Inverter insights: Repowering older solar projects

While solar panels generally come with 25-year warranties and can continue generating power well beyond three decades, the technology behind inverters and other balance of system components may become outdated much more quickly. The easiest fix to ensure solar projects are working at their peak is to replace inverters in a repowering situation. Solar Power World talked with Igor Mogilevski, product and solutions director for inverter manufacturer Solis, about repowering efforts and the small details one must consider before taking on this operational expense.

SPW: What is repowering?

Mogilevski: Repowering addresses the widespread aging of solar sites developed with central inverters about 10 or more years ago, and it is needed to maintain production on these sites. It is a particularly good option for system owners looking to get power back online while keeping costs low. Many repowering projects are focused on inverter replacement, as solar panels can maintain performance longer, but it can include upgrading additional system components.

What are the challenges for repowering projects?

Lack of spare or replacement parts and lack of warranty support, especially in situations where OEM companies have gone out of business. Compatibility can also be a huge issue. New central inverters often have significantly higher power capacity and voltage ratings compared to older models (1,500-V vs 600-V).

Central inverter alternatives, such as string inverters, can offer the flexibility you’ll need but require rewiring mainly on the AC side, which could be a significant challenge for owners due to additional labor cost and physical site limitations.

When does repowering make financial sense?

It’s all about weighing the capital expenditure (CapEx) cost of repairs against the potential revenue loss. Typically, only a portion of the site may underperform, prompting owners to evaluate repowering as a cost-effective option — here, labor is almost always the main cost and deciding factor. Therefore, the decision balances technical solutions with implementation labor.

What is the best way to select an inverter?

There are many factors to consider, but inverter selection is ultimately based on power and AC voltage requirements. For AC voltages ranging between 360 to 480, we would opt for our 75- to 100-kW series inverters; for 208 or 200 V, we’d use the 30- to 60-kW series inverter; and for higher voltages like 690 to 800, we will typically utilize our 255- or 350-kW inverters.At the end of the day, the grid voltage determines the type of inverter needed for connection.

What are the advantages of a string inverter over a central inverter when repowering?

A very big advantage, which almost goes without saying, is the plain fact that more string inverters and their components are available on the market right now — which also makes them easier to repair.

With central inverters, spare parts and repairs may no longer be available, leaving owners to handle issues independently, which can be especially challenging for non-technical people. Meanwhile, string inverters offer a flexible solution for various voltages and configurations, making them suitable for a wide range of applications and sites.

What are the advantages of swapping central inverters in a repowering situation?

It’s actually a very straightforward install process. With central, existing components can often remain in place, and the inverter is replaced in a one-to-one manner, which simplifies the whole thing.

Any disadvantages?

I’d say limited flexibility and availability. Current central inverter technology does not have the same kind of inverters for drop-in replacement, as they usually have a lot more power than older inverters. Custom-developed products are an option, but this can be very costly and result in long periods of reduced or halted power generation.

Can you talk about the benefits of a backward-compatible string solution?

String inverters have a history of being backward-compatible, unlike central inverters, which often require significant rewiring between generations. For example, our older generation 100-kW series is backward-compatible with our current series, simplifying replacements. This obviously cuts down on costs related to labor and equipment.

Can you give a brief overview of a repowering proposal scenario?

At Solis, we simplify the process. With just an existing single-line diagram, our engineers can build a technical/commercial proposal for repowering projects, including quotations for equipment-only situations that don’t have labor or other project costs, which are typically handled by the owner or EPC. We also assist in recommending products and configuring designs, ensuring each project’s unique needs are met.

Supply chain issues seem to be a common concern when looking to repower. How does Solis ensure supply?

I get it. The anticipation of a surge in repowering due to the aging of so many utility systems coupled with the competition for new installation resources only underscores this concern. However, because Solis has an annual manufacturing capacity of 80 GW, we are well-positioned to overcome any potential supply chain constraints. Plus, the automated nature of our manufacturing process ensures a steady output of products that are high in efficiency and reliability. In my opinion, it is a big reason Solis stands out in terms of resilience. SPW