Zero Export Device (ZED): How to Use Solar Before TNEB Net Meter Arrives

You paid ₹2 Lakhs for a Solar System. Installation is done. The panels are shining on the roof. But the TNEB Junior Engineer says: "Sir, no Net Meters in stock. Wait 1 month." or "Sir, the local Transformer is overloaded, we cannot approve export yet."

In the past, you had to shut down the plant and wait. In 2026, we use a Zero Export Device (ZED) (also called an "Export Limiter" or "Grid Limit Solution") to start the plant immediately.

This guide explains the technical details of ZED, how to install it, and why it is a game-changer for factories and impatient homeowners.

1. What is a ZED? The Concept

A standard On-Grid inverter blindly pumps out maximum power. If your house doesn't use it, it pushes it to the grid. Pushing to the grid without a Net Meter is illegal and can be dangerous for linemen.

A ZED is a control loop that asks: "What is the house load right now?" It forces the inverter to match that load exactly, ensuring Import is > 0 and Export is = 0.

The Mechanism: Real-Time Throttling

1. Measurement: A sensor measures current at the main gate.
2. Calculation: It calculates House Load - Solar Gen.
3. Command: If the result aims to be negative (Export), it sends a command to the inverter: "Limit Power to 40%!"
4. Reaction: The inverter drops generation instantly.

2. Wiring Guide: The "CT Coil"

The heart of the ZED is the Current Transformer (CT).

What it looks like: A small donut-shaped ring or a clamp. Where it goes:

• It must be clamped around the Main Phase Wire (Live) exactly after the Electricity Meter but before any loads in the house.
• Direction matters: The arrow on the CT coil must point towards the Grid (or Loads, depending on inverter brand). If you put it backward, the inverter will think you are exporting when you are importing!

The Connection:

• The CT coil has a thin wire (RS485 cable).
• This wire travels all the way to the Inverter's "Meter Port".
• Distance Limit: Usually up to 20-50 meters using shielded CAT6 cable.

Contact us for a ZED Installation Quote

3. Comparison: ZED vs Net Meter

Want to Start Using Solar Immediately?

Get a ZED-compatible inverter installed and start saving from day one, even before your TNEB net meter arrives.

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4. Advanced Feature: Diesel Generator (DG) Synchronization

This is critical for Factories and Hospitals in Cuddalore.

The Problem: You have a 50kVA Diesel Generator running during a power cut. It is consuming 10 Liters/hour. You want Solar to help.

• Risk: If Solar produces 20kW and Factory load drops to 10kW, the 10kW excess flows into the Generator. The Generator's alternator acts as a motor and burns out.

The ZED Solution: The ZED acts as a "DG Protection Unit".

1. It senses the grid is OFF and DG is ON.
2. It throttles Solar to always be less than the load.
3. Example: Load is 30kW. Solar provides 20kW. DG provides 10kW.
4. Result: You save 66% fuel, and the DG stays safe (no reverse power).

5. Troubleshooting Common ZED Issues

Issue 1: Inverter shows negative power.

• Cause: CT Coil direction is reversed.
• Fix: Flip the CT clamp 180 degrees.

Issue 2: Exporting small amounts (0.1kW) to grid.

• Cause: Control delay.
• Fix: Set a "Buffer" in settings. E.g., limit export to -50W instead of 0W to be safe.

Issue 3: Inverter not reading CT.

• Cause: RS485 cable too long or loose connection.
• Fix: Use shielded twisted pair cable. Check baud rate settings.

6. Compatibility List

Not all inverters support ZED.

• Native Support (Built-in ZED):
  • Deye (Hybrid & String)
  • Growatt (MIN-X / MOD-X Series)
  • Solis (5G models)
  • GoodWe (SDT G2)
• Requires External Device:
  • SMA (Needs expensive Energy Meter)
  • Polycab (Old models)

Recommendation: If you are buying a system today in 2026, ensure your inverter has "Export Limit Function" built-in. It costs nothing extra (just the coil), but gives you the freedom to start anytime.

Use Solar from Day 1. Don't let bureaucracy pause your savings.

Related Articles

• TNEB Net Meter Guide - Full net metering process
• Hybrid Systems - ZED-enabled hybrid inverters
• Understanding TNEB Bill - How billing will work later