Performance Characteristics and Efficiency Enhancement Techniques of Solar PV System: A review

Acronyms

ANSYS: Analysis of Systems Software

a-Si: H single: Hydrogenated amorphous Silicon with single-junction

BIPV: building-integrated photovoltaics

BL: Bridge linked

CdTe: Cadmium Telluride

CIGS: Copper indium gallium selenide

CIS: Copper Indium Selenide

DHI: Diffused Horizontal Irradiation

DSSC: Dye-sensitized solar cell

EFG-Si: Edge-defined Film-fed Silicon

FEM: Finite element method

FF: Fill Factor

FPV: Flexible photovoltaic

GaAs: Gallium arsenide

GHI: Global Horizontal Irradiation

HIT: Heterojunction Intrinsic Thin layer

I_sc: Short Circuit Current

MATLAB: Matrix laboratory

MBB: Multi bus bar

m-Si: Monocrystalline silicon

PERC: Passivated Emitter and Rear Cell

P_m: Maximum Power

PR: Performance ratio

p-Si: Polycrystalline silicon

PV: Photovoltaic

SILO-ED: Silicide on Oxide-based Electrostatically Doped

SPV: Solar photovoltaic

STC: Standard test condition

TiO₂: Titanium dioxide

TCT: Total cross tied

VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red

V_oc: Open Circuit Voltage

Introduction

As energy demands are increasing day by day, and expected to reach over 200% by 2040-50 as compared to 2020.¹ Therefore, the effectiveness and perfection of photovoltaic (PV) panels have now become a universal issue, particularly in developing countries like India.² Electricity energy generation is shifting towards renewables like solar energy internationally.³ The global dependence on electricity is growing, as environmental issues grow extra focus is being paid to solar energy.³ Solar irradiance can generate heat, cause a change in chemical progressions, or create power. The total solar light received onto the earth's surface exceeds the world’s present energy consumption needs.⁴ Thus the amount of solar energy received can meet human energy needs if properly utilized. In India, almost 62% of the total area receives a yearly average direct solar radiation of 5 kWh/m²/day.⁵

The solar PV cell works on the basic principle of photo electricity. The light photons of a specific wavelength 400-700 nm (visible light, near to infrared) are converted into electricity as direct current. In 1954, the first solar PV cell made up of silicon semiconductor material produced electricity when focused under solar light at Bell Laboratory.⁶ Under present harsh environmental conditions, solar electric power is the only eco-friendly and sustainable source of electricity generation for the future.⁷ In the commercial market, presently three basic types of solar PV modules are available: Monocrystalline, Polycrystalline, and Thin-film solar cells.⁷ Current research and progress has developed two more technology types; Passivated Emitter and Rear Cell (PERC) solar cells⁸ and half-cut solar PV cells.⁹ The performance of monocrystalline silicon solar cells has shown remarkable improvement in the past years, these designs originally showed only 15% efficiency in the 50s and then increased to 17% in the 70s and up to 28% presently.¹⁰ PERC solar cell technology/architecture has the best potential to produce high-efficiency solar cells at a competitive price.¹¹ This technology enables solar cell manufacturers to achieve high efficiencies as compared to standard solar cells. 1% absolute gain in efficiency is possible with PERC solar cell architecture as it enables improved light capture near the rear surface and gets most of the electrons out of the solar cell. This technology optimized the (i) light capture near the rear surface of the structure and (ii) optimize electron emission/capture. 24.7% efficiency has been recorded with PERC architecture solar cells.¹¹

This paper gives a brief review of the present status of solar PV systems, performance characteristics and efficiency enhancement, reasons, remedies, and technological aspects.

