Many Bangladeshi factories run diesel generators every day during load shedding. Ordinary grid-tied solar switches off at exactly that moment. A DG-PV hybrid system fixes this — here's how it works and what it saves.
Why ordinary solar goes quiet during load shedding
A grid-tied solar inverter is designed to disconnect when the grid fails. This "anti-islanding" protection keeps line workers safe and is required by standards. So when the grid drops and your generator starts, a standard solar plant simply stops — often during the sunniest hours, and while you are paying the most for power.
Why you can't just connect solar to the generator
If the inverters were simply allowed to run with the generator, two problems appear:
- Minimum load. Diesel generators need to run above a minimum share of their rating — the exact figure depends on the manufacturer. Run too lightly for long periods and they suffer carbon build-up and "wet stacking", which shortens their life.
- Reverse power. If solar produces more than the factory is using, power tries to flow back into the generator. At best the generator trips on reverse-power protection; at worst it is damaged.
What a DG-PV controller does
A DG-PV controller sits between your meters and your solar inverters:
- It measures the generator's output continuously through meters on each generator feeder.
- It calculates how much solar the site can safely absorb while keeping each running generator above its minimum load.
- It sends that power limit to the inverters, many times a minute, so solar never pushes the generator too low or into reverse power.
- When the grid returns, it switches automatically back to grid mode — where it can also enforce zero export if you don't have net metering.
What it saves
A diesel generator typically delivers only around 3 to 3.5 units (kWh) of electricity per litre of diesel — and fewer when it runs lightly loaded. So every unit of solar that replaces generator output saves roughly 0.3 litres of diesel. For a factory that runs generators for a couple of hours every day, that adds up quickly, on top of the savings from buying less grid power the rest of the time.
Sizing note: how much solar can run during generator operation is limited by your load and the generators' minimum loading. Adding battery storage, or scheduling flexible loads for generator hours, can raise that share.
Net metering and generators
Under the Net Metering Guideline 2025, only solar energy may be credited when generators are synchronised on site. Solar and net meters must keep 15-minute data so the utility can check this. A DG-PV controller with correct metering keeps your plant compliant. See our net metering guide for more.
Is DG-PV right for you?
- You have daily or frequent load shedding and run diesel generators.
- Your daytime load stays reasonably steady while the generators run.
- You want solar to keep earning its keep during outages, not just when the grid is up.
Our first project — a 400 kWp rooftop system for Sajan Polymer Industries Ltd. — uses DG-PV control for exactly these reasons. Ask us whether it suits your site.
Figures are typical values for general guidance; actual generator fuel consumption and solar output depend on equipment, loading and site conditions.