What Size Solar System Should I Get?

Choosing the right size for your solar system is crucial for maximising both energy production and financial returns. But how do you determine what size is the best fit for you? This guide walks you through key steps to make an informed decision.

What Does “System Size” Mean?

When it comes to solar energy, “system size” is a term that relates to the overall electrical output capability of your solar setup, usually denoted in kilowatts (kW). Essentially, this number tells you how much electricity your solar system can produce when it’s operating at peak performance.

In Australia, common system sizes typically range from smaller configurations like 5 kW to mid-range options like 8 kW, and go up to larger setups of 10 kW or more.

To put these common system sizes in perspective, consider a common scenario: an 8 kW solar system. This means that, under ideal conditions, it has the potential to generate 8 kilowatts of electrical power per hour (kWh), which is the standard unit of energy you’ll find on your electricity bills and frequently used in energy discussions. That 8kWh could power a combination of the following appliances:

Appliance	Energy Usage (kWh per hour)
Refrigerator	0.1 – 0.8
Air Conditioner (Window Unit)	1 – 2
Washing Machine	0.2 – 2
Clothes Dryer	2 – 6
Dishwasher	1 – 2
Oven	2 – 5
Microwave	0.6 – 1.5
Television	0.05 – 0.4
Computer	0.05 – 0.2
Vacuum Cleaner	0.5 – 1.5
Water Heater (Electric)	3 – 5

Why Does “System Size” Matter?

Solar is an investment for your home – you invest money now, up-front to buy the system (or arrange finance), and it returns savings (lower energy bills) over the life of the solar system which is the return on your investment. If done well this can result in a great return for your up-front money – higher than having the money sit in a bank account for example. However, if you miscalculate, you could end up with underwhelming returns.

A common mistake is incorrectly sizing your solar system. Both under-sizing and over-sizing come with their drawbacks, affecting your return on investment (ROI).

For example if you:

• Choose a system that’s too small, you’ll incur similar installation costs to a larger setup, but generate less power than you need. This essentially means you’ve overinvested in a system that doesn’t provide the savings you expected. You’ll find yourself still relying on grid electricity to fill the gap, which reduces the financial benefits and overall effectiveness of your solar investment.
• Choose a system that’s too large, and you’ll generate more power than you need, but at a higher upfront cost. While you might be able to sell some of this excess power back to the grid, the rate is usually lower than what you’d pay to buy power during cloudy or nighttime hours. Additionally, there may be a cap on how much power you can sell back, meaning some of your generated power goes to waste and generates no return for some of what you spent on your system up-front.

Choosing an appropriately sized system which takes into account your current and future energy usage, export limits and feed-in tariffs is integral for achieving optimal system efficiency and long-term reliability.

How To Work Out What System Size You Should Get

Working out what size system you need involves several steps:

Step 1: Work out How Much Energy You Will Need Now and in the Future
The first step in determining the ideal solar system size is to understand your annual energy consumption. To do this, gather at least a year’s worth of electricity bills to calculate your average daily usage. This annual approach accounts for seasonality, providing a more complete picture of your energy needs.

If you’re considering adding a solar battery to your setup, don’t forget to factor in its charging needs. Batteries offer the advantage of storing excess solar energy generated during the day, enabling you to use it during peak periods or power outages. The energy needed to charge the battery should be incorporated into your overall energy calculations.

Finally, it’s crucial to consider your future energy needs. Are you planning to purchase energy-consuming appliances like air conditioning units or electric vehicles? These additions will increase your future energy usage and should be taken into account when determining your ideal system size.

By assessing both your current and future energy needs on an annual basis, you’ll be well-equipped to make an informed decision about the size of the solar system that will best meet your requirements.

Step 2: Consider Electrical and Network Limitations
After you’ve determined your energy needs, the next action is to understand the electrical and network limitations that might apply. A vital aspect to examine is whether your home is supplied with single-phase or three-phase electricity.

• Single-Phase: Most Australian homes are on a single-phase electricity supply, suitable for typical residential requirements. For these homes, the maximum solar system size is 13.33 kW of panels with a 10 kW inverter.
• Three-Phase: Larger homes or those with more substantial energy needs may have or require a three-phase supply. This setup allows you to install up to 13.33 kW of solar panels and a 10 kW inverter per phase.

Being aware of your electricity network’s export limitations is also crucial. These rules specify the amount of surplus energy you can return to the grid, and exceeding these limits can result in financial or technical complications. For a single phase installation, export limitations are generally capped at 5 kWh. For a three-phase installation the export limitation is typically 15 kWh (5 kWh x 3 phases). This means that if your system is too big, any excess energy produced over and above what you consume and the export limit – is lost, making it essential to get your system size correct.

Step 3: Choose Your Equipment and Make Sure Any Limitations Are Taken into Account
Selecting the right equipment is crucial in determining your solar system size. Your choices regarding solar panels, inverters, and possibly batteries will significantly influence both the system’s performance and cost.

