When a home or business owner is looking to install solar panels, he or she will often ask: Which are the best? In this simple question are many other implied questions, such as: Which will produce the most power? And the related question: Which offer the highest efficiency? The best warranty? Which are the most durable?
Such questions go beyond the simple and natural vanity of wanting to have the nicest product. For constrained roof spaces, high output is a must to make the economics work, particularly as more and more of the costs of installing rooftop solar do not come from the hardware itself, but from balance of system costs which often cannot be reduced with a cheaper product.
As a guide to assist with these oft-asked questions, pv magazine has assembled a list of four leading, innovative high efficiency PV modules, selected by our editors.
The SunPower X-22
SunPower has long held a leadership position when it comes to high quality, high efficiency PV modules, and the X-22 is its top of the line. Like its E Series, SunPowers X Series PV modules incorporate its n-type monocrystalline Maxeon solar cells, which are based on an integrated back contact (IBC) design. SunPower says that this not only allows for the entire surface of the cell to be utilized to generate electricity, but argues that electricity is more effectively evacuated through a solid copper rear plate on the cell.
SunPowers IBC design allows for easily the highest efficiency of any single-junction PV cell in mass production, and the X-22-360 data sheet gives an impressive efficiency of 22.2%, the highest that pv magazine was able to verify as currently available on the market for rooftop PV. The 96-cell X-22-360 is rated at a massive 360 watts for a standard 1.6 square meter module.
SunPower also argues that its cells offer higher yield than standard crystalline silicon, which it credits in part to better low light and spectral response. And while yield claims are hard to evaluate, one verified factor is the X-Series low temperature coefficient of -0.30%.SunPower also claims that its modules are not affected by light-induced degradation (LID), and due to the use of n-type mono wafers SunPower modules are free from potential-induced degradation (PID).
Peeking beneath the hood, there are a couple of other notable details in the X-22. In addition to increased cell efficiency and evacuation of power, SunPower says that the solid copper backing to the cells makes the modules less prone to cracking and corrosion, and the modules additionally incorporate anti-reflective glass. Finally, the X-22 comes with a built-in microinverter, which allows better performance under partial shading.
SunPowers E-Series achieved the top ranking through the Fraunhofer ISE PV Durability Initiative in 2013, as well as maintaining 100% of its power in the Atlas 25+ Durability test. And while there are no Maxeon cell-based PV modules old enough to verify this, SunPower estimates that 99% of its PV modules will still deliver 70% of rated power after 40 years. The X-22-360 features a combined 25 year limited product and output warranty.
Panasonic HIT N330
Panasonic is another established producer of high efficiency modules, rolling out its first heterojunction with intrinsic thin layer (HIT) PV modules in 1997. HIT utilizes multiple layers of amorphous and crystalline silicon to maximize output (see pp. 70 73). HIT boasts high efficiencies, with Panasonics recently released HIT N-330 at 19.7%. Featuring 96 five inch cells, the HIT N330 is able to achieve a 330 watt power rating in a standard-sized 1.67 square meter module.
Like other heterojunction cells, HIT PV cells allow for not only higher efficiencies, but also better performance in high temperatures. Panasonics HIT N320-330 modules offer temperature coefficients of -0.29% per degree Celsius. This is only slightly better than SunPowers -0.30% but much better than that of most monocrystalline silicon, which tends to be at or above -0.40%.
Like SunPower, Panasonic is also concerned with making use of available sunlight, and pyramid-shaped microtextures on the surface of HIT cells allow for greater absorption of sunlight. Additionally, HIT PV modules employ a unique water drainage system at the edge, which the company notes avoids not only water accumulation but also stains after drying.
Panasonic offers a robust 15 year warranty, in addition to its 25 year performance warranty. The companys 19 year history with HIT is also far longer than its competitors in the high efficiency space, meaning that HIT has nearly 20 years of actual
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REC Twin Peak
REC Group (formerly REC Solar ASA) is challenging the convention that high efficiency means monocrystalline silicon with the release of high efficiency multicrystalline silicon-based PV modules. Among the four modules featured in this article, the REC Twin Peak is the only one based on multicrystalline wafers and cells.
The high efficiency design starts with the use of passivated emitter rear contact (PERC) cell technology, and REC Group is the only major PV maker known to pv magazine to use PERC with multicrystalline silicon. REC also notes that its modules are free from PID.
RECs Twin Peak features half-cut 6 inch cells soldered together and four busbars per cell as well as dual junction boxes, all of which the company says allow for more efficient evacuation of electricity at different levels. These innovations earned REC Group the Intersolar Award in 2015 for the Twin Peak module.
While the REC 280TP has achieved 17% module efficiency, the use of multicrystalline silicon is an obvious limiting factor compared to other high efficiency designs. Regardless, the module offers a 280 watt rating in a 120 (half-cut) cell design, at 1.65 square meters.
REC Group also advertises better performance in shaded conditions with the Twin Peak, which is likely due to the use of half-cut modules and dual junction boxes.
LG MonoX NeON 2
Saving the most innovative module in this series for last, LGs MonoX NeOn 2. Like SunPowers X-Series and Panasonics HIT, the LG MonoX NeON 2 is based on n-type mono wafers and cells. However, the innovation is in what connects these cells. In the NeON 2, LG utilizes copper wire mesh interconnection technology (pv magazine 04/2014).
LG has been guarded about revealing which companies supplied the tools and know-how for its Cello technology, which features a grid of copper wires on the surface of the cell instead of grid lines and busbars. Twelve of these wires link each individual cell, which offers multiple advantages including reduced electrical losses and less reflected light from the cell surface, but also a more durable interconnection.
Additionally, the technology offers the promise of lower cost due to the replacement of silver paste with low-cost copper. For these innovations LG was also a winner of the 2015 Intersolar Award, which also noted that the company has squeezed more electricity out of its cells.
The LG320N module has achieved a 19.5% module efficiency, with a 320 watt rating on a 1.64 square meter, 60 cell module. These modules are able to hold up under high wind and snow loads, with an enforced frame design allowing the modules to withstand 6,000 Pa of pressure.
LG has also increased its product warranty from 10 to 12 years for the NeON 2 and the company offers a 25 year output warranty.
More questions than answers: Silevo Triex