How Many Solar Panels Do I Need?

Last updated on April 9, 2025

A typical Australian home needs between 15 and 20 solar panels to power it fully, which is approximately equivalent to a 6.6kW system.

So, in most cases, a 6.6kW system with 15-20 panels is sufficient to offset a household’s electricity consumption. However, energy needs vary, and some homes may require larger systems (e.g., 10kW or more) if they use more electricity.

Australia is one of the sunniest countries in the world, receiving approximately 58 million petajoules of solar energy yearly (10,000x of the country’s energy needs).

With such an abundance, over 3.5 million Australian homes have embraced solar panels, making rooftop solar one of the fastest-growing energy trends.

Interestingly, this trend is not only driven by the abundance of solar energy.

Other driving factors include skyrocketing electricity costs, which increased in all regions by 49% to 134% in 2024 compared to the same quarter in the previous year, as reported by AER.

Moreover, Australia is slowly realizing the aftereffects of pollution and climate change due to burning fossil fuels to generate electricity. According to reports, more than a third of greenhouse gas emissions in the country come from electricity generation.

This calls for clean energy sources such as rooftop solar panels, which are a cleaner alternative.

But the big question an Australian going solar asks is, “How many solar panels do I need?”

Would 6.6 kW of solar be enough?

Will a 10-kW solar system be enough?

It’s a no-brainer that installing too few panels may leave you relying on the grid, while too many could mean unnecessary costs without significant returns.

So, How Many Solar Panels Do I Need?

How Many Solar Panels Do I Need infograph

To determine how many solar panels you will need for your home or your RV, you need to know multiple factors like your daily energy usage, peak sun hours in your location, size and rating of the solar system, and roof characteristics

If you need to save roof space, you may look at 100-watt smaller panels, where every 10 panels would equal 1 kW of power.

Wherever feasible, you should utilize all of the same kinds of solar panels instead of combining sizes or types. This will make it much easier to manage. If in doubt, opt for one more panel instead of one fewer.

Remember that rebates and government grants are offered in certain situations if your system qualifies at a certain level. That could affect your decision regarding how many solar panels you want to be installed.

The average break-even or payback period for a solar array in Australia is 4 to 6 years. If you looked into this some time ago, that may appear incredibly fast. More efficient solar panels, increased fossil fuel costs, and favourable government grants have resulted in these fast-break-even times.

How To Determine The Number of Solar Panels You Need

Determine Your Energy Consumption

Australian homes have different daily energy requirements determined by climatic factors, household size, and appliances used.

Based on the size of households, the Australian Energy Regulator estimates that a:

Three-person household: Consumes average daily energy usage of 18.71 kWh.
Four-person household: Typically consumes 21.355 kWh/day.
Five or more people: Usage increases to 25.43 kWh/day.

To determine your daily energy needs, check your utility bills. Most electricity providers indicate a household energy consumption over a billing period. For daily usage, you simply need to use the formula:

Daily Energy Consumption = Total Energy Consumption Over a billing period/ Days in the billing period.

Example

Suppose your account showed 600 kWh over a 30-day billing cycle. In this case, your daily electricity requirement would be

600 kWh/30 days =20 kWh/day

This would mean you use up to 20 kWh per day. You should, therefore, find the exact number of solar panels that can deliver such daily energy needs.

PRO TIP: Electricity use varies throughout the year. It can increase in summer due to air conditioning and in winter due to heating. Review your bills from different seasons to calculate an average daily usage and ensure your solar system meets year-round energy demands efficiently.

Consider Peak Sunlight Hours

Solar panels need sunlight to produce energy.

You must, therefore, determine the sunlight quantity in your region, measured as peak sunlight hours. Peak sunlight hours are the hours the sun is strong enough for solar panels to deliver their maximum capacity.

Although Australia receives sunlight for extensive periods, peak sun hours differ depending on the location. For instance:

Brisbane, Perth, Darwin: 5.5 – 6.0 hours/day
Sydney, Adelaide: 4.5 – 5.0 hours/day
Melbourne, Hobart: 4.0 – 4.5 hours/day

Assuming identical power usage, a home in Brisbane may need fewer panels than the same home in Melbourne.

Consider the following illustration to understand this better.

Assume two homes have identical energy needs – one in Brisbane and another in Melbourne. These homes install a 400W solar panel.

In Brisbane, where peak sunlight is 5.5 hours, the panel would give:

(400W × 5.5) ÷ 1000 = 2.2 kWh/day per panel

In Melbourne, with 4.5 peak sunlight hours, the solar panel delivers:

(400W × 4.5) ÷ 1000 = 1.8 kWh/day per panel

In this scenario, the solar output of the same solar panel in Brisbane is higher than that of Melbourne.

If homeowners in Brisbane need 10 solar panels, a typical one in Melbourne would need 11 to 12 panels to meet the exact needs.

When determining how many solar panels you need, consider their power rating, which is usually indicated in watts. The number of watts tells you the possible electricity the panel can produce under optimal conditions.

Check Solar Panel Power Rating

The most common solar panel wattage ratings in Australia are:

Lower-wattage panels: 300W
Mid-range panels: 350W – 400W
High-efficiency panels: 450W – 500W

Choosing higher-wattage panels means you need fewer of them than when working with low-wattage panels.

