Solar Panel Calculator
Estimate how many solar panels (Wp) you need to offset monthly electricity consumption (kWh) of a home. Everything in your browser.
Sizing a residential PV system
PV systems are sized from the monthly consumption in kWh. A typical 2024-2026 panel delivers 550-600 Wp (Watt-peak, measured at Standard Test Conditions). Brazil's average insolation is 4.5-5.5 kWh/m²/day, reaching 6+ in the Northeast sertão. A 1 kWp system generates roughly 110-150 kWh/month depending on the region. The simplified formula is panels = monthly_kWh / (Wp · peak_sun_hours · 30 · efficiency). Example: 400 kWh/month, 600 Wp panels, 5 peak-sun hours/day, 80% system efficiency → 400 / (0.6 · 5 · 30 · 0.8) ≈ 5.6 → 6 panels. Brazilian net metering is regulated by Law 14,300/2022 (the GD legal framework), with energy credits valid for 60 months. Residential payback is typically 4-7 years. Pick an on-grid inverter for systems tied to the utility or off-grid with batteries for autonomy.
Applications
Residential bill reduction, commercial and rural installations, financing pre-quotes via Solfácil/Volt and similar platforms, dimensioning for self-consumption, sizing for ESG and corporate sustainability reports.
FAQ
Why do peak-sun hours (HSP) matter more than total sunlight hours? Because HSP normalizes to 1,000 W/m² irradiance — it tells you how many equivalent "full" hours the panel produces, accounting for low-irradiance dawn and dusk periods.
Do I need batteries? Not for on-grid systems — the grid acts as a virtual battery via net metering. Batteries are only needed for off-grid or backup against outages, and they typically double the system cost.
How much roof area per panel? Modern 550-600 Wp panels measure ~2.3 m², so a 6-panel system needs roughly 14 m² of usable, well-oriented roof (north-facing in Brazil, with little to no shading).
Related Tools
Rent Adjustment Calculator
Compute annual rent adjustment by IGP-M or IPCA accumulated in the last 12 months (manually configurable).
Pregnancy Calculator
Compute estimated due date (EDD), gestational age and trimester from the last menstrual period (LMP).
Fertile Period Calculator
Compute fertile window and ovulation day from the first day of the last cycle and the average cycle length.
How many solar panels you need
Every solar energy project starts with the same question: how many panels will cover the electricity bill? The estimate comes from here, based on your monthly consumption in kWh and the panels' power in Wp.
The tool cross-references how much electricity you use per month with each panel's expected generation, then points to how many you'd need to zero out, or at least sharply cut, what you draw from the grid. It works as a solid starting point for sizing the project and the investment before you even call an installer.
It runs in the browser and counts as an initial estimate. Actual generation depends on location, roof tilt and shading, factors a professional design adjusts case by case for your home.