Solar That Keeps Working When the DG Starts: 40 kW on a Tin Shed at Prabhat Namkeen, Greater Noida

Why a factory with a DG needs more than ordinary solar

A standard on-grid inverter switches off the moment grid power fails. This is a safety feature called anti-islanding. At a factory with a DG, that means the solar sits idle for exactly the hours when the site is running on diesel, which is the most expensive power it buys.

Letting solar simply run alongside the DG is not safe either. If the factory's load drops, solar can push power back into the generator, which a DG cannot absorb. A DG synchronisation controller solves both problems. It lets the inverters run while the DG is on and holds back solar output so the DG always carries a safe share of the load.

Mounting on a tin shed roof

The roof is a profiled metal sheet. We screwed the mounting rails through the sheet, with a sealing washer at every fixing to close the hole against rain. The rails run across the ribs of the sheet so the load is spread over several ribs.

On the roof and down the electrical room wall, perforated cable trays keep the cables tidy and off the hot sheet.

What we installed

• Solar array: 40 kW of 595 Wp half-cut mono PERC modules on the production unit's tin shed roof
• Inverters: Growatt grid tie, 25 kW and 15 kW, wall mounted in an indoor electrical room
• DC distribution and array junction box panel beside the inverters
• DG synchronisation controller, so the plant runs with either the grid or the DG
• Mounting: rails screwed through the roof sheet, sealed with washers at every fixing

The two inverters add up to 40 kW, matching the array. Splitting the plant across two units also means that if one inverter needs attention, the other keeps generating.

How the plant behaves when power fails

• Grid present: solar supplies the factory load first and the grid makes up the rest
• Grid fails, DG runs: the controller lets the inverters work alongside the DG and limits solar so the generator is never back-fed
• Grid returns: the plant goes back to normal operation

Every unit of solar produced while the DG is running is diesel that does not have to be burned. Fuel savings depend on how many hours of outage the site sees, so we do not quote a fixed figure.

Maintained under a five year AMC

• Module cleaning and inspection
• Roof fixings and sealing washers checked for leaks
• Inverter fault logs, ventilation and cooling
• DG synchronisation controller checks
• Earthing and protection checks

What this means for other food units

Many food processing units around Surajpur and Kasna have metal sheet roofs and a DG set. Neither rules out solar. The roof needs a sealed fixing method, and the DG needs a synchronisation controller. With both in place, the plant earns its keep during power cuts as well as on normal days.

Frequently asked questions