Solar Panel Sizing

Different question, different stage. Solar Payback takes a system size (kWp) and tells you the financial return. Solar Sizing starts with your actual electric bill (monthly kWh) and tells you what size system you need in the first place. The honest order is: size first (this tool), then run payback (the other tool) to confirm the math.

'Peak sun hours' is the equivalent number of hours per day at full 1,000 W/m² irradiance. The actual sun is up ~12 hours, but it's weak in the early morning, late afternoon, and during clouds. NCR averages 4.8 peak-sun-hours/day (NREL/PAGASA solar resource maps); Visayas 5.0; Mindanao 5.3; Baguio/highlands 4.4 due to elevation cloudiness. The number bakes in PH's annual cloud coverage.

The gap between panel nameplate watts and what you actually use. Losses: inverter (3–5%), DC + AC wiring (2–3%), dust + soiling (3–5%), heat (panels lose 0.3–0.5%/°C above 25°C — and a PH roof at noon hits 60°C), shading (variable), and inverter clipping. 78% is the IEC 61724 standard mid-point. Premium microinverter systems hit 82%; cheap setups fall to 70%.

Depends on your net metering setup. (1) Net metering (ERC-approved): export credits offset import — sizing for 100% can make sense, but check your DU's import-export accounting. (2) Net billing (default for most): exported kWh is bought at generation-only rate (~₱4–6), much less than your ₱12+ retail rate — over-sizing wastes investment. (3) No export: you can't sell back, so 70–80% offset is typically the sweet spot for payback. Default to 80% unless you have ERC net metering.

Solar panels are discrete units — you can't install 0.7 of a panel. If math says 9.4 panels at 550W, you need 10 panels (5.5 kWp). The recommended kWp reflects this physical rounding. The required kWp shows the exact math number for sanity check.

Yes. Panel arrays need (1) 30–60 cm gaps between rows for tilt/heat dissipation, (2) walkway access for cleaning and inverter service per OSHA-style safety codes, (3) clearance from roof edges and obstructions like vents, antennas, A/C condensers, satellite dishes. A 10-panel array (23 sqm of panel) typically needs ~30 sqm of usable roof. Bungalows with simple rectangular roofs lose less; multi-pitch roofs lose more.

PH solar installer pricing as of 2026: turnkey residential 5 kWp grid-tie typically runs ₱45K–65K per kWp, including panels, hybrid inverter, mounting, wiring, breakers, labor, ERC permits. Solaric, Solar Philippines, Buskowitz Energy cluster around ₱50–55K. Premium brands (Enphase microinverters, LG/REC panels) reach ₱70–80K. Self-install kits without permits drop to ₱30K but lose net metering eligibility.

No. Pure browser math. Your kWh consumption and address zone never leave your device.