Curtailment

Curtailment refers to the intentional reduction of power output from a solar PV system—even when the system could generate more electricity—due to grid constraints, interconnection limits, oversupply conditions, or operational restrictions.

In simple terms, curtailment is when a solar plant is forced to “dial back” its production, not because sunlight is unavailable, but because the grid or system operator cannot accept the full output.

Curtailment is increasingly common in regions with high renewable penetration, as well as in systems with limited export capacity. It is especially relevant to developers, system designers, asset managers, and utility operators planning projects where grid flexibility, storage integration, or DC/AC ratio optimization play a role.

Key Takeaways

Curtailment is the intentional reduction of solar output to maintain grid or system stability.
It occurs even when the PV system could produce more electricity.
Reasons include export limits, oversupply, voltage rise, DC/AC oversizing, and operator constraints.
Curtailment must be included in yield modeling and financial projections.
Storage, smart controls, and optimized design strategies can reduce curtailment.

What Is Curtailment?

Curtailment is the practice of reducing a solar system’s power output below what it is capable of generating. This can be:

Grid operator–initiated (to maintain grid stability)
Utility-enforced (due to interconnection or export limits)
Self-imposed (as part of system design strategy)

Even when sunlight is strong, a solar system might be commanded to produce less energy to avoid:

Grid overload
Voltage instability
Frequency deviations
Transmission congestion
Exceeding export limits

Curtailment is not a system failure—it is a controlled operational adjustment.

Related concepts include Inverter Clipping, DC/AC Ratio, and Grid Interconnection.

How Curtailment Works

Curtailment typically occurs through commands or limits imposed on the inverter or power plant controller.

1. Grid or System Operator Signals a Reduction

Operators may send dispatch instructions to reduce output:

Manually
Automatically
Through SCADA or remote monitoring systems

See SCADA for more on remote control.

2. Inverters Reduce Power Output

The inverter receives a limit and adjusts:

Real power (kW)
Sometimes reactive power (kVAR)

3. PV System Operates Below Potential

Energy that could have been generated is intentionally not harvested.

4. Performance Modeling Reflects Lost Yield

Curtailment must be accounted for during:

Pre-construction yield modeling
Financial modeling
O&M reporting
Utility-scale dispatch planning

Tools like Solar Designing and performance analytics platforms help estimate curtailment impacts.

Types / Variants of Curtailment

1. Grid Curtailment

The grid operator limits solar output because:

Renewable supply > demand
Transmission lines are overloaded
Voltages rise above limits
Frequency stability needs protection

2. Export-Limited Curtailment

Systems with export limits (such as residential or commercial) may be restricted by:

Utility interconnection agreement
Feeder capacity
Transformer limits

See Export Limiting.

3. Curtailment Due to DC/AC Ratio

If a system is intentionally designed with a high DC/AC ratio, it may produce more DC than the inverter can convert during peak sun hours.

This often overlaps with Inverter Clipping but differs because clipping is an inverter limit, not a grid command.

4. Economic Curtailment

A plant may strategically reduce production when:

Energy prices go negative
PPA terms do not compensate additional generation

5. Operational Curtailment

When maintenance, faults, or safety conditions require a temporary reduction in output.

How Curtailment Is Measured

Curtailment is typically quantified using:

1. Curtailment Percentage

Curtailment % = (Potential Energy – Actual Energy) / Potential Energy × 100

2. Curtailment Loss (kWh)

Energy that could have been produced but wasn’t.

3. Lost Revenue

Especially important for:

PPA-based systems
Utility-scale projects
Merchant market projects

4. Curtailment Hours

The number of hours during which output was reduced.

Typical Values / Ranges

Curtailment varies by region and grid conditions:

Residential systems: 0–5%
Commercial systems: 0–10% (export-limited sites)
Utility-scale solar: 5–30%+ in congested markets
High renewable penetration areas (California, Australia, Germany, Hawaii) may see significant curtailment during midday oversupply.

Practical Guidance for Solar Designers & Installers

1. Review interconnection limits early

Use the Interconnection Agreement during the design stage to understand export or operational constraints.

2. Model curtailment impacts in financial projections

Tools like the Solar ROI Calculator help understand cost implications.

3. Use energy storage to reduce curtailment

Batteries absorb excess energy instead of wasting it.

See: Battery Size Calculator.

4. Optimize DC/AC ratios

Oversizing modules improves yield but may increase curtailment without proper tuning.

5. Add operational flexibility

Advanced control systems help reduce unnecessary curtailment.

6. Monitor performance via SCADA

Real-time data helps identify unnecessary or excessive curtailment events.

See SCADA.

Real-World Examples

1. Residential Export-Limit Case

A 10 kW system is limited to exporting 5 kW by the utility.

During midday, the inverter is commanded to cap output at 5 kW, causing curtailment.

2. Commercial Solar on a Weak Feeder

A 500 kW system experiences voltage rise during peak generation.

The utility remotely curtails the system 15–20 afternoons per month.

3. Utility-Scale Curtailment During Oversupply

A 100 MW solar farm in a high-renewable grid is curtailed 12% annually due to midday oversupply and transmission congestion.