An early 1.5 kW or 3 kW solar system may still work, but it rarely matches today's usage. Use this decision guide to choose between leaving it alone, adding a second system or replacing it outright, and what to check at each step. For most owners of an early 1.5 kW or 3 kW system, the choice comes down to three options: leave it running while it still works, add a separate new system beside it, or remove it and install a larger modern one. The right answer depends on the system's age and condition, how much roof space it occupies, whether you have any legacy tariff arrangement, and how much your electricity use has grown since it went in.
Why old small systems fall behind
Early systems were often sized around the budgets and incentives of their time rather than the household's usage. Since then, panels have become more efficient and far cheaper per watt, and many homes now run air-conditioning, pool pumps, home offices or an EV. Older panels were commonly around 13-16% efficient, while current panels are commonly around 21-23%, so the same roof area can hold substantially more capacity today. Our panel efficiency guide explains why that matters on a limited roof.
Age also shows in the equipment around the panels. Older installations may have rooftop isolators exposed to years of sun, cabling and connectors that have become brittle, and an inverter that is well past its expected life. None of that means the system is unsafe, but it does mean a professional inspection is worthwhile before you decide.
Work through the decision in order
- Is it still producing? Check the inverter display or app for normal operation and compare sunny-day production with what the system should make. When new, a 3 kW system in Sydney would typically produce around 11-12 kWh on an average day and a 1.5 kW system around 5.5-6 kWh; expect somewhat less after years of gradual degradation.
- How old is the inverter? Inverters commonly last around 10-15 years. An inverter at or beyond that age is the most likely point of failure, and replacing it is often the first real cost decision.
- Do you have a legacy tariff or arrangement? The old premium feed-in schemes have largely closed, but if you have any special arrangement, check with your retailer before changing anything, because modifying the system can end some legacy conditions.
- How much roof space is left? If there is room for a new array, adding a system is possible. If the old panels occupy the best roof area, replacement usually delivers more.
- What is your usage now? Compare a year of bills with what a new system of 6.6 kW or more would produce, and factor in plans such as an EV or battery.
Option 1: leave it as it is
Leaving the system alone makes sense when it works reliably, your usage is modest, there is no free roof space and you plan to move within a few years. Keep an eye on production, and budget for an inverter replacement if the inverter is more than ten years old. If it does fail, treat that as a natural moment to revisit the other options rather than automatically replacing it like for like.
Option 2: add a second system
A second, separate system with its own new inverter lets the old one keep running while you add modern capacity on another roof plane. Things to check:
- Export limits: your network sets limits on inverter capacity and export, and the old and new inverters are assessed together.
- Incentives: STCs generally apply only to the new capacity, and your installer confirms eligibility.
- Battery plans: choosing a hybrid inverter for the new system makes adding a battery later simpler.
- Switchboard space: two systems need two sets of protection devices.
- Monitoring: two inverters usually mean two apps unless consumption monitoring brings the data together.
You generally cannot simply add modern panels to an old string. Old and new panels have different voltages and currents, the old inverter is usually too small to accept more, and the original panel model is often no longer available.
Option 3: replace the whole system
Replacement suits you when the old panels sit on your best roof space, the inverter is near the end of its life, or your usage has grown well beyond the old system's output. Removing the old array and installing a modern system sized to your current usage makes full use of the roof and gives you one inverter, one app and a fresh set of warranties.
Timing matters if the roof itself is ageing. When tiles, sheets or flashings are due for work in the next few years, have that done before the new array goes up, because removing and refitting panels later adds labour you can avoid. Replacing the whole system is also a good moment to check the switchboard, since older boards often lack the space and protection devices a modern inverter, battery or EV charger needs.
| Option | Best when | Watch for |
|---|---|---|
| Leave it | Working well, low usage, no spare roof, moving soon | Inverter age and savings you are missing |
| Add a second system | Old system in good order and spare roof available | Export limits and two inverters to maintain |
| Replace | Old array on the best roof, ageing inverter, higher usage | Removal and disposal costs, roof repairs under the old array |
For budgeting, a new 6.6 kW system in Sydney is indicatively $4,500-$6,500 after STCs and a 10 kW system $7,000-$9,500, confirmed after a site assessment. Our system sizing guide helps you decide which size fits your current and planned usage.
Safety and removal
Removal, rewiring and any work on old isolators must be done by an accredited installer and a licensed electrician. Never try to disconnect or remove panels yourself: panels produce voltage whenever light falls on them, and older roofs can be fragile underfoot. Ask each installer how the old panels and inverter will be handled, whether disposal is included in the price and whether they will check the roof surface under the old array for damage once it is exposed.
Next steps
Note your inverter's age, check a year of bills and look at how much free roof space you have before you ask for quotes. The energy market lists a Solar System Upgrade & Additional Panels service from $2,990 and Inverter Replacement from $1,990 for a 5 kW inverter; both are indicative prices confirmed after a site assessment. To have your existing system inspected and all three options compared for your roof, request a free assessment from Blue Energy Solar.
Frequently asked questions
Can I reuse my old panels with a new inverter?
Sometimes. A new inverter must be compatible with the old panels' voltage and current, and the installation must meet current standards and network rules. Because older arrays are small, a modern inverter may be heavily oversized for them unless new panels are added on a separate input. In many cases, reusing old panels only makes sense as a short-term measure while you plan a larger upgrade.
What happens to old solar panels when they are removed?
Panels that still work can occasionally be reused, for example on a shed system installed by an accredited installer, while damaged or degraded panels should go to a recycling or e-waste service that accepts solar equipment. Ask your installer how removed panels and inverters will be handled and whether disposal is included in the quote, rather than leaving them for general waste.
Will my electricity bill change straight away after upgrading?
Savings begin once the new or upgraded system is connected and producing, but your first bill may include days before the upgrade. Some upgrades also need the meter reconfigured, which can take a few weeks after installation. For a fair picture of the change, compare bills from the same season in consecutive years rather than the months immediately before and after.
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