Upgrading your existing solar system in Perth: what's possible and what it costs

A solar system installed in 2013 might have 3kW of panels and a string inverter. In 2026, that household may have acquired an EV, a battery is now cost-effective, and the original system is nowhere near large enough. What are the upgrade options?

Perth solar upgrades fall into three main paths: adding panels to an existing system, swapping to a hybrid inverter to enable battery storage, and replacing a failed inverter with a larger model. Each has different Western Power approval requirements and costs.

Option 1: Adding panels to an existing string inverter

What it involves: Adding panels to expand the system's generation capacity. Possible if:

• The existing inverter is undersized relative to allowable panel ratio (most modern inverters allow 133% panel ratio — a 5kW inverter can accept 6.6kW of panels)
• The Western Power connection was approved for a higher capacity than currently installed

Approval requirements: Additions that keep the inverter within existing Western Power approval (same inverter, same connection point, staying under the existing approved export limit) typically don't require a new Western Power application — just a new electrical compliance certificate from the installer.

Additions that increase the inverter size, add a new MPPT input, or exceed the previously approved export limit DO require a new Western Power connection application ($150–300 processing fee, 4–20 weeks processing).

Cost of adding panels only (no new inverter):

• 4 panels (~1.5kW): approximately $800–1,400 installed
• 8 panels (~3kW): approximately $1,500–2,500 installed
• Includes new electrical work and compliance certificate

Limitation: You can't add unlimited panels to an old inverter. If the inverter is already at its maximum panel-to-inverter ratio (e.g., 6.6kW of panels on a 5kW inverter), no more panels can be added without a new inverter.

Option 2: Swapping to a hybrid inverter for battery readiness

What it involves: Replacing the existing string inverter with a hybrid inverter that has battery inputs. This allows a battery to be added now or later without further inverter work.

Popular hybrid inverters for Perth:

• Fronius Primo GEN24 (compatible with BYD Battery-Box)
• SolarEdge StorEdge or Home Hub
• Sungrow SH series (pairs natively with Sungrow battery)
• Goodwe DNS/ES/ET series

Approval requirements: A new hybrid inverter at the same capacity as the original inverter may not trigger a new Western Power approval — an updated electrical compliance certificate is typically sufficient.

A larger capacity hybrid inverter (e.g., replacing a 5kW string with a 8kW hybrid) requires a new Western Power application.

Cost of inverter swap (without battery):

• 5kW string → 5kW hybrid: approximately $2,000–$3,500 (labour + new inverter)
• 5kW string → 8kW hybrid: approximately $3,000–$4,500 (includes new Western Power application)

If you're adding a battery at the same time: Many installers will bundle the hybrid inverter swap and battery installation together, which is more cost-efficient than doing them in two trips.

Option 3: Replacing a failed string inverter with a larger model

String inverters fail. A 2012-era 3kW string inverter at end-of-life creates an opportunity: instead of a like-for-like replacement, upgrade to a larger inverter (5kW or 8kW) and add panels at the same time.

What this achieves:

• No wasted labour cost of a second installation visit for panels
• Increased system capacity for a household whose consumption has grown

Approval requirements: Increasing inverter size requires a new Western Power connection application. If the existing export limit was set at 3kW (matching the old inverter), the new application can request an increased export limit where network capacity permits.

Cost:

• 3kW inverter replacement → 5kW + 4 extra panels: approximately $3,000–4,500 total
• Includes Western Power application, new compliance, labour

What you cannot easily change

Export limit: If your suburb has a low export limit (e.g., 2kW) due to network congestion, this doesn't change just because you upgrade your system. You can apply to Western Power for a higher limit, but approval depends on network capacity — it's not guaranteed.

REBS tariff: If the system is on the legacy REBS export tariff (7.135c/kWh), certain types of upgrades may trigger a tariff review. Adding panels without changing the inverter or connection point is typically fine. Adding a battery or changing the inverter may be treated as a new connection and place the system on DEBS. Confirm with Synergy before any significant upgrade if you're on REBS.

Roof constraints: A solar upgrade may reveal that the original installation used the best roof sections, leaving remaining space on less-optimal faces (south or heavily shaded). A roof survey before committing to an expansion avoids discovering this after paying for panels.

Getting upgrade quotes

A good upgrade quote should include:

• What specifically is being added or replaced
• Whether a new Western Power application is required and who handles it
• Whether the existing panels and wiring need remediation (older DC cable or isolators may not meet current standards)
• Timeline including Western Power processing time
• Compliance documentation and updated system diagram

If the installer can't tell you whether a Western Power application is required, that's a gap in their knowledge — press for a clear answer.

Western Power connection application fees and processing times are indicative as of June 2026. REBS tariff implications should be confirmed directly with Synergy before any upgrade affecting the connection point or inverter.