How to size a solar battery bank for a Lahore home

The most common mistake on Lahore solar installs is picking the battery first and figuring out the load second. The right method runs the other way. Measure what the house actually uses overnight, decide how many cloudy or grid-out days the battery needs to cover, then pick the chemistry and capacity that match. This piece works through that calculation with real Lahore numbers.

Step one: measure overnight load in kWh

The battery only matters at night and during grid outages. Daytime load runs straight off panels. So the sizing question is what the house draws between sunset (roughly 7pm in Lahore summer) and sunrise (roughly 5:30am), plus any cloudy daytime period the battery has to cover.

A typical Lahore 10-marla home with two adults, two children and a maid running essentials plus one 1.5-ton inverter AC overnight in July consumes roughly the following:

Load	Watts	Hours	kWh
6 LED lights (12W each)	72	5	0.36
4 ceiling fans (75W each)	300	10	3.0
Refrigerator (cycling)	120 avg	10	1.2
WiFi router + ONT	15	10	0.15
1.5-ton inverter AC	1,100 avg	7	7.7
Phone chargers + TV standby	30	10	0.3
Total overnight load			12.7 kWh

That 12.7 kWh figure is the floor. A house that runs two ACs overnight pushes it to 18 to 22 kWh. A house that only runs essentials (no AC) drops to roughly 5 kWh.

Step two: pick the autonomy days

Autonomy days is the number of cloudy or grid-out days the battery has to cover without solar charging. For Lahore in 2026 the realistic numbers are these. Hybrid systems with net metering need 0.4 to 0.6 days of autonomy because the grid is the backup. Off-grid systems need 1.5 to 2.5 days of autonomy because there is no fallback. Most Lahore homes sit in between.

For a hybrid system the math is simple. Multiply overnight load by 1 (one night of coverage). For the 10-marla example above, that gives 12.7 kWh of battery storage needed.

For an off-grid system multiply by 2 (one full cloudy day plus overnight). The same 10-marla load becomes a 25.4 kWh requirement, which means four to five lithium packs or sixteen tubular cells.

Step three: account for depth of discharge

Battery capacity on the spec sheet is nameplate. Usable capacity is lower because pulling a battery all the way to zero damages it. The factors are:

Tubular lead-acid: 50 percent depth of discharge for daily cycling. A 200Ah 12V tubular nominal stores 2.4 kWh but only 1.2 kWh is usable per day without harming the plates.

Lithium LFP: 80 to 95 percent depth of discharge depending on chemistry and BMS. Pylontech UP5000 publishes 95 percent (4.56 kWh usable from a 4.8 kWh nameplate). Dyness BX51100 publishes 90 percent. Inverex IP and Soluna sit at 85 percent.

So for the 12.7 kWh overnight load, the nameplate capacity needed is:

Tubular: 12.7 / 0.50 = 25.4 kWh nameplate (roughly eight 200Ah 12V cells in series-parallel)

Lithium at 90 percent DOD: 12.7 / 0.90 = 14.1 kWh nameplate (three Dyness BX51100 packs)

Step four: check the inverter can handle it

A battery sized to push 4 kW continuously into the house at midnight needs an inverter sized to match. Pylontech UP5000 supplies a maximum 50A at 48V (roughly 2.4 kW) per unit. Two parallel units give 4.8 kW continuous, which fits the 10-marla example. A single UP5000 cannot run the 1.5-ton AC by itself once the fridge compressor kicks in at the same moment.

Dyness BX51100 supplies 100A continuous per unit (5.12 kW), which is more headroom for the same task. BYD LVS 8.0 supplies 200A continuous (10 kW) in a single cabinet.

The lesson is that battery sizing has two numbers, not one. The energy number (kWh) decides how long the battery runs. The power number (kW continuous) decides whether it can run the largest load at all.

The over-sizing trap

Some installers in Lahore push a 20 kWh battery on a house that needs 10 kWh, framing it as "future-proofing." The problem is that lithium packs cycle better when they are used. A 20 kWh bank that only ever discharges 8 kWh per night runs at 40 percent of intended cycling, which makes the calendar-life clock run faster than the cycle-life clock. The result is a battery that is half-empty at retirement and the owner paid for capacity that was never used.

The honest rule is to size for current load plus 15 to 25 percent headroom, not for some hypothetical future load. Lithium packs can be added later. Pylontech and Dyness both support adding a unit at any time within the warranty period as long as the new unit is bought from the same authorised channel.

The under-sizing trap

The other failure mode is sizing too tight. A 5 kWh lithium pack on a 10-marla home running an AC overnight gets fully discharged every night, plus a deeper drain during cloudy days. Lithium tolerates 95 percent DOD on the spec sheet, but real-world capacity retention degrades faster when the pack hits 100 percent DOD often. A pack that should last 10 years lasts 6 to 7.

