KhepriCoat®– the best-performinganti-reflective coating for solar cover glassSame sun,more power
KhepriCoat®2Boost module efficiencyMaximize light transmission by minimizing reflectionMinimum reflection, maximumtransmissionWherever glass meets air, about 4% of thelight hitting the glass at a perpendicularangle is reflected. And that percentage risessteeply as the light’s angle of incidenceincreases. Obviously, for solar energysystems, reflected light represents a wastedopportunity. KhepriCoat®minimizes thiseffect. In fact, it delivers a record-breakingperformance in terms of light transmission,outperforming all other AR coatings on themarket today. Plus, it is mechanically robustand highly durable – essential propertiesfor this outdoor application.Why KhepriCoat®is differentAR coatings – turning particles into poresKhepriCoat®is a unique technology,developed and patented by DSM. To achievethis breakthrough, DSM has turned thestructure of traditional nano-porous sol-gelcoatings “inside out”, by turning solidparticles into light-transmitting nano-pores.It is this structure that enables KhepriCoat®to deliver a unique combination ofmechanical and optical properties.Traditional coatingsThe cost price of solar panels is underconstant pressure. As a result, when itcomes to AR coatings, manufacturers mustuse single-layer systems to remain cost-effective. Whilst traditional single-layer ARcoatings can be applied in a single-stepprocess, they are limited in the opticalbenefits they can deliver, due to the waythey are structured. Traditional single-layerAR coatings consist of solid silica nano-particles “glued” together with a binderso that the spaces between the particlesact as nano-pores (see figure 1). Use toomuch binder, and this reduces the nano-porosity – and thus the AR performance– of the coating. Use too little binder, andthis leads to poor mechanical strength andlow durability. What’s more, the structure’sopen surface (see figure 1) makes thesilica layer of the coating vulnerable tohydrolysis when exposed to extremeweather conditions. And this can cause asharp deterioration of both the optical andmechanical properties.Over recent years, global demand for sustainable energy has grown steadily – and iscertain to continue growing. As a result, solar energy systems will play an increasinglycentral role in the energy economy of the future. And as the technology becomes moreefficient, their role will become even more critical. To help boost the price/performanceratio of solar energy systems, DSM is developing new breakthrough technologies –technologies such as KhepriCoat®. Set to contribute significantly to the hunt for grid parity,KhepriCoat®is the best-performing anti-reflective coating technology for solar cover glasson the market. By transmitting more light, it boosts module efficiency significantly.Advantages at a glance:• KhepriCoat®maximizes light transmission by minimizing reflection.• KhepriCoat®is tough, durable and easy to clean.• KhepriCoat®adds significant value by improving the price/performance ratio,thus lowering the cost/Wp.• KhepriCoat®can be used on both rolled (patterned) and float glass, and can beapplied on one or both sides of the glass.• KhepriCoat®can be used in a wide range of solar applications, including solarthermal modules, crystalline-silicon modules and thin-film photovoltaic modules.• KhepriCoat®can be applied using a range of deposition technologies, such asroll, spray, slot-die and dip coating.• KhepriCoat®does not need an additional curing step if the glass is tempered.