For solar panels, you have options for higher-wattage models that yield more electricity but come at a higher price. Alternatively, lower-wattage panels may be more budget-friendly but require more roof space. It’s a trade-off between upfront costs and power output.

When it comes to inverters, it’s an industry standard to oversize your solar panel capacity by 1.3 times the inverter’s capacity. The main reason for this is to ensure the inverter operates at maximum output consistently, thus optimising the overall system efficiency. For example, if you opt for a 10 kW inverter, you should aim for 13 kW of solar panels to maximise system performance.

When pairing panels and inverters you’ll also need to be aware of and take into account any limitations, such as panel and inverter compatibility. For instance, a 500W panel may be limited if paired with a 350W micro inverter.

If you’re considering adding a battery to your system, this will also influence the size of the solar setup you’ll need. Batteries are measured in kWh, much like your panels, and the size you choose should align with both your daily energy usage and the amount of solar production you aim to store. A battery allows you to utilise more of the solar energy you generate, thereby potentially reducing the size of the solar system needed.

By taking into account all these factors—panels, inverters, and batteries—you’ll be better equipped to decide on a solar system size that not only meets your energy needs but also adheres to any technical and financial constraints you may have.

Step 4: Can the Equipment Fit?
Theoretical calculations can provide a strong foundation, but it’s essential to consider the physical limitations of your property. Knowing your ideal system size is one thing; fitting it onto your roof is another.

Your roof’s dimensions, its structural integrity, and the available space for an inverter all play significant roles in the planning process. Panel orientation is another critical factor, as it directly impacts energy production. Even if the numbers make sense on paper, practical constraints could dictate adjustments.

It’s important to remember that the goal is not just to install a solar system but to install one that operates optimally in your specific setting. Issues like shading, roof angle, and even local regulations might necessitate smaller or differently arranged setups.

Example System Size Calculation

While a basic understanding of your energy needs is a good starting point, real-world calculations should be more detailed.

Here’s how to approach it step-by-step:

• Annual Energy Consumption: Let’s say your annual energy consumption averages to 6,000 kWh, considering seasonality factors like increased air conditioning in summer or heating in winter.
• Daily Energy Consumption: Divide your annual energy consumption by 365 days to get an average daily consumption. In this example, 6,000 kWh / 365 = approximately 16.4 kWh per day.
• Future Energy Needs: Planning for the future, such as charging an electric vehicle, you add an extra 5 kWh, making it 21.4 kWh per day.
• Electrical Infrastructure: Assume you have a single-phase electrical setup with an export limit of 5 kWh.
• Net Energy Needs: Adding the export limit to your daily needs, your system should ideally produce 26.4 kWh per day (21.4 kWh for personal use + 5 kWh for export).
• Panel Efficiency: You decide on high-efficiency panels rated at 440W each – which is the watts they output at peak performance (0.44kWh)
• Panel Output: Although the panels can produce 0.44kWh each per hour, its not peak sunny conditions 24 hours a day and other factors can influence their performance such as temperature. So for this example, we assume over a year, in our location, each panel outputs 70% of its maximum for an average of 5 hours per day = 1.54kw per day output per panel.
• Panels Needed: we want to produce 26.4 kWh per day and each panel can output 1.54kw per day, meaning we need 17.14 panels.
• Total System Size Needed: To meet the 26.4 kWh net energy needs, we need approximately 18 panels at 440W each. This is a system size of 8kW (440w x 18 panels) and would be support with a 6.15 kW inverter, adhering to the industry standard ratio of 1.3x panel capacity to inverter size.

By following this comprehensive example, you’d need an 8 kW system consisting of roughly 18 panels at 440W each and a 6.15 kW inverter. This meets your daily energy requirements while also allowing for grid export, optimising your solar investment.

How Professionals Like Arkana Calculate System Size Requirements

Sound easy so far? While the example calculation above gives you a basic understanding, it doesn’t cover all the factors that professionals take into account. This is where CEC-accredited solar system designers like 1KOMMA5° come into play.

We dive into the details, considering variables like your roof size, its orientation and tilt, as well as seasonal fluctuations in both energy usage and production. Shading issues and production losses due to heat are also considered. With advanced computer systems and a wealth of experience from over 10,000 installations, we can virtually model how sunlight will interact with your roof throughout the entire year.

Working closely with you, the homeowner, we develop a tailored plan that goes beyond general estimates. Although it’s helpful to have a rough idea of what system size you’ll need, entrusting this critical step to experienced professionals ensures you get a solar system that truly maximises your investment and meets all your energy needs.

Conclusion

After assessing your current and future energy needs, understanding your electrical and network limitations, and meticulously choosing your equipment, you’re now well-equipped to decide on the size of your solar system. It’s a decision that requires balancing various factors, including your home’s energy consumption, the physical space available for installation, equipment specifications, and budget.

This process might seem complicated, but remember, you’re making a long-term investment that will not only reduce your energy bills but also contribute to a more sustainable future. Consulting with experts, like our team at 1KOMMA5°, can provide invaluable insights tailored to your specific circumstances, helping you make the most informed choice possible.