SIMPLE FORMULA
Annual consumption × target coverage ÷ 1,200
The result gives an approximate system capacity in kilowatts.
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PRACTICAL GUIDE · SYSTEM SIZING
How to size a solar system based on consumption
Sizing is one of the most important steps in a solar project.
A system that is too small will not meet your needs. A system that is too large will cost more without necessarily delivering a real benefit.
This guide presents a simple method for establishing a realistic first estimate.
01
Start with your actual consumption
The starting point is your annual consumption in kilowatt-hours, ideally calculated over the last twelve months.
| Illustrative profile | Illustrative annual consumption |
|---|---|
| Small household / condo | 6,000 to 9,000 kWh/year |
| Average home | 12,000 to 16,000 kWh/year |
| Large home with an electric vehicle | 20,000 kWh/year or more |
| Three-season cabin | Highly variable depending on use |
These figures are general reference points. Your actual statements remain the best basis for calculation.
02
Define your target coverage
The right target depends on grid access, budget, roof conditions and how surplus energy will be used.
| Goal | Illustrative coverage | Why consider it |
|---|---|---|
| Bill reduction | 40 to 60% | A practical starting point when roof area or budget is limited |
| Partial autonomy | 60 to 80% | A common balance between production, use and investment |
| High coverage | 80 to 100% | Requires closer analysis of surplus production, seasons and storage |
These percentages are reference points, not universal recommendations. A grid-connected project must also account for net-metering rules.
03
Estimate the required capacity
Hydro-Québec uses a provincial average of about 1,200 kWh generated per year for each installed kilowatt.
EXAMPLE
12,000 kWh × 70% ÷ 1,200 = about 7 kW
This calculation is a starting point. A location-specific simulation should confirm expected production.
Actual production varies with location, orientation, tilt, shading, snow and system losses.
04
Adjust for the real context
ROOF
Orientation and tilt
A south-facing array is often favourable, but an east-west layout can also be relevant depending on the consumption profile.
ENVIRONMENT
Shading and snow
Obstacles, snow accumulation and seasonal conditions can significantly change production.
ARCHITECTURE
Inverter and storage
The inverter type, battery storage and interconnection limits influence the final configuration.
05
Common mistakes to avoid
- Sizing from a single high-consumption month
- Automatically targeting 100% without analysing surplus production and seasonal variation
- Ignoring system losses or counting them twice in the calculation
- Overlooking actual orientation, shading or available area
KEY TAKEAWAY
Good sizing starts with your consumption and your goal.
The simplified calculation provides a first estimate. Final sizing should be confirmed through a site assessment and, for a grid connection, by a qualified contractor.
Source: Hydro-Québec — Solar panels ↗
Source: Natural Resources Canada — Photovoltaic potential ↗
FROM ESTIMATE TO PROJECT
Would you like to validate your initial sizing?
Describe your consumption, roof and goal to clarify the next steps.