What size solar system you need depends on one number: how much electricity your household uses each day. For most Melbourne homes, a 6.6kW solar system covers daily usage of 16 to 22 kWh. That suits a family of two to four people with moderate appliance use. Understanding how solar works helps with sizing decisions, but the consumption calculation is the same regardless of system type.
Larger households, homes with a pool or EV, and all-electric homes converting from gas will typically need 10kW or more. Getting the size right matters as much as getting the brand right. An undersized system leaves bill savings on the table. An oversized system, however, may export most of its generation at low feed-in tariff rates, extending the payback period unnecessarily.
Helcro Solar is CEC-accredited with 18 years of experience in solar panel installation in Melbourne. This guide sets out the sizing methodology we use in every assessment. That way, you can arrive at a consultation already knowing what range makes sense for your home.
Key Takeaways
The starting point for sizing a solar system is your daily electricity consumption in kilowatt-hours (kWh). Specifically, this figure appears on every electricity bill under 'daily average usage' or 'average daily consumption'. It is the single most important input in the sizing calculation.
Divide your daily kWh usage by Melbourne’s average peak sun hours (4 hours) to get a base system size in kilowatts. For example, dividing 20 kWh/day by 4 gives a 5kW base requirement. In practice, most households choose a system 25 to 30% larger than that base figure, to allow for seasonal variation, inverter losses, and panel degradation over time.
Using that buffer, a household with 20 kWh/day of consumption should target a 6.5 to 7kW system. Since 6.6kW is the standard commercial configuration, it is the natural choice for this profile.
Notably, Victorian households use an average of 4,615 kWh per year, approximately 12.6 kWh per day, according to the Australian Energy Regulator. This is lower than the national average because around 88% of Victorian homes have at least one gas appliance, which reduces the electrical load. The table below shows typical daily consumption ranges by household size for Melbourne homes.
| Household | Daily Usage (gas appliances) | Daily Usage (all-electric) | Recommended System Size |
|---|---|---|---|
| 1 person | 8 to 10 kWh | 12 to 15 kWh | 3 to 5kW |
| 2 to 3 people | 13 to 16 kWh | 18 to 22 kWh | 5 to 6.6kW |
| 4 people | 17 to 22 kWh | 24 to 30 kWh | 6.6 to 10kW |
| 5 or more people/EV | 22 to 28 kWh | 30 to 40 kWh | 10 to 13kW |
| Pool + EV + large home | 28 to 40 kWh | 40 to 55 kWh | 13kW+ |
The all-electric column applies to households that have converted, or plan to convert, from gas to electric appliances. This includes hot water, cooking, and heating. Generally speaking, gas-to-electric homes see daily consumption rise by 40 to 80% as each appliance converts. For that reason, sizing for an all-electric future at the point of installation is almost always the right call. Note also that every grid-connected household pays a fixed daily supply charge regardless of solar generation, typically $1.10 to $1.40 per day in Victoria, which solar does not eliminate.
The daily usage table gives you a range. The household type guide below narrows that range to a specific recommendation based on what your home actually runs.
This size suits single-person households, couples without high daytime loads, and apartments with body corporate approval for individual systems. For example, a 5kW system generates 18 to 22 kWh per day in Melbourne and covers most daytime consumption for a household using under 16 kWh/day. Roof space requirement: 20 to 27 m².
It is the most commonly installed size in Melbourne and the right choice for most 3 to 4 person households. A 6.6kW system generates 24 to 28 kWh per day in Melbourne on average. It suits homes with reverse-cycle air conditioning and a washing machine running during the day. Installed prices in Melbourne typically run $5,000 to $9,000 after the STC rebate, depending on panel brand and inverter. Roof space requirement: 30 to 38 m².
A 10kW system generates 38 to 42 kWh per day. It suits households with a pool pump running 6 to 8 hours daily, a home EV charger, ducted reverse-cycle air conditioning, or five or more occupants. It also suits households planning a full gas-to-electric conversion. On a single-phase connection, a 10kW system requires network approval for export above 5kW. Your installer will confirm this before quoting. Roof space requirement: 45 to 55 m².
For homes with multiple EVs, large pools, or ducted zoned air conditioning across a large floor plan, 13kW to 15kW systems are the right fit. They deliver the generation needed to offset a daily consumption of 40 kWh or more. These installations almost always require a three-phase electrical connection or approval from the network distributor. Helcro Solar handles all grid connection approvals as part of our installation process.
NOT SURE WHICH CATEGORY YOUR HOME FALLS INTO?
Daily consumption tells you what size system you need. Your roof, however, tells you what size system you can install.
Modern solar panels measure approximately 1.7 m² each. For example, a 6.6kW system using 400W panels requires 17 panels and approximately 30 to 38 m² of usable roof space. A 10kW system using the same panels requires 25 panels and approximately 45 to 55 m². These figures allow for panel spacing, but not for obstructions such as skylights, vents, or chimneys, which reduce usable area.