Types of solar PV cells and their efficiencies

Basically, solar cells can be classified according to the 1^st, 2^nd, and 3^rd generations. 1^st generation cells include; polycrystalline and single crystalline solar cells. Under 2^nd generation; thin film solar PV cells are included. Solar PV of 3^rd generation comprises; polymer or organic solar cell (carbon-based organic compound’s thin layer), perovskite film (500 to 1000 nm, efficiency up to 25.2%) solar cell, multi-junction solar cell, transparent (absorb sunlight) and semi-transparent (absorb ultraviolet light) solar cell, concentrated (curved mirror/lenses) solar cell, DSSC (dye-sensitized solar cell) or light absorbing dye solar cells, nano thick materials based solar cell (absorb both sunlight and interior light).¹² Table 1 gives a screenshot comparison of efficiencies for different types of solar cells.

Literature review (performance parameters of different Solar PV installations)

Performance parameters and module efficiencies for different Solar PV installations at different locations have been briefly covered. How photovoltaics modules can be used in elevated performance, and how to explore their efficiency under various applications/situations, are discussed in this section:

Ahmad Fudholi et al. (2014) explored the determination of electrical and thermal performance at different radiation using a photovoltaic thermal water collector. Radiation level considered was 500 to 800 W/m² while mass flow rates range from 0.011 kg/s to 0.041 kg/s. The maximum performance was found at 800 W/m² while the flow rate was 0.041 kg/s. They recorded 68.4% absorber efficiency and 13.8% PV efficiency.²⁰

Jayanth K.G. & Venkatesh B (2017) in their work, comparisons between climate conditions were taken with a south-facing tilt and north-facing tilt, and the temperature was also monitored and the effect measured during performance analysis. Under partial shading conditions, at 15-degree tilt angle, current and voltage recorded was 0.14 A and 16 V (on South facing) and 0.1 A and 12 V (on North facing). Under without shading conditions, at 15-degree tilt angle, current and voltage recorded was 0.3A and 17 V (on South facing) and 0.26 A, 15 V (on North-facing).²¹

Pratish Rawat (2017) observed that solar PV panel is greatly responsive toward solar insolation as it is white light and composed of seven colors. In the study, wavelength is studied to examine the performance of the PV module and found each of these colors produced different efficiency, violet 7.52%, blue 6.89%, green 8.62%, yellow 8.54%, orange 7.91%, and red 9.73%. They concluded that best filter color is between yellow and red (wavelength between 600 nm to 700 nm) for best voltage produced in the range of 0.3137V to 0.2804V respectively.²²

Shahab Ahmad et al. (2021) focused on the issue of electrical performance degradation of on-field PV modules. This experimental work concluded that factors responsible for performance degradation are; environmental conditions where panels located, quality of material used to manufacture PV cells, processing techniques used, amongst other factors. Solder bond cracking and encapsulate charring are major reasons behind degradation of electrical parameters for solar cells. Short circuit current (I_sc) decreases and hence efficiency.²³

Yong Sheng Khoo et al. (2014) explored 3 different PV system models used to determine the effect of orientation and panel tilt angle in Singapore. They measured GHI (Global Horizontal Irradiation) and DHI (Diffused Horizontal Irradiation) hourly. For horizontal irradiance measurement the sensor position was 60° NE while for vertical irradiance measurement sensor facing North, South, East, and West. Different panel tilt angles tested were 10°, 20°, 30°, 40°. The solar panel tilted 10° facing east reported maximum power.²⁴

George Cristian Lazaroiu et al. (2015) evaluated the proficiency of a fixed photovoltaic and another equipped with sun tracker in the analytical approach. The inclusion of a sun tracker resulted in a significant increase in the energy generated by 12–21%. It does so because in the morning and evening the sun tracker system helps to increase the performance.²⁵

Nallapaneni Manoj Kumar et al. (2017) emphasize the techno-economic analysis of the anticipated crystalline-based solar PV plant. It has free position mounting also called an open frame/rake structure. As a result, this study concluded that 12 hectares is adequate for a 20 MW solar plant to meet the complete electrical necessities. When compared against the universal norm which was 1MW per 2 hectares, it clearly reduces the space required.²⁶

