Solar control
PV-DG synchronization: keep solar running when the DG starts.
When the grid fails, a grid-tied solar plant stops with it and the DG carries everything, at several times the cost of a grid unit. A PV-DG synchronization controller lets solar run alongside the DG by keeping the DG above its minimum load and away from reverse power. KONDUKTOR® EMS does this over Modbus, where the inverter allows it.
What PV-DG synchronization means
You will see it called PV-DG sync, DG-PV controller, solar DG synchronization, fuel save controller or solar diesel hybrid controller. They all mean the same control.
The name is a little misleading. The inverter already follows the voltage and frequency the DG sets. What it cannot do alone is decide how much power the DG can accept. That is the controller’s job.
Why solar and a DG cannot simply run together
- Reverse power. If solar exceeds the load, power flows back into the DG, which it cannot absorb. Its protection trips it.
- Low DG load. A DG pushed below its minimum load burns fuel poorly, and long light running can harm the engine.
- Sudden swings. When a large load stops, solar that fitted a moment ago no longer fits.
So many plants switch solar off whenever the DG runs, and burn full diesel through every sunny outage. Solar with DG needs a controller, not a lockout.
The one rule
Solar limit = plant load − DG minimum load
The DG always carries at least its minimum, and solar takes the rest. As the load moves, the limit moves with it. Your DG maker gives the minimum load for your set. A common figure is about 30% of rating.
A worked example
Take a 500 kVA DG, about 400 kW at 0.8 power factor, with a 30% minimum load of 120 kW and plenty of sun. These figures are illustrative.
Interactive · see it happen
The floor under the DG
| Plant load | DG minimum | Solar limit | DG carries |
|---|---|---|---|
| 300 kW | 120 kW | 180 kW | 120 kW |
| 200 kW | 120 kW | 80 kW | 120 kW |
| 120 kW | 120 kW | 0 kW | 120 kW |
In the first row solar supplies 180 units in an hour that the DG would have made. At an illustrative 3.2 units per litre, that is about 56 litres, or roughly ₹5,000 an hour at ₹90 a litre. Your own figure depends on your load, your sun and how your DG behaves at low load. Start with the DG cost per unit calculator.
What happens in a power cut
- Grid fails. The inverters stop, as they must.
- DG starts and takes the plant load.
- Controller sees the DG running and sets the solar limit before the inverters come back.
- Inverters reconnect and ramp up to that limit, which keeps following the load.
- Grid returns. The DG stops, and the limit lifts or returns to your export limit.
What the control needs from site
| Signal | Comes from | Why it is needed |
|---|---|---|
| DG running | Breaker contact through a Modbus I/O card, or the DG controller over Modbus | Tells the system when to apply the limit |
| DG output | A Modbus meter on each DG | Shows how close the DG is to its minimum |
| Solar output | The inverters, or a meter on the solar output | Shows what solar is really giving |
| Inverter limit | Written to the inverters over RS-485 Modbus | Holds solar at the limit |
The inverter’s voltage and frequency settings must also accept the DG’s output, or it will refuse to connect. Your installer can confirm this. More on setting power limits is in solar inverter control.
Plants with more than one DG
With two or more DG sets, the minimum load is the sum of the sets running. When a second DG starts, the solar limit falls at once, and it rises again when that set stops. The system reads each set’s status and meter, so the limit always matches what is really on the bus.
What it does not replace
This is not a DG synchronizing panel. Paralleling DG sets with each other, load sharing between them and AMF changeover stay with your sync panel or AMF panel. The PV-DG control works alongside them, and only sets how much solar the running DGs can accept.
Built to fail safe
Control sits above your electrical protection, never in place of it. The reverse power relay on the DG stays: it trips the DG, and the control keeps you from reaching it. Each project is engineered so that if the DG or meter signal is lost, the inverters go to 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.
Solar and DG in KONDUKTOR® EMS
- DG load hour by hour, DG units generated and DG running hours.
- Every source against the plant load in one energy balance chart. See solar, DG and grid.
- Solar held below the load while the DG runs, by throttling inverter kW over Modbus where the inverter allows it, engineered for your plant as part of your project.
- The same control holds export at your limit once the grid returns. See zero export controller.
- History, dashboard and control all on site, with no cloud server, and no Internet needed to run.
Common questions
What is PV-DG synchronization?+
Control that lets a grid-tied solar plant run alongside a DG. It reads the load and the DG, and limits the inverters so the DG stays above its minimum load and never sees reverse power.
Can solar run with a DG?+
Yes, with a controller limiting the inverters. Without one, solar can push the DG below its minimum load or into reverse power, which is why many plants switch solar off while the DG runs.
What is the minimum load on a DG with solar?+
Your DG maker sets it for your set. A common figure is about 30% of rating. The controller keeps solar low enough that the DG never carries less than that.
How much diesel does a PV-DG controller save?+
Every unit solar supplies is a unit the DG does not make, down to the DG’s minimum load. The saving depends on how many sunny hours your DG runs and on your load. Your own meters will show it.
Do we still need a reverse power relay?+
Yes. Protection stays with the relay. The PV-DG control works to stop reverse power happening, and the relay remains the safety layer if it ever does.
Is this the same as a DG synchronizing panel?+
No. A sync panel parallels DG sets with each other. PV-DG control sets how much solar the running DG sets can accept, and works alongside that panel.
Does it work with more than one DG?+
Yes. The minimum load is the sum of the DG sets running, so the solar limit changes as sets start and stop.
Will it work with our inverter?+
It works where the inverter accepts an active power limit over RS-485 Modbus, and its settings accept the DG’s voltage and frequency. We check your model against its manual first. See the common makes in India.
What does a PV-DG controller cost?+
We quote per plant, based on your inverters, meters and what you need to connect. Book a demo or message us with your plant details and we will tell you what it takes.
Keep solar running when the DG starts.
Book a live demo and see solar, DG and grid against the plant load on meters like yours.