How do I calculate the solar system size I need?

Divide your monthly electricity bill by your tariff rate to get kWh consumption, then divide by your location's specific yield (kWh/kWp). For example, a $150 bill at $0.12/kWh = 1,250 kWh/month, requiring approximately a 9.5-10 kWp system in most climates.

What size inverter do I need for my solar panels?

Inverter size is typically 75-85% of your DC array size (a 1.15-1.35 DC/AC ratio). For an 11.5 kWp array, a 10 kW inverter is standard. Always check the inverter's maximum DC input voltage and MPPT voltage range.

How many solar panels do I need for a 5kW system?

With 550W panels, a 5kW system requires 9 panels (4.95 kWp actual). With 580W panels, you need 8 panels (4.64 kWp). Always round up to the next panel count to ensure sufficient winter generation.

What is the difference between lead-acid and lithium solar batteries?

Lithium LiFePO4 batteries offer 90% depth of discharge, 95% round-trip efficiency, and 6,000+ cycles. Tubular lead-acid batteries offer 50% DoD, 75% efficiency, and 1,500 cycles. Over 10 years, lithium has a lower levelized cost of storage ($0.15/kWh vs $0.43/kWh).

How much roof space do I need for solar panels?

A 550W panel is 2.58 m². With 30% fire setback, a 10 kWp system (18 panels) needs approximately 66 m² (710 sq ft) of roof area. Use our Spatial Fit Validation module with your actual roof dimensions.

What is DC/AC ratio in solar systems?

DC/AC ratio compares the DC panel array size to the AC inverter capacity. A 1.25 ratio means 11.5 kWp of panels on a 9.2 kW inverter. This oversizing is normal because panels rarely operate at nameplate power due to heat, irradiance, and angle losses.

How long does it take for solar panels to pay for themselves?

Solar payback periods range from 3-8 years depending on location, electricity rates, and system cost. In high-tariff markets like Germany or the UK, payback is faster. Lower-tariff markets see 6-8 year payback. Average system lifespan is 25-30 years.

What is the difference between P50 and P90 solar yield?

P50 is the median annual energy yield (50% probability of exceedance), used for financial projections. P90 is a more conservative estimate (90% probability), used for bankable loan assessments. P90 is typically 10-15% lower than P50.

Solar System Size Calculator — Free PV Sizing & Battery Tool

Solar Site Intelligence Report

Free Solar PV System Size & Engineering Calculator

Enter your Monthly Bill and Unit rate to check the system capacity you need.
Click any module to add it to this report. Each module checks a different aspect of the solar system - from space and hardware to costs and energy savings.

Global Baseline Calculated: 0.0 kWp

What Is Solar Metrix Pro?

Solar Metrix Pro is a free, browser-based solar PV engineering toolkit that lets you:

Size your solar system - enter your monthly bill & tariff rate to get kWp, panel count, and inverter size instantly
Simulate P50/P90 climate yield - uses 5 years of TMY weather data from your exact coordinates
Size batteries - compare tubular lead-acid vs lithium LiFePO4 with Ah/kWh and 10-year LCOS
Check hardware compatibility - MPPT string sizing with cold-weather voltage safety
Calculate ROI - payback period, 10-year ROI, and 25-year lifetime profit using P90 bankable yield
Compare vendor quotes - cost-per-watt audit with yield quality check

All data stays on your device. No signup required.

Who Can Benefit From This Solar PV Estimator?

Solar Installation Companies & EPC Contractors: Generate professional solar site survey reports for clients in minutes. Present bankable P90 energy yield estimates, inverter sizing recommendations, battery LCOS analysis, and competitive quote comparisons. Win more projects by showing clients exactly what they need with data-backed engineering.

Individual Solar System Installers: Quickly perform off-grid solar system sizing, on-grid PV system design, and hybrid solar configuration. Use the battery backup calculator to determine exact battery Ah rating and kWh needed for client loads.

Homeowners & Commercial Property Owners: Analyze your upcoming solar panel installation before making any commitment. Enter your monthly electricity bill and tariff rate to see what solar system size (kWp) you need. Get a 10-year return on investment projection and understand your solar payback period.

1. System Size Baseline (PV Sizing Engine) - Enter your monthly electricity consumption from your bill and tariff rate to calculate the required solar array capacity in kWp. Configure your preferred solar panel wattage to get exact panel count and string configuration.

Company & Client Info - Solar companies can add their company name, logo, website, and contact info alongside client name and site location to produce professional solar proposal reports.

Future Expansion Planner - Planning to add air conditioning, EV charger, water pump, or induction cooktop later? This module calculates the additional energy requirement (kWh) and recommends the right solar inverter size.

Spatial Fit Validation (Roof Area Calculator) - Enter your roof or ground area to check if your solar panel array will physically fit. Uses a 30% fire safety setback margin.

Geospatial Site Vectoring - Auto-detects your location to determine the optimal solar panel orientation (azimuth) and best panel tilt angle.

P50/P90 Climate Yield Simulation - Uses 5 years of historical TMY weather data from Open-Meteo to calculate your P50 expected annual yield and P90 bankable minimum.

Battery Backup Sizing Calculator - Calculate exactly what battery capacity (Ah and kWh) you need for your day and night loads.

Tariff & Storage Optimizer - Compares net metering (grid as battery) vs hybrid solar with battery storage.

Battery LCOS Analysis (10-Year Cost) - A levelized cost of storage comparison between tubular lead-acid and lithium-ion batteries over 10 years.

Hardware Compatibility (MPPT String Sizing) - Ensures your solar inverter MPPT specs match your PV module electrical characteristics.

Vendor Quote Audit - Compare solar installation quotes side-by-side. Calculates cost per watt (CPW) and flags inflated yield promises.

Soiling Loss & Cleaning ROI - Calculates daily revenue lost due to dust and dirt on solar panels and cleaning payback period.

System ROI & Financial Analysis - Get your complete solar investment analysis including annual savings, payback period, 10-year ROI %, and 25-year lifetime net profit.

Available Modules

0. Report Header

1. Core Sizing & Returns

2. Site Analysis

3. Hardware Configuration

4. Battery Storage

5. Procurement

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0. Report Header

1. Core Sizing & Returns

2. Site Analysis

3. Hardware Configuration

4. Battery Storage

5. Procurement

6. Maintenance

Solar Metrix Tools

SolarMetrix App

AI-Powered 5-Year Climate Engine for solar yield simulation, P50/P90 analysis & financial returns

Diagnostic Tool

Analyze actual solar performance vs physics targets, get system health score & detailed reports

Chemistry Class	10-Yr Hardware Buy	Hidden Heat Waste	Total 10-Yr Cost (LCOS)
Tall Tubular	--	--	--
Lithium (LiFePO4)	--	--	--

Solar Metrix Pro

Free Solar PV System Size & Engineering Calculator

What Is Solar Metrix Pro?

Who Can Benefit From This Solar PV Estimator?

Available Modules

0. Report Header

1. Core Sizing & Returns

2. Site Analysis

3. Hardware Configuration

4. Battery Storage

5. Procurement

6. Maintenance

Solar Metrix Tools

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Energy Generation Estimate (P50/P90)

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Battery vs Grid Comparison

Battery True Cost (10-Year LCOS)

Battery Backup Sizing Calculator

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Company & Client Details

System ROI Analysis

Panel Cleaning - Is It Worth It?