A Novel Method for Optimizing Power Efficiency of a Solar Photovoltaic Device

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Transactions on Electrical and Electronic Materials

ISSN 1229-7607

Trans. Electr. Electron. Mater.

DOI 10.1007/s42341-020-00183-2

A Novel Method for Optimizing Power Efficiency of a Solar Photovoltaic Device

Sabuj Sarkar & Md. Mostafizur Rahman

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Transactions on Electrical and Electronic Materials https://doi.org/10.1007/s42341-020-00183-2

REGULAR PAPER

A Novel Method for Optimizing Power Efficiency of a Solar Photovoltaic Device

Sabuj Sarkar¹ · Md. Mostafizur Rahman²

Received: 25 October 2019 / Revised: 7 February 2020 / Accepted: 14 February 2020

Abstract

Most recently, photovoltaic energy has made an incredible technological advancement for the forthcoming decades towards mitigating the ever-increasing energy demand worldwide through generating electric power. Present paper proposes a novel solar photovoltaic (SPV) device model that achieves optimal power efficiency from simulation and graphical performance analysis of SPV device characteristics. First of all, power as well as current performances is compared for varying irradiance and temperatures circumstances. Then, output current characteristics of the SPV device for the proposed as well as existing model with variable temperatures is plotted. Later, power versus voltage performances of a SPV device for the proposed model with varying irradiance and temperature criterions is compared. Finally, power–voltage characteristics are plotted graphically for the existing as well as proposed SPV device model that achieves significant amount of output power for the proposed model than the existing model and optimal power efficiency is obtained for the novel SPV device model.

Keywords Photovoltaic (PV) · Solar photovoltaic (SPV) · Irradiance · Power–voltage · Optimal power efficiency (OPE)

1 Introduction

Among the world’s renewable energy resources, the solar photovoltaic energy demand is rapidly increasing worldwide for providing safe, secure, sustainable and affordable energy.

Maximum power for SPV device model is achieved from the graphical representation of current–voltage (I–V) characteristics according to the maximum power transfer theorem.

For fulfilling the increasing energy demands of worldwide, solar cell classifications as well as its appliances are studied [1]. Salient features of photovoltaic technology, prin- ciples of power generation, material absorption as well as implementations are explained [2]. In order to achieve environment dependent parameters, an innovative PV module

single-diode model is proposed [3]. Solar cell behavior of a PV module is represented by analyzing the electrical performance of two mono-crystalline PV cells [4]. Energy scavenging characteristics of a SPV device and modules for irregular shading and deviating situations along with bypass diode arrangements are discussed [5, 6]. A novel solar PV parameter evaluation technique for existing methods along with analytical combining, simulated annealing and derived modeling is explained [7]. In presence of irregular shading circumstances, maximum power point characteristics for a novel analytical model are represented [8]. In order to explain the irradiance and temperature effect of a PV module parameter, Matlab simulink is implemented [9]. A well-known numerical solar cell model along with software based simulation is represented [10]. The simulation characteristic of current–voltage behavior for an enclosed slab of a PV module is carried out [11]. By applying Matlab simulink, design and performance of solar photovoltaic cell block is characterized [12]. Using the fundamental theorem of one and two diode PV model, the simulated performance of photovoltaic module and array is expressed [13]. With the application of single-diode model principle along with series and shunt resistances, a PV array model is described [14, 15]. Imperfect shading effects of a PV system is simulated [16]. Using a single-diode mode, relative modeling

Online ISSN 2092-7592 Print ISSN 1229-7607

* Sabuj Sarkar

[email protected] Md. Mostafizur Rahman [email protected]

1 Department of Electrical and Electronic Engineering, Khulna University of Engineering and Technology, Khulna 9203, Bangladesh

2 Department of the Electronics and Communication Engineering, Khulna University of Engineering and Technology, Khulna 9203, Bangladesh

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as well as estimation of a PV cell is represented [17]. By applying an inclusive modeling method, photovoltaic arrays simulation is proposed [18]. Considering the photovoltaic impact of power system, continuing adaptation principle of a PV generation is explained [19]. In order to achieve maximum power from the solar photovoltaic panel, perturb and observe tracking algorithm is studied [20]. With the application of maximum power point tracking principle, photovoltaic arrays for a wide variety of techniques are explained [21]. In presence of varying environment circumstances, an advanced single diode PV modeling method is explained [22]. Internal model parameter of PV solar cell is described [23]. From the comparisons of different PV model characteristics, maximum power transfer criterion between the source and load is concentrated [24]. By a novel simulation and estimation method, irradiance on an irregular PV shaded plane for grid connected PV systems is studied [25]. In presence of irregular shading circumstances, the PV array characteristics with Matlab simulation modeling is implemented [26]. With the aim of compensating the energy crisis for the upcoming decades, photovoltaic energy obviously would be a key source of power for the future generation. However the main complexity associated with the photovoltaic energy is its low power efficiency along with high production cost.

