BACKGROUND OF THE INVENTION
Enhancement of terrestrial photovoltaic (PV) conversion efficiency has been an essential and urgent research goal in recent decades to mitigate energy and climate crises. Concentrator photovoltaics (CPV) or Concentration photovoltaics is a photovoltaic technology that generates electricity from sunlight. It uses lenses and curved mirrors to focus sunlight onto small, but highly efficient, multi-junction (MJ) solar cells. Multi-Junction (MJ) concentrator solar cells show the highest theoretical conversion efficiency among the available solar cell technologies. The conversion efficiency of the MJ cell based on III-V compound semiconductors have already exceeded 40% and may reach 50%.
Concentrator photovoltaics (CPV) is a promising technology owing to its high conversion efficiency for direct normal irradiation with a reduced MJ cell area. The conversion efficiency of high-concentration CPV (HCPV), which is based on Direct Normal Irradiance (DNI), exceeds 30% at the module and system levels and currently reaches up to 40% at the sub-module level. However, high-concentration optics are unable to concentrate diffuse sunlight owing to their limited acceptance angle resulting from optical limitations of the solar concentrator. Therefore, HCPV is an advantageous technology for high-DNI geographical regions (annual total DNI > 2000 kWh/m2, but is less suitable for mid-range DNI regions (annual total DNI < 2000 kWh/m2). If the HCPV module could generate power not only from direct, but from diffuse sunlight as well, the energy yield per unit module area would become higher. Consequently, the potential market for HCPV could be expanded from only high-DNI to mid-range DNI regions, which covers a large area worldwide.
In particular, the HCPV harvesting diffuse sunlight could be advantageous in space-constrained applications, which require high power generation in a limited module area (i.e., installation area), such as urban streets, rooftops, and parking lots.

SUMMARY OF THE INVENTION
In one of the embodiment of the invention, a hybrid module concept has been proposed to address the above-mentioned problem. In the hybrid module architecture, an array of high-efficiency solar cells receives most of the concentrated sunlight, while an additional array of lower cost less efficient solar cells captures the diffuse sunlight, as well as a part of the direct beam. In other words, the direct sunlight energy is "partially" concentrated onto the high-efficiency solar cells, and we may refer to this concept as "partial CPV." Partial CPV modules employing Fresnel lenses and micro-aspherical lenses have been studied. The potential of the global normal irradiance (GNI)-based module efficiency //GNI has also been discussed using outdoor test results.
However, the contribution by the generated power from diffuse sunlight has not been maximized as the c-Si area being smaller than the lens aperture area. The current invention therefore endeavors to overcome this drawback.
In one of the embodiment of the current invention, the three-junction (3-Junction) cells and the secondary optical elements (SOEs) have been mechanically stacked on a wide-area c-Si cell. The prototype four-terminal sub-module delivered >/GNI = 27.7% for thetdiffiuse-to-global ratio of y = 0.19. The effects of the size of the module element on lens optical efficiency, cell temperature, and conversion efficiency have been studied, diffuse sunlight transniittance of the module was characterized through ray-tracing, measurements, and power generation performance has been evaluated by outdoor experiments. Furthermore, tolerance to tracking error angle under various sunlight conditions was also experimentally assessed, which has not been attempted heretofore.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
FIG.l (a). Represents the schematic cross section of the designed sub-module showing the dimensions of the lens and each solar cell.

FIG.l (b) represents the sub-module showing glass substrate with three-junction cells and screen-printed Ag circuit pattern, overview of the assembled sub-module
FIG.2 represents simulated temperature, cell conversion efficiency, and lens optical efficiency as functions of module elementary unit size.
FIG.3 represents measured spectral irradiance of artificial diffuse sunlight and spectral diffuse sunlight transmittance of the transparent CPV sub-module.
FIG.4 represents Photograph of the setup for the outdoor experiment.
FIG.5 (a) represents measured open-circuit voltage Voc , Pmax , and irradiance data (GNI, DNI) on a Clear-sky condition, y < 0.30
FIG.5 (b) represents measured open-circuit voltage Voc , Pmax , and irradiance data (GNI, DNI) on a partly cloudy condition, y = 0.30-1.0
FIG.6 represents relationship between the GNI-based module efficiency and the diffuse-to-global ratio for newly developed, previous and sun-tracked commercial PV modules.
FIG.7 represents Power generation improvement of the present sub-module compaied with die sun-tracked flat PV module (//GNI = 19.4%).
FIG.8 represents tracking error angle dependence of the generated power Pmax of the prototype sub-module under two weather (diffuse-to-global ratio) conditions. (a) y = 0.24-0.25. (b) y = 0.37-0.43.

