Solar control
Zero export controller: use your solar, and send nothing to the grid.
A zero export controller, also called an export limiter or zero feed-in controller, stops a rooftop solar plant pushing power back into the grid. It watches the grid incomer and throttles the inverters to match your load. KONDUKTOR® EMS does this over Modbus where the inverter allows it, and helps you use the surplus before it is thrown away.
What a zero export controller does
Solar does not wait for your load. On a Sunday, a holiday or a lunch break the panels keep producing while the plant draws little, and the surplus flows out through your incomer into the grid. A zero export controller holds that flow at zero, or at the export limit you set.
You will also see it sold as a zero export device, zero injection controller, solar export limiter or anti-reverse-flow controller. The job is the same. A meter tells you export happened. A controller stops it happening.
Why a plant needs zero export
- No net metering. The connection has no net metering or net billing agreement, so exported units have nowhere to go.
- Solar above the approved capacity. The plant is larger than what your DISCOM allows to export, or the feeder has no room left.
- Approval still pending. The solar plant is built and the paperwork is not, and you want to run it without export in the meantime.
- Behind-the-meter captive solar. The plant was built for self-consumption only.
- Export pays less. Exported units often earn less than imported units cost, so a unit used on site is worth more.
- A DG on site. A running DG cannot take reverse power at all. See PV-DG synchronization.
Rules differ by state and DISCOM, and they change. Check yours before you settle on a limit.
How zero export control works
- Read. A Modbus meter at the grid incomer shows whether power is flowing in or out, and how much.
- Compare. The controller checks that against your target, usually a small import rather than exactly zero.
- Throttle. As the margin shrinks, it writes a lower active power limit to the inverters over RS-485 Modbus.
- Release. When the load rises, it raises the limit in steps, so solar returns without overshooting.
- Record. Every limit and change is logged with its time, so you can see how often solar was held back.
A worked example
Take a 300 kW rooftop solar plant at noon on a Sunday, with the plant nearly shut. These figures are illustrative.
Interactive · see it happen
200 kW with nowhere to go
| At noon on Sunday | Figure |
|---|---|
| Solar the panels can give | 240 kW |
| Plant load | 40 kW |
| Export with no control | 200 kW |
| Import margin you choose to keep | 5 kW |
| Inverter limit the controller sets | 35 kW |
| Export with control | 0 kW |
| Solar held back | 205 kW |
Export is gone, and so are those 205 kW of free solar. That is the price of zero export, which is why the next step matters.
Use the surplus before you throttle it
A zero export controller on its own throws surplus away. KONDUKTOR® EMS can spend it first. Through Modbus I/O cards it can start the loads you choose when surplus appears: chillers and cold rooms cooling ahead, water pumps filling tanks, compressors charging the receiver. The inverters are throttled only for what is left. This is engineered for your plant as part of your project.
Zero export or an export limit
| Setting | Use it when |
|---|---|
| Zero export | No export is allowed, or exported units earn nothing |
| Export limit in kW | Your approval allows export up to a set figure |
| Solar limit on DG | The DG is running, so solar stays below the load. See PV-DG synchronization |
The inverter’s own limiter or a plant controller
Many inverters have a built-in export limit that works with their own meter or CT. For one inverter on a simple site, that may be all you need. A plant-level controller earns its place once the site gets bigger.
| What you need | Inverter’s own limiter | Plant controller |
|---|---|---|
| One inverter, one make | Often enough | Works, may be more than you need |
| Several inverters, or two makes | Each acts alone and they can fight each other | One limit shared across all of them |
| A DG on site | Usually sees nothing of the DG | Reads the DG and holds its minimum load |
| Surplus used before throttling | No | Starts chosen loads through Modbus I/O cards |
| Solar seen against plant load | In the inverter app, if at all | On the same dashboard as every meter |
More on running several inverters as one plant is in solar inverter control.
Get these right at commissioning
- Meter position. The meter must sit on the grid side of the point where solar joins, so it sees the net flow.
- CT direction. A reversed CT reads export as import, and the controller then raises solar when it should cut it.
- Import margin. When a big load stops suddenly, a little export can pass before the next correction. A small import margin absorbs it.
- Inverter access. Remote power limiting often has to be enabled in the inverter’s installer settings.
- One controller. Two controllers on the same inverters will fight each other.
Built to fail safe
Control sits above your electrical protection, never in place of it. Each project is engineered so that a lost connection leaves the inverters at a safe limit agreed with your team, where the inverter supports one. Operators keep a manual override, only authorised users can change limits, and every change is logged. If your DISCOM asks for a reverse power relay, it stays. The relay trips the supply. The controller keeps you from reaching it.
Zero export in KONDUKTOR® EMS
- Grid import and export at the incomer, live and hour by hour.
- Solar generation, share used on site and export, against the plant load. See solar, DG and grid.
- Export held at zero or at your limit by throttling inverter kW over Modbus, where the inverter allows it, engineered for your plant as part of your project.
- Chosen loads started through Modbus I/O cards to use surplus solar first.
- The same system guards demand. See Maximum Demand controller.
- History, dashboard and control all on site, with no cloud server, and no Internet needed to run.
Common questions
What is a zero export controller?+
A system that stops a rooftop solar plant sending power into the grid. It reads a meter at the grid incomer and lowers inverter output whenever the load falls below what solar can give, so export stays at zero.
Is an export limiter the same as zero export?+
Nearly. An export limiter holds export at a set kW figure. Zero export is that same control with the limit set to zero.
Do I need a zero export device without net metering?+
Usually yes, because without net metering or net billing your exported units have nowhere to go. Rules differ by state and DISCOM, so check what yours requires for your connection.
Does zero export reduce solar generation?+
Yes. Solar that cannot be used or exported is held back. KONDUKTOR® EMS can reduce that loss by starting chosen loads through Modbus I/O cards when surplus appears, before the inverters are throttled.
Will it work with our inverter?+
It works where the inverter accepts an active power limit over RS-485 Modbus. Many commercial inverters do, but it varies by make and model. We check your model against its manual first. See the common makes in India.
Does zero export keep solar running in a power cut?+
No. A grid-tied inverter stops when the grid goes, by design. To run solar on a DG during an outage you need PV-DG control, which keeps the DG above its minimum load.
Does it need the Internet?+
No. The meters, the controller and the inverters talk on site, so control keeps running with no Internet connection.
What does a zero export controller cost?+
We quote per plant, based on your inverters, meters and what you need to control. Book a demo or message us with your plant details and we will tell you what it takes.
Use your solar, export nothing.
Book a live demo and see grid import, export and solar against the plant load on meters like yours.