Solar battery backup sizing calculator
The battery capacity you need for the hours of backup you actually want, once losses are counted.
Your details
Rough guide: LED lights (5) 50W, Ceiling fans (2) 150W, Television 100W, Refrigerator 200W.
Lithium costs more up front but you can use far more of its capacity.
Your estimate
Battery capacity you needEstimated
188 – 203 Ah
At 24V, to run 500 W for 4 hours. Suggested bank: 2 × 200 Ah (24V).
- Suggested bank
- 2 × 200 Ah (24V)
- Energy the load uses
- 2,000 Wh
- Energy to store
- 4,504 – 4,862 Wh
- Usable depth
- 60%
- Lost to conversion
- 57%
- Inverter efficiency
- 92%
The nearest practical combination of standard batteries.
Before any losses are counted.
More than the load needs, because you cannot use it all.
How much of a tubular battery you may draw without shortening its life.
The share of stored energy the load never sees.
DC from the battery becoming AC for your appliances.
This is an estimate, not a quote.
This is an estimated range based on average conditions in your area. Your actual numbers depend on site-specific factors we verify before quoting.
Rates last verified 2026-08-06
Get the number we stand behind
Origian Power stands behind the number our engineer gives you after a free site visit — not the number above.
- What you actually want running during a cut, measured rather than estimated
- Starting surge on motors and compressors, which sizes the inverter
- Where the bank can sit, which needs ventilation and access
A battery buys continuity, not savings
This is the distinction that decides whether you need storage at all. On a reliable grid connection, net metering already banks your surplus and returns it at night, and it does so far more cheaply than any battery. Adding storage there costs money and saves none.
What a battery buys is power during a cut. If your supply is unreliable, or there is no supply at all, that is worth paying for, and off-grid and hybrid systems are built around it.
The capacity figure here is deliberately larger than the energy your load consumes. Depth of discharge and inverter losses mean a meaningful share of what you store never reaches the appliance, and a system sized on nameplate capacity runs short exactly when it is needed.
Questions about this estimate
Why do I need more capacity than my load uses?
Because you never get to use all of a battery. Drawing a lead-acid battery flat destroys it, so only part of its capacity is usable, and the inverter loses more converting DC to AC. A 150 Ah battery does not give you 150 Ah of use, and sizing on the nameplate figure is the most common reason a backup system disappoints.
Is lithium worth the extra cost?
Often, for backup. You can draw far more of a lithium battery without harming it, so a smaller nameplate capacity delivers the same usable energy, and it lasts through many more cycles. The up-front price is higher; the cost per usable unit over its life usually is not.
Does a battery make my solar system cheaper to run?
No, it makes it more expensive. A battery buys you power during a cut, not savings. On a reliable grid connection, net metering already stores your surplus more cheaply than any battery can. Add storage when you need continuity, not when you want a lower bill.
What size inverter goes with this?
It depends on starting surge rather than running load. Motors and compressors draw several times their rated wattage for a moment when they start, so a fridge or a pump sizes the inverter well above its steady figure. That is one of the things worth checking on site.
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