Solar Array & Battery Autonomy Calculator
A site using 20 kWh a day needs about a 4.5 kWp array in the Philippines — and if 40% of that use is after dark, about 10 kWh of battery keeps the evening running on stored sunshine. Sized right, that is roughly ₱7,300 a month off the bill.
Enter your daily consumption and how much of it happens after dark. The calculator sizes the array (kWp = kWh ÷ sun hours × derate), the LFP battery (load × hours ÷ DoD ÷ efficiency), and recommends the iVOLT bundle that fits — sized to what you use, not what you could export.
Your Consumption
System Sizing
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The Formulas
Array size (PSH = peak sun hours; derate covers wiring, temperature, inverter and soiling):
Battery nominal capacity (load carried × hours, grossed up for usable DoD and round-trip losses):
Method & Sources
- Peak sun hours 4.5–5.5 for the Philippines — Global Solar Atlas regional data; the 5.5 default matches our iVOLT solar calculator so the two tools agree. Set your own city's figure.
- System derate 0.80 — PVWatts-style allowance for temperature, wiring, inverter and soiling losses. Clean roofs in breezy sites do a little better; hot flat roofs a little worse.
- LFP battery: 90% usable DoD, ~95% round-trip — manufacturer convention for LiFePO₄ modules; the calculator sizes in standard 5.12 kWh module steps, the same modules as the iVOLT range.
- Night-share method — the battery is sized to carry your after-dark load for the autonomy you choose, not to absorb the whole array. That is what keeps storage affordable.
- What we leave out — roof orientation and shading (site-specific), seasonal variation, and degradation. A proper quote includes them.
Related Free Tools
Frequently Asked Questions
How many kW of solar do I need per kWh of daily use?
Daily kWh ÷ (peak sun hours × derate). At 5.5 PSH and 0.80 derate, each kWp gives about 4.4 kWh/day — so 20 kWh/day needs roughly 4.5 kWp. Cloudier regions or east-west roofs need more.
What is a peak sun hour?
One hour at the standard test intensity of 1,000 W/m². The Philippines averages roughly 4.5–5.5 a day by region and season (Global Solar Atlas). It is not daylight hours — a hazy 12-hour day might deliver only 4.
How big a battery do I need for brownouts?
Nominal kWh = load carried × hours ÷ DoD ÷ round-trip efficiency. Carrying 8 kWh of evening load needs ~9.4 kWh nominal — two standard 5.12 kWh LFP modules. Size on the loads that matter, not the whole switchboard.
Why size for self-consumption instead of exporting?
Exports are credited at the generation rate — roughly half the import price. A kWh you use yourself is worth about double one you sell, so size to your daytime use plus a battery for the evening, not to the biggest array the roof holds.
Does a battery pay for itself?
It depends on two things: how much of your use is after dark, and what an outage costs you. Day-heavy sites get the fastest payback from panels alone; the battery earns its keep where evening use is heavy or where brownouts stop tills, pumps or production. Run your night share above and look at the numbers.
Want This Sized Against a Real Bill?
Send us a photo of your electricity bill. We will size the array and battery to your actual usage pattern and tell you plainly what it saves — and how long it takes to pay back.
Send Us Your Bill