Export Limiting

Export limiting is a control method used in grid-connected solar systems to restrict the amount of electricity exported from an inverter to the utility grid. Many utilities require export limits to protect local distribution networks, maintain voltage stability, and prevent backfeed into feeders that were not designed for high levels of distributed generation.

In practical terms, export limiting ensures a solar system never sends more than a specified maximum kW back to the grid. If production exceeds on-site consumption, the inverter automatically reduces output to stay within the permitted export level. Export limiting is essential for homes and businesses in areas with strict interconnection rules, and it directly affects system design, ROI, and energy modeling.

Export limiting is also integrated into modern design workflows inside tools like Solar Designing, grid compliance workflows in project planning tools such as Solar Project Planning & Analysis, and inverter configuration processes linked to Stringing & Electrical Design.

Key Takeaways

Export limiting restricts how much solar power is sent to the grid.
Used when utilities require zero-export or limited-export interconnections.
Automatically controls inverter output using sensors and EMS logic.
Helps protect feeders, transformers, and local grid stability.
Works best when combined with batteries and intelligent load management.
Essential concept for modern grid-connected PV design and permitting.

What Is Export Limiting?

Export limiting is the practice of controlling a solar inverter’s AC output so that the electricity sent to the grid does not exceed a utility-approved limit. These limits may be:

Zero-export (no power exported at any time)
Partial export (e.g., max 2 kW or 5 kW export allowed)
Site-specific export limits based on feeder capacity or transformer size

Export limiting is typically enforced through:

Inverter firmware
Smart meters
External controllers
Energy management systems
CT (current transformer) sensor feedback
Utility monitoring interfaces

Related concepts include Grid-Tied System, Inverter Sizing, and Load Analysis.

How Export Limiting Works

1. Solar production is measured in real time

Sensors or CT clamps monitor how much solar power and load power are flowing through the site’s main panel.

2. The system calculates grid export

Grid export = Solar Production – On-Site Consumption

3. The inverter receives export data

The inverter communicates with a controller or smart meter to determine whether export is approaching the utility limit.

4. The inverter throttles power if needed

If export exceeds the limit, the inverter automatically reduces output by adjusting MPPT and DC-to-AC conversion.

5. Export remains within permitted levels

The system continues dynamically adjusting to maintain compliance regardless of sunlight or load changes.

This behavior is similar to zero-export constraints, but with more flexible output rules—see Zero-Export Constraint.

Types / Variants of Export Limiting

1. Zero-Export Limiting

No energy can leave the site at any time.

Common in places with sensitive grids or areas lacking net metering.

2. Fixed Export Limit

A limit is set (e.g., 1.5 kW, 5 kW, 10 kW), and the system must not exceed it.

3. Dynamic Export Limiting

Utilities provide real-time dynamic export allowances depending on grid conditions.

4. Phase-Based Export Limiting

Limits applied per phase on three-phase sites (e.g., max 2 kW export per phase).

5. Controlled Export with Batteries

A battery stores excess energy instead of exporting it, reducing throttling.

Related: Battery Energy Storage.

How Export Limits Are Measured

Export limits are always measured in kilowatts (kW) at the point of interconnection, typically at the main service panel or grid-side meter.

Engineers measure export using:

CT sensors
Smart meter export registers
Inverter communications
EMS readings

Export is evaluated based on:

Real power (kW)
Phase balance (for 3-phase systems)
Voltage rise compliance
Utility-specific rules

Typical Values / Ranges

These ranges vary by region, but common export limits include:

Utility export limits are often paired with Net Metering or non-export programs.

Practical Guidance for Solar Designers & Installers

1. Start by confirming export rules with the utility

Every jurisdiction has unique export rules—always validate before designing.

2. Use software to simulate export-limited behavior

Tools like Solar Designing and performance modeling tools help visualize the impact on kWh production.

3. Pair export limiting with battery storage

Use Battery Sizing Tools to store excess production instead of wasting it.

4. Ensure correct CT placement

Improper CT wiring causes export limit failures.

5. Plan for inverter clipping and throttling

When export limiting is active, part of your solar production may be curtailed.

6. Accurately model load profiles

Use Load Analysis to predict how often export limits will be triggered.

7. Optimize for self-consumption

Consider adjusting system size to align generation with consumption when export limits are low.

Real-World Examples

1. Zero-Export Residential System

A home with no export approval uses export limiting to prevent any power from entering the grid. Inverter output is capped whenever the home’s load is low.

2. 5 kW Export-Limited Commercial Rooftop

A warehouse receives a utility approval allowing only 5 kW export. Auto-throttling ensures compliance even when the 50 kW system peaks.

3. Battery-Backed Export-Limited System

A business with a 10 kW export limit installs a battery. Excess power charges the battery instead of being curtailed, improving ROI.