Do Solar Panels Work During a Power Cut? (And Why Not)

Bright afternoon in Delhi, sun hammering down on your brand-new rooftop panels, electricity meter visibly running backwards five minutes ago. The grid trips, as it does. Fans stop, lights go out, and you are sitting in the dark wondering what you just paid for.

A solar panel on your roof is not the same thing as backup. A pure grid-tied (also called on-grid) solar system is deliberately built to switch OFF the instant the grid fails — not a fault, not a bad installer, not a dead inverter. It is a safety behaviour with a name: anti-islanding. There are only three ways to put solar on a home, and the right one depends almost entirely on how often your power goes out, your budget, and whether you already own an inverter and battery.

A grid-tie inverter takes DC from your panels and converts it to AC mains (230V single-phase for most homes, 415V three-phase on larger connections). On a sunny day it pushes surplus back through your meter onto the DISCOM lines for neighbours to use. Your roof becomes a tiny power station feeding the street — that is how it saves you money, by offsetting and exporting.

The grid goes down for a fault or scheduled maintenance, and a lineman climbs a pole to repair a cable he believes is dead. If your solar kept pushing power onto those same lines, he could be electrocuted by a wire that should have no voltage on it. This unwanted back-feed into a dead grid is called islanding — your system has formed its own electrical island on lines that are supposed to be off.

Every grid-tie inverter must detect grid-voltage loss within a fraction of a second and immediately disconnect its output. No grid voltage means no output, even at high noon with perfect sun on the panels. In India the rule flows from the CEA Technical Standards for Connectivity of the Distributed Generation Resources; the inverter proves compliance through standards such as IS 16169 / IEC 62116. A pure grid-tied system has no battery and offers zero backup by design. Its only job is to cut your bill, not to keep your lights on.

Some homes do keep solar running through a cut — those homes are not running pure grid-tied. They have a battery and a different kind of inverter that is allowed to intentionally form its own island, safely isolated from the grid so nothing back-feeds the street.

Strip away the brand names and the marketing and there are exactly three solar topologies. Everything sold in the market is one of these three, or a combination of them.

SMU is the cheapest, gives backup through your old battery, and offers modest solar use. PCU/hybrid gives genuine backup plus solar in one box at a higher price, with daily battery wear. Grid-tied gives the best bill savings but no backup at all. A grid-tied-with-battery hybrid does both — export and backup — but it is the priciest of the lot; the comparison table covers the detail.

Three columns matter most for this question: can it keep power on during a cut, can it reuse the inverter you already own, and what does it cost to start.

The SMU is the only option that both gives backup during a cut (through your existing battery) and reuses hardware you have already paid for — that is the lowest-cost way for an existing inverter owner to go solar. A PCU or hybrid cycles your battery every single day, wearing it faster than a backup-only inverter that only discharges during cuts. Grid-tied's bill savings depend entirely on getting net-metering approval from your DISCOM, which is a process in itself.

The SMU column has the most 'reuse existing' cells — that is why it is the cheapest entry for someone who already owns a working inverter and battery.

More panels does not mean more backup. Your backup duration during a cut is set by your BATTERY size, not your panel wattage. Panels only decide how fast the battery refills the next morning and how much grid you offset during the day.

Two questions settle it: how often does your power go out, and do you already own a working inverter and battery?

For every branch, the same two sizing rules apply: size the BATTERY to the load you must keep alive and for how long, then size the PANELS to your roof area and budget. If your cuts are rare, do not pay for a backup-capable system you will seldom use. If your cuts are frequent, do not buy pure grid-tied and end up sitting in the dark.

Most people have never heard of this path, yet it is the cheapest and highest-return option for the large number of Delhi NCR homes already running a home inverter with a tubular battery. A Solar Management Unit is a controller that lets your EXISTING inverter battery charge from solar panels, prioritising free sunlight over grid power.

Your panels feed the SMU, which charges the battery and helps carry the daytime load, so your inverter draws much less from the mains and your bill drops. When a cut hits, nothing special needs to happen — your inverter runs the house off that battery, except the battery has been topped up by the sun all day. No new backup hardware is involved.

You add solar panels, a mounting structure, the SMU / charge controller, and cabling. You keep your existing inverter and battery. One prerequisite: an electrician must confirm compatibility — battery voltage (12V single-battery versus 24V two-battery), inverter VA rating, and whether the SMU's charge current suits your battery's Ah. Match these and the retrofit is genuinely simple.