Zoltán Nagy et al. (2016) explored the building integration photovoltaics (BIPV) opportunities of flexible thin film PV (FPV) solar cells. Partial shading conditions and curved PV system were been analysed and tested. They suggested that with a flat and horizontal shape modules its efficiency is 12.5 to 13%. On the other hand, when the same modules are curved, it resulted in only a 6% efficiency.²⁷

Ahsan, et al. (2016) created a study considering the economic analysis of an off-grid PV system of 1KW capacity setup at 28.5616° N, 77.2802° E, and located in India 293 m above sea level. It gives a rate of return of 1.714% on investment on the assumption of cost of energy at Rs. 0.9724/kWh and life of the product at 25 years. The study is restricted to a moderate home in a rural area. This system produced solar energy of approximately 3100 kWh per year. Out of which, 2933 kWh per year is delivered to the user, while approximately 170 kWh of energy is unexploited, owing to battery full condition or short demand.²⁸

Elias M. Salilih et al. (2019) explored a model which considered constant load conditions at 2, 4, and 6 Ω under the performance of a distinctive PV module or panel. The region was tropical Jigjiga Eastern Ethiopia, (9.35° N, 42.8° E). By a detailed numerical algorithm, the electrical properties of the given module have been determined. It is found that the load of 4 Ω resulted in the maximum daily energy output, it is also concluded that all weather conditions do not result in the same load conditions being favourable.²⁹

Chong Li (2018) in their study used seven different types of PV systems in the same region, at the coordinates of 32.0438° N and 118.7785° E, approximately 68 m above sea level, measurements based on ambient temperature and monthly average solar irradiation were taken. This is a performance-focused analysis of the module, this study tested different PV constructions and found different efficiency: polycrystalline silicon (p-Si) at 6%, cadmium telluride (CdTe) thin-film at 6.3%, monocrystalline silicon (m-Si) at approximately 9.3%, Copper Indium Selenide (CIS) thin film 7.8%, Edge-defined Film-fed Silicon (EFG-Si) 8.0%, Heterojunction Intrinsic Thin layer (HIT) 15.7%, and Hydrogenated amorphous Silicon with single-junction (a-Si: H single-PV) 3.15%. They concluded that HIT is the most optimum architecture, and p-Si and CdTe as the appropriate choices for the area considered.³⁰

Cuce et al. (2013) explored the effects of two major environmental conditions; solar intensity (200 to 1000 W/m²) and panel temperature (15–60°C). As the temperature of the cell rises, the voltage level drops dramatically. As the light intensity level fluctuated, the shunt resistance of photovoltaic modules stayed nearly constant. With the increase in cell heat, a linear drop in the resistor has been seen. As a result, shunt resistance is very sensitive to temperature coefficient (Tc) and both series resistance and shunt resistance linearly decreases with increasing Tc. High illumination intensity (W/m²) was unaffected by the disparities of intensity in light.³¹

Ramaprabha & Mathur (2012) analyzed the power production by the SPVA (solar photovoltaic array) under different shading conditions (75%, 20%, and no shading). They also tested designs in a different arrangement such as parallel, series, series-parallel (SP) and total cross-tied (TCT), bridge-linked (BL) as-well-as honeycomb (HC) configurations. For the above analysis, a generalized M-code was developed using Matrix laboratory (MATLAB). Research has resulted in conclusions that to get the highest probable power output under partially shading situations, it is compulsory to attach a bypass diode in anti-parallel with a module of cells. The best configuration found in TCT arrangement for maximum power output, however, HC was also near to TCT.³²

Kamal sign at al. (2021) experimentally investigated the performance of poly crystalline silicon based conventional PV panel using water circulation for cooling. Cupper tubes (6.35 mm diameter) have been attached behind the panel using single cupper absorbing plate to circulate water as cooling fluid. With water flow rate of 0.0166 kg/sec, 15.23% temperature reduction was achieved and nearly 6% increment in electrical efficiency reported.³³

