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Basics of Solar Energy Concentrators

Habiba Mushtaq, Amina Khan and Haq Nawaz Bhatti*

Department of Chemistry, University of Agriculture, Faisalabad, Pakistan

Abstract

The expenditure on fossil fuels drastically affects our global environment and requires cost-effective and eco-friendly energy resources. Solar power concentrators have been gaining ever-increasing attention from academic researchers and industrial developers owing to their stationary feature for solar energy collection with higher efficiency and the fact that they are economically feasible, have a green nature, and are easily accessible. The solar energy concentrator captures the sun's energy with large lenses or mirrors that focus the sunlight onto the receiver surface. It first transforms into thermal energy that rotates the generator's turbines to produce electricity. Solar concentrators enhance irradiance by implementing optical techniques like a tracking system, lenses, and mirrors. Various mathematical models and computational methods are used to view the theoretical detail and calculate heat and electricity generation in CSP. This study aims to supply a broad understanding of CSP-based theories and models and provide help to researchers, engineers, etc. The CSP has the potential to reconstruct renewable energy resources and to transition globally toward a clean and sustainable energy system in the future.

Keywords: Azimuth, CSP, radiations, power plant, trackers

1.1 Introduction

There is a need for substitute energy sources to meet the demand for power in the world due to the increasing emergence of appliances such as computers, mobile phones, televisions, etc. There is a need to enhance the efficiency and lower the price of electricity production. Different alternatives are used to meet this requirement [1]. Concentrating solar power (CSP) is a system that produces power. It transforms solar energy into heat energy through a solar concentrator and then heat energy into power generation. The photovoltaic system is a comparatively different system than concentrating solar power. The heat energy from the sun is utilized by the CSP system rather than the photon energy used by the PV system, as shown in Figure 1.1. CSP has four main categories: (1) parabolic trough, (2) power tower, (3) linear Fresnel, and (4) dish. The dish uses the Stirling engine system to concentrate thermal energy. The CSP system consists of mirrors or lenses to target a vast area of sunlight, while solar power energy (SPE) focuses on confined spaces. A heat energy source is enlarged when solar power plants are coupled with a fossil fuel burner [2].

The previously published data have demonstrated that solar energy photovoltaic transformation productivity increases when radiation intensity falls on a photoelectric converter, and the productivity of solar energy photovoltaic conversion increases, similar to transformation into SPE. The capability of solar energy photoelectric conversion increases with the high concentration of radiation descending upon the solar converter [3]. Lowering energy production costs and improving efficiency using concentrated solar radiation are feasible. There is another alternative way to increase power capacity, that is, by photovoltaic cells, which can be adjacent to the CSP system. One of the main options is to use high-energy photovoltaic cells depending on solar cell arrangement with big solar energy concentrators. These concentrators work by collecting rays that have been refracted or reflected into a central axis focal point, where a radiation converter-receiver is mounted [2].

Figure 1.1 Mechanism of a solar energy concentrator.

1.2 Solar Tracking Systems (STS)

Many scholars have continuously developed solar trackers to facilitate the productivity of solar energy captured during dawn. To ensure optimum energy capture, solar cells are positioned optimally in the daytime. Efficiency using the sun tracking approach is 6.7% greater than efficiency using the fixed angle. The solar panels would be placed so that sun tracking would maximize electricity and boost production by 30%-40%, which is substantial enough to make sun tracking a practical option. This system keeps the solar insolation perpendicular to the solar radiation beam in solar cells. Solar cells are projected to carry the solar beam vertically to the PV panel. The position of the tracking method can attain the optimum angle of incidence. The astrotracker's role ought to reach an optimum angle of incidence, and the PV panel generates the highest amount of electrical energy.

The accurate positions of the tracking system are solar irradiance, solar azimuth angle, elevation angle, inclination angle, declination angle, and zenith angle. The altitude and azimuth angle are essential to demonstrate the sun's position [4, 5]. The light source's solar power and luminescent flux compute the solar irradiance. Solar tracking systems can move automatically or manually. A solar tracking system usually involves several components, including one or two motors, several kinds of optical sensors, and a backup energy source. These elements are categorized according to numerous parameters like the force that moves their portable devices and the mode of working.

1.2.1 Types of Solar Trackers Based on Techniques

A solar tracker is divided into three main types based on technologies that direct the Pv panel fluctuation: (1) passive tracker, (2) active tracker, and (3) chronological tracker system [5, 6]. Table 1.1 shows the comparison between these tracking systems.

1.2.2 Passive Solar Tracker

Without mechanical drives, it can point its sensor units toward the solar radiation beam. The passive tracker uses direct energy generated by the sun's thermal energy, as shown in Figure 1.2. These trackers typically have two actuators loaded with expandible gas or an alloy. This tracker has used the principle of thermal expansion or variation in pressure between two sites at the end of this system. When the position of the PV panel is erect to the sun, both sides of the tracker are balanced. One side of the tracker becomes heated, expanding and coming into touch with the other when the sun rotates, which causes the PV panel to rotate. Zomeworks Corporation unveiled the first passive solar tracking device for commercial use in 1969. Compared to fixed PV panels on Zomeworks Track Racks, PV panels with tracking systems can produce 25% more electricity [7]. This system makes operation more straightforward because most include two actuators competing and balanced by equal illumination. A passive tracker is affordable due to cheap and easy repairs but is less accurate. The tracker has a shock absorber that blocks the tracker from the sudden movement of the wind [8]. However, the precision of this method of tracking the sun could be better, and it mostly depends on the local weather. The site chosen for installing the solar tracker is essential since it must get enough continuous sunshine for an effective heating method [9].

Table 1.1 Differences between different solar trackers.

Technology Description Advantages Disadvantages Passive

• Thermal expansion material or imbalance in pressure between two points at the both end of tracker

• Work without using motor or actuators
• Easy installation
• Low maintenance cost

• Strong dependance in weather condition
• Low in accuracy

Active

• Use sensors and motor

• More accurate
• Efficient in tracking the position of sun

• Require the extra power consumption
• Not very accurate under cloudy day

Chronological

• Time based tracking system
• Rotate at 15° per hour

• No energy looses
• Low tracking error

• Continuous rotation requires more energy
• Unnecessary work under cloudy day

Figure 1.2 Passive solar tracker.

1.2.3 Active Solar Tracker Active

This system has an electric system and a photoresistor, which controls the motor to regulate tracker movement. The astrotracker continually determines the location of the sun using the available sensors. A sensor will cause a motor or actuator to move its fixture in response to sun radiation [9]. If the sun's radiation is not right on the tracker, one light sensor will be illuminated differently from another. The direction is calculated using the difference when the tracker must be pointed perpendicular to the sun. A light-dependent resistor with a variable resistor, which relies on radiation incidence, is a commonly used photo sensor. Due to an electrical component that is climate- and lightning-sensitive, this device has a low level of reliability. It operates on the sensor. Thus, its tracker may become blocked, causing significant issues and impeding energy production. As a result, this system is constantly under observation [10]. It is classified into four types placed on their tracking techniques. Microprocessors, electro-optical sensors based on date and time, auxiliary bifacial solar cells, and a combination of the...