Solar Battery Size Calculator
Find the battery capacity you need to keep the lights on through a brownout or overnight — four inputs, instant estimate.
Sizing for LiFePO4 (usable depth ~90%). Real sizing depends on which loads you back up and inverter limits — treat this as a starting point.
Compare backup batteries & power stations →How to size a solar battery
Battery sizing comes down to how much energy you use and how long you want to run without the grid or sun. Take your daily kWh, multiply by the days of backup you need, and gross it up for usable depth of discharge (LiFePO4 batteries safely use most of their capacity) and inverter losses. The result is the battery size in kWh — bigger than the raw energy figure because no battery is 100% usable.
This pairs with the is a battery worth itand battery types guides. To shop actual units, see our backup power picksand the sizing guide.
Battery sizing FAQ
Frequently asked questions
What size battery do I need for my solar system?
Multiply your daily energy use in kWh by the number of days of backup you want, then divide by about 0.8 to allow for usable depth and losses. For a home using 10 kWh a day wanting one day of backup, that is roughly a 12 kWh LiFePO4 battery. The calculator does this for you.
How do I find my daily energy use?
Divide your monthly kWh (on your electric bill) by 30. A ₱8,000 Meralco bill is very roughly 590-600 kWh a month, or about 20 kWh a day. If you only want to back up essentials, add up just those appliances instead of your whole bill — most homes back up far less than their total use.
What are peak sun hours in the Philippines?
Around 4.3 to 5.5 hours a day on average, depending on location — a bit lower in cloudier, mountainous areas like Baguio. It is the number of hours of full-strength sun your panels effectively get. The calculator defaults to 5, which is reasonable for most of the country.
Do I need a battery at all?
Not for bill savings. A grid-tied system with no battery still cuts your daytime bill and costs less. A battery only earns its cost if you need power during brownouts or at night, which is common in typhoon-prone areas.