Industrial · Faisalabad, Lahore, Punjab
Solar + Generator Hybrid System for Factories: How It Works
Short answer
A solar and generator hybrid system lets a factory run solar panels alongside its diesel or gas generator during load-shedding, so the generator burns less fuel while solar carries part of the load. The key part is the controller: it keeps the solar output below what the generator can safely accept, so the generator never runs too lightly or receives power back. Without that controller, most grid-tied solar simply switches off when the grid fails.
Why ordinary solar stops when the grid goes
Most factory solar plants use on-grid (grid-tied) string inverters. These inverters need a stable grid voltage and frequency as a reference. When the grid fails, they shut down within moments. This is a safety feature: it stops solar from feeding a dead line that a lineman may be working on.
When your generator starts, it creates its own local "grid". Many inverters would happily synchronise to it. That sounds useful, but it is where problems begin.
Solar with a generator
Without control
Reverse power and under-loading can harm the generator
With hybrid controller
Solar is limited to keep the generator safely loaded
The two risks of mixing solar and a generator
1. Reverse power into the generator
A generator is built to push power out, not to absorb it. If solar produces more than the factory is using at that moment, the surplus has nowhere to go except back into the generator. The generator's protection will usually trip on reverse power. In the worst case, the alternator or engine can be damaged.
2. Running the generator too lightly
Diesel engines do not like light loads. If solar carries most of the factory load, the generator may idle at a small fraction of its rating. Long periods at low load can cause incomplete combustion, carbon build-up and fuel in the exhaust (often called wet stacking), and they raise maintenance costs. Each generator manufacturer states a minimum recommended load for its sets.
So the aim is not "as much solar as possible during an outage". It is "as much solar as the generator can safely share with".
How the hybrid controller works, in plain words
A diesel generator with solar needs a controller that watches both machines and adjusts the solar in real time. The logic is simple:
- Measure. Current transformers and a meter on the generator output tell the controller how much power the generator is supplying, many times a second.
- Set a floor. The engineer sets a minimum generator load, based on the generator manufacturer's figure and a safety margin.
- Limit solar. If the generator's load falls towards that floor, the controller tells the inverters to reduce output. If the factory load rises, it lets solar increase again.
- Never export. The controller keeps generator output above zero at all times, so power never flows back into it.
- Switch modes. When the grid returns, the controller releases the limit and solar runs at full output again, in parallel with the grid.
In short: grid on, solar runs freely; generator on, solar runs only up to a safe share. The controller must be compatible with the inverters it commands, which is one reason inverter brand and model are chosen together with the control scheme, not separately.
What about the changeover?
The switching between grid and generator is done by a changeover switch or an automatic transfer arrangement. The controller needs a signal from it so it knows which source is live. Our guide to the changeover switch for solar, generator and WAPDA explains the safety side, including why nothing should ever backfeed the grid.
Where a battery (BESS) fits
A battery changes what the hybrid system can do. With a BESS added:
- Short outages can be carried by battery and solar, so the generator may not need to start at all.
- Generator load can be smoothed. The battery absorbs the swings from motors starting and stopping, while the generator runs at a steadier, more efficient load.
- Solar surplus during an outage can charge the battery instead of being curtailed.
- Evening load can use solar energy stored during the day.
Batteries add cost, so they need a clear job. Our guide Battery storage (BESS) for factories: when does it pay? walks through each case. For commercial batteries we supply Luminey (Oasis C&I, SunESS), Sungrow PowerStack and Solis / GoodWe C&I systems, with hybrid inverters from Sungrow, Solis and GoodWe, chosen per project.
Three common hybrid layouts
| Layout | What it includes | Best for |
|---|---|---|
| Solar + grid + generator, with controller | On-grid inverters, generator controller, changeover | Factories with daytime outages and a large existing generator |
| Solar + grid + generator + BESS | As above, plus battery and power conversion | Frequent short outages, critical processes, evening shifts |
| Solar + generator (no grid) | Inverters, controller, often a battery | Sites with no or very weak grid supply |
Most Punjab factories fit the first or second layout. Three-phase inverters are standard at this scale; see three-phase vs single-phase inverters.
