5 Solar Mistakes That Cost Australian Homeowners the Most Money

Most homeowners who go solar end up leaving thousands of dollars on the table — and they don't even know it. It's not because solar doesn't work. It's because they made mistakes at the start that are completely avoidable. In Episode 2 of the Off The Grid Podcast, SEG co-founders Jason and Cam break down the five mistakes that show up most often, and what to look for before you sign anything.

We see it constantly — homeowners who spent good money on solar and are still paying a power bill that barely moved. The system is on the roof. It's producing. But the returns don't match what they were promised. In almost every case, at least one of these five mistakes is the reason why.

Mistake 1: Buying an Off-the-Shelf Package System

You've seen the ads. A 6.6kW system for $X, or a 10kW for $Y. Packaged, priced, and ready to go. What the ad doesn't tell you is that the person selling it has never looked at your power bill, your roof, your daily usage, or your family's situation. They're selling a product, not designing a solution.

The problem starts with fit. Your neighbour's 6.6kW system works well for them — two people, small house, no pool. You've got a young family, two cars, a swimming pool, and an EV on the way. The same system leaves you with a power bill that barely moves.

The second problem is what happens after the install. Many of the companies offering these packages are large, multinational operations that import container loads of the cheapest product available. When something goes wrong in year three or four — and something always eventually does — you call the company. They don't exist anymore. Or they redirect you to the installing contractor, who redirects you back. Nobody owns the problem, and you're stuck in a blame loop with a system that's not performing.

"We didn't install it. Give the contractor a call. That guy might not be around anymore. He couldn't sustain himself." — Cam, Off The Grid Podcast

A properly designed system is built around your home, your usage patterns, and your future needs. That takes an actual conversation — not a package selection.

Mistake 2: An Undersized System

The most common version of this: someone calls up, gets asked what their power bill is, and the salesperson says "sounds like you need a 10kW." No audit. No review of usage patterns. No look at the roof. Just a rough guess that gets them to a sale.

The result is a system that covers maybe half your usage when it should cover 80–90%. You still have a power bill. You're still paying retail rates every quarter. The system pays itself back eventually, but you've left years of savings on the table.

One customer we saw recently had a 15kW system installed four years ago. They spent $30,000. They're still paying $2,000 a month in electricity. The system was never properly designed for their actual usage — it was sold on the back of a quick call and a bill amount.

The other version of undersizing is future blindness. A family with a six-year-old today has a very different power profile in ten years — a teenager with a gaming setup, a TV in every room, potentially an EV. Power usage across Australian households has risen every year as more devices, appliances, and vehicles rely on electricity. A system sized for your usage today is already undersized for tomorrow.

Mistake 3: An Oversized System With No Storage

Oversizing is the flip side, and it's just as costly in a different way.

If your household uses 10–15 kilowatt hours a day and you install a 13kW system, you're generating 30–50kWh you can't use. All of that goes back to the grid. In return, you get the feed-in tariff — currently around 3 cents per kilowatt hour. You then buy back the same power at 33–35 cents that night.

That's 3 cents earned, 35 cents spent, on the same unit of electricity. Dead money.

And it's only getting worse. Feed-in tariffs have been dropping for years — from 44 cents at the beginning of the program down to approximately 3 cents today. Under the Solar Share Offer launching July 1, the free power window during peak solar production hours will further devalue daytime export. Eventually, the tariff phases out entirely.

Without a battery, excess solar is excess waste. With a battery, that same power charges your storage for free and powers your home at night at zero cost.

Mistake 4: Not Adding Battery Storage

Solar covers your daytime usage. Battery covers your night. Without one, you're dependent on the grid for a solid eight to twelve hours every day — at full retail rates.

The numbers are straightforward: sending excess solar to the grid earns 3 cents per kilowatt hour. Storing that same power and using it at night saves 33–35 cents per kilowatt hour. The difference is the difference between a power bill that barely moves and one that drops to near zero.

Battery sizing matters here too. Undersized batteries leave you drawing from the grid before morning. Oversized batteries, particularly those pushed by the original rebate structure before the May changes, tie up capital in storage you can't fully utilise.

The rebate change on May 1 has created a new problem: people are now incentivised to install smaller batteries because the rebate steps down sharply above 24kW. Someone who genuinely needs 40–50kW of storage sees only an extra $800–$1,000 in rebate for the additional capacity, and talks themselves out of what they actually need. The result: a system that runs out by 10pm and reverts to grid power for the back half of the night.

The question isn't which battery size attracts the best rebate. The question is which battery size closes the gap on your power bill permanently. The right answer pays for itself many times over across a 15–20 year system life.

Mistake 5: Installing in Shade (or Being Told You Can't Go Solar Because of It)

There are two versions of the shade mistake, and they pull in opposite directions.

The first is shade that was ignored at installation — panels placed on a roof face that's shaded for a meaningful part of the day because the installer took the path of least resistance or didn't conduct a proper site assessment. We see this regularly when we go out to quote batteries on existing systems. The solar is producing, but well below what it should. Nobody told the homeowner.

The second mistake is the opposite: homeowners told they can't go solar because they have partial shade. That's almost never true.

Modern panels still produce under UV in cloudy or diffuse light conditions. Partial shade reduces production — it doesn't eliminate it. If trees shade one side of the roof, panels on the other side still work. DC optimisers can drop a shaded panel out of the string so the rest continue operating at full efficiency.

South-facing roofs are another common objection. The perception is that south-facing panels are basically useless in Australia. In reality, they produce roughly 30% less than a north-facing equivalent — not zero. Over summer, when the sun tracks near directly overhead, south-facing panels perform well. "South is the new north" isn't just a sales line — it reflects genuine changes in panel technology and summer solar angles.

If your roof has partial shade, that's a conversation about design, orientation, and the technology options available to maximise what you have — not a reason to write off solar entirely.

The Questions You Should Be Asking Before You Sign

Most of these mistakes aren't made by homeowners — they're made by whoever designed or sold the system. But knowing what a thorough process looks like helps you identify who's doing it right.

Before you commit to any system, the person designing it should be:

• Reviewing your actual power bills — not just asking the total amount
• Understanding your daily usage patterns and when you're home
• Asking about future usage: EVs, pools, growing family, planned additions
• Assessing your roof's orientation and any shading — ideally during a site visit
• Explaining the feed-in tariff situation and whether battery storage makes sense
• Giving you a system designed for your home — not a package from a catalogue

If the conversation jumps straight to price and package size without covering those bases, that's your signal. The companies who consistently sell the cheapest packages are optimising for the sale. The companies worth working with are optimising for how your bill looks in year five and year ten.

You can also watch the process: are they designing the system in front of you, or handing you a pre-prepared quote? Are they asking about your family's future plans, or just the current bill? The quality of those questions tells you everything about the quality of the outcome.

Frequently Asked Questions