DETAILED DESCRIPTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS.
Fig. 1 shows the schematic representation of a sub-module in accordance with one of the embodiment of the invention.
Sub-module design and fabrication
The three-junction cells and the secondary optical elements (SOEs) have been mechanically stacked on a wide-area c-Si cell. The prototype four-terminal sub-module delivered ^GNI =
21.1% for the diffuse-to-global ratio of y = 0.19. The present module design performance was evaluated in detail. The effects of the size of the module element on lens optical efficiency, cell temperature, and conversion efficiency were simulated, diffuse sunlight transmittance of the module was characterized through ray-tracing simulation and measurements, and power generation performance was evaluated by outdoor experiments. Furthermore, tolerance to tracking error angle under various sunlight conditions was also experimentally assessed, which has not been attempted heretofore.
The said sub-module comprises a 4 x 4 silicone lens array (101), III-V triple-junction (three-junction) cells (GalnP/GalnAs/Ge) (102), and a bifacial c-Si cell (103). The sub-module with a bifacial Si cell has the advantage of enhanced power generation per unit module area. The present sub-module is a four-terminal stack built from the transparent CPV sub-module, in which the three-junction cells are encapsulated by the silicone lens and receives concentrated direct sunlight (104) atop the bifacial Si cell for capture of the diffuse sunlight (106). A silver circuit pattern has also been screen-printed on the glass substrate (105), with the minimal non-transparent area to maximize the diffuse sunlight transmission. The ratio of the transparent area of the glass substrate to its aperture area is about 95.7%.
The three-junction cells are mounted on the circuit pattern by die bonding and wire bonding. The concentrator lens array can be made up of silicone resin with the geometrical concentration ratio Cg= 100x (unit lens aperture area: 10 mm x 10 mm, and three-junction cell area: 1.0 mm x 1.0 mm). The lens and cell sizes have been optimized considering their performance, as well as the

lens-cell alignment accuracy. The shape of the a-spherical lens has been optimized by carrying out optical analysis using commercially available software based on geometrical optics theory and the global optimization technique to maximize die amount of direct sunlight reaching the three-junction cell. A CPV sub-module with a similar lens-encapsulating design showed the DNI-based module efficiency of 37.1%.
To determine the optimal size of the module elementary unit, the relationship between the unit size and solar cell temperature, conversion efficiency, and lens optical efficiency for direct sunlight to the three-junction cell has been studied by three dimensional (3-D) heat transfer simulation using commercial finite-element-metiiod-based software and 3-D ray-tracing simulation using commercial software. The 3-D simulation model comprised a single unit formed by the silicone lens, a three-junction cell (Ge), an electrode pattern (Ag), a glass substrate, and a Si cell. For the heat transfer simulation, the absorbed heat flux in the three-junction cell and silicone lens (Q3J, 671 ens ) were modeled using the following equations:
Q3J = B x ^lens x ;,optD x (1 - n3J) (1) glens = B x ^lens x alens (2)
where B [W/m2] is the direct sunlight irradiance, -41ens [m2] is the aperture area of the lens (projected area), //opt D is the optical efficiency for direct sunlight from the lens aperture to the three-junction cell calculated by ray-tracing simulation, 7/3J is die conversion efficiency of the three-junction cell as a function of the temperature, and alens is the absorptance of the lens, also calculated by the ray-tracing simulation. It should be noted that the absorbed but unconverted iiTadiance in the Si cell was neglected in this simulation because the heat generation density of the Si cell is significantly smaller than that of the three-junction cell, i.e., —1/300 of a three-junction cell. A direct sunlight irradiance of B - 1100 W/m2, which is slightly higher than the usual irradiance conditions, was applied to emulate a possible higher temperature case for the three-junction cell. The following boundary conditions were implemented; die ambient temperature was set to 35 °C; the heat transfer coefficient from the module's outer boundary to die ambient air was 4.8W/(m2-K), approximating natural convection, i.e., a no wind condition; thus, no forced convection was present; periodic boundary conditions were applied to the unit to

