Solar Panel Sizing Guide

1. What “array size” actually means

When we talk about a “4 kW solar array”, we mean the total peak DC power of all panels under standard test conditions. For example:

• 6 × 400 W panels ≈ 2.4 kW array
• 10 × 450 W panels ≈ 4.5 kW array
• 16 × 600 W panels ≈ 9.6 kW array

This is the starting point for estimates. Your actual energy over a year depends on how much sun you receive, roof direction, tilt and local climate.

2. The key ingredients in panel sizing

To size a solar array you need three main pieces of information:

1. How much electricity you use over a typical year (kWh).
2. How much solar energy 1 kW of panels can produce at your location in a year (kWh per kW of panels).
3. How much of your usage you realistically want to cover with solar (offset level).

SolarPVSizer assumes that you want to offset most of your annual usage with solar, with the understanding that actual self-consumption depends on load patterns, battery size and grid rules in your country.

3. How SolarPVSizer uses solar yield data

The tool queries a trusted external solar database for your coordinates and roof orientation. That database provides:

• Annual solar yield per kW of panels, often written as kWh/kWp per year.
• Monthly solar yield so the report can draw the production chart.

In the report this shows up as:

• Annual yield in kWh/kWp on the map tile.
• The bar chart of monthly production based on your chosen system size.

The annual yield figure is what connects your electricity use to the array size the calculator proposes.

4. The core sizing formula

Once the annual yield per kW of panels is known, the core calculation is simple:

Array size (kW) = your annual electricity use (kWh) ÷ annual solar yield (kWh per kW of panels)

SolarPVSizer does this in the background:

1. Converts your monthly kWh to an annual figure.
2. Fetches annual yield for your chosen tilt and direction.
3. Divides your annual load by that yield.
4. Rounds to a sensible figure with two decimal places.

If your site has above average sun, you will need less panel power for the same usage. If it has modest sun, you will need more panel power for the same usage.

5. Turning kW into number of panels

The report also shows an estimated panel count such as:

12 × 600 W panels

This comes from dividing the proposed array size by an assumed panel wattage. SolarPVSizer uses a modern panel size (for example around 600 W) to keep the count realistic for current products.

In practice, your installer may choose a different panel wattage that fits better on your roof, for example 420 W or 550 W modules. The key thing is the total kW of the array, not the exact panel size.

6. Roof area estimation

The tool also estimates the roof area required for the proposed array. It multiplies:

• The number of panels,
• By a typical panel footprint,
• Then adds a small allowance for gaps and walkways.

The result is shown as an approximate roof area in square metres and square feet. This is not a layout drawing, only a quick way to judge whether the suggested system size is physically realistic for your roof.

7. Why array size and inverter size are not always identical

In a real system the solar array rating and inverter rating do not have to be exactly the same. It is common to:

• Connect a slightly larger array to a given inverter to improve production in weaker months.
• Use a similar or slightly smaller array in very sunny locations.

SolarPVSizer:

• Sizes the array from your annual energy use and local solar yield.
• Sizes the inverter from your monthly use and typical power needs.

This means the ratio between array size and inverter size can vary slightly between locations and usage patterns. For a planning tool this is acceptable and reflects how systems are often tuned in practice.

8. What the panel sizing in your report is (and is not)

The panel sizing in your SolarPVSizer report is intended to be:

• A realistic starting point for system discussions.
• Grounded in local solar yield rather than generic “peak sun hours”.
• Expressed in both kW and an approximate panel count.

It is not:

• A final roof layout.
• A structural engineering check.
• A substitute for local electrical and building code requirements.

A qualified installer or designer should always check shading, roof structure, cable routes and formal compliance.