How Many Batteries for a Full Night of Backup?

Our main battery sizing guide explains the basic method. This page focuses on one question: what it takes to get through the whole night, and what changes when you need a full 24 hours.

Step 1: How long is "a full night" for a battery?

The battery does not start at sunset. It starts when your panels can no longer carry the house, which in Punjab is usually late afternoon, and it runs until the panels take over again the next morning.

As rough planning figures for Punjab (illustrative, not measured):

Winter nights are longer, but summer nights carry the ACs. That is why the summer night with an AC is usually the case that sets the battery size.

Diagram

Battery for a full night

Night load

What runs after sunset

Hours

Sunset to sunrise

Capacity

Usable kWh needed

Step 2: Night loads are not flat

A household's night does not draw the same power every hour. It has three parts:

• Evening (about 6 to 11 PM): lights, TV, fans, kitchen, sometimes the iron or the water motor. The busiest stretch.
• Sleeping hours (about 11 PM to 6 AM): fans or ACs, the fridge, the router. Steady.
• Early morning (about 6 to 8 AM): water motor, kettle, geyser in winter, lights. Short but heavy.

For sizing, an average load over the whole window is good enough, as long as the inverter can handle the busiest moment.

Step 3: Worked scenarios

Round illustrative numbers, summer night window of 14 hours, planning factor of 0.85 for depth of discharge and losses. These are not measurements from any customer's home.

AC energy varies a lot with outside temperature, thermostat setting, room insulation and the AC itself. A hot, humid night in June can use more than the 1 kW average used here. See solar for AC for AC-specific sizing.

Converting kWh into "number of batteries". A common 48 V, 100 Ah lithium module stores roughly 5 kWh nominal; the exact usable figure is on the datasheet. High-voltage batteries are built from stacked modules, so the count works the same way. If you are comparing Ah ratings, our guide to 100 Ah, 200 Ah and 16 kWh batteries shows the conversion.

What about tubular batteries?

Tubular lead-acid batteries should not be discharged as deeply as lithium. As a generic planning figure, plan to use only about half of a tubular battery's rated energy. A 12 V, 200 Ah tubular battery stores about 2.4 kWh nominal, so about 1.2 kWh is usable.

For Scenario A, 7.4 kWh would need around six such batteries, and because they must be wired in sets that match the inverter's battery voltage, a 48 V inverter would need two sets of four. That is a lot of weight, space and maintenance for one night of essentials, which is one reason most new full-night systems use lithium. See LiFePO4 vs tubular batteries.

Step 4: Check the battery can deliver the power, not just the energy

Energy (kWh) gets you through the night. Power (kW) gets you through the busiest moment. Each battery module has a maximum continuous discharge rate. If an AC, the fridge and the water motor all run at once, one module may not be able to supply that much power even when it is full, and the system may alarm or trip.

More modules usually means more available power as well as more energy. Our guide to kW vs kWh and C-rate explains this, and high-voltage vs low-voltage batteries covers how larger stacks behave.

Step 5: Can your panels refill it?

A battery that is not full at sunset will not last the night. After your daytime loads are covered, the panels must put back roughly the night's energy plus losses.

Example arithmetic only: for Scenario B, you would need to put back about 17 kWh. At an illustrative 5 useful sun hours, that is about 3.5 kW of panels over and above what your daytime loads already use. In winter, with fewer sun hours and fog, the same battery may often start the night only part full.

This is why we design the panels and battery together, never the battery alone.

When you need 24 hours, not just the night

Some homes and sites need to run through a whole day without the grid: long load-shedding, a weak rural feeder, or a fault on the line. Two cases:

Sunny day, grid off. The panels run the house in the day and recharge the battery, and the battery covers the night. The night sizing above still applies; you simply need the panels to do both jobs.

Cloudy or foggy day, grid off. The panels may produce only a fraction of normal. Now the battery has to cover part of the day as well.

Example arithmetic only: essentials averaging 450 W for a full 24 hours is about 10.8 kWh; divided by 0.85, about 12.7 kWh, which is around three 5 kWh modules. Two such days in a row would need about twice that, or a backup source.

Designers call this "days of autonomy". For city homes with the grid as backup, one night is usually enough. For off-grid or very weak-grid sites, a day or more of autonomy, or a generator, is part of the design. See off-grid solar inverters.

Do you even need a full night?

If the grid is available at night, a full-night battery is a choice, not a necessity. Under net billing, storing midday surplus and using it in the evening is worth your full tariff instead of the low export rate, which can justify a bigger battery; see sizing under net billing. Charging the battery from the grid at night to cover the next evening rarely saves money; see charging from the grid.

If your main concern is load-shedding, size for your longest typical outage rather than the whole night, and add modules later if needed. Many batteries can be expanded with the same model; see replacing or expanding a battery. If you want the whole house, not just a few loads, on solar, read can you run your whole house on solar.

Price by number of battery modules

We supply batteries from Huawei, Sungrow and Luminey. Brand options and single-unit prices are on our lithium battery price page. Manufacturer warranty is per product. To keep a battery healthy through years of nightly cycling, see lithium battery lifespan and care.

Get today's price or a free site survey

Send us a list of what you want running at night and your usual load-shedding hours. Our engineers will size the battery, inverter and panels together.

• WhatsApp or call: 0336 666 4321
• Email: info@solarworks.pk
• Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
• Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
• Hours: 9:00 AM to 6:00 PM, daily

We serve all of Punjab. Start with the solar calculator, or contact us for a site survey, which is normally free.

Frequently asked questions

How many batteries do I need to run fans and lights all night?

For fans, lights, a fridge and a router through a 13 to 14 hour summer night, plan for about 7.5 to 10 kWh of lithium, which is about two 5 kWh modules. The exact figure depends on how many fans and how long they run.

How many batteries for a 1.5 ton AC all night?

The AC alone, averaging about 1 kW for 8 hours, uses around 8 kWh. With essentials and losses, plan for about 15 to 20 kWh, or three to four 5 kWh modules. Hot, humid nights can need more.

Is one 5 kWh battery enough for a whole night?

For a few light loads, yes. For a typical household with fans and a fridge through a full summer night, one module usually runs out before morning unless loads are kept very low.

How many batteries do I need for 24 hours of backup?

On a sunny day, the night battery is enough if the panels can run the house and recharge it. For a cloudy day without the grid, roughly double the night battery, or plan for a generator or the grid as backup.

Do winter nights need a bigger battery?

Winter nights are longer, but without ACs the load is usually lower. The bigger winter problem is recharging: fewer sun hours and fog mean the battery may not be full by evening.

Can I start with two batteries and add more later?

Often yes, if the inverter and battery model support expansion. Plan the first stage with expansion in mind and add the same model later.

Why does my battery not last the whole night even though the kWh looks right?

Common reasons are a battery that was not fully charged by evening, higher night loads than expected (especially ACs), and a reserve setting on the inverter that stops discharge early. Your installer can check the charge level at sunset and the settings.