applied sciences Article Optimization of the Secondary Optical Element of a Hybrid Concentrator Photovoltaic Module Considering the Effective Absorption Wavelength Range 1,2, 1,2, 1 1,2 Woo-Lim Jeong y , Kyung-Pil Kim y, Jung-Hong Min , Jun-Yeob Lee , Seung-Hyun Mun 1,2, Jeong-Hwan Park 1, Jang-Hwan Han 1, Won-Kyu Park 3, Sewang Yoon 4 and Dong-Seon Lee 1,2,* 1 School of Electrical Engineering and Computer Science, Gwangju Institute of Science and Technology, Gwangju 61005, Korea; [email protected] (W.-L.J.); [email protected] (K.-P.K.); [email protected] (J.-H.M.); [email protected] (J.-Y.L.); [email protected] (S.-H.M.); [email protected] (J.-H.P.); [email protected] (J.-H.H.) 2 Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 61005, Korea 3 Korea Advanced Nano Fab Center, Suwon 16229, Korea; [email protected] 4 194 Central-ro, Yeonsu-gu, Incheon 22003, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-62-715-2248 These authors contribute equally to this work. y Received: 27 February 2020; Accepted: 10 March 2020; Published: 18 March 2020 Abstract: Hybrid concentrator photovoltaic (CPV) architectures that combine CPV modules with low-cost solar cells have the advantage of functioning well in modest direct normal irradiance (DNI) regions as well as high-DNI regions, where these architectures allow for higher performance in a limited space. For higher performance of a hybrid CPV module, we optimized the secondary optical element (SOE) using raytracing software and conducted experimental measurements that consider the effective wavelength range. Our experiments with the optimized SOE (θ = 30◦, h = 15 mm) demonstrated a maximum output power on the triple-junction cell and polycrystalline silicon cell of 212.8 W/m2 and 5.14 W/m2, respectively. Keywords: hybrid concentrator photovoltaic; secondary optical element; Fresnel lens 1. Introduction The origin of the technique to obtain solar energy effectively using a concentrator is considered to be a combination of reflector and thermal collector, since the late 1970s [1,2]. The technique has been further advanced, and concentrator photovoltaic (CPV) modules have been actively studied to reduce costs and improve performance [3–12]. CPV modules are highly efficient power generators in high-direct normal irradiance (DNI) regions near the equator, but less effective in the global normal irradiance (GNI) mid-latitude regions, where these modules do not perform as well as flat photovoltaic (PV) modules. To overcome these limitations, several researchers have studied hybrid CPV modules that combine a CPV module with low-cost PV modules [13–16], since these hybrid CPV architectures can collect sunlight in modest-DNI regions, which allows the same solar module design regardless of region. In addition, hybrid CPV modules can maximize power generation in the high-DNI regions without requiring as much volume, since they absorb scattered light more efficiently [11]. Lee et al. experimentally analyzed two types of hybrid CPV modules with concentration ratios of 18X and Appl. Sci. 2020, 10, 2051; doi:10.3390/app10062051 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 2051 2 of 9 Appl. Sci. 2020, 10, 2051 2 of 9 1000X and showed high power generation efficiency [12]. Yamada et al. combined the two-terminal triple-junctiontwo-terminal triple-junction (TJ) solar cell and (TJ) bifacial solar cell crystalline and bifa siliconcial crystalline solar cell forsilicon their solar hybrid cell CPV for modules, their hybrid and performedCPV modules, analyses and performed based on the analyses (GNI–DNI) based/GNI on ratiothe (GNI–DNI)/GNI [13]. While many ratio studies [13]. haveWhile been many conducted studies onhave the been secondary conducted optical on the elements secondary (SOEs) optical used elem in conventionalents (SOEs) used CPV modulesin conventional [17–19 ],CPV we havemodules not seen[17–19], a study we have on the not SOEs seen ofa study hybrid on CPV the modules.SOEs of hybrid In this CPV paper, modules. we analyzed In this the paper, mirror-type we analyzed SOE forthe themirror-type hybrid CPV SOE modules for the and hybrid optimized CPV itmodules through simulationand optimized and experimentalit through simulation measurements and underexperimental high-DNI measurements conditions. under Especially high-DNI analyzed conditions. were the Especially shading lossesanalyzed of thewere silicon the shading solar cells losses by theof the SOEs silicon on the solar hybrid cells CPV by the modules. SOEs on In the addition, hybrid the CPV two-terminal modules. In TJ solaraddition, cell, mainlythe two-terminal used in CPV TJ modules,solar cell, cannotmainly convertused in CPV light modules, of wavelength canno abovet convert about light 1.3 ofµ wavelengthm, due to the above current about limit 1.3 of μ them, due top cellto the [20 current,21]. This limit longer of the wavelength top cell [20,21]. light is This also lo notnger absorbed wavelength by the light silicon is also solar not cells absorbed in the hybridby the CPVsilicon modules solar cells around in the the hybrid TJ solar CPV cell. modules For this around reason, the we TJ considered solar cell. theFor ethisffective reason, wavelength we considered range forthe theeffective optimization wavelength of the range SOE. Thesefor the hybrid optimizati CPVon modules of the areSOE. promising These hybrid as the nextCPV generationmodules are of thepromising thermal as collector the next system. generation of the thermal collector system. 