The size of the solar system you need depends on your home’s energy consumption rate, the available roof space and how you use energy throughout the day.
This guide explains how to calculate the right solar setup for your home, how common sizes compare, and how to decide whether you need a smaller system, a slightly larger system, or future capacity for a solar battery.
Table of contents
How solar system size is calculated
The easiest way to find out how many solar panels you’ll need is by grabbing your latest bill and doing a quick calculation.
Solar system size is calculated by matching your household electricity usage, available roof space, location, and expected energy output to determine the most suitable size and design.
To do it we work backwards.
- How much power do you use each day?
- Match with a system size that can generate that amount of power.
- Build a system based on roof space.
No. of panels = Size of the system (W)Â x Output of panel (W)
Let’s go ahead and make some calculations for your system.
Calculate the right solar system size for your home
You can calculate the right solar system size by working through your electricity usage, roof space constraints, sunlight levels, and future energy needs step by step.
This process mirrors how a solar calculator works, but understanding the logic helps you judge whether the result actually suits your electricity usage and home layout.
Step 1: How much electricity does your household use?
our household’s average daily electricity usage in kilowatt-hours (kWh) is the starting point for working out the best system size.
Your electricity bill shows how much power your home uses over a billing period. Dividing that total by the number of days gives your daily usage, which is what sizing calculations are based on.
As a general guide:
- Low-usage homes use under 10 kWh per day
- Average households use around 15–25 kWh per day
- High-usage households may exceed 30 kWh per day
The amount of electricity you use determines how much solar energy the system needs to generate to reduce reliance on the grid.
Step 2: How much roof space do I have?
Available roof space, combined with panel output, limits the size of the system you can install.
Once you determine daily power requirements, you can estimate system size and panel count, while confirming that your available roof space can support the system you want to install.
Modern panel size is 1.7m2. So if you require, for example, around 28kWh of power daily, a 6.6kW system is commonly suitable in many Australian homes, depending on location and roof conditions.Â
15 x 440W panels = 6,600W
Roof Orientation, tilt, shade from trees or nearby buildings, and roof obstacles all reduce usable space.
Step 3: Do you expect your electricity usage to increase?
Future energy needs should be included when calculating size to avoid installing a system that becomes too small.
If you plan to add an electric vehicle, install a solar battery, upgrade appliances, or electrify heating and cooking, your electricity usage will increase.
Considering your future electricity requirements often leads to choosing a slightly larger system if roof space and inverter limits allow. This helps ensure you install enough solar panels now rather than needing to upgrade later.
Step 4: Doing the math
Your solar system size is worked out by comparing your daily electricity usage to the typical energy output of a solar system in your location, then checking that the result fits your available roof space.
At this point, you already know:
- How much electricity your household uses per day
- How much roof space you have available
- Whether your usage is likely to increase over time
The final step is translating daily usage into a system size that can realistically produce that energy.
Rather than assuming a single fixed output, solar sizing uses a daily production range. This range accounts for differences in sunlight hours, seasonal conditions, and system losses.
Example sizing calculation
If your household uses around 25–29 kWh of electricity per day, a system in the 6–7 kW range is commonly suitable in many Australian locations.
| Daily electricity usage (kWh) | Typical system size | Approx. number of panels* |
|---|---|---|
| 10–14 kWh per day | 3–4 kW | 7–10 panels |
| 15–19 kWh per day | 4–5 kW | 10–12 panels |
| 20–24 kWh per day | 5–6 kW | 12–14 panels |
| 25–29 kWh per day | 6.6 kW | 15 × 440 W panels |
| 30–35 kWh per day | 8–10 kW | 18–24 panels |
A 6.6 kW system is widely used because it can produce enough solar electricity across most of the year to offset this level of daily usage, while still fitting on standard residential roofs.
Your exact result may vary depending on location, orientation, and shade, which is why calculators and installers work with ranges rather than fixed outputs.
Once this step confirms the system size and panel count fit your roof, you have a realistic answer to what size system you need before comparing options or getting quotes.
Solar system sizing chart
How many solar panels for a 5kW solar system?
Between 15 and 20 solar panels. It all depends on the power capacity of the solar panels you use during the installation. Most owners opt for the solar panels with outputs ranging from 250W and 330W.
If you use 250W solar panels, you’ll need around 20 panels for the 5kW solar system. But if you use 330w solar panels, you’ll only need 20 panels.
The trick to choosing panels for a 5kW solar system lies in your available roof space. If you don’t have a large space, go for the more expensive but efficient 330 – 350W panels.
But if space isn’t an issue, you can opt for the lower-priced, less efficient solar panels.
How many Solar panels do I need to power my home?
Approximately 20 – 28 solar panels. It will depend on the size and energy requirements of your home. Homes can be subdivided into small, medium, and large.
The more people who reside in your home, the more energy you’re likely to consume daily. Therefore, bigger homes need more solar panels than smaller homes. For instance, a 6.6kW solar system, which is a medium system serving 4 – 5 people, requires more panels than a 3kW or 4kW solar system serving 2 – 3 people.
 The table below shows how many panels you’ll need for your home, depending on the size.
| Suits home size | System size | No. of panels | No. of People |
|---|---|---|---|
| Small | 1.5KW | 6 | 1 – 2 |
| Small – Med | 2KW | 8 | 2 – 3 |
| Medium | 3KW | 12 | 3 – 4 |
| Med – Large | 4KW | 16 | 4 – 5 |
| Large | 5KW | 20 | 5 – 6 |
| X Large | 6KW | 24 | 6 – 7 |
| XX-Large | 7KW | 28 | 7 – 9 |
| Space Ship | 8KW | 32 | 9 – 12 |
How many solar panels do I need to run home utilities?
The average Australian home would require 6 – 14 solar panels to run the home utilities efficiently. This could include the refrigerator, the Air Conditioning unit, and Central air conditioning as well as the heated swimming pool.
A regular fridge rated 250W, running for 4 hours a day will consume about 1kW in a day. Assuming you have 300w solar panels, you’ll only need around 3 panels to run it.
Other devices like the AC would need about 2 – 4 solar panels while bigger consumers like a swimming pool, an outdoor bathtub, and maybe an electric vehicle may double your panel requirements to between 8 – 12 panels.
Keep in mind; these numbers are all subject to change depending on your location and solar system size.
Knowing the number of panels each home appliance will require makes it so much easier to determine the number of panels you’ll need for your home.
Should I OVERSIZE my solar system to save even more?
This is a common practice, especially going from a 5kWh to a 6.6kWh system. Basically, with the RIGHT size system and feed-in tariffs, you can save up to 90% of your total power costs.
If you get a system 20% larger than your home needs, you can eliminate 100% of your bills as the system sells more to the utility company than you need to use.
You’ll also receive a much larger rebate amount for a bigger solar system than you would for a small solar system. Oversizing your solar system will also streamline your path to getting a solar battery.
With your solar system generating a lot more electricity, an oversized system will produce more than enough power to run your home and also send the excess to the solar batteries.
For all these benefits, you should definitely oversize your solar system.
💡Pro tip: Many homeowners are weighing up a 6.6kW vs 10kW system to accommodate for a future EV purchase.
FAQs
Yes! Although running a house seemed impossible a few years back, advancement in solar technology now allows you to run an entire house with solar power. All you need is a highly efficient solar panel, good inverters, and reliable solar batteries.
