LONGi Sets a New Solar Cell Efficiency Record

Chinese solar manufacturer LONGi has increased the efficiency of its perovskite-silicon tandem solar cell to 35.5%.

This means that it can generate significantly more electricity from the same surface area than today’s commercially available photovoltaic panels.

LONGi’s new perovskite-silicon tandem solar cell achieved an efficiency of 35.5%, as independently certified by the European Solar Test Installation, or ESTI. The facility is part of the European Commission’s Joint Research Centre and specialises in the precise measurement and calibration of photovoltaic devices.

However, LONGi’s official announcement does not include a product designation, the dimensions of a finished panel, rated output, voltage, current, weight, temperature coefficient, warranty conditions or a planned market launch date. The company has presented a photovoltaic cell—the electrically active component from which solar panels are assembled.

LONGi has therefore set a new world record in the category of crystalline silicon-perovskite tandem solar cells.

The world’s most efficient solar cells use considerably more expensive multi-junction semiconductors made from III-V materials. In 2022, for example, the US National Renewable Energy Laboratory, NREL, achieved an efficiency of 39.5% with a triple-junction solar cell under standard sunlight conditions.

However, these cells are many times more expensive and are mainly used in space technology and other specialised applications.

LONGi’s result is more relevant to conventional photovoltaics because it combines a perovskite layer with silicon, the material on which almost the entire current solar market is based. In the future, manufacturers could potentially use existing silicon cells, production lines and supply chains and add an extremely thin perovskite layer.

For now, however, the word “could” is doing a considerable amount of work.

Two Layers Use Sunlight More Efficiently Than One

A conventional silicon solar cell contains a single active semiconductor junction.

Silicon processes part of the visible and infrared spectrum effectively, but when it absorbs higher-energy photons, some of their energy is converted into heat. At the same time, photons with insufficient energy cannot be used at all.

A tandem solar cell divides the work between two layers with different bandgaps.

The upper perovskite layer primarily captures the higher-energy part of the solar spectrum. Lower-energy light passes through to the silicon cell underneath, which converts it into electricity.

Each layer therefore processes the part of the solar spectrum for which it is better suited.

Using the same tandem technology, LONGi achieved an efficiency of 33.9% in November 2023 and 34.6% in June 2024. This was followed by efficiencies of 34.85% and 35.2%, before development reached the current record of 35.5%.

More important than the record achieved on a small laboratory cell are the results obtained on larger surfaces.

LONGi achieved an efficiency of 34.3% with a cell measuring 261 cm² and 32.2% with an area of 274 cm². These dimensions are already close to the size of cells suitable for industrial production.

What Does 35.5% Efficiency Mean in Real Numbers?

Manufacturers measure the performance of photovoltaic devices under standard test conditions.

Under these conditions, solar radiation with an intensity of 1,000 W falls on one square metre, the cell temperature is maintained at 25 °C, and the laboratory uses the standardised AM1.5 solar spectrum.

An efficiency of 35.5% therefore means that one square metre of active solar-cell area can provide approximately 355 W of electrical power under these conditions.

For a panel with an area of 2.25 m², this would correspond to an output of almost 800 W.

The remaining energy is reflected, transmitted through the cell or converted into heat.

This does not mean that the cell will convert exactly 35.5% of all sunlight falling on a roof every day. In real operating conditions, the intensity of solar radiation constantly changes, and the cell usually operates at a significantly higher temperature than 25 °C.

For comparison, we can use the commercially available LONGi Hi-MO X10, whose mass-produced versions achieve a maximum efficiency of 24.8%.

Under standard test conditions, one square metre therefore represents approximately 248 W of output, or around 550 W from a conventional 2.25 m² panel.

A record-breaking cell with an efficiency of 35.5% could theoretically provide up to 43% more power from the same active surface area.

However, this comparison places an individual solar cell against a complete solar panel.

A finished panel loses part of its usable active area due to the gaps between cells, the frame, conductors, electrical connections and protective layers.

A fairer comparison would therefore be between a commercial panel with an efficiency of 24.8% and LONGi’s research tandem module with an efficiency of 31.4%.

The tandem module would provide approximately 314 W per square metre, which is around 26.6% more power.

A 10 kWp Solar Power Plant Would Require Significantly Less Space

With panels operating at an efficiency of 24.8%, approximately 40.3 m² of panel surface area is required to achieve a nominal output of 10 kWp.

With a tandem module operating at an efficiency of 31.4%, the same output would require approximately 31.8 m².

The difference is 8.5 m², representing a surface-area saving of around 21%.

In other words, a 10 kWp solar installation would require approximately four fewer panels.

Should the manufacturer eventually succeed in transferring the full 35.5% cell efficiency to a large-format panel without additional losses, a 10 kWp system would theoretically require only 28.2 m².

That would represent almost another two panels fewer. Compared with an efficiency of 24.8%, the required area would decrease by approximately 30%.

However, LONGi does not currently offer such a panel. This is therefore only a theoretical calculation based on the physical efficiency of the cell, not an actual product specification.

We can also look at the calculation from the opposite perspective.

On a roof with 40 m² of usable area, panels with an efficiency of 24.8% would provide an installed capacity of approximately 9.92 kWp.

A module with an efficiency of 31.4% would provide approximately 12.56 kWp on the same surface area.

Assuming a model annual yield of 1,100 kWh for every installed kWp, the first solar installation would generate approximately 10,900 kWh of electricity per year, while the second would generate approximately 13,800 kWh.

The difference would amount to around 2,900 kWh per year.

This calculation assumes the same orientation, roof pitch, shading, inverter losses and operating conditions.

Higher efficiency does not mean that a 10 kWp solar power plant will somehow generate more energy than another 10 kWp system under identical conditions. A ten-kilowatt power plant remains a ten-kilowatt power plant.

However, higher efficiency makes it possible to install the same capacity on a smaller area or to fit more capacity onto a roof whose size cannot be increased.

Why Are Fewer Panels Required?

For the same total installed capacity—such as the previously mentioned 10 kWp—higher panel efficiency can reduce the number of panels required.

In our theoretical example, the number of panels could be reduced by four. Instead of 18 panels, only 14 would be required. Depending on the final panel efficiency and power output, the number could potentially fall to 13 or even 12 panels.

An installation company would consequently require fewer mounting rails, brackets, connectors, cables, mounting points and power optimisers. The installation time could also be reduced.

In large-scale solar power plants, higher efficiency saves land, mounting structures, cable routes and part of the long-term maintenance costs.

However, these savings may not automatically compensate for the higher price of tandem panels.

The economic viability of the technology will depend on the price per watt, service life, degradation rate and actual energy yield over several decades—not merely on the efficiency record stated on a certificate.

LONGi has not yet published long-term testing results, a degradation curve or planned warranty conditions for the cell with an efficiency of 35.5%.

Until the manufacturer presents a full-size panel that passes the relevant certification tests and offers a service life comparable to current silicon modules, the record will primarily remain a demonstration of the technology’s potential.

Nevertheless, an efficiency of 35.5% shows that the combination of perovskite and silicon could take photovoltaics significantly beyond the limits of silicon technology alone.

For customers, successful commercialisation could mean more installed power from a limited roof area or fewer panels for the same total system capacity.

For now, however, we do not know the price, service life, dimensions, output or planned sales date.

We also do not know how much of the record-breaking efficiency will remain once the cell is integrated into a full-size solar panel—or after several years of real-world operation.

For the time being, we will simply have to wait.

Source: TECHBOX