Green Energy: Renewable Power Generation from Solar PV Cells

Impact of Irradiation, Materials and Aging on Solar Power Generation, and Green Materials for Solar Power Extraction

M. A. ASHA RANI¹’, M. CHAKKARAPANI², and PRANJIT BARMAN³

¹ Department of Electrical Engineering,

National Institute of Technology, Silchar 788010, Assam, India

department of Electrical and Electronics Engineering, Madanapalle Institute of Technology and Science,

Madanapalle 517325, Andhra Pradesh, India

department of Chemistry, National Institute of Technology, Silchar 788010, Assam, India

*Corresponding author.

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ABSTRACT

Concern over the limited stock of conventional energy sources such as coal and other petroleum products has fuelled efforts toward the development of renewable sources of energy that have a lesser footprint on the environment. Materials and technologies play a vital role that can offer promising solutions to achieve renewable and sustainable pathways for the future. Of these renewable sources, solar radiation is the most abundant and freely available and can be directly harnessed by the use of photovoltaic (PV) modules. This chapter is based on the renewable power generation from solar PV cells. In this chapter, we will discuss about the renewable power generation scenario; working of a solar cell; model of solar PV module; the impact of PV cell material in PV characteristics; the effect of DC link capacitor material in power converters; challenges involved in solar power generation, and their mitigation techniques; and green materials using green chemistry for fabricating the future solar PV cell and DC link capacitors.

INTRODUCTION

Escalating demand for energy, the depleting fossil fuel reserves and the growing concerns over environmental degradation have brought in new paradigms in the global perspective and in India as well. Concern for clean energy reducing the dependence on fossil fuels has provided a huge impetus to the search for alternative renewable energy sources that have a lower carbon footprint on the environment. The use of renewable energy supplements the energy needs and thereby reduces the environmental impact, which is the prime concern of many countries around the world. Renewable energy sources such as wind and solar become more competitive in the market owing to the technological advancements, reduced cost, and governmental incentives. Among these renewable alternatives, solar energy is freely available in unlimited quantity, and the conversion of solar energy to electricity using photovoltaic (PV) modules does not require any moving parts. The amount of solar radiation striking our earth’s surface is about 10,000-times higher than the current global electrical energy consumption. PV cells convert sunlight directly to electricity and can be influential in meeting the world’s energy demand. Hence, this technology is gaining popularity due to its reducing cost, substantial investment in research and development, and attractive government subsidies.

RENEWABLE POWER GENERATION SCENARIO

Based on the geographical location and climatic conditions, there is a tremendous scope of harnessing the solar power using the unutilized space and wastelands around the fields and buildings. Thus, installing and commissioning solar power plants will be the appropriate cost effective solution for an environment friendly power generation mitigating the dependence of fossil fuels.

Solar energy has a tremendous potential with an average availability of 300 solar days per year. Via several energy policies, state and central governments of various countries are providing incentives for solar power generation and also for various solar applications in addition to the technical forums and seminars/conferences conducting worldwide for creating awareness.

Confederation of Indian Industry (CII) generally organizes conferences in India on an annual basis at different parts of the country, which serves as an ideal platform for participants to gain a strong understanding of the power scenario in the near future, challenges to be addressed, opportunities for industries and the role of various stakeholders in this. The prime objectives of the conference are to explore the opportunities for organizations in the power and renewable sector; to connect with key stakeholders on the issues pertaining to power and renewable sector, and understand the measures to be taken at various levels that will ensure reliable power for all, both in quality and quantity; to convene thoughts and ideas on making power sector in South India more vibrant to support the national GDP goals; to bring in experts from across the globe to know the clean energy drive; and to understand new and innovative technologies, systems, and business models in power sector.

Similarly, Ministry of Science and Technology under Government of India regularly conducts seminars and is looking for innovative ideas in order to overcome the challenges related to global climate change and energy crisis.

In India, government has set a goal that solar energy should contribute to 8% of India’s total consumption of energy by 2022 such that solar is going to play a key role in shaping the future of Indian power sector.

Also, Government of India has taken initiatives to enhance renewable power generation in an effective way that includes no further installation of thermal power plants to avoid carbon emission, electrifying all the light motor vehicles by 2030, and electrifying all the vehicles including heavy duty vehicles by 2050 to minimize the emission of CO, by 0.3 kg/unit of thermal power generated.

