Have you ever wondered, “What size solar system do I need for my home?” You’re not alone. This is one of the most common questions among Aussie homeowners considering a switch to solar energy. 

With the rising cost of electricity and the increasing awareness of our environmental footprint, more and more Australians are looking to solar power as a solution. But figuring out the right size for your solar system can feel overwhelming.

As a company that has helped countless households transition to solar and we get it, you want to make sure you’re getting the right setup without overspending or undershooting your needs. 

In this article, you’ll learn exactly how to determine the best-sized solar system for your home, ensuring you get the most bang for your buck.

Ready to shine some light on your solar journey? Let’s dive in.

Understanding Your Energy Needs

Before you can decide on the right size solar system, you need to understand your household’s energy consumption. This isn’t as complicated as it sounds. Here’s a simple 3 step guide to help you get started:

1. Check Your Energy Bills:

Grab your recent electricity bills and look at the “usage” section. This shows how much energy your household uses each day, usually measured in kilowatt-hours (kWh). It’s a good idea to look at bills from different seasons to get an average annual usage since energy consumption can vary throughout the year. (This is also why at Lenergy we request 3 electricity bills in our quoting process.)

2. Calculate Your Daily and Monthly Usage:

Most bills will show your daily average usage. If not, you can divide your total monthly kWh by the number of days in the billing period. For a more accurate annual estimate, add up your total usage for the year and divide by 365.

Example Calculation:

Suppose your bills show a usage of 2160 kWh for the quarter. 2160kWh ÷ 90 Days in the period = an average daily usage of 24kWh (remember this number we will use it later 🤭).

3. Consider Future Changes:

Think about any future changes that might affect your energy consumption. Planning to buy an electric vehicle? Adding a pool? Expecting an addition to the family? These changes can increase your energy needs.

Why This Matters:
Understanding your current and future energy needs helps you size your solar system correctly, ensuring it can cover your consumption and maximise your savings. For instance, we would size your solar system from your winter usage as typically, everyone uses more electricity in winter than summer, and this is also when your future system won’t be producing as much. This ensures your usage is matched in winter and that you will be in credit during the warmer months. 

How to Calculate the Right Solar System Size

Now that you know your energy needs, let’s get into the calculation.

Determine Your Peak Sun Hours:
Peak sun hours are the hours during which sunlight is strong enough to generate a significant amount of solar energy. In Australia, this typically ranges from 2 to 7 hours per day depending on your location.

Calculate the System Size with this simple formula:

System Size (kW) = Daily Energy Usage (kWh) ÷ Peak Sun Hours

​At Lenergy we use a conservative average of 3.6 peak sun hours to determine the approximate size solar system necessary for your needs. This is then cross-checked using our solar designing software.

For example, if your daily usage is 24 kWh and you get 3.6 peak sun hours per day, your system size would be:

Inverter System Size: 24 kWh ÷ 3.6 hours = 6.66kW

So to produce 24kWh per day, you need at least a 6.6kW inverter. 

It is also industry best practice to oversize the inverter up to 33% to account for heat and cable losses and provide a more constant output. 

This means we oversize the solar panels that are paired with the inverter. For example 7.92kW of solar panels on your 6.6kW inverter. 

Customer Case Study:

One of our customers was using 24kW a day and after evaluating their usage, goals and future plans, we sized a 7.92kW system for them.

This tailored solar system came to $7,130.46 with a substantial STC rebate saving of $3,349.50.

Because this system was correctly sized to meet their current usage and future plans, their return on investment is outstanding. The careful sizing ensures they’re not just covered for today’s energy needs, but also prepared for any future increases in usage. As a result, their payback period is impressively short, just 2-3 years. With a remarkable 620% return on investment, they’re seeing substantial financial benefits. 

Additionally, they’re saving $2,339.39 annually on their electricity bills. This means more money in their pocket every year! Investing in the right solar system has proven to be a wise financial decision that offers both immediate and long-term rewards.

Other Factors Influencing Solar System Size

Roof Space and Orientation: 
The amount of roof space you have and its orientation (north, south, east, west) can affect how many solar panels you can install and how efficiently they will produce energy. North-facing roofs are ideal in Australia as they receive the most sunlight throughout the day.

The Angle of Solar Panels:
The ideal angle for solar panels is approximately 30 degrees facing north. For roofs with a lower angle, i.e. 5 degrees, we can either install tilts or increase the system size to compensate for a sub-optimal angle.

Available Budget:
Solar systems come in various sizes and prices. Your budget will influence the size and type of system you have installed. Remember, while larger systems have a higher upfront cost, they often lead to greater savings in the long run.  But you don’t have to navigate this alone. That’s why solar companies often recommend starting with a call. We can assess your current and future energy needs, along with your budget, to help determine the optimal size of your solar system.

There are several financing options available to make solar energy more accessible, including $0 upfront payments and low % finance plans. 

Additionally, the recent announcement of the Home Energy Upgrade Finance (HEUF) with Plenti introduces further discounted green loans for solar and battery installations.

A green loan is a financing option specifically designed to support environmentally friendly projects, such as solar and battery installations. These loans typically offer lower interest rates and favourable terms to encourage the adoption of sustainable energy solutions and reduce the environmental impact.

This HEUF  initiative offers homeowners an affordable and attractive way to transition to solar power, ensuring that financial barriers are minimised while maximising the benefits of renewable energy.

Energy Goals:
Are you aiming to be completely energy-independent or just offset a portion of your energy usage? Your goals will dictate the size of your solar system. For example, if you aim to go off-grid or use power at night, you’ll need batteries. 

In addition to the recent announcement of the Home Energy Upgrade Finance (HEUF) with Plenti, starting in November 2024 a home solar battery rebate will launch, making it even more cost-effective to incorporate batteries into your solar system for greater energy independence.

Common Pitfalls and How to Avoid Them

Avoiding mistakes when sizing your solar system is crucial for getting the most out of your investment. Here are some common pitfalls and how to avoid them:

Overestimating Your Needs:
While it’s good to plan for future energy increases, don’t go overboard. Installing a system that’s too large can lead to unnecessary costs and wasted energy.

Underestimating Seasonal Variations:
Energy production and usage can vary with seasons. Ensure your system can handle peak demand during less sunny months. 

Ignoring Shading Issues:
Trees, buildings, and other obstructions can significantly impact solar panel performance. Whether you need a microinverter over a string inverter system will influence your upfront cost, as well as your return on investment. 

Not Accounting for System Degradation:
Solar panels lose efficiency over time. Factor in a slight degradation rate when calculating your system size to ensure long-term performance. Most high-quality solar panels have an annual degradation of approximately 0.4%, which means they will be about 90% efficient after 25 years.

It is important to choose a quality panel that is going to withstand the test of time and the elements and fit your exact location needs. 

Watts Next?

Now that you have a better understanding of how to size the right solar system, you’re in a much better position to make informed decisions. When you receive your quotes, you’ll know exactly what to expect, ensuring that you get the most out of your investment and maximise your savings.

However, the process can still feel overwhelming, and that’s perfectly normal. Consulting with a solar expert can offer personalised advice tailored to your specific needs, giving you peace of mind. They can answer your questions, address your concerns, and help you navigate any uncertainties.

Investing in solar energy is a significant step towards a more sustainable future and financial savings. By correctly sizing your solar system, you’re not just making a smart financial decision, but also contributing to a greener planet.

So, take your time, consult the experts, and rest easy knowing you’re on the right path to a brighter, more efficient future.