If your usable roof area is smaller than your ideal system size requires, your installer has two options. First, higher-wattage panels (430W to 460W) reduce the panel count for the same output. Alternatively, your installer can design a split array across multiple roof faces.
North-facing panels in Melbourne produce the highest annual generation. By contrast, east and west-facing panels produce roughly 80 to 85% of north-facing output. They are commonly used when the north face is too small or obstructed. South-facing panels are rarely used in Melbourne as they produce significantly less in winter, when generation is most needed.
If your roof can only accommodate panels on an east or west face, your installer may therefore recommend increasing the system size by 15 to 20%. This compensates for the reduced output per panel, effectively addressing the orientation penalty through additional capacity.
Shading from neighbouring buildings, trees, or chimneys reduces system output significantly. Importantly, it should be assessed at the site visit stage, not after installation. A shaded panel reduces the output of all panels connected to the same string unless microinverters or DC optimisers are used. We assess shading at every site inspection and recommend the appropriate inverter architecture to minimise its impact.
Adding a battery to your solar system does not change how you calculate the panel size. The panels are still sized to your daily consumption. However, the battery changes your self-consumption rate. Instead of exporting surplus solar at 5 to 8 cents/kWh, you store it and use it in the evening at the full grid rate value. In practice, this is where storage delivers its strongest financial return.
The most common sizing mistake is choosing a battery first and then sizing the panels around it. The correct sequence is straightforward: first, calculate the panel size your consumption requires. Next, determine how much surplus generation that system produces. Then size the battery to capture that surplus. For a household using 20 kWh/day, a 6.6kW system generates a daily surplus of roughly 8 to 12 kWh. A 10 to 13 kWh battery captures that surplus completely.
A 3 to 4 person household with a 6.6kW system and 10 kWh of battery storage can typically cover most evening consumption without drawing from the grid. Similarly, a household with an EV or high evening consumption should pair a 10kW system with 13 to 15 kWh of battery storage. The solar battery cost for a 10kWh system in Melbourne runs $8,000 to $12,000 installed in 2026, varying by brand and capacity. The technical requirements for solar battery installation in Melbourne depend on your existing inverter type and switchboard configuration, which we assess as part of every battery consultation.
For most Melbourne families of two to four people with gas, hot water and cooking, yes. A 6.6kW system generates 24 to 28 kWh per day in Melbourne, which covers the daytime consumption of a household using 16 to 22 kWh daily. However, for households that are fully electric, have a pool pump, or are adding an EV charger, 6.6kW is likely to leave a significant portion of evening and high-demand consumption uncovered. In those cases, a 10kW system is worth considering. We recommend a site-specific assessment to confirm.
A 10kW solar system generates 38 to 42 kWh per day in Melbourne and is sufficient for most large family homes. This includes homes with a pool pump, ducted reverse-cycle air conditioning, and moderate EV charging. For households using more than 40 kWh per day, typically large all-electric homes with multiple EVs, a 13kW system is generally a better fit. The key metric is matching daily generation to daily consumption, not simply selecting the largest available system.
The 20% rule is an informal guideline suggesting your solar system should generate at least 20% more energy annually than your household uses. Specifically, this accounts for seasonal variation, panel degradation over time, and shading losses. In practice, a well-designed Melbourne system using the sizing formula in this guide will naturally incorporate this buffer. A 6.6kW system produces roughly 25% more than the average household needs annually, which is why it has become the standard residential size.
In most cases, yes, particularly for households with moderate to high evening energy use or those on time-of-use tariffs. A 6.6kW system produces a daily surplus of 8 to 12 kWh that would otherwise be exported at 5 to 8 cents/kWh. A 10 kWh battery captures that surplus and makes it available at night, converting a low-value export into a high-value bill reduction. Additionally, the federal Cheaper Home Batteries Program provides a rebate of around 30% off eligible batteries from July 2025, significantly improving the payback for adding storage.
The biggest drawback for most Melbourne households is the mismatch between when solar generates electricity and when households use it most. Specifically, solar production peaks between 10am and 2pm, while household consumption typically peaks in the early morning and evening. As a result, without a battery, a significant portion of generated energy is exported to the grid at low feed-in tariff rates rather than consumed at home. The solution is either shifting high-draw appliances to daylight hours using delay-start timers, or adding battery storage to capture the surplus for evening use.
The Right Solar System Size Starts With Your Usage
System size is the most consequential decision in a solar installation. Get it right and the payback is fast, the bill reduction is meaningful, and the system performs for 25 years. Get it wrong and you are either leaving savings on the table or exporting cheap energy to the grid for a decade. The formula is straightforward: divide your daily kWh by 4 and size up 25 to 30% for a real-world buffer.
Helcro Solar carries out site-specific sizing assessments across Melbourne, based on your actual electricity bills, roof orientation, and future energy plans. Every assessment results in a written system recommendation with cost, payback, and rebate figures specific to your home.
Helcro Solar's CEC-accredited team has designed and installed solar systems, battery storage, and home electrification solutions across Melbourne and Victoria for over 18 years. Every assessment is site-specific, every system is built to perform.
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