WORKING OF SOLAR CELL

A solar cell is a photo detector with a p-n junction illuminated to generate DC current. A typical silicon solar cell is composed of a thin wafer layer of 11-type (pentavalent dopant) silicon as top layer, and a thicker p-type (trivalent dopant) silicon layer at bottom as shown in Figure 5.1. The contact between the two materials forms the p-n junction, which has a built-in electrical field in the depletion region.

The photovoltaic process of current generation in a solar cell involves two steps. The first step is the absorption of incident photons to generate electron-hole pairs. Electron-hole pairs can be created only if the incident photons have energy greater than the semiconductor bandgap. In the second step, electrons and holes are separated by the electrical field in the junction depletion region and flows through the external circuit.

Generally, solar panels are connected in series or parallel to meet the energy demand as detailed below.

(a) Connecting Solar Panels in Series

Generally, solar panels are connected in series to increase the terminal voltage of the solar PV system. By connecting the solar panels in series (similar solar panels), the total output voltage of the array obtained will be the sum of individual panel voltages as shown in Figure 5.2.

FIGURE 5.2 Series coimection of solar panels.

(b) Connecting Solar Panels in Parallel

Solar panels are connected in parallel to enhance the overall system current. By connecting the solar panels in parallel, the total output voltage remains the same as if in a single panel, whereas the output current will be the sum of the output currents of individual panels as shown in Figure 5.3.

MODEL OF A SOLAR PV MODULE

A solar PV module consists of several cells in series. A single cell, expressed by its single diode equivalent circuit, is shown in Figure 5.4. Therefore, the characteristics of the PV module can be obtained by connecting the models of several such cells in series. The relation between voltage and current of a PV module can be expressed as:

where, 7_pv is the current generated by the module; I _h is the light generated current; / is the reverse saturation current; V_pv is the PV voltage; and A = nkT/q. Here, n_s is the number of series-connected cells; к is the Boltzmann's constant; T is the temperature of the module in Kelvin; q is the elementary charge; and R_t and R_A are the series and shunt resistances, respectively. The light generated current (Kadri et al. (2011)) is given by the equation:

where, I is the short circuit current of the module at standard iiradiance G_o (1000 W/m²) and standard temperature Г (25°C), and a._{ is the module’s temperature coefficient for current.

IMPACT OF SOLAR IRRADIATION ON PV CHARACTERISTICS

From eqs (5.1) and (5.2), it is clear that the module output current is directly proportional to the irradiance level G. The specifications of a typical PV module at standard test conditions (STC) of 1000 W/nf, 25°C and air mass (AM) are given in Table 5.1.

TABLE 5.1 PV Specifications at STC 1000 W/nf, 25°C, AM 1.5.

Figures 5.5 and 5.6 illustrate the current-voltage characteristics and the power-voltage characteristics of the above PV module.

FIGURE 5.5 I-V characteristics of the PY module for different irradiance levels.

FIGURE 5.6 P-V characteristics of the PY module corresponding to the I-V curves of Figure 5.2.

It is observed from Figure 5.6 that there is a unique operating point called the maximum power point (MPP), at which the PV module generates power that is greater than that at all other points on the curve. Further, the maximum power and the voltage at which the maximum power occurs are different under different insolation conditions as shown in Figure 5.6. Therefore, it is clear that the MPP of the PV module varies according to the solar irradiance, under varying environmental conditions.

Here, the variation in short circuit current (7 ) is proportional to the solar irradiation, whereas open circuit voltage (F_oc) varies logarithmically with irradiation and hence the power also changes with respect to irradiation. From the characteristics (Fig. 5.6), it is evident that Fmpp is decreasing when the irradiation decreases from 1000 to 250 W/m². However, Fmpp is almost constant with slight decrement with respect to the irradiation.

In addition, the important thing to be noted is that there is a significant impact of the material used for making the PV cell on the P-V characteristics of the module since all the parameters mentioned above such as PV power, open circuit voltage, short circuit current, MPP voltage, and MPP current will vary due to the variation of series and shunt resistances, R_t and i?_sh, respectively, and a, is the module’s temperature coefficient for current in eq 5.2. This is discussed in Section 5.4.