Panel count is the wrong first question. Work out your daily energy use and your local sun hours first, and the number of panels falls out of the arithmetic on its own.
Ask five installers how many panels your house needs and you will get five answers, because almost none of them start from the only figure that matters: how much energy you consume in a day, measured in watt-hours.
There are two ways to get this number. The accurate way is your electricity bill — find the kWh used for the month and divide by 30. A bill showing 300 kWh means you use about 10 kWh, or 10,000 watt-hours, per day.
The other way is to add up your appliances: wattage × hours used per day, item by item. This is slower but it shows you where the energy is going, which matters if you plan to power only part of the house.
| Appliance | Watts | Hours/day | Wh/day |
|---|---|---|---|
| Ref, inverter type | 120 | 24 | 2,880 |
| Aircon, 1.0 HP inverter | 750 | 8 | 6,000 |
| Ceiling fan | 75 | 10 | 750 |
| 6 × LED bulbs | 54 | 6 | 324 |
| TV | 120 | 5 | 600 |
| Rice cooker | 700 | 1 | 700 |
| Router, chargers, CCTV | 40 | 24 | 960 |
| Total | 12,214 |
Notice which line dominates. The aircon is half the total. Any serious conversation about solar starts with the two or three biggest lines, not the light bulbs.
Our load profile tool remembers your appliances and feeds every calculator.
Peak sun hours are not daylight hours. A panel only makes its rated output under full, direct sun. Twelve hours of daylight in Metro Manila might deliver the equivalent of four and a half hours at full power.
Across most of the Philippines, a reasonable planning figure is 4.5 to 5.5 peak sun hours as an annual average. Two adjustments matter locally:
A 400W panel does not deliver 400W of usable household energy. Between panel heat, wiring, the charge controller and inverter conversion, plan on keeping about 75%. Heat is a real factor here: panels lose efficiency as they get hotter, and a black roof in Philippine sun gets very hot.
Array size (W) = Daily watt-hours ÷ Peak sun hours ÷ 0.75
For our 12,214 Wh household at 4.5 sun hours:
12,214 ÷ 4.5 ÷ 0.75 = 3,619 W. At 400W per panel that is
10 panels, or a 4kW array once you round up to whole panels.
Now sanity-check the roof. Ten 400W panels occupy roughly 20 square metres and weigh around 220 kilos before mounting hardware. On an older house, the roof structure deserves a look before the electrical design.
Enter your daily watt-hours and sun hours for a panel count, battery size and controller rating.
This is the fork in the road, and it changes the cost far more than panel count does.
Cheapest per watt. Your panels offset consumption while the sun is up. The catch is that when the grid goes down, so does your system — standard grid-tied inverters shut off for safety. If your main motivation is surviving brownouts, this option does not solve your problem.
Panels run the house by day, surplus charges a battery, and the battery carries you at night and through outages. This is what most Filipino households actually want, and the battery is typically the single largest line item.
To size the battery, decide how many hours or days without sun you want covered:
Battery Ah = (Daily watt-hours × Days of autonomy) ÷ (System volts × Usable fraction)
For 12,214 Wh, one day of autonomy, a 48V system and LiFePO4 at 80% usable:
(12,214 × 1) ÷ (48 × 0.8) = 318 Ah at 48V. That is a serious battery
bank, which is why most households start by putting only essential circuits on solar — lights, fans,
router, ref — and leave the aircon on the grid.
Under the Philippine net-metering scheme, qualifying systems up to 100kW can export surplus generation to the distribution utility for credit. Rules, application processes and credit rates vary by utility, so confirm current terms directly with your distributor before you size for export.
Between panels and battery sits a charge controller, and it must be rated for the current your
array produces. Divide array watts by system volts and add 25% headroom: a 4,000W array on a 48V
battery gives 4,000 ÷ 48 × 1.25 = 104 A.
Choose MPPT rather than PWM for anything above a few hundred watts. MPPT controllers typically harvest 15–30% more energy from the same panels, which pays for itself quickly.
If the full-house number gave you sticker shock, that is the normal reaction. Most successful installations here start smaller and grow:
Size each stage properly rather than buying one oversized system on credit. And before signing any quote, ask what happens to your system during a brownout — the answer tells you which of the two designs above you are actually being sold.