How Apartments Can Use On-Grid Rooftop Solar During Power Cuts — Safely
Every apartment society knows this moment. The grid fails, lifts pause for a second, corridor lights flicker, and the diesel generator starts with a familiar roar.
“Generator chalu karo…”
Power returns — but so do diesel fumes, noise in the basement, and another invisible cost added to the society’s monthly expenses.
Meanwhile, on the rooftop, the solar plant sits idle under full sunlight.
Even though the sun is available, on-grid solar systems shut down during power cuts.
Solar–DG synchronization exists to solve exactly this problem.
Why On-Grid Solar Stops During Power Cuts
Grid-connected solar inverters are designed with anti-islanding protection. This is a mandatory safety requirement.
The moment grid supply is lost, the inverter shuts down to prevent back-feeding electricity into the grid and risking the safety of utility workers.
Result: Even in bright daylight, solar generation drops to zero during an outage.
If a diesel generator is present, the entire apartment load shifts to DG — while solar remains unused.
The Real Cost of Running Only on Diesel
Diesel generators are dependable, but extremely inefficient when used alone.
- High diesel consumption
- Rising fuel prices
- Frequent servicing and breakdown risk
- Noise, vibration, and resident complaints
- Reduced DG lifespan due to poor load management
In most apartments, DGs rarely run at optimal load.
Solar–DG Synchronization — What Actually Changes
Solar–DG synchronization allows rooftop solar and diesel generators to operate together during grid outages — without compromising safety or equipment health.
The key principle is simple:
⚙️ A DG must always run at a minimum stable load ☀️ Remaining load can be safely supplied by solar
Understanding the 30% Rule (This Is Important)
Diesel generators typically require a minimum loading of around 30% of their rated capacity to operate safely and avoid wet stacking or engine damage.
With Solar–DG synchronization:
- DG continues to supply the minimum 30% load
- Up to 70% of the load can be supplied by solar
- Solar output is dynamically controlled in real time
This is how on-grid solar becomes usable even during power cuts.
How the System Maintains Stability
The system continuously measures DG power using an energy meter installed at the DG LT panel.
Data is communicated over RS485, allowing the controller to:
- Ensure DG never drops below 30% load
- Increase or reduce solar output automatically
- Prevent reverse power flow into the DG
Diesel Savings — Real Numbers (1 Hour Power Cut)
Let’s consider an apartment with a 50 kW rooftop solar plantoperating during a 1-hour grid outage.
| DG Capacity | Minimum DG Load (30%) | Solar Contribution* | Diesel Saved (per hour) |
|---|---|---|---|
| 30 kVA | ~9 kW | ~15–18 kW | 2–3 litres |
| 40 kVA | ~12 kW | ~20–25 kW | 3–4 litres |
| 62.5 kVA | ~18 kW | ~30–32 kW | 6–7 litres |
| 100 kVA | ~30 kW | ~20–25 kW | 4–5 litres |
| 125 kVA | ~38 kW | ~12–15 kW | 2–3 litres |
*Solar contribution depends on actual apartment load and available solar generation. Diesel savings assume ₹95–₹105/litre and standard DG fuel curves.
Even 1–2 hours of power cut per day can translate to monthly savings of ₹15,000–₹50,000 depending on DG size.
Why Apartment Societies Are Adopting This
- Immediate diesel cost reduction
- Better ROI on existing solar investments
- Lower DG maintenance expenses
- Improved sustainability metrics
- No operational complexity for staff
Final Thoughts
Apartments already own rooftop solar. Letting it shut down during power cuts is an avoidable loss.
Solar–DG synchronization allows societies to safely use on-grid solar even during outages — reducing diesel usage without replacing existing infrastructure.
When the grid goes down, your solar doesn’t have to.
