Why are we talking about PERC Solar?
Several module manufacturers are introducing new lines of PERC solar modules which have 1% or more, higher efficiency than conventional modules. While conventional solar cells have now reached their physical efficiency limits, this new PERC architecture allows manufacturers to increase the module efficiency.
The above graphic shows how PERC solar has an edge over conventional mono modules.
So what is PERC Solar?
PERC or Passivated Emitter Rear Cell is a new solar module architecture. As compared to technologies such as Perovskite Solar which is a dramatically different cell which needed breakthrough at the crystal level, PERC is an innovation in cell and module assembly.
But why does PERC Solar work?
In conventional solar cells, there is an aluminum metallization layer which makes contact across the full area of the back of the cell. Photons enter the cells and excites electrons- these electrons generate electricity only if they reach the top emitter layer. Longer wavelengths typically excite electrons near the bottom of the cell which are likely to get reabsorbed and may never reach the emitter layer- resulting only in heating of the module.
PERC technology improves efficiency by increasing the cell’s ability to capture light at longer wavelengths, i.e. specially during early morning, evening or in cloudy conditions.
In PERC solar cells, a thin dielectric layer is added between the cell and aluminium layer. Any light that has passed through the cell without generating electrons is reflected back by this layer- this light thus has a second chance to generate electrons.
Why aren’t we buying PERC Solar Modules yet?
As with any new technology, PERC solar is experiencing some growing pains:
- Higher Cost: Due to the presence of one more layer, there are more steps in maufacturing of PERC solar cells which results in higher cost. Currently PERC solar modules are available at a premium of 2-4 c/ Wp. The good thing is the efficiency gain is fast overtaking the cost increase and trends indicate that PERC will overtake and replace conventional cell architecture.
- LID: Light Induced Degradation referes to the loss of a percentage of power after first exposure of module to light. Due to the higher doping levels commonly applied in PERC cells, the negative effect due to LID is increased with PERC technology. Even manyfacturers are quoting a higher loss in the first year with PERC modules as compared to conventional. The real test with be field results which are eagerly awaited.
Our Verdict on PERC Solar Modules:
PERC solar’s main benefit is a higher peak wattage per module, with a potentially negative impact on life performance due to LID. The benefit in Wp gain is currently about 6%, i.e. it starts to become apparent only in very large solar plants.
2c/Wp is too high a premium for a mere 6% reduction in plant area.
Thus we would advise you to wait a year or so before investing in PERC solar so that the issues with LID can be resolved and until costs start to match conventional modules. Unless of course, you pride yourself in being an early adopter.
We at Sunkalp Energy are looking forward to field experience with PERC modules. If you have used PERC at any of your solar plants, do comment with your experience!