Generation of clean energy is one of the main challenges of the 21st century. Solar energy is the most abundantly available renewable energy source which could be supplying more than 50% of the global electricity demand in 2100.
Technological advancements in solar module manufacturing components have led to predictions that power generated using solar would be as cheap as or cheaper than fossil fuel. The integral components of high efficiency modules are solar cells efficiency at a manufacturing scale and the cell to module (CTM loss) loss percentage. The latter is dependent upon the module soldering process and bill of material (BOM) composition of the module.
While BOM cost is a targeted area of cost improvements, cell efficiency is of greater importance as this represents ~80% of the total component cost excluding fixed cost amortization and capital charges. In the area of cell efficiency improvements, there have been several theories in pursuit.
The holy grail of the solar module industry is to achieve the highest possible efficiency, while lowering manufacturing costs. One of the leading advancements in solar cell design has been the improved light capture on the surface. Passivated Emitter Rear Cell (PERC) is a technology conducive to high-volume manufacturing at increased efficiencies of up to 21 percent using p-type monocrystalline. Over the course of last few years, advancements with R&D and manufacturing processes have demonstrated the true value of this solar cell technology and commercial scope.
This extra passivation layer substantially reduces electron recombination—the tendency of electrons to recombine and block the free flow of electrons through the cell, which hinders efficiency.
The chart below depicts the variances in solar cell efficiencies of varying technologies that are currently dominant in the industry and the impact of PERC on solar cell architecture.
Of interest, may the simplistic formula to compute cell efficiency to module power output for a multicrystalline cell is as follows:
Cell Efficiency * 0.24336 = Cell Power Output (watt)
Power Output/Cell * Number of Cells = Module Power Output (watt)
For illustration purposes, if the multicrystalline cell efficiency is 18%, then the module power output would be 262.83 watts (18% * 0.24336 * 60). This would be binned at a 260 watt module with a power tolerance of +0 to +5 watts.
To compute the output using PERC p-type monocrystalline cells, the formula is as follows:
Cell Efficiency * 0.24336 = Cell Power Output (watt)
Power Output/Cell * Number of Cells = Gross Module Power Output
Gross Module Output * 0.98 = Module Power Output
For illustration purposes, if the PERC p-type monocrystalline cell efficiency is 20.8%, then the module power output would be 297.63 watt (20.8% * 0.24336 * 60 * 0.98). This would be binned at a 295watt module with a power tolerance of 0 to +5 watts.
While the module procurement function may not focus on solar cell efficiency, technological improvements are an integral part to continued reduction in the cost of solar technology. Based on the above, higher solar efficiency is important to realizing greater power output per square foot and hence lower costs in labor, transportation, BOS andreal estate..
An overview of PERC technology
The improved PERC cell structure significantly reduces recombination losses on the solar cell rear side by minimizing the contact area between the silicon and the contact metal without incurring a significant impact on the contact resistance. This technology increases conversion efficiency through increasing light capture. This is achieved by adding a dielectric passivated layer to the back side of the solar cell.
A conventional technology based solar cell consists of two silicon layers (base and the emitter) of varying electrical properties. PERC technology improves the solar cell devices by improving emitter and laser process parameters which result in higher open circuit voltages and short circuit current. The dielectric layer reflects back into the cell any light that has passed through to the rear without generating electrons. The reflection is a renewed opportunity to generate current.
The graphic highlights the differences between standard cells and PERC technology structure. Through the use of monocrystalline wafers plus a dielectric passivation layer, PERC delivers higher efficiency cells and thereby modules.
PERC technology enhances cell light absorption at longer wavelengths thereby increasing yield – particularly important with increased cloud cover or either ends of the day. These wavelengths between 450 to 495 nm (referred to as blue light) are higher under these conditions. The wavelengths of 620 to 750 nm (referred to as red light) are generally converted into energy. Cells capturing red light are on average more powerful. PERC reflective technologies increase the absorption of red light under wider light conditions thereby delivering higher energy yields.
The light reflective nature of the dielectric layer in a PERC solar cell back into to the cell reduces the internal cell temperature thereby increasing current and output yield – this particularly holds true in the case of light in wavelengths greater than 1100nm (as depicted in the spectral response chart). In a conventional cell, light is absorbed by the metallization layer (particularly wavelengths greater than 1180nm) thereby increasing cell temperature and reducing yields.
B &C-Series PERC Module – Introduction of a New Technology
Centrosolar has introduced a new cell design into module production that includes the PERC technology. The technology has been developed for use on a monocrystalline base by our value chain partners and is the driver to enable cell production of cells with average efficiencies greater than 20 percent.
Developed as part of our product development roadmap, the new cell combines the cost-effective basis of a polysilicon platform with an emerging technology to differentiate from mono p-type and n-type products in the marketplace. Increasing cell efficiency using PERC technology for higher power output from a monocrystalline cell is a driving force behind realizing higher power density modules.
Higher power density modules are particularly beneficial to the commercial and residential segments of the solar industry as often there are limitations of roof space and maximizing the power plant size is important. Higher efficiencies modules also drive savings in several areas such as, labor, BOS and real estate. These savings (our estimate for savings is 10-13% relative to using lower powered modules) more than offset the marginal higher costs of modules – total installed cost remains less or unchanged.
Centrosolar recently introduced our 285 and 290 watt – all black – modules on a 60 cell format. Manufacturing these modules with a white back sheet enables us to deliver 295, 300 and 305 watts respectively. Our product roadmap charts a course toward a 300 watt all black module (305 watt with white back sheet) toward Q4/16.
For the utility scale projects, Centrosolar offers a 325, 330 and 335 watt modules on a 72 cell format. Centrosolar expects to be in the market with module offerings of up to 360 watt in Q4/16.
Centrosolar look forward to your continued support and feedback so that, it mayanalyze its offerings and continually make further investments to better address your respective needs.
For more information, please email us at firstname.lastname@example.org or call (646) 942.7488
Centrosolar America, Inc.
8350 East Evans Road, Ste. E-1
Scottsdale, AZ 85260