Solar System Size Calculator
How much electricity do you use, and what should solar cover?
Start from your monthly electricity units (from your electricity bill), this tool recommends a solar system size with a recommended range, plus the panels, inverter, DC/AC ratio, estimated annual generation and module area. Every number is labeled Calculated, Estimated or Preliminary so you always know what is certain and what is a planning figure.
Analysis Inputs
Choose one method to size from, your monthly usage is the most reliable. The other method stays available for comparison in the cross-check below.
Sizing basis: Bill-based consumption, only this method drives the sizing, so the result is never mixed.
Enter the exact kWh from your electricity meter when possible. Use the average from your last 6–12 bills for a more reliable result. This is the sizing input when "Monthly electricity units" is selected. The Monthly Usage box in the top bar fills this field automatically.
Your effective rate = bill ÷ units on a recent bill. Only used for the rough bill estimate in the cross-check below. Leave it blank and the bill estimate is skipped entirely.
Don't know your units? Estimate them from your bill, analysis only.
Warning: deriving usage from a bill is a rough estimate, electricity tariffs include tiered slabs, fixed charges, taxes and fuel adjustments, so bill ÷ rate under- or over-states real units.
Entering the exact kWh from your electricity meter is highly preferred.
Bill-based consumption appears in the consumption cross-check only; the system size always follows the units you enter above.
List the appliances you run. Power values are rated / input power, actual average consumption can differ considerably, especially for appliances with variable-speed operation (inverter ACs, modern fridges). The usage level scales each estimate toward an average.
Energy (kWh) is what sizes the array. Peak power (kW) is shown so an installer can check the inverter, the wiring and any backup system against the worst moment - it does not change the array size, and the inverter recommended below is chosen on the DC/AC ratio rather than on this figure.
Estimated Daily Load
-- kWh/day
Estimated Monthly Load
-- kWh/month
Peak Appliance Load
-- kW
Suggested System
-- kWp
Enter latitude and longitude or use Locate. Location is what makes this a real sizing tool rather than a rule of thumb: the calculator fetches five years of historical sun and temperature data for your exact coordinates and integrates it hour by hour, so sun hours, weather, temperature and sun angle are all specific to where you live. Without it you get a generic 4 h/day planning yield instead.
Optional — refine your estimate
The system is sized for current use plus this future margin, and both are shown in the results.
Affects how confident the P50/P90 range is, not the size of the system. The array is sized from your consumption and your location.
Does not change your required solar size — only how many panels it takes to build it.
-- kWp
Calculated requirement: -- · Practical configuration: --
Enter your usage to see the recommended range.
Enter your monthly electricity usage to calculate your system size.
Why this size?
Run a sizing to see the step-by-step calculation.
Estimated Annual Generation
--
Example Configuration
--
Recommended Inverter
--
DC/AC Ratio
--
Module Footprint
--
The system is sized to cover 100% of the monthly kWh you entered, using the solar resource for your location. Annual generation and module footprint are planning estimates, not guarantees.
Visual Analysis
Two charts: monthly generation vs consumption, and the inverter DC/AC comparison.
Monthly Consumption vs Solar Generation
Monthly solar output versus your monthly consumption. When location is enabled, production is estimated from historical weather data for your location; otherwise a latitude-based seasonal planning estimate is used. Actual generation varies with weather, temperature, shading, system losses and orientation.
Enter your usage to see the monthly profile.
With location enabled, the generated units come from five years of historical weather data for your coordinates; without it, from a generic planning yield. Your actual bill depends on generation timing versus your usage pattern and how exported electricity is compensated.
Detailed weather-based generation estimate and actual weather data analysis for your specific location.
Inverter Size Comparison
How the DC/AC ratio compares across the nearby standard inverter sizes (the two below and two above your recommendation). The green band is the preferred 1.15–1.35 range (above 100 kW, industrial inverters use their own tighter standard). Your recommended inverter is the highlighted bar. In simple terms: your panels are deliberately sized larger than the inverter's AC capacity — staying in the green band means the inverter runs efficiently without wasting solar.
This is a sizing comparison, not a final selection, verify the manufacturer's surge, MPPT voltage range and current limits before designing the system. The exact numbers are in the Installation Planning layer below.
Sizing Basis
Sizing Basis
Where the recommendation comes from, every input and result labeled.
Quick Answers (No Jargon)
Quick Answers (No Jargon)
Installation Planning (For Installers)
Installation Planning (For Installers)
Inverter candidate comparison
| Inverter | DC/AC | Result |
|---|
The recommended inverter is the best-fit candidate, not simply the next size above the array. Verify the actual manufacturer's surge and MPPT ratings before final design.
Panel options for your target size
| Wattage | Panels | Array (kWp) | Module footprint |
|---|
Estimated module area is a planning figure only, actual usable roof area depends on panel dimensions, orientation, access paths, setbacks and obstacles. Use the Roof Space Calculator for a real fit check.
Future load
Configuration notes
String configuration requires the panel's electrical specifications (Voc, Vmp, Isc, Imp) and the inverter model (max DC voltage, MPPT range, max input current, minimum temperature). This calculator does not guess a string design from a panel count.
Energy Performance
Generation confidence, methodology and environmental estimates.
Advanced Technical Analysis (For Engineers)
Advanced Technical Analysis (For Engineers)
Expected annual generation (P50)
--
Conservative annual generation (P90)
--
Specific Yield
--
P50 is the expected central production estimate; P90 is the conservative planning level used for risk assessment. When your location is enabled, these figures come from historical weather data for your location; otherwise they use a latitude-based planning baseline. For a bankable figure, run the Energy Yield location simulation (historical weather, P50/P90).
Calculation methodology
Run a sizing to see the step-by-step methodology.
Assumptions
Environmental Impact (estimate)
Environmental Impact (estimate)
A rough, indicative estimate using accepted conversion factors, not an exact figure.
🌍
CO₂ Emissions Avoided
-- kg/yr
🌳
Trees Planted Equivalent
-- trees/yr
⛽
Petrol Saved
-- L/yr
Estimates based on accepted conversion factors: ~0.82 kg CO₂ per kWh of grid electricity avoided, ~21 kg CO₂ absorbed per tree per year, and ~2.31 kg CO₂ per litre of petrol burned. Values are indicative, not exact.
Check the Space/Area required for this system
See the area required for the recommended system here, with your consumption, panel wattage and location already filled in.
Your system, sized here
Monthly consumption
--
System size
--
Panel wattage
--
Location
--
Next: does it fit, and will it deliver?
You have a system size. Three questions come next, and each one has its own tool.
Fitting on the roof
Roof Space Checker
Does the array actually fit your roof, with setbacks, obstacles and access for maintenance?
OpenReal generation
Energy Yield Estimation
What that size really produces month by month, and how wide the P50-to-P90 spread is.
OpenMoney math
ROI & Payback Analysis
Whether the system pays for itself at your tariff, and in how many years.
OpenEverything in one page
Open the Complete Setup Calculator
Analyze every aspect of your solar project, sizing, roof space, battery, yield, string design and ROI, in one place, and generate a downloadable report of your results.
Open Complete Setup CalculatorQuick estimate available on mobile
For detailed engineering analysis, charts, inverter comparison, P50/P90, sizing basis and the full installation planning layers, use the desktop view.
Curious how the sizing works? Read the System Size Calculator Guide — why location drives the result, peak load vs total load, and what the DC/AC ratio really means. Looking for a different tool? See the full calculator map — every tool, and the question each one answers — or browse the Learning Center.