emulate a multiple lens-cell array module. The thermal conductivities considered for the silicone
lens, three-junction cell electrode pattern, glass substrate, and Si cell were 0.2, 60.2, 429, 1.0,
and 168 W/(m-K), respectively, based on and manufacturer-provided thermal properties for die
silicone. The thermal radiation emissivity of the silicone lens was considered to be 0.95. In the
ray-tracing simulation, Fresnel reflection at the interface between dissimilar materials and
absorption loss in the lens were considered. A perfect reflection mirror (107) (100% reflectivity)
was assumed at the side surfaces of the lens to emulate a periodic boundary condition. The light
source, which had the same area as the lens aperture, emitted rays with the AM 1.5D spectrum
and the divergence angle of ±0.27°. The optical efficiency was calculated as the ratio of the
irradiance at the three-junction cell to that emitted from the light source. The assumed efficiency
temperature coefficients of the three junction cell and the Si cell were -0.15%/°C and
-0.45%/°C with reference efficiencies of 40% (three-junction) and 20% (Si) at 25 °C,
respectively. The balanced steady-state cell temperature was determined by iterative calculations.
Fig. 2 shows the dependence of cell temperature, conversion efficiency, and optical efficiency on
the module's elementary unit size under the constant geometrical concentration ratio (Cg =
100x). Here, we assumed tiiat the lens height, side length, and volume, as well as the Si cell side
length, increased proportionally with the three-junction cell side length, whereas the thickness of
the solar cells and glass substrate remained constant. The simulation results show that the
module performance improves with downscaling; the cell temperature decreases mainly due to
rapid lateral heat dissipation from the solar cells [28], and optical loss decreases mostly because
the volumetric absorption loss in the lens decreases. Specifically, the simulated lens absorptances
alens are 26.7%, 19.5%, 13.5%, 7.3%, and 4.3% and the lens optical efficiencies >/opt D are
68.3%, 75.5%, 81.5%, 87.7%, and 90.7% when the lens heights are 171, 86, 43, 17, and 8.6 mm,
respectively. The heat from the three-junction cell is mainly dissipated by heat conduction to the
glass substrate via interconnects (circuit pattern), whereas there is a relatively little heat transfer
through the silicone lens because of high thermal resistance (low thermal conductivity and large
thickness). At the glass surface and the lens surface, heat is mainly dissipated by convection to
the ambient air. To maintain the three-junction cell temperature under 100 °C, and lens optical
efficiency over 85%, the three-junction cell size should be below 1.0 mm. For the 1-mm cells
used in this work, the expected three-junction cell temperature and lens optical efficiency are 97
°C and 87%, respectively.

Characterization of Diffuse Sunlight Transmission
The diffuse sunlight transmittan.ce of the prototype sub-module without a bifacial Si cell, i.e., the transparent CPV sub-module, was simulated and experimentally measured. Diffuse sunlight with the AM 1.5G spectrum was emitted from a hemispherical light source and penetrated the module placed at its center. The diffuse sunlight incident angle ranged from 0° to 50° with isotropic angular radiance distribution. According to the observation data at the university campus in Nagaoka city (Japan), 80% of the diffuse component came from the incident angle smaller than 50° . Diffuse sunlight transmittance was calculated as the ratio of the incoming irradiance at the Si cell to that of the incident light on the lens' top surface. Estimated diffuse sunlight transmittances were 75.4% for full solar spectrum (280^4000 nm) and 82.6% for the effective wavelength range in the spectral response of a typical Si cell (350-1050 nm).
To validate the simulation result, the diffuse sunlight transmittance of the transparent CPV sub-module was measured under artificial diffuse sunlight emitted from a commercial solar simulator (Iwasaki Electric Co., Ltd.; ESC0436 H134). The solar simulator follows the Class C specifications for spectral matching, as defined in EEC 60904-9. Artificial diffuse sunlight showed nearly isotropic angular radiance distribution. The amount of light passing tiirough the sub-module was measured by the Si cell placed beneath the glass substrate of the sub-module. The transmittance was determined as the ratio of the Si cell short-circuit current with the sub-module to that without the sub-module. The active area of the Si cell was the same as that of the lens aperture. The measured transmittance of the tested sub-module was 82.0%, matching the simulated value. The spectral diffuse sunlight transmittance of the transparent CPV sub-module was also measured. The optical receiver of the spectro-radiometer (EKO Instruments Co., Ltd.; MS-720) was placed beneath die glass substrate of the sub-module in place of the Si cell. The optical receiver (29.5 mm diameter) was positioned at the center of the sub-module (40.3 mm x 40.3 mm), the optical receiver active area becoming 3.3% smaller than that without the sub-module due to the shade cast by the electrode pattern on the glass substrate. Spectral transmittance rk was estimated as the ratio of the measured spectral irradiance with the sub-module to that without the sub-module for each wavelength. Fig. 3 shows the estimated xk and