Kazem & Chaichan (2016) investigated the output power loss due to dust deposition on PV modules in Oman. They considered different-sized dust particles collected from six locations in Oman. The majority (64%) of the dust particles had sizes ranging from 3 to 62 μm. The amount of dust deposited on solar panels differed from one place to the next. The low surface weight concentration of dust (1 g/m²) did not result in any substantial energy yield loss. However, after being exposed to the outdoors for more than 3 months, the results indicate that the PV module's output drops by up to 35–40%, suggesting that cleaning should be done every 3 months.³⁴

Hussain et al. (2017) experimentally studied the effect of duct on solar PV panels. They concluded that up to 60% power loss reported with different size and weight of dust particles. With rise husk deposited on panels, 3.88 W power loss concluded.³⁵

Veeramanikandan et al. (2022) experimentally investigated the effect of temperature on the performance of solar PV panel at Coimbatore, Tamilnadu, India. They analyzed transient temperature distribution in panels using Ansys software. They concluded that temperature is the most critical parameter that significantly impacts on panel efficiency.³⁶

A comprehensive review of SPVS installed at various locations with a variety of efficiency at different process parameters is given in Table 2. Some important information drawn from the Table 2 are; (i) process parameters affecting the SPVS efficiency include panel surface temperature, shading of solar cells, irradiance, tilt of panel, series-parallel/total cross tied combinations, solar cell materials, dust deposition, fabrication techniques used by the different manufacturers, etc. (ii) research work is going on worldwide to improve the SPVS efficiency considering economics and Installation/space requirements. (iii) Practically 12-20% efficiencies reported by different researchers for different SPVS installations worldwide with different types of solar cells and design architecture.

Conclusion

This review discussed the most important operating parameters like solar irradiation, PV panel temperature, tilting angle effect, parallel and series combination effect of diode, shading, environment impact, different types of solar panels, PV materials, and different light wavelengths and their effect on the efficiency of the solar PV system. Also, socio-economic, techno-economic, and recent improvements in SPV technologies have been discussed. Significant conclusions are:

Solar irradiation is always advantageous for higher efficiencies however, simultaneously it increases the temperature of the solar panel which adversely affects it. In India, the value of solar irradiation ranges from 100 W/m² to 900 W/m² (per season). Solar panels are designed to work in cool environment near to 25°C. Hence, in India appropriate cooling technologies are advantageous to optimize the power output.

Solar panel temperature between 15°C to 35°C is advantageous. Panels are designed to perform at peak efficiency between this ranges. The optimum temperature considered is 25°C (77°F). Each degree increase of panel temperature would cause efficiency drop by 0.5%.

The tilt angle of solar panels ideally is 15° added to the latitude during winter and subtracting 15° from latitude during summer in the northern hemisphere (like in India) and panel facing south, while it reverses in the southern hemisphere. This is the optimum condition for maximum solar irradiation. For the city of Jabalpur, Madhya Pradesh, India optimum tilt angle is (23.18 plus 15°) 38.18°.

Shading of solar panels adversely affects the efficiency of PV modules. Shading just one solar cell in the module can lead to zero power output. 1% shading can reduce 50-70% of power output. The use of a bypass diode in proper string and blocking diodes is the best way to prevent failure of solar panels and discharging battery. Module-level power electronics are also beneficial to reduce shading losses.

Solar PV cell manufacturer is another important criterion to be considered when selecting system configuration and electrical components matching. Manufacturing and architecture processes reasonably direct affect the performance and efficiency of the PV modules, panels as well as the overall system. Manufacturing factors affecting efficiency include; cell design, silicon type, cell layout and configuration, and solar panel size. Presently, companies (like LonGi, Canadian Solar, Trina Solar, SunPower, LG, Panasonic, REC Solar, CSUN, and Solaria) manufacture/assemble solar panels with 20-23% panel efficiency and supplying commercially in the market.