Solar System Sizing: How Many Panels Does an Erina Home Actually Need?
How many solar panels does an Erina home actually need? Often more than homeowners think, sometimes less than installers quote. The answer depends on three things, how much electricity your household uses, how much of that you want to offset, and how the system pairs with future plans like an EV or a battery. Getting the sizing right matters because oversized systems waste money and undersized systems leave the household importing expensive grid power for years.
### What you're sizing against
The size of a residential solar system in Australia is described in kilowatts (kW), the peak DC power capacity of the panels. A 6.6 kW system uses around 16-18 panels at typical 2026 panel wattages. A 10 kW system uses around 24-26 panels.
The system's value is determined not by its size in kW but by how much energy it generates and how much of that energy the household actually uses. Two metrics matter:
- Annual generation (kWh per year), total energy the system produces over a year - Self-consumption rate, the percentage of generated energy used directly by the household, rather than exported
Higher annual generation is straightforward, bigger system = more energy. Self-consumption is more interesting and harder to optimise.
### Step 1: Find your annual electricity consumption
Before sizing the panels, find out what the home actually uses. The cleanest source is your electricity bills, most NSW retailers show daily and total consumption on each quarterly statement.
For an Erina household: - Small (1-2 people, no aircon): 3,000-5,000 kWh per year - Medium (2-4 people, moderate aircon): 5,000-8,000 kWh per year - Larger (3-5 people, heavy aircon, pool, hot water on electric): 8,000-15,000 kWh per year - Very large (heavy electrical loads, multiple aircon zones, EV charging, all-electric home): 15,000+ kWh per year
If you don't have a year of bills, the next best source is the consumption summary on My Energy or your retailer's online portal, most show the past 12 months of usage.
### Step 2: Estimate solar production by system size
On the Central Coast, typical annual generation per kW of installed solar:
- 6.6 kW system: ~9,000-10,500 kWh per year (with good orientation and minimal shading) - 10 kW system: ~13,500-16,000 kWh per year - 13.2 kW system: ~18,000-21,000 kWh per year
These figures assume north-facing arrays at reasonable tilt. East or west-facing arrays produce 10-15% less. Heavily shaded sites can be significantly lower.
### Step 3: Match production to consumption, with the self-consumption caveat
The naive approach is to match annual production to annual consumption, if the household uses 9,000 kWh per year, install a system that produces 9,000 kWh per year. But this misses the self-consumption point.
Solar production happens during the day. Most household consumption happens in the morning before everyone leaves, and in the evening after everyone returns. Without behavioural changes or storage, typical Australian households self-consume about 30-40% of their solar production, the rest is exported at the low feed-in tariff.
A system producing 9,000 kWh per year on a household using 9,000 kWh per year will: - Cover 30-40% of consumption directly (3,000-3,600 kWh) - Export the remaining solar production (5,400-6,000 kWh) at feed-in rates - Still need to buy 5,400-6,000 kWh from the grid for evening and overnight usage
This is the source of the most common complaint: "my system covers my annual usage on paper but my bills are still high." It's because the timing of generation and consumption don't align without active management.
### Step 4: Adjust for your actual goals
Three common sizing strategies:
The minimum-cost approach. Size to maximise self-consumption with no exports. Typically a smaller system (4-5 kW) sized to roughly the daytime base load. Best for households with low daytime consumption and short payback expectations.
The standard residential approach. Install 6.6 kW (the most common size due to STC sweet spots and inverter sizing). Self-consume what you can, export the rest. Payback typically 4-7 years on the Central Coast in 2026.
The future-ready approach. Install 10-13.2 kW now, anticipating future electrification, heat pump, EV charging, all-electric cooking, possibly a battery. The system covers current consumption easily and absorbs future loads as they come. Higher upfront cost but the longest-term value.
### How EV charging and batteries change the calculation
Adding an EV. An electric vehicle adds 2,000-4,000 kWh per year to household consumption (depending on driving patterns). Charging on daytime solar can absorb 80%+ of this load, but only if the system has capacity to spare. Households planning for an EV typically size 30-50% larger than their pre-EV consumption.
Adding a battery. A battery shifts solar consumption from daytime to evening, effectively raising self-consumption from 30-40% toward 60-80%. This makes larger systems more attractive (more solar to store) and increases the value of every kWh generated.
Adding both. EV + battery + home solar is the highest-value configuration but also the highest upfront cost. Modelling this scenario properly requires either consumption analysis software or experience from an installer who's designed similar setups.
### What size NOT to install
A few cautions worth flagging:
Don't install much smaller than your daytime base load. A 2-3 kW system on a household with significant daytime consumption usually has poor payback because it never produces enough to make a real dent.
Don't oversize wildly without a battery or future load. A 15 kW system on a household using 4,000 kWh per year is exporting most of its production at low feed-in rates. The marginal solar production is worth very little.
Don't ignore connection limits. Most NSW residential connections are limited to 5 kW per phase export. Single-phase homes can install much larger systems than 5 kW (the excess is self-consumed or export-limited via software), but the design has to account for this.
### Frequently Asked Questions
#### Is 6.6 kW the right size for a typical Erina home?
For a typical 2-4 person Erina household with moderate consumption, 6.6 kW is a reasonable default, it's the most common residential size, fits well within standard inverter ranges, and the STC value scales nicely. Whether it's optimal for your specific home depends on actual consumption and future plans.
#### What if my consumption is much higher than 6.6 kW can cover?
Most modern residential systems scale to 10 kW or 13.2 kW without significant complexity. The inverter and grid connection arrangements change, but the technology and install process are similar. The choice is about whether the larger system pays back within your timeframe.
#### Can I install a small system now and add more panels later?
Yes, adding to an existing system is possible, but the rules are nuanced. The additional panels need to be compatible with the existing inverter (or a new inverter is added), the grid connection may need re-approval, and the STC value of the new panels is calculated separately. It's usually more cost-effective to install the right size from the start.
#### What about systems where I have unusual electrical loads, like a workshop or pool heating?
Heavy or unusual loads change the sizing conversation. A home workshop with intermittent high-draw equipment, a pool heat pump, or a granny flat with separate metering all need specific analysis. Many installers offer consumption monitoring as a pre-design step for complex sites, it's worth doing if your usage is significantly above the typical residential profile.
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