Up to date, a small amount of output power can be taken from the existing PV models that are far below than the accepted level. Present paper concentrates on a novel solar PV model which raises the output power to a significant amount by achieving optimal power efficiency than the existing methods.

2 Formation of PV Device

Photovoltaic device is basically a semiconductor device that transfers photon energy into electric energy. Photovoltaic effect is a physical as well as chemical incidence that pro- duces voltage as well as current when the p–n junction of a photovoltaic device is exposed to photon light by means of solar radiation. In PV devices, a wide variety of semiconductor materials are doped with silicon composites.

Usually, flat pieces of p type and n type materials are used to form PV device when p–n junction is created between the p- type and n-type layer. In addition, PV devices can also be fabricated by using several other composites such as copper indium di-selenide (CIS), cadmium telluride (CdTe), and gallium arsenide (GaAs) etc.

Figure 1 describes the construction diagram of a PV device. Solar radiation by means of photon energy emits into the p–n junction of glass lens that generates a potential difference across the junction. As a result, the device allows current to flow through the circuit when the connec- tion between end terminals is made via metallic electrodes.

3 Photovoltaic Principle of PV Device

According to the basics of photovoltaic law, energy of sunlight is converted into electricity. It was Edmond Bec- querel who first discovered the photovoltaic effect in 1839.

Photovoltaic principle of a solar PV device is expressed in Fig. 2.

When photon energy hits the p–n junction of a solar PV device, electrons and holes are released from the junction with a certain amount of energy. Light energy is emitted only when the photon energy is equal to or greater than the band gap energy. An electron current called the electric current is created when the released electron flows through the circuit. This process continues by allowing electron to return back into the PV device system. Current–power characteristics of a PV device is shown in Fig. 3. The I–V curve of a PV device exhibits the downward characteristic while the power curve shows the upward characteristic.

When photolight energy emits from the p–n junction of a solar PV device and creates photon current, I_ph . The equation comprising diode current, short circuit current and open circuit voltage can be represented as:

Fig. 1 PV device construction diagram

Fig. 2 Photovoltaic principle of a solar PV device

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where I_d , I_ph , I_sc indicates the diode current, the photon current and the short circuit current respectively whereas V_oc denotes the open circuit voltage.

Figure 3 explains the output current and output power characteristics of a solar PV device for variable voltage criterions. At initial state when no resistance is present and the voltage across the circuit is zero then it is in the short circuit state and PV device draws maximum current termed as short circuit current, I_sc . In contrast, at open circuit condition when resistance is very much high then current flows through the circuit is usually zero and maximum voltage termed as open circut voltage, V_oc appears across the PV device.

At Short Circuit State, I = I_sc, V = 0, Power, P = V×I = 0×I_sc = 0

At Open Circuit State, I = 0, V = V_oc, Power, P = V × I = V_oc × 0 = 0

Thus at short circuit state, as the voltage drop across the PV device is zero and the maximum current, I_sc is drawn from the circuit, the power taken from the device is zero.

With increasing voltage causes power to increase while current magnitude remains almost steady and maximum power, P_max is achieved at a certain voltage, V_mpp and above that voltage current as well as power magnitude decreases abruptly and ultimately reaches to zero at open circuit state.

4 Equivalent Circuit of Single Diode PV Device

Figure 4 describes the equivalent circuit diagram of an ideal single diode PV device. The overall current–voltage curve of the equivalent circuit can be treated as a continuous function for a pre-defined set of operating criterions.

(1) I_d=I_sc

[ exp

(qV_oc nkT

)]

−I_ph

The operating principle for this equivalent circuit in terms of total output current, I_t can be expressed according to Kirchoff’s current law as the equation stated as follows:

where the photovoltaic current, the diode saturation current and the current that flows through the shunt resistances can be represented as I_ph,I_d,sat , I_sh respectively.

