Finding the Right Commercial Solar System Size for Your Perth Business

Switching to solar power can significantly reduce operating expenses for businesses in Perth, while also providing energy independence and contributing to a sustainable future. However, one of the most important steps in making the switch is determining the correct commercial solar system size for your business.

Choosing a system that is too small can lead to heavy reliance on grid power and missed savings opportunities, while an oversized system can result in unnecessary costs and wasted energy generation.

This guide explains how Perth businesses can evaluate their energy needs, understand solar capacity options, and identify the ideal system size for long-term benefits.

Why Solar Sizing Matters for Perth Businesses

A properly sized commercial solar system in Perth, WA, ensures that your business maximises cost savings, minimises reliance on the grid, and gets the most value from available government incentives.

The right size also impacts payback periods, which can be particularly important for Perth companies where energy rates and peak usage patterns vary by industry.

Key benefits of getting the size right include:

Lower energy bills by covering most of your electricity needs with solar generation.
Faster payback period, as systems that match consumption offer the best return on investment.
Reduced demand charges if your system offsets peak energy use.
Future-proofing your operations, as a well-sized system can accommodate growth in energy demand.

Oversizing or undersizing can result in either higher upfront costs or an overdependence on grid electricity, so accurate calculations are crucial.

How to Calculate the Ideal Commercial Solar System Size

The following steps outline how to accurately determine the ideal commercial solar system size:

Step 1: Assessing Your Business Energy Consumption

The first step in determining size of the right commercial solar system in Perth is understanding your energy consumption patterns. This involves analysing when, where, and how much electricity your business uses daily, weekly, and seasonally.

How to Gather Your Energy Data

1. Review your electricity bills for the past 12 months

Look for total kilowatt-hours (kWh) consumed each month.
Identify seasonal variations (higher summer air conditioning loads or winter heating).

2. Use interval data if available

Many Perth energy retailers provide 15 or 30-minute interval data.
This helps identify peak demand times and whether your operations run heavily during daylight (when solar output is highest).

3. Account for operational changes

If you plan to expand your business, extend operating hours, or add new equipment, include the projected energy increase.

Understanding Daily and Peak Loads

Commercial solar systems are most effective when designed to offset your daytime loads. If most of your usage occurs at night, solar alone may not offset enough power without storage. In these cases, a combination of solar and batteries may be worth considering.

Step 2: Estimating Your Solar Generation Potential in Perth

Perth is one of Australia’s sunniest cities, with an average of around 5.8 hours of peak sun per day. This makes the city ideal for solar generation, but understanding your site’s solar potential is essential before selecting a system size.

Factors That Affect Solar Output

Roof orientation and tilt: North-facing panels at around 30 degrees generally produce the most energy in Perth.
Shading: Buildings, trees, or nearby structures can reduce generation.
Available roof space: The size and structure of your roof determine how many panels you can install.
System efficiency: High-efficiency panels and quality inverters can increase output from limited roof space.

For a rough calculation, a 1 kW solar system in Perth typically produces between 4.4 to 4.8 kWh per day on average, depending on conditions. This means a 30 kW system would generate roughly 132 to 144 kWh per day.

Step 3: Calculating the Right Commercial Solar System Size

Once you know your energy consumption and potential solar output, you can begin estimating the right size for your business.

Basic Sizing Formula:

To get a rough system size estimate:

System size (kW) = Daily energy use (kWh) ÷ Average daily solar production per kW (kWh)

For example, if your Perth business uses 300 kWh per day and a 1 kW system generates 4.6 kWh per day:

300 ÷ 4.6 ≈ 65 kW system size.

However, this is just a starting point. You’ll need to adjust based on:

Your peak demand times (matching solar generation with operating hours).
Energy tariffs and export limits (selling excess power to the grid may not always be profitable).
Future energy demand projections (business growth or electrification plans).

Step 4: Common Commercial Solar System Sizes in Perth

While every business is unique, there are common system sizes that suit different types of operations.

Small Businesses (10 kW – 30 kW)

Ideal for small offices, retail shops, and warehouses with modest daytime loads. These systems can offset a large portion of energy usage without requiring substantial roof space.

Medium-Sized Operations (30 kW – 100 kW)

Perfect for larger warehouses, supermarkets, and small manufacturing facilities. Many Perth businesses in this range aim to cover 50 to 80 percent of their energy needs during daylight hours.

Large Commercial and Industrial Sites (100 kW – 500 kW or more)

Manufacturing plants, distribution centres, and multi-shift facilities often benefit from large systems. Systems over 100 kW require additional approvals and can involve export limitations, so a professional feasibility assessment is crucial.

Step 5: Considering Batteries and Energy Storage

For many Perth businesses, solar alone may not cover all energy needs, especially for operations that continue after sunset. Adding battery storage allows you to store excess daytime solar energy and use it later, reducing reliance on the grid and improving energy resilience.

When Batteries Make Sense:

Your operations run heavily during evening hours.
You want to protect against rising electricity prices by storing more self-generated energy.
You face export limitations, meaning excess energy would otherwise go to waste.

While batteries increase upfront costs, they can improve your overall system efficiency and shorten payback time if your business has high evening energy use.

Step 6: Payback Period and Financial Considerations

System sizing directly impacts the financial return on investment. A correctly sized system generally pays for itself in 3 to 5 years, depending on your energy rates, system size, and available incentives.

Key Financial Factors to Consider:

Upfront installation cost: Larger systems cost more but often deliver lower cost per kW.
Electricity tariffs: Businesses on time-of-use tariffs can benefit more if their solar generation offsets peak charges.
Government incentives: Small-scale Technology Certificates (STCs) and potential feed-in tariffs can lower the net cost.
Financing options: Power purchase agreements (PPAs) or leasing can help manage cash flow for larger systems.

Oversized systems can stretch payback periods, especially if excess generation earns minimal returns from export tariffs. Conversely, undersized systems may miss out on significant savings.

Step 7: Professional Assessment and System Design

While you can estimate system size using your energy data, a professional solar provider can help you fine-tune the numbers. They use advanced tools to analyse interval data, model solar generation based on your specific site, and factor in future energy needs.

A commercial solar assessment typically includes:

On-site inspection of your roof and electrical systems.
3D solar modelling to account for shading and roof orientation.
Analysis of your energy bills and interval data.
Recommendations for solar panel types, inverters, and storage options.
Detailed financial modelling, including payback period and long-term savings estimates.

Conclusion: Making the Right Solar Investment

Finding the ideal commercial solar system size for your Perth-based business is a process that requires a detailed understanding of your energy consumption, your site’s solar generation potential, and your financial goals. The right system will reduce your electricity bills, deliver a strong return on investment, and help your business transition toward sustainable energy.

Working with experienced solar installers in Perth can ensure your system is tailored to your specific operations, both for today and the future. With Perth’s abundant sunshine and rising electricity prices, investing in the right-sized solar system is one of the most strategic decisions your business can make.