No solar backup at night: what went wrong

The call that comes every July

A homeowner in Model Town spent close to a million rupees on solar last year. Bills dropped nicely. Then a July evening outage hits at 9 pm, the house goes dark, and the phone rings with a fair question: what exactly did that money buy?

Four different situations produce that same dark house. They need completely different answers, and one of them needs no money at all. Work through them in order.

Reason one: it is an on-grid system, and it never could do this

Start here because it accounts for more of these calls than the other three combined.

An on-grid inverter has no battery port. It converts DC from the panels into AC that is synchronised with the LESCO supply, and it needs that supply present as a reference. When the grid goes, the inverter shuts down within a second or two. This is deliberate, it is called anti-islanding, and it exists so a lineman working on a dead feeder is not electrocuted by your rooftop. Every certified inverter in Pakistan behaves this way.

So a pure on-grid build in Lahore gives daytime savings and net metering credits, and nothing at all during an outage. Not at night, not at 2 pm during a fault. Many buyers were never told this clearly, or heard "solar system" and assumed the UPS behaviour they were used to.

How to check yours in thirty seconds: look at the inverter for a terminal or menu labelled Battery or BAT. If there is none, the build is on-grid. Also check whether the house has a separate backup distribution board, because a hybrid install almost always has one. The distinction is covered in detail across on-grid systems and hybrid battery systems.

What it costs to change that

Converting means a new hybrid inverter plus storage plus rewiring the circuits you want backed up. A 5kW hybrid is PKR 165,000, a 6kW is PKR 158,000, a 10kW is PKR 295,000. Add a 5kWh lithium pack at PKR 285,000 or a 3.5kWh Pylontech at PKR 195,000. Add labour at PKR 20,000 and an electrical items kit at PKR 35,000. The old on-grid inverter usually resells in the local market for something, which softens it. The full picture sits in the hybrid with battery guide.

Reason two: the bank is undersized for the loads on it

The second most common. A hybrid is fitted, a battery is fitted, and backup lasts twenty minutes instead of the night. Usually the battery was sized to a price point rather than to the house.

Real numbers for a Lahore home, using usable capacity rather than the sticker rating.

Load	Draw	Hours from 2.5kWh usable	Hours from 4.5kWh usable	Hours from 9kWh usable
6 fans plus LED lights	350W	7.1	12.8	Overnight easily
Fans, lights, fridge, TV	600W	4.1	7.5	15
Above plus 1 inverter AC (1.5 ton)	1,500W	1.6	3.0	6
Above plus 2 inverter ACs	2,600W	0.9	1.7	3.4
Water pump start surge	2,200W peak	May trip the cutoff	Usually fine	Fine

Those usable figures already account for depth of discharge and conversion losses. A 5kWh lithium pack does not give 5kWh. Reserve settings hold back 10 to 20 percent, and inverter conversion costs another 5 to 8 percent, so about 4 to 4.5kWh actually reaches the house. On a tubular bank the gap is far wider, because discharging lead acid past 50 percent regularly destroys it inside two years.

The trap in Lahore is the AC row. A family that wants one bedroom AC running through a July night needs roughly 9 to 12kWh of usable storage, which is two to three 5kWh modules at PKR 285,000 each. Very few people are quoted that honestly at the point of sale. Sizing method is set out in battery bank sizing, and the AC question specifically in summer AC load on solar.

Reason three: depth of discharge and reserve settings

A battery showing 35 or 40 percent while the house sits dark confuses everybody. Two settings cause it.

The first is the reserve, sometimes called minimum SOC or back-up SOC. Installers set it to protect the pack, commonly at 20 percent on lithium and 50 percent on lead acid. Everything below that line is unavailable by design. On a 5kWh pack with a 30 percent reserve, only 3.5kWh is on the table before the inverter hands the house back to a grid that is not there.

The second is the low voltage cutoff, which reacts to instantaneous voltage rather than state of charge. When a fridge compressor or a water pump starts, the pack voltage dips sharply for a moment. On an ageing pack, or one with cell imbalance, that dip crosses the cutoff and the inverter drops the load even though the meter says 40 percent. That behaviour is a strong hint the pack is degrading, and the diagnostics for it sit in solar battery not charging.

Reserve settings can be lowered, within reason. Taking lithium down to a 10 percent reserve is generally acceptable and buys real hours. Taking a tubular bank below 50 percent is a false economy that shortens its life dramatically, and the honest comparison between the two chemistries is in lithium vs tubular.