An SMU charges your own battery for self-consumption, not exporting surplus to the grid, so it does NOT earn net-metering credits. Its solar benefit is capped by your battery size and daytime load — once the battery is full and the daytime load is met, extra sunshine is wasted. For moderate solar plus reliable backup it is excellent; for zeroing a very large electricity bill, you want grid-tied export.

The controller itself is the cheap part: basic 12V units start from under Rs 1,000, popular LCD models run roughly Rs 2,200 to Rs 3,400, with larger units costing more — confirm current pricing before you buy. The full retrofit cost is dominated by panels and installation, not the controller. Adding an SMU plus panels to an inverter you already own is a fraction of the cost of a whole new PCU-based solar system; our team can quote the full retrofit for your specific kit.

Settle the 'more panels equals more backup' myth on paper with a load typical of a Delhi home in the evening: 3 ceiling fans (about 75W each = 225W), 4 LED lights (about 10W each = 40W), an LED TV (about 100W), and a Wi-Fi router (about 15W). That totals roughly 380W of running load. Assume a common 150Ah, 12V tubular battery.

Nominal energy is 150Ah × 12V = 1,800Wh. A sensible usable depth of discharge for a tubular battery is around 60%, giving about 1,080Wh of usable energy. Apply roughly 85% inverter efficiency and about 918Wh actually reaches your appliances — divide by the 380W load and you get roughly 2.4 hours. A lighter load runs longer, a heavier one shorter, and a tired three-year-old battery can give noticeably less.

Adding solar panels does NOT change that 2.4-hour figure. The battery is the fuel tank; panels are the refilling hose. To get longer backup you add battery capacity, not panels.

Grid-tied gives 0 hours — it trips off the moment the grid fails. An SMU gives the full battery-limited 2.4 hours, with the bonus that the battery was pre-charged by the sun and is more likely to be near full when the cut hits. A PCU gives the same battery-limited 2.4 hours, but if the cut happens during daylight, the PCU can keep pulling from the panels mid-cut and stretch that time. The battery sets the floor in every case.

A rooftop array in Delhi generates on the order of 4 to 4.2 units (kWh) per kW of panels per day averaged across the year, with bright spring days running higher and winter-smog or monsoon days running lower. A modest 2kW array makes roughly 8 units on an average day; at Rs 6 to Rs 8 per unit in the higher domestic slabs plus PPAC surcharges, that is very roughly Rs 50 to Rs 65 of value per average day. Tariff slabs and surcharges change with each DERC tariff order, so check your own latest bill for the rate you actually pay, and plan on the yearly average rather than a sunny-day peak. For your own load and roof, /sizing gives rough numbers in a couple of minutes; /contact gets you a precise on-site visit.

Only grid-tied or hybrid export setups earn net-metering credits, and the process runs through your Delhi DISCOM — BSES Rajdhani, BSES Yamuna, or Tata Power-DDL — with sanctioned-load and capacity rules governing how much you can export. An SMU retrofit does not export to the grid and needs no net-metering approval at all. Verify the current rules with your DISCOM as they do change; a dedicated guide is linked below.

Solar panels last the longest, typically carrying a performance warranty of around 25 years to a guaranteed output percentage plus a shorter product warranty. The inverter or PCU sits in the middle, commonly a few years of warranty in the Indian consumer segment. The battery is the wear item with the shortest life — in a PCU/hybrid setup it cycles every single day, using it up faster than a backup-only inverter would. Confirm the exact warranty terms on the specific panel, PCU, and battery you are quoted, as they vary by brand and model.

A grid-tie inverter must be anti-islanding compliant — look for IS 16169 / IEC 62116 type compliance. PV modules should meet IS 14286 (equivalent to IEC 61215) for design qualification and IS/IEC 61730 for module safety. A reputable installer will not blink when you ask about these.

We have been doing this across Delhi NCR for 25+ years, multi-brand rather than locked to a single manufacturer; when a battery needs replacing we handle old-battery exchange and buyback, plus on-site service and AMC. Use /sizing for rough numbers, browse the category that matches your branch above, or book a site visit at /contact for an honest recommendation. The right answer is the setup that matches how often your power actually goes out — not the most expensive box on the shelf.