3 KhepriCoat®DSM uses core-shell particles that have a polymercore and a silica-based shell. In the coating stage,a 100-150 nanometer layer of these particles isdeposited on the surface of the glass. Thespaces between the core-shell particles are at thesame time filled with a modified silica binder.The binder immediately forms a solid networkbetween the core-shell particles. During thecuring step, the polymer cores of the particles areremoved, leaving a glass layer with a high internalporosity (figure 2).Furthermore, because the coating layer and itsglass substrate have similar compositions, theadhesion of the coating layer to the glass surfaceis excellent.The optimized nano-pore/binder ratio ensuresKhepriCoat®delivers both outstanding opticaland mechanical properties. And because it has asmooth, “closed” surface (see figure 3), therisk of hydrolysis is sharply reduced, enablingKhepriCoat®to withstand extreme weatherconditions and making it ideal for solar-cellcover glass. In addition, this prevents dirt frompenetrating the coating’s surface, making it veryeasy to clean.Why KhepriCoat®is differentAR coatings – turning particles into poresKhepriCoat®avoids this trade-off between optical andmechanical properties by turning the structure of the coatinginside out. Instead of being formed in the spaces betweensolid nano-particles, the nano-pores in KhepriCoat®areactually hollow particles.BinderSolid silica particlesGlass substrateFigure 1: The structure of a traditional sol-gel nano-porous AR coatingCoating layer(100-150 nm)Glass substrateFigure 2: The structure of a single layer of KhepriCoat®Figure 3: SEM picture of KhepriCoat®showingthe closed modified silica surface and highproportion of nano-poresCoating200 nm
KhepriCoat®4Breaking records in light transmissionMake huge gains when the sun is high……and even larger gains when the sun is lowAnd when the light’s angle of incidence is notperpendicular, the average gain in transmittance canbe as high as 8% per coated side (see figure 6).Leading to larger energy yieldsThe increase in light transmission leads to acomparable rise in the energy yield of the solarmodule. In fact, the increase in a module’s outputcan exceed 20%, especially at low angles ofincidence ( figure 7).In practice, the actual improvement in energyyield depends on several parameters: forexample, on the type of cover glass, on the typeof solar cell and on the local cycle of the sun. Thetypical daily improvement in module efficiencywill be in the range of 4% for PV modules and6-8% for solar thermal modules.Solar cover glass that is coated with KhepriCoat®will transmit, on average, around 3% more,per coated side, of the light hitting it at a perpendicular angle of incidence, see figure 4 forsingle and double sided coated float glass and figure 5 for patterned glass.Figure 7: Angle dependent output gain of modules coated with KhepriCoat®Figure 6: Comparing the average angle-dependent gain in transmittanceof 4 mm low-iron float glass when either uncoated or coated withKhepriCoat®on both sides.Figure 5: Transmittance spectra of 3.2 mm rolled (patterned) glass(uncoated, single and double sided coated with KhepriCoat®)Figure 4: Transmittance spectra of 3.2 mm low-iron float glass (uncoated,single and double sided coated with KhepriCoat®)90919293949596979899100400 500 600 700 800 900 1000 1100Uncoated glassSingle sided coated glassDouble sided coated glass 8990919293949596979899100400 500 600 700 800 900 1000 1100Influence of KhepriCoat®on the transmittance of rolled glassWavelength [nm]Transmittance[%]Influence of KhepriCoat®on the transmittance of float glassWavelength [nm]Transmittance[%]Uncoated glassSingle sided coated glassDouble sided coated glass 90919293949596979899100400 500 600 700 800 900 1000 1100Uncoated glassSingle sided coated glassDouble sided coated glass 8990919293949596979899100400 500 600 700 800 900 1000 1100Influence of KhepriCoat®on the transmittance of rolled glassWavelength [nm]Transmittance[%]Influence of KhepriCoat®on the transmittance of float glassWavelength [nm]Transmittance[%]Uncoated glassSingle sided coated glassDouble sided coated glass 024681012141618205055606570758085909510080 70 60 50 40 30 20 10 0Transmittancegainrelativetoreference(%)Averagetransmittance370-800nm[%]Angle of light incidence [degrees]uncoated glassAR-coated glassRelative transmittance gain(right axis)Relative transmittance gain of double sided glass coated with KhepriCoat®vs uncoated glass051015202590 75 60 45 30 15 0%PowergainAngle of light incidence (degrees)Power output gain (%) of modules with KhepriCoat®coated glass vsuncoated reference modules as a function of angle of incidence