Reason four: load profile mismatch

This one is subtle and it catches thoughtful buyers. The system is correctly hybrid, the bank is a sensible size, and the house still runs out at 1 am.

What happened is that the battery never started the night full. Charging depends on surplus production after the daytime house load is served. Consider a 5kW array making 22 units on a June day, with a house that consumes 26 units between 8 am and 6 pm because the ACs run all afternoon. There is no surplus at all. The battery ends the day exactly where it started.

Things that create this pattern in Lahore:

• Daytime AC use during summer, which is exactly when production peaks. The array is feeding compressors, not the battery.
• A monsoon week where daily output drops to 13 units and the house still needs 25.
• Smog season from November to January, where a 5kW build can fall to 11 or 12 units a day. Detailed in winter output.
• Grid charging switched off in the settings, so nothing tops the bank up overnight.
• A charge current limit set too low, so even with surplus the pack only takes a trickle.

The fixes range from free to expensive. Enabling a timed grid charge between 11 pm and 5 am is free and puts the bank at 100 percent every morning, though at PKR 48 to 65 per unit it is bought reliability rather than saved money. Shifting laundry, iron and water pumping to mid-morning frees up afternoon surplus. Adding panels is the real solution when the array is genuinely too small, and at PKR 19,500 for a 585W Tier-1 panel plus PKR 7,000 per kW of mounting, four extra panels is often cheaper than another battery module.

How to work out which reason applies to you

Answer these in order and the diagnosis usually falls out on its own.

1. Does the inverter have a battery terminal or battery menu? No means reason one, and nothing else matters until that changes.
2. At 7 pm on a clear day, what state of charge does the app show? Under 70 percent points at reason four. Near 100 percent rules it out.
3. When the house cut, what did the app show? A number well above zero points at reason three. Near zero points at reason two.
4. What was actually running when it cut? Add up the wattage honestly, including the AC nobody mentions. Compare against the table above.
5. Does it also cut during a daytime outage? Yes with a healthy battery suggests a backup wiring problem rather than a storage problem.

That last point deserves a note. On many Lahore hybrid installs only selected circuits are wired to the backup output, typically bedrooms, lights, fans and the fridge. If a plug point in the drawing room dies during an outage while the bedroom fan runs, nothing is faulty. That socket was simply never put on the backup board. Whether to expand it is a rewiring decision, quoted as part of any installation or repair visit.

What honest storage costs in Lahore right now

No point discussing fixes without prices. Current 2026 rates:

• Lithium 2.5kWh: PKR 130,000 to 145,000
• Pylontech 3.5kWh: PKR 195,000
• Lithium 5kWh: PKR 285,000
• Tubular 200Ah: PKR 48,000 to 52,000 each, typically four to eight units for a 48V bank
• 5kW hybrid inverter: PKR 165,000, 10kW hybrid: PKR 295,000
• Electrical items kit PKR 35,000, installation labour PKR 20,000

A complete 5kW hybrid with battery installed lands somewhere between PKR 700,000 and PKR 900,000. A 10kW hybrid with a serious bank runs PKR 1,400,000 to PKR 2,200,000. Anyone quoting overnight AC backup at the bottom of those ranges is not being straight with you.

The caveat that gets left out of sales conversations: batteries do not pay for themselves in Lahore the way panels do. Panels have a payback of roughly three years against LESCO rates. Storage is bought for comfort and continuity during outages, and on pure arithmetic it rarely returns its cost before it needs replacing. That is a fair trade for many households, but it should be a decision made with eyes open rather than a surprise in year six. Related reading in batteries for load shedding, IPS vs solar battery and is solar still worth it in 2026.

What to do next

If the build is on-grid, the choice is between living with daytime-only savings and converting to hybrid. Many households in DHA and Johar Town keep the on-grid system, keep the net metering arrangement intact, and add storage only for the circuits that genuinely matter at night.

If the bank is undersized, add modules rather than replacing the pack, provided the existing modules are under three years old and the same brand. Mixing ages and brands in one bank causes the weakest module to set the ceiling for all of them.

If the problem is load profile, start with the free changes: enable grid charging, move heavy daytime loads, and check the charge current limit. Measure for a week before spending. For houses in Bahria Town and Model Town where outages are shorter but frequent, that alone often solves it. Sizing anything new starts at the calculator or a conversation through contact. If the grid connection itself is unreliable enough that backup matters more than export, off-grid and the off-grid guide are worth reading too.