Curtailment Modeling is the analytical process used to predict, quantify, and simulate how often a solar PV system may be forced to reduce or stop exporting power to the grid. Curtailment occurs when grid operators, utilities, or system constraints limit the amount of electricity a solar plant can deliver—even when the system could produce more.

For solar designers, developers, and project financiers, accurate curtailment modeling is essential because it directly affects energy yield, financial returns, inverter loading decisions, and project bankability. Modern platforms like Solar Designing incorporate system losses, grid constraints, and AC export caps to help designers understand real-world production impacts.

What Is Curtailment Modeling?

Curtailment modeling evaluates when and how much a solar system’s output must be reduced due to limitations such as:

• Utility-export restrictions
• Interconnection limits
• Grid congestion
• Voltage or frequency control
• DC/AC ratio clipping
• Contractual constraints (PPA export caps)

The model simulates system behavior at different times of the day and under different irradiance conditions to estimate lost generation (kWh) due to curtailment.

Related concepts include Inverter Clipping, DC/AC Ratio, and Performance Modeling Engine.

How Curtailment Modeling Works

While tools vary, most curtailment modeling workflows follow these steps:

1. Identify System Constraints

These may include:

• Interconnection export limits (e.g., 100 kW maximum AC export)
• Utility-imposed curtailment windows
• PPA-based export ceilings

2. Run Solar Production Simulations

The model calculates potential energy production throughout the year.

3. Compare Potential Output vs. Allowed Output

Whenever the system’s production exceeds the allowed export limit, curtailment is triggered.

4. Quantify Lost Energy

The model computes the difference between potential AC output and allowed AC output, producing a curtailment loss factor.

5. Apply Curtailment Schedules or SCADA Signals

In advanced models, utility curtailment events (manual or automated) can be simulated.

6. Integrate Curtailment Into Financial Models

See Solar ROI Calculator for understanding loss impact.

Types / Variants of Curtailment Modeling

1. Static Export Limit Modeling

Fixed export cap (e.g., 15 kW max export at all times).

Common for residential and small commercial systems.

2. Dynamic Grid Curtailment Modeling

Models real-world curtailment events based on:

• Peak congestion
• Low system load periods
• High renewable penetration
• Voltage instability

3. Economic Curtailment Modeling

Used in large C&I and utility-scale markets where curtailment happens when energy prices go negative or low.

4. PPA-Based Curtailment Modeling

Some power purchase agreements impose export restrictions.

5. Battery-Integrated Curtailment Models

Storage absorbs excess energy before curtailment.

Related term: Battery Energy Storage System (BESS).

How It’s Measured

Curtailment modeling uses the following metrics:

1. Curtailment Amount (kWh or MWh)

Total energy lost due to limits.

2. Curtailment Percentage (%)

Curtailment % = (Lost Energy / Potential Energy) × 100


3. Curtailment Frequency

How often curtailment events occur.

4. Export Limit Cap (kW)

Maximum allowed AC export.

5. Duration of Curtailment

Length of each event.

Typical Values / Ranges

Regions with high renewable penetration may experience significantly higher curtailment levels.

Practical Guidance for Solar Designers & Installers

1. Always review utility interconnection limitations

Before finalizing design, check export caps and apply them early.

2. Use DC/AC ratios strategically

Lower DC/AC ratios reduce clipping but lower energy yield; higher ratios increase yield but may increase curtailment.

3. Add storage where economical

Batteries can absorb energy that would otherwise be curtailed.

Use tools like the Battery Size Calculator.

4. Model curtailment before proposal creation

Use Solar Proposal Tools and Generation Financial Tool to present accurate savings.

5. Incorporate seasonal and hourly variations

Curtailment often peaks during mid-day, low-demand seasons, and high-production months.

6. Validate curtailment assumptions in AHJ and utility documents

Documentation often specifies mandatory curtailment windows or controls.

Real-World Examples

1. Residential Export-Limited System

A 10 kW system is limited to 5 kW AC export.

When the system produces 8 kW AC, 3 kW is curtailed automatically by inverter control.

2. Commercial Flat Roof with Utility Export Caps

A 200 kW system is constrained to 100 kW export.

During peak summer production, the building loads absorb some power, but 20–40 kW may still be curtailed mid-day.

3. Utility-Scale Solar Farm in a Congested Grid Region

A 50 MW solar farm models 12–25% curtailment due to grid congestion during low-load periods, affecting PPA revenue projections.