PERC versus Heterojunction (HLT) panels

At the Solar and Storage exhibition in March, we saw a number of solar panels now reaching 720w – 760w of production at 26% efficiency. To put that in perspective, currently in SA, the prominent Photovoltaic (solar panels) are 550w at a 21 to 22% efficiency. What has changed in the manufacturing process to bring about panels with higher wattage and greater efficiency? One such technology is the emergence of Heterojunction technology. Although not new, HJT has been very expensive to manufacture, but with improved technology, the higher cost is offset by the greater productivity.

Here we explore the differences between (Passivated Emitter and Rear Cell)PERC and HJT technology, to provide some insights into the future of solar panels.

PERC (Passivated Emitter and Rear Cell) and heterojunction (HJT) are two advanced technologies used in the manufacturing of solar panels. Here’s a detailed comparison between the two:

1. Basic Principle:
– PERC: PERC solar cells are an advancement of traditional silicon solar cells. They feature a passivation layer at the rear side of the cell, which reduces electron recombination and improves efficiency.
– Heterojunction: Heterojunction solar cells use multiple layers of different semiconductor materials, typically amorphous silicon (a-Si) and crystalline silicon (c-Si), to create a more efficient cell with reduced electron-hole recombination losses.

2. Efficiency:
– PERC: PERC technology typically achieves efficiency improvements of 1-2% compared to traditional solar cells, reaching efficiencies of around 20-22%.
– Heterojunction: HJT panels generally offer higher efficiencies compared to PERC, often exceeding 22%, and some have reached efficiencies over 24%. This is due to the superior passivation properties and reduced recombination losses in HJT cells.

3. Manufacturing Complexity:
– PERC: Manufacturing PERC cells involves modifying existing production lines to include additional steps for applying the passivation layer. While this adds some complexity, it is not as challenging as some other advanced technologies.
– Heterojunction: HJT panels require more complex manufacturing processes due to the deposition of multiple semiconductor layers. This complexity can increase production costs and requires specialized equipment.

4. Temperature Coefficient:
– PERC: PERC panels typically have a lower temperature coefficient compared to traditional solar panels, meaning their performance degrades less in hot temperatures.
– Heterojunction: HJT panels also have relatively low temperature coefficients, but they may vary depending on the specific materials used in their construction.

5. Shading Tolerance:
– PERC: PERC cells generally have better shading tolerance compared to traditional solar cells due to their improved rear-side passivation. However, shading still significantly affects overall system performance.
– Heterojunction: HJT cells also exhibit good shading tolerance due to their multi-layer construction, which can mitigate losses from partial shading.

6. Durability and Longevity:
– PERC: PERC panels are known for their durability and reliability, with many manufacturers offering warranties of 25 years or more.
– Heterojunction: HJT panels also boast excellent durability, though their longer-term performance may depend on the stability of the various materials used in their construction.

7. Cost:
– PERC: PERC technology is relatively mature and has been widely adopted in the industry, resulting in lower production costs compared to some other advanced technologies.
– Heterojunction: HJT panels tend to be more expensive due to the complexity of their manufacturing processes and the materials involved. However, as production scales up and technology matures, costs are expected to decrease.

In summary, both PERC and heterojunction technologies offer significant efficiency improvements over traditional solar cells, with HJT panels generally achieving higher efficiencies but at a higher cost and manufacturing complexity compared to PERC. The choice between the two depends on factors such as budget, desired efficiency, and specific project requirements.