From the single diode model and according to Shock- ley equation, the diode saturation current I_d,sat can be expressed as:

where the diode ideality factor is termed as n . The series resistance, the diode reverse saturation current and the thermal voltage can be represented as Rs,I0 and V_T respectively.

The relation between Boltzmann’s constant k and charge car- riers temperature T_c can be expressed by means of thermal voltage, V_Th as follows:

In Eq. 4, q indicates the charge magnitude.

By combining Eqs. 2, 3 and 4, the total output current for a single diode PV device can be represented as:

This is the current equation for a single diode PV device equivalent circuit in which all the five parameters are essential.

By considering a PV device with identical and uniformly arranged N_s number of series cells. At equal irradiance and temperature states, I_e=I_device , and V_e=N_s×I_device . Thus, the maximum current, I_me for an existing single diode PV device becomes

For a single diode PV model, the existing peak current and voltage values is termed as I_e and V_e respectively.

(2) I_t=I_ph−I_d,sat−I_sh

(3) I_d,sat=I₀

[ exp

(V+IR_s nV_Th

)

−1 ]

(4) V_Th= kT_c

q

(5) I_t=I_ph−I₀

[ exp

(V+IR_s nV_Th

)

−1 ]

−V+IR_s R_sh

(6) I_me=I_ph−I₀

[ exp

(V_e+I_eN_sR_s nN_sV_Th

)

−1 ]

−V_e+I_eN_sR_s N_sR_sh

Fig. 3 Current–power characteristics of a PV device

Fig. 4 Equivalent circuit diagram of a single diode PV device

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The ratio of the electrical power output, P_out to the solar irradiance input, P_in is known as the energy efficiency, 𝜂 of a single diode PV model. In order to achieve the maximum efficiency, output power (P_out) must be equal to maximum power (P_max) because maximum efficiency can be obtained only when the maximum power is obtained from its output.

The input power, P_in can be attained by multiplying the incidence light irradiance and the PV device surface area. The maximum efficiency, 𝜂_max of a PV device can be achieved only when the PV cells is kept under the same irradiance and temperature conditions. The efficiency of PV device reduces when power is dissipated from the internal resistances. These internal resistances of the equivalent circuit can be represented as the paral- lel shunt resistance ( R_sh ) and the series resistance ( R_s ) respectively. For an ideal PV device, shunt resistance ( R_sh ) is very high and allows the circuit to pass current through an alternate path and the series resistance R_s remains very low ensuring no further voltage reduce for no load condition.

5 Proposed Novel PV Device Model

In order to achieve maximum power from the PV device, a current enhanced sensor is connected with the existing device. Figure 5 describes the equivalent circuit diagram of the proposed novel PV device in which total output current is increased because the photovoltaic current, I_ph is multiplied by Is . Is is the current that flows through the current enhanced sensor. Thus the total output current taken from proposed novel PV device can be expressed as follows:

(7) 𝜂= P_out

P_in ⇒𝜂_max= P_max P_in =

V_meI

me

P_in

(8) INovel=Is∗Iph−Id−Ish

5.1 Current Enhanced Sensor

In case of identical and uniformly arranged N_s series connected PV device with equal irradiance and temperature states, Inovel=Idevice , and Vnovel=Ns×Idevice . Thus, the maximum current, I_mn for the proposed PV device model becomes:

For the proposed novel PV device model, the peak current and voltage values can be expressed as I_mn and V_mn respectively. For the proposed model, the maximum efficiency becomes as follows:

The optimal power efficiency, η_opt for the proposed novel model can be achieved by the following equation.

While the existing PV device model only includes voltage, current as well as related PV parameter values, the proposed novel device model considers an extra current enhanced sensor. The current drawn from the current enhanced sensor is multiplied by photovoltaic current of the existing device model. Then output power for the proposed novel model along with the existing device model is graphically plotted and from the comparison of the two models, the optimal power efficiency, η_opt is achieved. The power efficiency increases significantly for the novel PV device than the existing PV device. In order to mitigate the global energy crisis towards the upcoming decades, this technology of solar PV device might open a new potential window.