2. Simulation Setup The angle angle at at which which sunlight sunlight refracts refracts from from the the primary primary optical optical element element (POE) (POE) of the of hybrid the hybrid CPV CPVmodule module depends depends on the on wavelength, the wavelength, which whichcreates createschromatic chromatic aberration aberration [22]. In [addition,22]. In addition,infrared infraredrays with rays wavelengths with wavelengths above 1.3 above μm are 1.3 notµm absorbed are not absorbedin either TJ in sola eitherr cells TJ solar or silicon cells orsolar silicon cells, solar due cells,to current due tolimits current in the limits top cell in the and top limited cell and semi limitedconductor semiconductor bandgap energy, bandgap respectively. energy, respectively. Therefore, Therefore,we considered we considered the effective the e ffwavelengthective wavelength range rangewhile whilewe optimized we optimized the theSOE SOE of ofthe the hybrid hybrid CPV module. ToTo analyze analyze the the hybrid hybrid CPV architecture,CPV architecture, we used we the used TracePro the (LambdaTracePro Research (Lambda Corporation, Research Littleton,Corporation, Massachusetts, Littleton, Massachusetts, USA) raytracing USA) software, raytracing based software, on a Monte based Carlo on methoda Monte with Carlo the method xenon lampwith the spectrum xenon lamp (1000 spectrum W/m2), to (1000 create W/m the2), three-dimensional to create the three-dimens model shownional model in Figure shown1. Assuming in Figure modest-DNI1. Assuming regions,modest-DNI sunlight regions, was designedsunlight withwas designed 80% DNI andwith 20% 80% di DNIffuse an light.d 20% We diffuse selected light. a 254 We × 254selected3 mm a 2543 Fresnel × 254 × lens 3 mm made3 Fresnel of polymethyl lens made methacrylate of polymethyl (PMMA; methacrylate refractive (PMMA; index = refractive1.49 at 500 index nm) × and= 1.49 an at Al 500 mirror nm) (92%and an reflective Al mirror at 500(92% nm) reflective as the POEat 500 and nm) SOE, as the respectively. POE and SOE, The focal respectively. length of The the POEfocal waslength 250 of mm, the POE and thewas body 250 mm, size and was the 254 body254 size253 was mm 2543 .× We 254 placed × 253 mm the3 silicon. We placed solar the cell silicon 8 mm × × awaysolar cell from 8 themm TJ away solar from cell in the position TJ solar #2, cell and in the position spacing #2, between and the the spacing silicon between solar cells the was silicon 3 mm. solar For easecells ofwas cleaning 3 mm. theFor module,ease of cleaning the flat side the ofmodule, the Fresnel the flat lens side faced of the sun,Fresnel and lens the faced stepped the side sun, faced and the solarstepped cells. side We faced placed the a high-performance solar cells. We placed TJ solar a cellhigh-performance (10 10 mm2; concentration TJ solar cell ratio(10 ×= 10645X) mm at2; × theconcentration center of the ratio hybrid = 645X) CPV at modulethe center to of collect the hy thebrid concentrated CPV module DNI. to collect Around the the concentrated TJ solar cell, DNI. we spreadAround 12 the silicon TJ solar solar cell, cells we (80 spread55 mm 122) silicon to collect solar light cells that (80 was × scattered55 mm2) from to collect the concentrator light that was and × discatteredffuse solar from irradiance. the concentrator and diffuse solar irradiance. Figure 1. (a) The raytracing model and (b) raytracing results of the hybridhybrid concentrator photovoltaic (CPV) modulemodule combinedcombined withwith low-costlow-cost siliconsilicon solarsolar cells.cells. Appl. Sci. 2020, 10, 2051 3 of 9 Appl. Sci. 2020, 10, 2051 3 of 9 3.3. Simulations 3.1.3.1. Optimization ofof SOESOE DesignDesign FigureFigure2 2 shows shows our our SOE SOE designs designs with with di differentfferent anglesangles whenwhen placedplaced onon thethe TJTJ solarsolar cells.cells. AtAt thisthis point,point, wewe fixedfixed thethe SOESOE heightheight atat 1515 mmmm andand maintainedmaintained aa constantconstant distancedistance betweenbetween thethe FresnelFresnel lenslens andand thethe TJ solar cell. Using Using these these SOEs, SOEs, we we calculated calculated the the irradiance irradiance on on the the TJ TJ solar solar cell cell and and on on the the 12 12silicon silicon solar solar cells cells (positions (positions #1 #1 to to #12 #12 in in Table Table 1).1).