The fix is to add either 25 percent headroom in kWh or a second smaller pack in parallel. Both options are cheaper than replacing the bank early.

The worked answer for the 10-marla example

For the 10-marla home above (12.7 kWh overnight load, hybrid system with grid backup), the right battery bank is one of the following:

Two Dyness BX51100 (10.24 kWh nameplate, 9.2 kWh usable). Cost: PKR 915,000 installed. Covers 95 percent of nights with grid backup for the remaining 5 percent. This is the most common pick in DHA, Bahria Town and Johar Town for 2026.

Three Pylontech UP5000 (14.4 kWh nameplate, 13.7 kWh usable). Cost: PKR 1,560,000 installed. Covers 100 percent of overnight loads including the AC with comfortable headroom. Right pick for buyers who want premium and have the budget.

One BYD LVS 8.0 plus expansion module (12 kWh usable). Cost: PKR 1.45 million installed. Right pick for new builds where the inverter and battery are specified together.

Sizing for smaller and larger homes

The 10-marla example is the middle of the bell curve. For 5-marla homes the overnight load typically runs 3.5 to 5.5 kWh (essentials plus one ceiling-mount AC or none). A single 5 kWh lithium pack is the right answer at PKR 415,000 to 465,000 installed. A pair of 230Ah tubulars (PKR 145,000 installed) is the right answer if the budget is tight and the family does not run the AC overnight.

For 1-kanal homes the overnight load runs 18 to 26 kWh (two or three ACs plus essentials). The right answer is 20 to 25 kWh of lithium, which lands at PKR 1.85 to 2.4 million installed depending on brand. Tubular cannot match this duty cycle at any sensible bank size, so the answer is always lithium at this scale.

For commercial loads (small clinics, offices, restaurants) the sizing is driven by daytime backup needs rather than overnight cycling. A clinic running ultrasound equipment, refrigerated drug storage and AC across a 10-hour day needs 25 to 35 kWh of lithium just to cover a 6-hour grid outage during business hours. The math runs the same way but the autonomy days calculation pushes the answer higher.

Common sizing errors specific to Lahore

Three errors push battery banks 25 to 40 percent away from the right size in Lahore installs. The first is using sticker wattage rather than measured wattage for the AC. A 1.5-ton inverter AC has a sticker rating of 1,500W but the actual average draw across an overnight cycle in July is 950 to 1,200W because the compressor modulates. Using the sticker number oversizes the battery and pushes the cost up unnecessarily.

The second is ignoring the standby load. Refrigerators, internet routers, satellite receivers and inverter standby together pull 80 to 130W around the clock. That is 1.0 to 1.6 kWh per day of pure standby load, which has to be added to the night-time cycling load.

The third is sizing for the worst-case July night and ignoring the rest of the year. A battery that needs to deliver 14 kWh on the hottest night of summer only needs to deliver 4 to 6 kWh in March and October. Lithium tolerates this variable load fine. Tubular tends to undercharge in the cooler months because the cells do not need as deep a recovery, which causes long-term sulphation. The fix is to run a monthly equalisation cycle in winter.

How net metering changes the sizing answer

Hybrid systems with active net metering have a smaller battery requirement than off-grid or grid-tied-no-net-metering systems. With net metering, daytime excess solar exports to the grid for credit, and overnight import draws from the grid at the same unit rate. The battery only needs to cover grid outages, not full overnight load.

For a typical 10-marla Lahore home with net metering active, a 5 to 8 kWh lithium pack often suffices because grid outages average 1 to 3 hours per day rather than full overnight blackouts. For the same home without net metering (or with the new 2026 gross metering rules in effect), the battery needs to cover the full overnight load to avoid paying the high evening tariff. That pushes the sizing from 5 kWh to 12 to 16 kWh.

Buyers planning a system in 2026 should clarify with their installer which metering scheme applies to their connection and size the battery accordingly. The wrong sizing assumption can mean spending PKR 500,000 more or PKR 500,000 less than needed.

The hybrid inverter capacity rule

One sizing consideration buyers often miss is that the inverter has to be able to drive the maximum simultaneous load, not just deliver the daily kWh. A 16 kWh battery bank can theoretically deliver enough energy for two ACs plus essentials, but only if the inverter can supply 6 to 7 kW of instantaneous power. A 5 kW hybrid inverter chokes when both compressors fire at the same moment.

The rule for matching inverter to battery in Lahore residential installs is roughly 0.5 kW of inverter capacity per kWh of usable storage. A 10 kWh bank wants an 5 kW inverter minimum. A 16 kWh bank wants an 8 kW inverter. A 25 kWh bank wants a 12 kW inverter (typically the 10 kW class three-phase unit). Sizing the inverter too small for the battery is a common error that limits the usable backup performance.