How to Size Your Off-Grid Solar System in the Philippines

Why Sizing Matters

The most common mistake in DIY solar is buying panels before calculating your actual power needs. You end up with a system that can't run your appliances — or one that's way oversized for your budget.

This guide walks you through the sizing process step by step, using Philippine-specific data.

Step 1: List Your Appliances

Start by listing every appliance you want to power with solar. For each one, note:

• Wattage (check the label or manual)
• Hours of use per day

Here are common Filipino household appliances and their typical wattages:

• LED Light: 10W
• Electric Fan: 50W
• Ceiling Fan: 75W
• TV 32": 60W
• Laptop: 65W
• Phone Charger: 10W
• WiFi Router: 12W
• Refrigerator: 150W (runs ~8 hours/day on average)
• Rice Cooker: 700W (typically 30 minutes/day)

Step 2: Calculate Daily Energy Use

Multiply each appliance's wattage by its hours of use, then add them all up:

Daily Energy (Wh) = Watts x Hours x Quantity

Example for a typical Filipino household:

• 5 LED lights x 10W x 6 hrs = 300 Wh
• 2 electric fans x 50W x 10 hrs = 1,000 Wh
• 1 TV x 60W x 5 hrs = 300 Wh
• 1 laptop x 65W x 4 hrs = 260 Wh
• 2 phone chargers x 10W x 3 hrs = 60 Wh
• 1 WiFi router x 12W x 24 hrs = 288 Wh

Total: 2,208 Wh/day (about 2.2 kWh/day)

You can use our Power Consumption Calculator to do this automatically.

Step 3: Calculate Panel Wattage

The Philippines gets an average of 4.5 peak sun hours per day. This varies by region — Manila gets about 4.2, Cebu about 4.8, and Davao about 5.0.

Factor in system losses (wiring, controller, battery charging efficiency) — typically about 25%:

Panel Wattage = Daily Wh / Peak Sun Hours / 0.75

For our example:

• 2,208 Wh / 4.5 hours / 0.75 = 654W of panels

Round up to the nearest available panel size. You'd need about 3x 200W panels or 2x 300W panels.

Step 4: Calculate Battery Capacity

For off-grid, you need enough battery to store your daily use plus some reserve for cloudy days.

Battery Capacity (Ah) = Daily Wh x Days of Autonomy / Battery Voltage / Depth of Discharge

• Days of Autonomy: 1 day for mostly sunny areas, 2 days recommended, 3 for rainy areas
• Depth of Discharge (DoD): 50% for lead-acid, 80% for LiFePO4
• Battery Voltage: 12V for small systems, 24V for 1-3kW, 48V for larger

For our example (12V system, LiFePO4, 1 day autonomy):

• 2,208 Wh x 1 / 12V / 0.80 = 230 Ah

You'd need about 2x 120Ah LiFePO4 batteries or 1x 200Ah + some headroom.

Step 5: Size Your Inverter

Your inverter needs to handle the peak load — all appliances that might run simultaneously.

Inverter Size = Peak Watts x 1.25 safety margin

If your peak load is 500W (fans + lights + TV + laptop running at once):

• 500W x 1.25 = 625W inverter minimum

A 1000W pure sine wave inverter gives comfortable headroom.

Step 6: Size Your Charge Controller

Controller Amps = Panel Wattage / System Voltage x 1.25

For our example:

• 654W / 12V x 1.25 = 68A

You'd need a 60A or 80A charge controller. MPPT is recommended for systems above 400W.

Use Our Free Calculator

Don't want to do the math manually? Use our Power Consumption Calculator — select your appliances, set hours, and get instant sizing recommendations. Then head to the DIY Builder to browse compatible components with real prices.