How HEA Sizes Solar Systems Using Real Usage Data

Most solar installers size your system from your electricity bill — specifically your average daily usage in kilowatt-hours. This is fast. But it's not particularly accurate. Here's what HEA does differently and why it produces a better result.

The Problem with Average Usage

Your electricity bill tells you roughly how much electricity you used in a quarter. Divide it by the number of days, and you get an average daily consumption — say, 18 kWh/day.

An installer using this number might recommend a system that generates around 18 kWh/day. Sounds logical. But there's a significant flaw: solar generates electricity in the middle of the day, and your household may not use much electricity in the middle of the day.

If most of your usage happens in the morning before 8am, and then again in the evening after 5pm, a large solar system mostly generates electricity you'll export to the grid at a low feed-in rate — not electricity you actually use. The self-consumption rate is low. The payback is poor.

What NEM12 Data Actually Shows

NEM12 is the standard file format for electricity interval data in Australia. Your smart meter records your consumption every 30 minutes. Powercor stores this data, and with your consent, we can request it on your behalf.

What we get: 12 months of half-hourly readings. 17,520 data points that show us exactly when your household uses electricity, how much it uses at each time of day, how that varies by season, and what your overnight baseline looks like.

This is far more useful than an average. It lets us answer the question that actually matters: what percentage of a given system's generation will this household actually self-consume?

How We Model Your System

Once we have your interval data, we overlay it against actual solar generation data for Bendigo — by season and time of day — adjusted for your roof's orientation and any shading.

We can model different system sizes and see the self-consumption rate for each. A well-sized system for a household with high daytime usage might achieve 60–70% self-consumption. An oversized system for the same household might achieve 40%.

The financial difference is significant. Self-consumed solar replaces electricity you'd otherwise buy at ~30 cents/kWh. Exported solar earns you a feed-in tariff of around 4–6 cents/kWh in Victoria. The ratio determines your payback period.

The Practical Result

For most Bendigo households, this process means we recommend a system that's smaller — or differently sized — than what a generic installer might quote.

Sometimes a larger system genuinely makes sense — if you have high daytime usage, an EV to charge, or you're planning a battery. We'll model those scenarios and show you the numbers.

The goal is simple: the system that pays itself off fastest for your specific household. That's usually under 10 years. That's what we target on every job.