Unlocking value through solar PV repowering: A focus on module replacement and DC/AC optimisation

Many solar farms built between 2010 and 2015 were designed around technologies that are now significantly outdated. Early‑generation crystalline modules, conservative DC/AC ratios, fixed‑tilt layouts and less efficient central or first‑generation string inverters were typical of the period. As a result, many mid‑life sites are no longer constrained by land or grid access but by their original technology choices.

With today’s improved module efficiencies, more robust inverters and modern design standards, repowering offers a compelling opportunity to boost yield and extend asset life. This is especially relevant against the backdrop of a congested UK grid, where securing new connection capacity has become increasingly challenging.

Repowering opportunity in the UK market

Across the UK, around 60% of the utility scale[1] (>5 MWp) ground-mounted fleet, which represents roughly 5 GW of capacity, was commissioned between 2010 and 2015. These mid‑life assets are prime candidates for targeted upgrades that maximise value without requiring full site reconstruction.

The most common repowering actions include:

• Module replacement: Selectively replacing degraded or failed modules to restore performance without altering installed capacity.
• Inverter repowering: Replacing ageing inverters with modern and higher-efficiency units.
• Inverter DC/AC ratio optimisation [2]: Increasing the DC/AC ratio where original designs were conservative and accepting moderate losses in exchange for improved energy yields.

Additional repowering actions may include:

• Monitoring & controls upgrades: Enhancing SCADA for improved fault detection, curtailment loss reduction and increased plant availability.
• System hybridisation: This typically involves the addition of battery energy storage systems (BESS) to monetise the grid connection, reduce negative pricing exposure, and increase project returns.

This article focuses on two of the highest impact strategies: module replacement and DC/AC ratio optimisation.

Module replacement: Efficiency gains and lifetime extension

Solar modules installed 10–15 years ago were typically crystalline silicon panels operating at 14–16% efficiency. Modern monocrystalline modules (TOPCon, PERC, HJT, and emerging IBC variants) commonly achieve 21–23% efficiency. Power density has increased from 140–160 W/m² to 210–225 W/m² or more.

Temperature coefficients have also improved significantly, from around –0.45 to –0.50%/°C in older polycrystalline modules to –0.30 to –0.40%/°C in modern monocrystalline technologies, reducing thermal derating and improving real-world energy yield.‑world energy yield.

Overall, replacing older modules with modern equivalents can deliver 10–30% uplift in yield, subject to site specific constraints, while extending operational life well beyond 25–30 years. A detailed technoeconomic assessment remains essential to quantify the benefits.‑specific constraints, while extending operational life well beyond 25–30 years. A detailed techno‑economic assessment remains essential to quantify the benefits.

Considerations for switching to bifacial modules

Switching from a typical old asset that was based on monofacial technology to bifacial technology requires careful evaluation. The bifacial energy gains are highly sensitive to ground clearance, albedo, and module height, meaning that, in the majority, older assets used monofacial module technology and fixed structures with limited clearances. The mounting systems must be structurally suitable to accommodate the higher weight of glass bifacial modules, rear-side shading from racking, DC cabling, and permitting implications (e.g., module height, visual impact, glare changes). Additionally, compatibility with the existing electrical infrastructure needs to be confirmed, including inverter voltage and current limits, MPPT operating ranges, string layouts, cabling, and others.

DC/AC ratio optimisation: Unlocking additional yield

Before 2015, UK PV systems were typically designed following more conservative approaches. The inverter oversizing tolerance was more constrained due to the evolving nature of power electronics. They were less robust in handling high loads, heat management, and, especially, long-term reliability under overload conditions that could lead to greater risks of thermal stress, component fatigue, and failures. Design strategies focused on minimising clipping losses[3]. At the time, PV modules often represented approximately 50% of the project CAPEX, and their relatively high module costs made significant DC oversizing less economically attractive than maintaining a more balanced DC/AC ratio closer to 1.1 to 1.2.

Today, module prices have fallen substantially, and modern inverters can reliably manage higher DC loading. Costs typically represent only around 30-40% of the project CAPEX. As a result, higher DC/AC ratios can be more widely adopted, as the marginal cost of additional DC capacity is relatively low compared with the potential gains in annual energy production. Modern solar inverters feature improved power electronics, higher efficiencies, and greater tolerance to DC oversizing, allowing them to operate reliably with increased clipping levels. For modern PV plants in the UK, DC/AC ratios of 1.25 to 1.50 are typical, averaging 1.30 to 1.40 or higher in collocated configurations with BESS. Therefore, given that inverters now represent a smaller proportion of overall project costs, moderate clipping can result in an economically beneficial trade-off.

Land availability

Because modern PV systems require less land per MW installed, repowering may open new opportunities, such as:

• Increasing site capacity (where grid and planning allow)
• Adding BESS for export only or hybrid operation‑only or hybrid operation
• Implementing environmental enhancements
• Exploring lease or sub‑lease options

Repowering constraints

In the UK, non-technical factors often dictate what is feasible. In particular, the subsidy status of legacy schemes (FiT and RO), planning thresholds (module heights and installed capacities), and existing grid export limits frequently determine which repowering measures are realistically feasible. These factors will influence the extent to which installed capacity or system configuration can be modified and should therefore be assessed in the early stages of repowering evaluation. It is important to note that while such constraints do not necessarily preclude repowering, they must be appropriately considered when assessing the technical viability and developing the business case for any repowering scenario.

While this article focuses on the UK market, the underlying repowering principles and considerations discussed are broadly applicable to other markets, subject to local regulatory, grid, and commercial frameworks.