6 Performance Analysis and Discussions

The performances are analyzed and evaluated through simulation of different parameters from their graphical comparisons. The simulations are done by using Matlab simulink toolbox. Current and power versus voltage characteristics of PV device is graphically represented in Fig. 6 for variable temperature circumstances. In the first plot of Fig. 6, photovoltaic current is represented for variable voltages and temperatures that shows at initial state i.e. short circuit condition, photovoltaic voltage is zero while photovoltaic current

(9) I_mn=I_s∗I_ph−I₀

[ exp

(V_novel+I_novelN_sR_s nN_sV_Th

)

−1 ]

− V_novel+I_novelN_sR_s N_sR_sh

(10) 𝜂= P_out

P_in ⇒𝜂_max= P_max P_in =

V_mnI

mn

P_in

(11) η_opt= P_novel−P_existing

P_existing

Fig. 5 Equivalent circuit diagram for proposed novel PV device

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is maximum. The photovoltaic current remains nearly constant for a certain increasing photovoltaic voltage with increasing temperatures and at a certain point, it decreases and reaches zero. It is seen that the higher the temperature, the earlier the open circuit condition occurs i.e. the current reaches zero than the lower temperatures. In the second plot of Fig. 6, power characteristics of a PV device for varying temperatures are represented. Initially i.e. at short circuit state, power taken by photovoltaic device remains zero.

Power increases linearly with increasing voltage as well as temperature and at a certain voltage reaches peak value and finally drops down to zero at open circuit condition. Thus it is evident that maximum power is achieved at higher values of photovoltaic voltage and lowest temperature compared to higher temperatures. Figure 7 describes I–V and P–V characteristics of a PV device in presence of varying solar irradiance and at 75 °C temperatures.

Based on intensity of variable solar irradiance, photovoltaic current and power achieve different magnitudes with increasing voltage. Thus maximum current and power are different for different solar irradiance. From the comparison, it is seen that for lowest irradiance and at lower temperature, lowest current and power is achieved than the higher temperature. As temperature increases, the power and voltage magnitude of PV device becomes higher and reaches the highest value when the irradiance is maximum. The maximum power achieved at a voltage of 17 V and after that voltage–power decreases and reaches zero. Figure 8 represents a comparison of PV device output current characteristics with existing as well as proposed model with varying temperature circumstances. Photovoltaic current performance of PV device exhibits different values for both of the proposed

and existing model with variable temperatures. For both of the proposed and existing model, PV device draws higher current with higher temperature values. The photovoltaic current reaches maximum at 85 °C for both the cases and proposed model shows greater photovoltaic current than the existing model.

Output power versus output voltage characteristics of a PV device for proposed model at varying temperature and irradiance circumstances is described by Fig. 9. From the figure, it is obvious that the PV device exhibits higher power at lower temperature than the higher temperature. As temperature increases, the PV device gets more and more warm, as a result the power magnitude decreases with increasing

Fig. 6 Photovoltaic current and power comparison of a PV device for

varying temperatures Fig. 7 Power and current versus voltage characteristics of a PV

device at varying sunlight conditions

Fig. 8 Performance comparison of PV device output current characteristics between proposed and existing model

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temperature values. This figure clearly insists that maximum power is obtained for proposed novel model in presence of highest irradiance and lowest temperature than that of lowest irradiance and highest temperature. Comparison of power versus voltage characteristics between the proposed novel model and existing model for varying temperature and irradiance conditions is carried out in Fig. 10. This comparison clearly depicts that the maximum power obtained for the proposed model is greater than the existing model.

Comparison of output power and temperature at varying voltage and irradiance conditions is represented in Table 1.

From the table, it is seen that at 20 °C and 1500 W/m², maximum power of 1813 W is obtained. The maximum values of power obtained for the proposed novel model and existing

model are 1813 W and 1500 W respectively at the voltage of 340 V. Thus the optimal power efficiency is obtained for the proposed novel PV model compared to the existing model and the optimal power efficiency for the novel method equa ls = [(1813 − 1500)/1500] = 21%.

7 Conclusions

The simulation studies for the output power and current of a PV device for the existing as well as the proposed model with varying temperature, voltage, solar irradiance circumstances are carried out. From all of the comparisons and measured values, it is obvious that power efficiency is improved significantly for the proposed novel model than the existing PV device model when all the parameters are varied concurrently. The optimal power for the novel PV device model is 1813 W which is obtained at 20 °C and thus the optimal power efficiency obtained for the novel model is approximately 21% above than the existing model.

Acknowledgements

The authors would like to acknowledge the support of Wireless Com- munication Laboratory, Department of Electronics and Communication Engineering, KUET, Bangladesh.

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