Let’s find out how with an example:

Suppose you require 20 kWh/day. If you choose a low-wattage panel like the 300W panel, it will give 1.5 kWh per day. The total number of panels you will need will be:

20kWh ÷ 1.5kWh = 14 panels

However, if you go for 400W panels, you will have 2 kWh/day. The number of panels needed would be:

20kWh ÷ 2kWh = 10 panels

Evaluate Roof Characteristics

Your roof size, angle direction, and shading determine how many solar panels you can install and how efficient they will be:

Roof Size

Solar panel sizes in Australia vary based on wattage

300W Panel → 1.6m² Approx 1.7m × 1m
400W Panel → 1.7m² Approx 1.8m × 1m
500W Panel → 2.2m² Approx 2m × 1.1m

To determine how many panels your roof can hold, divide your available roof space by the panel size

For example if your roof is 40m² and you use 400W panels 1.7m² each

40 ÷ 1.7 = 23 panels maximum capacity

Roof Angle

The best tilt matches your city latitude, e.g. Sydney 33°. A roof that is too flat or steep reduces efficiency by 10–20%, meaning you may need extra panels to compensate

Direction

North-facing panels get the most sunlight. East or west-facing panels generate 10–15% less power, so more panels may be needed to produce the same energy

Shading

Shadows from trees or chimneys can cut output by 20–40%. You may need more panels or optimizers to offset the loss.

Determine System Efficiency and Energy Losses

Even in the most optimal conditions, it’s likely that some electricity produced by your solar panels isn’t utilized effectively. An energy loss occurs for many reasons, which may force you to install additional panels:

Shading and Obstructions: Structures like chimneys and trees can impede the efficiency of modules.
Dirt and Debris: If not cleaned often, dust, leaves, and bird excrement can lower output by up to 2-5%.
Inverter Efficiency: Most inverters stand at 90-95%, meaning they lose 5-10% energy conversion.
Cable and Wiring Losses: Overly long cable runs tend to cause minimal voltage drops, which lowers output efficiency.

Specialists suggest increasing the overall size of systems by 10-20% to balance the losses. For example, a home that requires 10 panels would need 11 or 12 to guarantee adequate power production throughout the year.

Consider Future Energy Needs

Will your energy needs remain the same, or will there be an increase later on? An increase in consumption may happen when you:

Buy Electric Vehicles: If you buy an electric vehicle, your consumption will rise by 10–20 kWh/day. So, you will need more solar panels
Expand a Home: If you add more rooms, appliances like AC, or a pool, your power needs will rise, calling for more panels.
Extra Battery Storage: You will need more panels if you install more storage batteries. This is the only way to ensure you achieve full charge.
Family Growth: As your family grows, more energy will be needed, and so will the need for more panels.

Making plans for future growth in power use lets you get the right size now so you don’t have to deal with more installations later.

Factor in Costs and Government Rebates

In Australia, solar panels can cost between $3,500 and $12,000, depending on the system size, location, and quality of the panels.

Cost by system size is as follows:

3kW: Around $3,500–$5,000
5kW: Around $4,500–$7,000
6.6kW: Around $5,000–$8,500
10kW: Around $8,000–$12,000

This cost can affect the number of solar panels you need. For example, suppose you want approximately 10kW of solar power.

You could install two 5kW systems, costing $9,000–$14,000. Instead, opting for a single 10kW system, which would cost $8,000–$12,000, could save you money while delivering the same power output.

Government incentives further impact this choice.

The Small-Scale Renewable Energy Scheme (SRES) provides Small-Scale Technology Certificates (STCs), which can reduce upfront costs by $3,000 – $6,000, depending on your system size.

Additionally, states like Victoria offer solar rebates of up to $1,400, making solar more affordable. If you can access these and hold other factors constant, you can attain your desire to install more solar panels.

Get Expert Advice

Although DIY tools and calculators offer rough estimates, a professional solar installer will ensure you are not over- or under-provided with the number of panels required for your home. Experts evaluate:

Condition of the Roof: Does your roof have the capacity to bear the solar panels? If the answer is no, then reinforcement might be needed.
Shading & Placement: Professionals have access to solar mapping technologies, which determine which parts of the property are prone to shading and recommend an efficient layout of the panels.
Optimal System Size: They determine the exact amount of energy one requires, considering the inverter efficiency, panel degradation, and future power consumption.
Government Incentives: Assists in getting the maximum savings by guiding one through solar rebates, feed-in tariffs, and loans.

Calculating the Number of Solar Panels

The number of solar panels you need depends on your energy usage, panel wattage, and available sunlight. The formula is

Number of Panels = Total Energy Requirement kWh per day ÷ Panel Wattage kW × Sunlight Hours per Day

For example, if your home uses 30 kWh per day and you install 400 W panels in Sydney, where the average sunlight hours are 4.5 per day. You will need

Number o 40W f panel => 30 ÷ 0.4 × 4.5 = 17 panels

However, if you install a 300W panel, you will need

Number of 300W panels => 30 ÷ (0.3 × 4.5) = 23 panels

Final Thoughts:

The key factors above influence the number of solar panels you need.

Consider these when determining the panels required to meet your energy needs efficiently. Please never do things blindly! Make informed decisions to get the best results. If you need help, consult a reputable solar installation expert.