What size solar system do I need for my home?

System size depends on your annual electricity usage. Divide your annual kWh by your province's solar production factor (typically 1,000-1,200 kWh per kW). A home using 10,000 kWh/year in Ontario needs approximately 8-10 kW. Our calculator provides precise sizing based on your actual usage.

How many solar panels do I need?

Divide your system size (in watts) by your panel wattage. For example, an 8 kW system with 500W panels needs 16 panels. Each 500W panel is about 24 sq ft, so 16 panels need roughly 384 sq ft of usable roof space.

Should I oversize my solar system?

It depends on your province's program. With net metering, slight oversizing (10-15%) accounts for panel degradation and ensures you generate enough over the system lifetime. For zero-export systems (Ontario), oversizing wastes production since excess energy is curtailed.

How does roof space affect system size?

After accounting for obstructions (10%) and shading, usable roof space determines maximum panel count. A 1,000 sq ft south-facing roof with minimal shade can fit about 28 panels (14 kW). Complex roofs with dormers, vents, and shade may only fit 60-70% of theoretical maximum.

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What Size Solar System Do I Need?

Find the right solar system size for your home based on your electricity usage, roof space, and province. Simple sizing guide with usage-to-system mapping.

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Usage-to-System Size Guide

Find your approximate system size based on annual electricity usage. Sizes vary by province due to differences in solar irradiance.

Annual Usage	Approx Bill	Ontario Size	Alberta Size	Panels (500W)	Min Roof Space
5,000 kWh/yr	$55-65/mo	5 kW	4 kW	8-10	200 sq ft
8,000 kWh/yr	$85-100/mo	7 kW	6 kW	12-14	310 sq ft
10,000 kWh/yr	$110-130/mo	9 kW	8 kW	16-18	400 sq ft
12,000 kWh/yr	$130-160/mo	10 kW	9 kW	18-20	470 sq ft
15,000 kWh/yr	$165-200/mo	13 kW	11 kW	22-26	580 sq ft
20,000 kWh/yr	$220-260/mo	17 kW	15 kW	30-34	780 sq ft

Ontario sizes based on 1,100 kWh/kW production factor. Alberta based on 1,300 kWh/kW. Roof space includes 2.5cm panel spacing.

How to Determine Your System Size

Find Your Annual Usage

Check your utility bills or online portal for total annual kWh. Most Ontario households use 8,000-12,000 kWh/year. If you only have monthly bills, multiply by 12.

Calculate Base System Size

Divide annual kWh by your province's production factor. Ontario: ÷ 1,100. Alberta: ÷ 1,300. BC: ÷ 1,050. Example: 10,000 kWh ÷ 1,100 = 9.1 kW for Ontario.

Check Roof Space Constraints

Each 500W panel needs ~24 sq ft. After 10% obstruction and shading allowances, ensure your usable roof area fits enough panels. South-facing sections are ideal.

Adjust for Program Type

Net metering: add 10-15% for degradation buffer. Zero-export (Ontario): size to daytime consumption only, as surplus is curtailed. Battery: size system to charge battery + cover daytime usage.

Oversizing vs Right-Sizing

When Oversizing Makes Sense

You have net metering with full retail credits
You plan to add an EV or heat pump in the future
You want to account for 25 years of panel degradation
Your province allows systems larger than annual usage

When to Right-Size

Zero-export system (Ontario) — surplus is wasted
Export credits are much lower than retail rate
Budget is a constraint — invest in battery instead
Ontario 10 kW AC inverter limit applies

Get Precise System Sizing for Your Home

Our calculator analyzes your actual roof dimensions, shading, and usage patterns for precise panel count and system size.

Get Your Free Estimate

What Size Solar System Do I Need?

Usage-to-System Size Guide

How to Determine Your System Size

Find Your Annual Usage

Calculate Base System Size

Check Roof Space Constraints

Adjust for Program Type

Oversizing vs Right-Sizing

When Oversizing Makes Sense

When to Right-Size

Get Precise System Sizing for Your Home

Frequently Asked Questions

Related Resources

Solar Panel Cost Canada

Best Solar Panels Canada

Solar Payback Period

Methodology

Net Metering Canada

Solar Calculator