die measured spectral irradiance. The spectral distribution of xk was determined as almost uniform. The overall transmittance T, which is weighted by the AM1.5G spectrum and Si cell spectral response, was 80.0%, being consistent with the simulated result (82.6%) and experimental result (82.0%) using the Si cell.
The power generation performance of the present sub-module was evaluated by outdoor experiments. To compare the present sub-module performance with that of the previous sub-module [22], die same experimental methodology was applied.
Fig. 4 shows the experimental setup. The prototype sub-module was mounted on a dual-axis sun tracker (EKO Instruments Co., Ltd.; STR-22). DNI and GNI were measured by using a pyrheliometer (EKO Instruments Co., Ltd.; MS-54) and a pyranometer (EKO Instruments Co., Ltd.; MS-402) mounted on die tracked surface. The diffuse-to-global ratio y represents the proportion of the diffuse sunlight irradiance on the module aperture area to GNI, i.e., y = (GNI -DNI)/GNI. A gray-colored paper with a hemispherical solar reflectance for the AMI. 5 G standaid spectrum of -0.38 was placed on the back side of the bifacial Si cell at a distance of —300 mm to emulate moderate ground reflectance and prevent input of excess irradiation from the surroundings to the back side of the bifacial Si cell. It is noted that the reflectance of the ground
surface (i.e., albedo) widely varies from-0.1 for dark wet soil to-0.9 for fresh snow depending on die materials and surface condition. The typical reflectance of soil, glass, and sand are less than 0.4, whereas that of concrete is slightly higher at -0.5 [30]. Considering this, we set the value of 0.3—0.4 as moderate reflectance of the ground surface. The on-sun current-voltage (I-V) characteristics of the three junction and bifacial Si cells in the prototype sub-module were independently and simultaneously measured by using a two channel source/measure unit (Keysight Technologies, B2902A) at die university campus in Nagaoka city (Japan). Fig. 5 shows the measured time variation of the open-circuit voltage Foe, maximum generated power per unit module area Pmax, and solar irradiance for clear-sky and partly cloudy conditions. "Clear sky" implies a low y condition (y <0.30), whereas "partly cloudy" implies a middle (0.30 < y < 0.60) or high (y >0.60) condition, y =1.0 represents an utterly cloudy situation, where the module aperture receives only diffuse sunlight. The total generated power Pmax was defined as the sum of the maximum power of the three-junction cell and the bifacial Si cell. As shown in

Fig. 5(a), under clear-sky conditions, although the three-junction cell generated the most power, the bifacial Si cell produced as high as 27% of the total daily generated electricity. Moreover, the estimated maximum average three-junction cell temperature was 76 °C during the measurement, which was calculated from the reference Koc at room temperature (2.92 V/pcs at 19.4 °C) and its temperature coefficient (-4.57 mV/°C) provided by the cell manufacturer. The average three-junction cell temperature is, therefore, expected to be below the operating limit temperature (110 °C) recommended by the manufacturer. Impact of the localized heat on the three junction cell should be carefully investigated in future research because it may cause thermal stress on the cell and the surrounding materials. As shown in Fig. 5(b), under partly cloudy conditions, the three-junction cell power diminished with a decrease in DNI, while the bifacial Si cell produced comparatively more power from diffuse sunlight.
In the present stack design, the fill factor reduction of the Si cell due to factors such as non¬uniform shade cast by the three-junction cells and the circuit pattern was negligible. The
measured fill factor of the Si cell was approximately identical to that under outdoor ~l-sun
uniform irradiance (—76%). Fig. 6 shows the relationship between the GNI-based module efficiency ;;GNI and y obtained from 15 days of measurements, during April and June 2017. Only the case when die back side of the bifacial Si cell was completely shielded is plotted because the definition of //GNI does not consider backside irradiation, this case being hereafter referred to as "single-sided." A typical module efficiency of the sun-tracked commercial flat PV (19.4%) is also plotted, which is the efficiency of the front side of the bifacial Si cell used in the present sub-module. The single-sided present sub-module (blue plot) achieved a maxi- mum rjGNl. of 30.7% for y = 0.17, which is 2.6%, greater than that of the previously reported sub-module (green plot). In addition, the single-sided present sub-module (blue plot) showed 1.4 times higher tjGNI than the previously reported sub-module (green plot) for y — 1.0, proving a significant diffuse sunlight transmission enhancement.
Fig. 7 shows the improvement factor for power generation, defined as Pmax/Pflat PV. Here, Pmax of the present sub-raodule was determined by linear regression of measurement data collected for 15 days; Pflat PV is the estimated power generated by the sun-tracked flat PV module (/7GNI = 19.4%). The bifacial Si cell case shows higher power generation than the sun-

