System Size Guide
Compare 3kW, 5kW, 10kW, and 15kW packages with panel counts, roof space needs, and battery capacities.
Engineering-Grade Solar & Battery Sizing Calculator • 2026 Edition
Free Solar Calculator: Panels, Battery & Payback Sizing
Calculate how many solar panels, inverters, and LiFePO4 batteries you need from your electric bill or monthly kWh. Instant 25-year financial ROI, PEC & NEC wire sizing, and free engineering proposals.
Interactive Solar Estimator
Instant Solar System Sizing & Generation
Adjust your monthly electricity consumption below to instantly forecast recommended rooftop solar capacity, panel count, required roof area, and expected annual clean energy generation.
Currency & Regional Cost Calibration
Adjusts tariff rates & turnkey cost
Location & Solar Irradiance
Calibrates peak sun hours
Average Monthly Electricity Bill
Drag slider or enter exact bill
Calibrated for 4.0 Peak Sun Hours (PSH) & 550W Tier-1 modules. Tailor specific irradiance, battery autonomy, and local tariffs in the full calculator.
System Size
5.5 kWp
Roof Area
~24 m²
Estimated Annual Savings
$1,296 / yr
Payback Period
5.2 Years
Solar Engineering Hub
Explore Sizing Guides & System Architectures
Everything you need to plan, size, and verify your rooftop solar and energy storage installation.
System Architectures
Learn the vital differences between Grid-Tied, Hybrid with Storage, and Off-Grid standalone architectures.
Engineering Standards
Review our 14-formula calculations compliant with Philippine Electrical Code (PEC Art 6.90) and NEC 690.
Solar FAQ & Help
Clear answers to questions regarding air conditioning loads, LiFePO4 battery lifespan, and net metering credits.
Solar Engineering Principles
How to Calculate Solar Panels & Battery Storage
Understanding the mathematical relationship between electric bill consumption, geographic irradiance, and battery autonomy.
1. Daily Kilowatt-Hour Demand
Rooftop solar sizing begins by determining your average daily energy usage in kilowatt-hours (kWh). Divide your monthly electric bill kWh by 30 days. For instance, a household consuming 450 kWh per month requires an average of 15 kWh per day. Sizing tools separate this into daytime consumption (directly powered by solar PV) and nighttime consumption (drawn from battery storage or the utility grid).
2. Peak Sun Hours & Derating
Solar irradiance varies by location. Peak Sun Hours (PSH) represent the equivalent hours of full 1,000 W/m² sunlight your roof receives daily—ranging from 4.0 to 5.5 PSH in tropical countries like the Philippines. Professional engineering applies a 1.30 safety factor (20% system derating) to compensate for ambient heat coefficients, inverter conversion efficiency (~97%), wiring resistance, and dust soiling.
3. LiFePO4 Battery Bank Sizing
Energy storage is sized based on nighttime critical loads and required autonomy days. Modern Lithium Iron Phosphate (LiFePO4) chemistry allows up to 90% Depth of Discharge (DoD) without rapid cell degradation, delivering over 6,000 charge cycles (15+ years). For example, a 10 kWh nightly demand is reliably met by a modular 10.24 kWh (2x 51.2V 100Ah server racks) 48V battery bank.
Quick Answers
Frequently Asked Solar Sizing Questions
Essential answers to help you plan your rooftop solar system, estimate costs, and choose hardware.
A standard 5kW (5,000 Watt) residential solar installation requires 9 to 10 monocrystalline panels using modern 550W Tier-1 modules (550W × 9 = 4.95 kWp, or 550W × 10 = 5.5 kWp). This array needs roughly 22 square meters (236 square feet) of unshaded rooftop space and generates an average of 600 to 750 kWh of clean electricity each month, offsetting typical monthly electric bills between $100–$180 (₱7,000–₱13,000).
Yes! A standard 1.0 HP to 2.0 HP inverter air conditioner draws between 800W and 1,800W of electrical power. A 5kW system generates up to 5,000W during peak sunny daylight hours, easily running 2 to 3 inverter air conditioners simultaneously while powering refrigerators, computers, and lighting. If paired with a 10 kWh LiFePO4 battery bank, you can also run an air conditioner overnight for 8 to 10 hours during utility power outages.
A Grid-Tied system has no battery; it synchronizes with your electric utility to lower daytime power bills and exports surplus energy through Net Metering, giving you the fastest payback (3 to 5 years). However, it shuts off during blackouts. A Hybrid system adds an intelligent LiFePO4 battery bank, providing seamless uninterruptible power supply (UPS) within 10 milliseconds during utility brownouts while still staying connected to the grid.
Most residential solar systems achieve complete financial payback in 3.5 to 6 years for grid-tied systems, and 4.5 to 7.5 years for hybrid systems with battery storage. Over a full 25-year lifecycle, Tier-1 solar panels continue generating power at over 80% of their initial rated capacity, yielding massive cumulative savings and shielding homeowners from recurring utility electricity tariff inflation.
Our interactive AI Solar Engineering Advisor runs directly alongside your live calculation inputs. It analyzes your daily kilowatt-hour demand, geographic peak sun hours, and battery storage targets to answer specific technical questions—such as comparing hybrid inverters vs grid-tied units, sizing wire gauges according to Philippine Electrical Code (PEC Art 6.90), and optimizing LiFePO4 battery lifespan.
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