How to estimate fuel saving for your own site
We do not publish fuel-saving figures, because every factory's outage hours, load and generator are different. You can estimate your own case with simple arithmetic. The numbers below are round illustrative values only, not a forecast.
For example, if a factory's generator runs 3 hours on a typical working day, at an average load of 200 kW, it supplies about 600 kWh. Suppose the controller allows solar to carry, say, 40% of that load during those hours, after keeping the generator above its minimum. Solar would then supply about 240 kWh, and the generator about 360 kWh.
To turn that into rupees, you need three numbers from your own records:
- Fuel used per kWh at that load, from your generator's fuel logs or the manufacturer's fuel curve.
- Fuel price per litre on the day.
- Generator running days per year.
Note that fuel use per kWh rises at lower load, so a generator running lighter is less efficient per unit. A good engineering proposal accounts for that, states its assumptions, and shows the working. Treat any result as an estimate, not a guarantee.
What to record before a site survey:
- generator rating (kVA), age, fuel type and fuel logs;
- monthly running hours and when outages usually happen;
- 12 months of electricity bills, including MDI (see what MDI means on your bill);
- which loads are critical and which can be shed.
Hybrid system price
The cost depends on solar capacity, the controller and metering, any battery, and the integration work on your existing panels and changeover. Factory systems are quoted per project after design.
| Item | What drives the cost | Price |
|---|---|---|
| Generator controller and metering | Number of generators, inverter brand, communication setup | WhatsApp for today's rate |
| Solar plant (per kW, industrial) | Panel and inverter brands, structure type, cable runs | WhatsApp for today's rate |
| BESS (optional) | Usable kWh, power rating, enclosure and cooling | WhatsApp for today's rate |
How Solar Works Pakistan designs hybrid systems
Integrated hybrid power is one of our specialist areas. Solar Works Pakistan was founded in 2021, but our power-generation experience goes back to the 1980s through our founder, Akram Ullah Khan, whose career includes WAPDA and Saudi Electricity Company. The family business later imported and supplied generators. We no longer sell generators, but we understand how they behave, and we integrate your existing set into the design where appropriate.
- In-house engineering: load analysis, feasibility, AutoCAD design and the control scheme.
- One system, not parts: solar, grid, generator, battery, inverters and monitoring designed together.
- Own teams: installation, testing and safe commissioning by our staff.
- Support: remote monitoring subject to equipment capability, and a 48-hour target to send service personnel after a complaint is registered.
We have served 300+ customers, including 50+ industrial clients, across textile, dyeing, looms and other industries. See how this applies in solar for Faisalabad textile, dyeing and loom units, or visit industrial and commercial solar.
Get today's price or a free site survey
Send us 12 months of bills, your generator rating and running hours. Our engineers will tell you plainly whether a solar generator hybrid makes sense for your factory.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad (Faisalabad page)
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM, daily
We serve all of Punjab, and site surveys are normally free. You can also contact us online.
Frequently asked questions
Can I run my solar system with a diesel generator?
Yes, with the right controller. Without one, solar can push power back into the generator or make it run too lightly, which can trip or harm it. The controller limits solar output so the generator always stays above a safe minimum load.
Why does my solar system stop when the generator is on?
Many installations are set up so on-grid inverters stay off on generator power, because no controller has been fitted. That is the safe default. Adding a proper generator controller lets solar share the load safely.
How much fuel can a solar generator hybrid save?
It depends on outage hours, factory load, generator size and how much solar the controller can allow. We do not quote a fixed figure. Use your fuel logs and the example method in this guide, or ask us to work it out from your data.
Do I need a battery for a genset solar hybrid?
No. A controller alone lets solar and the generator share load. A battery adds the ability to cover short outages without starting the generator, smooth motor starts and store surplus solar.
Does this work with gas generators too?
The same principles apply: avoid reverse power and keep the set above its minimum load. The exact limits come from the generator manufacturer, so the design is checked against your specific set.
Do you sell generators?
No. Solar Works Pakistan no longer sells generators. We integrate your existing generator into a hybrid design where appropriate.
Which inverter brands do you use for hybrid systems?
We choose per project from approved brands, including Huawei and Sungrow commercial inverters, and Luminey, Sungrow PowerStack or Solis / GoodWe for BESS. The inverter and controller must be compatible, so they are selected together and listed by model in the BOQ.