Longi unveils 690 W back-contact solar module with 25.54% efficiency

Longi Green Energy, a leading Chinese solar‑cell manufacturer, has just unveiled its latest breakthrough in photovoltaic technology: the Hi‑MO X12 back‑contact solar module. With a nominal power rating of 690 W and a record‑setting conversion efficiency of 25.54 %, the new panel pushes the limits of what utility‑scale solar farms can achieve. The announcement comes at a time when the solar industry is racing to deliver higher output per unit area, lower balance‑of‑system costs, and greater reliability for the expanding global renewable‑energy market.

What Happened

During a press event in Shanghai, Longi introduced the Hi‑MO X12 series, a family of back‑contact modules that replace the traditional front‑side soldered ribbons with an integrated conductive backsheet. This backsheet, made of a metal‑foil circuit, serves as the primary current‑carrying pathway, effectively eliminating the need for dozens of individual solder joints on the cell’s front surface. Longi’s engineers claim that each module now contains more than 15,000 fewer potential failure points, a change that could dramatically improve long‑term reliability under harsh field conditions.

The company also highlighted a modest but meaningful power boost: each 690 W panel delivers an extra 6 W to 8 W compared with its predecessor, the Hi‑MO X11. While the increase may seem small in absolute terms, it translates to a 1 %‑plus gain in energy yield over the lifetime of the module, especially when deployed in large solar farms where thousands of panels are installed.

Key Details

The Hi‑MO X12 utilizes Longi’s latest P-type monocrystalline cells, which feature a cell size of 210 mm × 210 mm and a cell efficiency of 25.6 %. By moving the interconnects to the back of the module, the front surface is left uninterrupted, allowing more light to reach the active silicon area. The conductive backsheet is fabricated from a copper‑aluminum alloy foil, laminated to a polymer layer for weather resistance. This design not only improves current‑carrying capacity but also reduces resistive losses that typically occur at solder joints.

In terms of mechanical robustness, the back‑contact architecture simplifies the module’s lamination process and reduces the risk of micro‑cracks that can develop around soldered ribbons during thermal cycling. Longi reports that the new modules have passed IEC 61730 and IEC 61215 certification tests, including damp‑heat, thermal‑cycle, and hail‑impact assessments, confirming their durability for 30‑year operating lifetimes.

From a cost perspective, the backsheet eliminates the need for expensive front‑side ribbon material and the associated assembly steps, potentially lowering the module’s balance‑of‑system (BOS) cost. Longi estimates a 2 %‑3 % reduction in manufacturing expenses per watt, a figure that could be passed on to developers seeking to maximize the economic return of solar projects.

Background

Back‑contact solar cells are not a brand‑new concept; they have been explored by several manufacturers over the past decade as a way to improve module efficiency and reliability. Traditional front‑contact cells require soldered metal ribbons that can degrade over time due to thermal expansion, moisture ingress, and mechanical stress. By moving the contacts to the rear, manufacturers can also achieve a more aesthetically pleasing, uniform black appearance, which is increasingly valued in residential and commercial installations.

Longi, founded in 2000, has become the world’s largest producer of monocrystalline silicon wafers and has consistently set new efficiency records. The company’s previous Hi‑MO X11 series, launched in 2023, already delivered a record 24.9 % efficiency and 680 W power output. The X12 builds on that foundation, incorporating lessons learned from large‑scale deployments and the company’s extensive R&D in wafer‑level passivation, advanced cell interconnection, and high‑temperature processing.

Why It Matters

The 25.54 % efficiency figure pushes the theoretical limits of single‑junction silicon cells closer to the Shockley‑Queisser limit, indicating that there is still room for incremental gains without resorting to multi‑junction or exotic materials. Higher efficiency means more power can be generated per square meter of land, a critical advantage in densely populated regions or areas with limited available space for solar farms.

Reliability is equally important. By eliminating thousands of solder joints, the Hi‑MO X12 reduces the probability of hotspot formation—a common cause of module degradation. This improvement can translate into higher capacity factors and lower operation‑and‑maintenance (O&M) costs over the module’s 25‑30‑year lifespan, strengthening the financial case for long‑term renewable‑energy investments.

What Happens Next

Longi has already begun pilot production of the Hi‑MO X12 at its Yunnan facility, with full‑scale manufacturing slated to commence in the second quarter of 2027. The company is actively engaging with major EPC contractors and utility developers in China, Europe, and the United States to secure early orders for the new panels. In parallel, Longi plans to integrate the back‑contact technology into its upcoming X13 series, targeting power ratings above 720 W and efficiencies exceeding 26 %.

Industry analysts expect the back‑contact design to become a new benchmark for high‑power modules, prompting competitors such as JinkoSolar, Trina Solar, and Canadian Solar to accelerate their own research into rear‑contact architectures. If the market adopts this technology widely, the cumulative effect could be a noticeable shift in the cost curve of utility‑scale solar, further accelerating the transition to carbon‑free electricity.

In summary, Longi’s 690 W Hi‑MO X12 back‑contact module represents a significant step forward in photovoltaic engineering. By marrying record‑high efficiency with a more reliable, streamlined design, the company is setting a new standard for what solar panels can achieve. As the technology moves from pilot lines to commercial projects, its impact will be felt across the entire solar value chain, driving down costs, improving performance, and reinforcing the role of solar power in the global clean‑energy future.