Grid-Tie Load-Following and Zero Export

In Vietnam, exporting surplus electricity to the grid is capped and poorly compensated, so many systems are configured to avoid backfeed or export only a negligible amount. The two core concepts are grid-tie load-following and zero export. This document explains how they work, the role of the current sensor, and how to reduce curtailed energy.

For: technicians configuring systems and installing sensors, sales staff explaining why the system does not sell electricity to the grid, and newcomers who need to understand anti-backfeed operation.

Quick Summary

Grid-tie load-following means the inverter runs in parallel with the grid but prioritises supplying power precisely in line with the load’s actual consumption, without pushing any surplus onto the grid. Zero export is a stricter mode that keeps the power exported to the grid at zero.

The mechanism relies on a current sensor placed at the grid connection point, measuring bidirectional current and reporting continuously to the inverter so that the inverter can throttle its output before any backfeed occurs.

When solar generation exceeds the load and no battery is present to absorb the surplus, the excess is curtailed: this is called power curtailment. The ways to reduce this loss are to right-size the system for actual demand, shift high-consumption appliances to daytime operation, and add battery storage to capture the midday surplus.

Grid-Tie Load-Following and Zero Export

A grid-tie load-following system operates in parallel with the grid, synchronising on frequency and phase, but prioritises supplying the household load in line with actual real-time consumption. When solar generation exceeds the load, the inverter automatically throttles its output to avoid pushing the surplus onto the grid, or exports only a negligible amount. The goal is to maximise solar self-consumption and prevent backfeed.

Zero export is an operating mode of a grid-tied system in which the power exported to the grid is kept at zero. This configuration is particularly important in Vietnam because, as discussed in Chapters 03 and 05, current regulations cap the volume of surplus electricity that can be sold to the grid and offer a low buy-back rate, making self-consumption far more beneficial than exporting.

Current Sensor and Control Logic

The heart of this mechanism is a current sensor placed at the grid connection point. The sensor measures current in both directions: both power drawn from the grid and power about to be pushed onto it. Readings are transmitted continuously to the inverter, which uses a closed control loop to reduce output the moment it detects imminent backfeed, keeping the exported power close to zero.

In practice, zero export means the system strives to keep export at zero rather than achieving it instantaneously in absolute terms. Due to control latency, a very small amount of power may still reach the grid for a brief moment when the load drops suddenly. This is normal behaviour.

Power Curtailment and How to Reduce the Loss

When solar production exceeds what the load is consuming and no battery is available to absorb the surplus, the inverter is forced to throttle its output to avoid exporting to the grid. The energy that could have been generated but is discarded is called power curtailment. This phenomenon is most pronounced at midday when irradiance is highest and household loads are low.

There are three ways to reduce the loss. First, size the system capacity to match actual daytime electricity demand, avoiding panel arrays that are significantly oversized relative to the daytime load. Second, shift high-consumption appliances to run during the day (such as washing machines, dishwashers, water pumps, and EV chargers) so consumption aligns with peak solar availability. Third, install battery storage to capture the midday surplus and use it in the evening, converting energy that would otherwise be curtailed into usable electricity.