tracked flat PV module over die entire y range. Specifically, the bifacial Si cell case achieves power generation 1.1-1.3 times higher than the single-sided Si cell case and 1.1-1.7 times higher than the sun-tracked flat PV module over the y range of 0.17-1.0. The enhancement in the optical efficiency for both direct sunlight to the three-junction cell and diffuse sunlight to the Si cell successfully contributed to the improvement in ?/GNI and Pmax. The reasons for the optical efficiency enhancement as compared with [22] are the following:
1) the present design has one less transition from the refractive index of 1.5 to air, i.e., less Fresnel reflection loss;
2) reduced occluded area of the three-junction cell connection circuit, i.e., less non-transparent area;
3) adoption of a partial CPV approach, where some of the direct rays are allowed to fall on the Si cell instead of the three-junction cell by eliminating the SOEs used in the previous work. This approach also allows some diffuse rays, which would otherwise be reflected by the SOEs and exit the module, to fall on the Si cell.
Tolerance to Tracking Error
To evaluate the tolerance to tracking error, the prototype sub-module was mounted on a dual-axis sun tracker with a tracking accuracy sensor (Black Photon Instruments, SE-202-TA). The generated power was measured, while the sun tracking motion was intentionally stopped for 25 min.
Fig. 8 shows the tracking error angle dependence of the generated power Pmax of the prototype sub-module with a bifacial Si cell under the clear-sky condition (y = 0.24-0.25) and partly cloudy condition (y = 0.37-0.43). The backing error angle 6 shown in the first horizontal axis was calculated by using the output of the tracking accuiacy sensor and the sun's path during the measurement. It is noted that the tracking error angle dependence obtained by the above-described method may differ depending on the time of day and season, owing to the differences in the sun's apparent path. In Fig. 8, the dotted green and blue lines indicate 90% of the Pmax at 6 — 0 (maximum value) for the system (three-junction + Si) and the three-junction cell, respectively. For the sub-module using three-junction cells only, the angle at this reference level is often defined as the acceptance half angle. The acceptance half angles are marked on the first

horizontal axis in colors corresponding to the colors of the respective dashed lines. Under clear-sky conditions (y = 0.24-0.25), the three-junction cell power dropped to 90% of maximum at 1.1° error angle, while the total power (three-junction cell power + Si cell power) reached the same power output at 6— 1.5° and remained over 62% of die on-axis power for the sub-module using three-junction cells only, even over a larger error angle range. The total power at 6= 1° was 1.3 times higher than the three-junction cell power. Under partly cloudy conditions (y = 0.37-0.43), the total generated power was always higher than 90% of the three-junction-only maximum for all tracking error angles. These results indicate that the additional Si cell improves the tolerance as compared with the sub-module using three-junction cells only. Merely comparing the sub-module power at certain tracking error angles is not sufficient for evaluating the actual performance of a tracker system causing a tracking error angle distribution. Therefore, we also estimated the impact on the generated power for sun tracking uncertainty models based on the normal (Gaussian) probability distribution assuming a tracking accuracy of X°, in which X equals 2a of the distribution, defining a 95% confidence interval. In this model, the mean tracking error angle is assumed zero. Sun trackers with feedback control may exhibit such a tracking error characteristic. To quantify the tracking accuracy effect on power generation, the evaluation factor C is defined as the ratio of the generated power considering the above-mentioned assumption to that at zero tracking error, calculated by the following equation:
£= Q° Pmax (0)f(6)dG
Pmax(0=O°) X 100%
where 6 [°] is the tracking error angle, Pmax(ff) [W/m2] is the generated power expressed as a function of the tracking error angle as shown in Fig. 8, andj^ff) [—] is the probability density function of normal (Gaussian) distribution.

