What Happens When the Grid Goes Down?

Grid-Tied Solar: It Shuts Down

This surprises most people. A grid-tied solar system — panels connected to a grid-tie inverter with no battery — stops generating power the moment the grid goes down. Your panels are producing electricity, the sun is shining, and your house is dark. This isn't a malfunction. It's a safety feature called anti-islanding protection.

Why Anti-Islanding Exists

When the grid goes down, linemen work on the power lines to fix the fault. If your solar system keeps pushing electricity into the grid, those "dead" power lines become energised — potentially at lethal voltages. A lineman touching a wire they believe is de-energised could be electrocuted by your solar system's output.

Anti-islanding is mandatory for all grid-connected inverters worldwide (IEC 62116, IEEE 1547, India's CEA Technical Standards for Connectivity). The inverter continuously monitors grid voltage and frequency. If grid voltage drops to zero (outage) or drifts outside the acceptable range (47.5–51.5 Hz, 180–270 V for single phase), the inverter disconnects within 2 seconds and stops converting DC to AC. It remains off until the grid is restored and stable for 5 minutes (the reconnect timer).

Hybrid Solar: It Keeps Running

A hybrid solar system has a battery and an inverter/charger that can operate in both grid-connected and standalone (island) modes. When the grid goes down:

1. Grid fault detected (within 20–100 milliseconds)
2. Automatic transfer switch (ATS) disconnects the house from the grid (prevents backfeed to linemen)
3. Inverter switches to island mode — it generates its own AC waveform from the battery, at 230 V / 50 Hz
4. Solar panels continue operating — charging the battery and powering loads simultaneously
5. When grid returns: the system detects stable grid voltage for 5 minutes, then reconnects and resumes grid-tied operation

The transfer from grid to battery takes 10–20 milliseconds for quality inverters. This is fast enough that most electronics (computers, routers, TVs) don't notice the switch. Clocks don't reset. WiFi doesn't drop. The only appliances that might notice are motor-driven loads in the middle of a start cycle.

System Type	Power During Grid Outage	Backup Duration	Transfer Time
Grid-tied (no battery)	None — complete shutdown	0 hours	N/A
Grid-tied + basic UPS	UPS loads only (computer, router)	15–30 minutes	5–10 ms (offline UPS)
Hybrid (solar + battery)	All loads up to inverter capacity	4–24 hours (depends on battery)	10–20 ms
Off-grid (solar + battery)	All loads — no grid dependency	12–48+ hours	0 ms (always on battery)

How Long Does Battery Backup Last?

Backup duration depends on three variables: battery capacity, load, and whether the sun is shining.

Nighttime outage (no solar generation):

Battery Capacity	Light Load (500 W avg)	Medium Load (1.5 kW avg)	Heavy Load (3 kW avg)
5 kWh LFP	8.5 hours	2.8 hours	1.4 hours
10 kWh LFP	17 hours	5.7 hours	2.8 hours
15 kWh LFP	25.5 hours	8.5 hours	4.3 hours
20 kWh LFP	34 hours	11.3 hours	5.7 hours

Assumes 85% DoD for LFP and 92% inverter efficiency.

Daytime outage (solar generating): If solar generation exceeds the load, the battery charges while powering your home — backup is essentially unlimited until sunset. If solar generation is less than the load (cloudy day), the battery supplements the shortfall and backup duration extends proportionally.

Load Shedding Strategy During Outages

A well-designed hybrid system doesn't just provide backup — it manages backup intelligently. The priority stack:

1. Critical loads (always on): Lights, fridge, WiFi router, phone charging, medical devices, security system, gate motor
2. Important loads (on if battery > 50%): Fans, TV, laptop, water purifier
3. Comfort loads (on if battery > 70%): AC (at reduced setpoint), washing machine
4. Deferrable loads (on if battery > 90% or solar surplus): Water heater, iron, induction cooktop, EV charger

This can be implemented through separate circuits on the distribution board — critical loads on the inverter-backed circuit, deferrable loads on a grid-only circuit that loses power during outages. Or through smart energy management that controls individual loads based on battery state-of-charge.

How Often Does the Grid Go Down?

Location Type	Annual Outage Hours (avg)	Typical Outage Duration	Main Causes
Bangalore urban (BESCOM)	30–60 hours	30 min – 2 hours	Planned maintenance, tree falls, equipment failure
Bangalore suburban	60–120 hours	1–4 hours	Transformer overload, cable faults, monsoon damage
Semi-urban Karnataka	120–300 hours	2–8 hours	Load shedding, infrastructure age, weather
Rural Karnataka	300–1,000+ hours	4–12 hours	Scheduled load shedding, single feeder, limited maintenance
Remote/agricultural	1,000–3,000+ hours	6–18 hours	Agricultural supply timing, infrastructure absence

Urban Bangalore consumers experience 30–60 hours of outages per year — roughly an hour per week. Rural consumers can face 3–8 hours daily. For rural and semi-urban properties, battery backup isn't a luxury — it's the difference between functional living and regular disruption.

Grid-Tied Owners: What Are Your Options?

If you already have a grid-tied system without battery and want backup capability, you have two paths:

• Add a hybrid inverter + battery: Replace your grid-tie inverter with a hybrid inverter that supports both grid-tied and island mode, and add a battery bank. Cost: ₹1.5–3 lakh for 5–10 kWh LFP + hybrid inverter. Your existing panels are reused.
• Add AC-coupled battery: Keep your existing grid-tie inverter and add a separate battery inverter/charger with battery. The battery charges from the grid-tie inverter's AC output. More complex wiring but avoids replacing the existing inverter. Cost: ₹1.5–2.5 lakh.