Optimising the benefits from solar PV retrofits

• Geronimo Advisory Principal Nishantha Manjula shares key tips for onsite solar PV system retrofit projects
• Right-sizing systems to balance incentives, performance, and compliance
• Making informed technology choices for long-term returns
• Ensuring quality delivery through oversight and commissioning

In pursuing net zero for an existing building, installing solar PV to supply a portion of the base building’s energy demand is often a key priority, both for its cost-saving potential and its reputational value. While it is feasible to source all building electricity through a GreenPower purchase agreement, this approach lacks the visible demonstration of commitment to renewables that on-site panels provide. Moreover, the lifecycle cost of electricity from solar panels is typically lower than grid supply over the system’s lifetime.

To maximise the benefits of a solar installation, it is essential to consider the project within the broader context of energy efficiency, electrification, risk management, and cost–benefit analysis.

Right Sizing

The available subsidy and incentive schemes for solar PV systems are partly determined by system size. Systems larger than 100 kW must apply for Large-scale Generation Certificates (LGCs), while systems under 100 kW qualify for Small-scale Technology Certificates (STCs). These STC rebates are often applied upfront by the system supplier, effectively reducing the total project cost.

Another key consideration in determining system size is whether the project remains below the threshold that triggers state grid connection requirements or electricity retailer obligations for a Power Purchase Agreement (PPA). For example, in Western Australia, approval processes and responsible authorities vary depending on system capacity, with thresholds typically set at 30 kVA–150 kVA, 150 kVA–200 kVA, 200 kVA–1 MVA, and above 1 MVA. Larger systems may also need to meet additional technical standards to ensure grid stability and protection.

The energy demand profile is another crucial factor in right-sizing a solar PV system. Typically, a solar installation is owned by the building owner and supplies energy to the base building, except in specific cases such as when an embedded network is established to supply tenants.

Before installation, a comprehensive energy use assessment should be undertaken to understand how and when building services consume energy. Planned energy efficiency initiatives and electrification projects such as converting hot water, catering, or space heating systems to electric, should also be modelled to forecast future demand.

By analysing the load profile over a full year, the optimal system size can be determined to minimise peak grid demand, maximise self-consumption of solar energy, and deliver the best cost savings over time.

Technology Decisions

When it comes to selecting solar PV components, cheaper is not always better. The right choice depends on available space, desired power output, and the expected payback period.

If roof or site space is limited, high-efficiency panels may be preferable, although they generally come at a higher cost. Conversely, if there is ample space and the aim is to stay below the 100 kW threshold, lower-efficiency panels can be more cost-effective while still meeting energy needs.

The payback period is influenced by several factors, including total project cost, the cost per kilowatt of generated solar energy, and prevailing grid electricity prices. The structure of the electricity tariff also plays a significant role. Both the consumption rate (¢/kWh) and the fixed supply charge vary between retailers, and many commercial contracts include peak demand charges.

For example:

• If a building’s electricity contract includes high peak demand charges, a solar PV system that offsets base building loads and reduces peak demand can deliver strong financial returns.
• If the tariff has a high consumption rate but low fixed charge, on-site solar generation becomes highly beneficial.
• However, where tariffs feature low consumption rates and high fixed charges, the payback period will typically be longer.

A detailed solar PV feasibility study should therefore include a financial analysis to determine the projected payback period and confirm the investment rationale.

Aside from the panels, the other key component influencing return on investment is the inverter. If renewable energy storage is planned, allowing use of generated power outside daylight hours a hybrid inverter will be required. Even if battery storage is not installed immediately, a hybrid inverter provides flexibility for future upgrades. These systems also allow buildings to consume generated solar energy directly rather than exporting it all to the grid.

We also recommend using Maximum Power Point Tracking (MPPT) inverters, which optimise power generation even when some panels are shaded. Unlike conventional inverters – where shading on one panel can reduce output across the entire string – MPPT inverters enable the unshaded panels to continue generating at maximum capacity, improving overall system performance.

Getting It Right in Delivery

To ensure that the modelling, design, and delivery of the solar PV project align with the intended outcomes, it is essential to maintain strong project oversight and engage an independent commissioning agent. Independent review helps verify that the installed system performs as modelled and that all design assumptions have been properly implemented.

There have been instances where installers have altered panel layouts during construction, sometimes due to site constraints or convenience without consulting the design team. Even small changes in panel orientation, tilt, or placement can significantly affect system performance, leading to results that deviate from the original modelling.

The connection point is another critical factor. For systems designed to supply the base building, the solar output must connect into the Base Building Distribution Board (DB). If it is mistakenly connected to a tenant’s DB, the base building will not benefit from the generated energy—a problem that may only be identified later when discrepancies appear in energy bills.

Thorough commissioning and verification are therefore vital at project completion. This should include confirming the correct operation of the system and inverter, verifying connection points, and ensuring that all relevant documentation such as warranties, technical manuals, design models, and system calculations is accurate and complete. Proper close-out ensures the system performs as intended and supports the building’s long-term energy and sustainability goals.

Payoffs

Once the system is operational, the use of energy monitoring software and analytics becomes an essential part of managing performance. Continuous monitoring enables the facilities manager and building management team to verify that the system is performing as expected and delivering the projected savings.

During this operational phase, valuable data outputs are generated such as emissions avoided, reductions in grid energy consumption, and patterns of generation and usage. These insights not only help fine-tune system performance but can also inform future energy initiatives across other assets in the portfolio.

In addition, performance data supports stakeholder reporting, providing tangible evidence of environmental benefits and operational savings. This information is increasingly valuable for engagement with tenants, investors, and sustainability reporting frameworks, demonstrating the organisation’s commitment to renewable energy and long-term carbon reduction.