5 KhepriCoat®Add proven value to your productsIEC 61215) and to abrasion-resistance tests.KhepriCoat®surpassed all test criteria, withonly minor changes in transmission beingobservable following these tests.Suitable for cSi and thin-film modulesBy optimizing the coating’s thickness, itsproperties can be tailored to suit a variety ofdifferent module types, including both wafer-based and thin-film modules.Apply KhepriCoat®on one –or both – sidesOne-sided coatings of KhepriCoat®can beapplied using various coating technologies,such as roll coating, spray coating andslot-die coating.In the solar glass industry, roll coating is themost commonly used deposition technologyfor AR-coatings. KhepriCoat®can be appliedin both the forward and the reverse coatingmode. At its Application TechnologyDevelopment Center in The Netherlands,DSM has a commercial-scale roll coater thatit uses during product development and forproducing samples for customers (figure 8).In addition, DSM has adapted existing slot-die-coating technology for the high-speeddeposition of optical coatings on rigidsubstrates. This new system can even carryout in-line coating at speeds as high as 20meters per minute. Using this technology,DSM has achieved a coating thickness of100–150 nm with a thickness tolerance ofjust ± 2 nm. Patents are pending for thisprocess, and a pilot line is available forcustomer trials at DSM (see figure 9).When it comes to solar-thermalapplications, AR glass is usually coatedon both sides. A two-sided coating ofKhepriCoat®can be applied using standarddip-coating equipment, or by using asingle-sided coating process to apply eachlayer separately in turn.The best light transmissionThe strongest proof that KhepriCoat®is thebest AR coating available today is that it wasused by independent research institute ECNto help set a new world record for conversionefficiency in multi-crystalline solar panels.DSM can enable you to break your ownrecord, by helping you to optimize yourKhepriCoat®coatings to match the absorptionspectrum of the specific cells you use.Demonstrable durabilityThe durability of solar cover glass coatedwith KhepriCoat®has been evaluatedextensively. It has been subjected toextended damp-heat tests, humidity-freezetests, thermal cycling tests (all according toFigure 8: Roll coating unit in DSM’s Technology Development Center
KhepriCoat®6An investment that paysWith a license from DSM, you can produce andsell high-performance AR solar cover glass coatedwith KhepriCoat®, using coating formulation thatis produced by DSM in-house and delivered to youdirectly. The coating equipment requires a relativelylow capital investment. And most importantly, thisinvestment will provide you with optimized returns,as the proven added value of glass coated withKhepriCoat®fully justifies a premium price.DSM also licenses the technology to thin -filmmodule producers, who can apply the coating to thecover glass before the active layers are deposited onthe glass. Depending on the process conditions, aseparate (pre) curing step may be necessary.As pressure from governments and from public opinionis expected to grow in the future, project developers willincreasingly ask for ever more efficient solar modulesin their hunt for grid-parity. In order to help you answerthis demand, KhepriCoat®can enable you to furtherdifferentiate your business, and tailor your products to suitthe rapidly growing solar cover glass market.KhepriCoat®in summary:• Offers excellent optical properties in a single-layer coating.• Can be applied 1- or 2-sided on all types of glass, using a range of depositiontechnologies.• Increases the output of PV modules by up to 4%.• Is highly robust, withstands extreme weather conditions and is easy to clean.• Meets the durability criteria as specified in IEC61215 and is TÜV certified.• Can be tailored to suit a variety of different cells and types of solar cover glass.• Offers you a quick return on investment.• Is supported by a high level of design and engineering services.• Helps you to maintain or improve your position in a fast growing market byproviding a differentiated product offering.Figure 9: DSM’s pilot slot-die coating lineTempered glass? No pre-curing,drying step or chemicals neededIf your solar cover glass is thermally tempered, thereis no need for a separate thermal treatment (such aspre-curing or drying) or for a chemical curing step.As a result, you do not need to invest in specialovens, and there is no additional variable cost. Andbecause you don’t need to handle chemicals forcuring, DSM’s KhepriCoat®technology is very safeand environmentally friendly.The expert support you needIf you are not yet coating glass in-house, DSM cansupply you with a complete engineering packageand the technical support you need to constructand get started with coating facilities. Drawingon its technical support teams and applicationdevelopment labs based in Europe and China, DSMcan offer this technical support globally. Get in touch,and we will help you prepare for the future.Choose KhepriCoat®To make your products truly stand out
7Khepri is the name of one of the majorGods in ancient Egyptian mythology.He was believed to push the sun acrossthe sky and is responsible for the dawn.This name was chosen as sunrise andsunset are the times when the benefitsof KhepriCoat®offer the highest yieldincrease versus normal solar glass.DSM – Bright Science. Brighter Living.™Royal DSM is a global science-based company active in health, nutrition and materials.By connecting its unique competences in Life Sciences and Materials Sciences,DSM is driving economic prosperity, environmental progress and social advances tocreate sustainable value for all stakeholders. DSM delivers innovative solutions thatnourish, protect and improve performance in global markets such as food and dietarysupplements, personal care, feed, pharmaceuticals, medical devices, automotive,paints, electrical and electronics, life protection, alternative energy and bio-basedmaterials. DSM’s 22,000 employees deliver annual net sales of about €9 billion. Thecompany is listed on NYSE Euronext. More information can be found at www.dsm.comKhepriCoat®