Table I shows the calculated ffor the two y ranges plotted in Fig. 8 and for the three tracking accuracy cases. Under high-DNI (y = 0.24-0.25) and mid-range DN1 (y =0.37-0.43) conditions, the power generated by the present sub-module (three-junction + Si) remains over 90% and 80% of the power level generated in the zero tracking error case, even when the tracking accuracy error is 2° and 3°, respectively in contrast to the power generated by die sub-module under same conditions. Therefore, the present partial CPV sub-module achieves better tolerance to tracking error compared with the sub-module using three-junction cells only under the current assumption.
The invention disclosed herein with reference to the accompanying drawings therefore provides for a Multi junction III—V/Si partial CPV module with high diffuse sunlight transmission and enhanced performance The sub-module without SOEs exhibited difftise sunlight transmission of over 80%, improving the GNI-based module efficiency up to 30.7% for single-sided Si cell case under the diffuse-to-global ratio of 0.17. Widi a bifacial Si cell, the sub-module achieved 1.1-1.3 times greater power per unit module area than that of a single-sided Si cell and 1.1-1.7 times greater tiian that of the sun-tracked commercial PV module. Moreover, the high diffuse-sunlight transmission characteristic of the partial CPV sub-module combined with the bifacial Si cell improved the tolerance to tracking error compared with the conventional CPV, especially in the case where the uncertainty of the sun tracking error conforms to a normal distribution. Under these conditions, the power generated by the proposed sub-module could maintain over 90% of the level of power obtained under no tracking error condition, even when the sun tracker's tracking accuracy was 2°.
It should be construed that die embodiments disclosed at this time is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the claims and it is intended that any changes in the claims, equivalent meaning and ranges are included therein.

I Claim:
1. A Partial Concentrator Photovolatic (CPV) Module with a stacked structure, the said stacked structure comprising, a highly transparent CPV sub-module having a silicone lens array (101), a bifacial c-Si cell (103), minors (107) encapsulating the sub-module, a glass substrate (105) having a silver circuit pattern printed on the glass substrate, 3-junction cells mounted on the said silver circuit pattern of the glass substrate by die-bonding or wire-bonding, characterised in that the Bi-facial c-Si Cell (103) is placed in between the glass substrate (105) such that the bi-facial c-Si Cell also captures the diffused-sunlight (106) for more power generation.
2. A partial concentrator photovolatic module as claimed in claim 1 wherein the bifacial Si cell transmits 80% of the diffused sunlight light to the glass substrate.
3. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the 3-junction cells are III-V triple junction cells made up of GalnP/GalnAs/Ge.
4. A paitial concentrator photovolatic module as claimed in any of the preceding claims wherein die direct sunlight energy is partially concentrated on to the high efficiency 3-junction cells.
5. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the diffused sunlight is concentrated in die bifacial c-Si cells.
6. A paitial concentrator photovolatic module as claimed in any of the preceding claims wherein the 3-junction cells and the secondary optical elements are mechanically stacked on a wide area c-Si cell.
7. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the optical efficiency (vj opt D) of the lens (101) is maximized by optimizing the lens height and the lens absorptance (a lens).
8. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the lens optical efficiency (TJ opt D) of more than 90% is achieved at the lens height of 8.6mm and lens absorptance (a lens) of 4.3%.

9. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the electricity produced by the said bifacial Si Cell is more than 27% of the total daily generated electricity.
10. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the average maximum temperature at the 3-junction cell is between 70-110° C, preferably 76° C.
11. A partial concentrator photovolatic module as claimed in any of the preceding claims wherein the power generated by the said partial concentrator photovolatic has an improved tolerance to tracking error as compared to the conventional CPV systems.
12. A paitial concentrator photovolatic module as claimed in any of the preceding claims wherein the power generated by the said module could be maintained over 90% of the level of the power obtained under no backing error condition.