renewable generators limits curtailment for commercial merit-order reasons, but it cannot override physical grid-security requirements.
• Curtailment is distinct from renewable variability: variability changes potential generation, whereas curtailment deliberately keeps actual generation below that potential.

Consequences and remedies

Curtailment causes foregone clean generation, lowers plant utilisation and revenue, and can weaken the environmental benefits expected from new renewable capacity.

• New transmission corridors, substations and stronger interconnections expand evacuation capacity.
• Energy storage, flexible demand, improved forecasting and geographically diversified generation can absorb or smooth renewable surpluses.
• Coordinated generation and transmission planning prevents renewable capacity from being added faster than the network needed to carry its output.