Usage of solar trackers in PV systems

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1 POSTER 2017, PRAGUE MAY 23 1 Usage of solar trackers in PV systems Badma BALZHINIMAEV 1, Dept. of Economics, Management and Humanities FEE, CTU in Prague, Technická 2, Praha, Czech Republic balzhbad@fel.cvut.cz Abstract. This paper discusses the usage of a solar tracker as the way to rease efficiency of PV system. In this paper the technique which allows to calculate solar radiation falling to the Earth s surface at any angle to the horizon and oriented in any direction on any given day is presented. The paper shows three different variants of power supply of a decentralized object and their economic evaluation. The economic model is conducted by using Excel. The present net value and the minimum price per 1 kwh are used as a financial criteria for evaluating. Keywords Solar energy, solar tracker, photovoltaic system, renewable energy sources, economic evaluation, net present value. 1. Introduction At the present time, the energy is an essential service for every human being in every country. It s noticed that the energy consumption has been rapidly reasing in the world over the last 60 years. Due to depletion of conventional energy sources people see the need of usage of renewable energy sources, and their utilization is reasing. In comparison with all available non-conventional energy sources the solar energy looks as the most promising direction of renewable energy development. The solar energy mainstreaming is characterized by the following advantage factors: ease of operation, inexhaustible resources, environmentally friendly and widespread energy. Today among diverse types of solar energy technologies photoelectric conversion of solar radiation is one of the perspective directions to produce electrical energy. The most relevant and cost-effective way of utilization of PV systems is as a power supply of decentralized objects in remote areas. The substitution of diesel generators for PV systems in case of decentralized objects allows to solve energy and ecology problems, in a large number of cases it is economically feasible. Thus the rease of efficiency of PV system is relevant and important task. But on the other side a PV system has a number of disadvantages. Along with the high cost and low efficiency of photoelectric cells, there is one of the main problems of PV system utilization - decrease of its efficiency when disordered orientation to the Sun is occurred. In this work, the solution of the problem is usage of solar tracker. 2. Solar tracker A solar tracker is a device that is designed to track the Sun s position. These devices change their orientation throughout the day to follow the Sun s path in order to maximize energy capture. Sun tracking systems are divided into systems with single axis orientation and dual axis orientation. Single axis orientation systems are usually set at a fixed angle to the horizon and only take into account the azimuthal movement of the Sun. Two-axis orientation systems track by both coordinates - the azimuth and zenith angles. We can also classify solar trackers by methods of driving (rotating): passive, active and manual. 1. The mechanism is considered as a passive tracking system when low boiling compressed gases are used in the rotary mechanism. Low boiling compressed gases under the influence of the sun's heat pass into the gas state, then they begin to move and the photoelectric converter changes its position. The passive sun tracking system have a lower efficiency of tracking. 2. Active tracking systems are controlled by using programmable controllers, microprocessors or control devices with GPS navigation. So, photoelectric converter changes its position using predetermined program which uses time-dependent function. In addition to this function of time, tracking can be performed with the functions depending on the solar radiation. Electro optical control unit tracks the sun by a solar detecting device that is sensitive to solar radiance. Changes occur according to the signals produced by photo sensors. When these different signals reach the control system, they are evaluated and then the required instruction signal is sent to the motor, which moves the PV panel. Se active systems rely on motors, gear trains or hydraulics they require additional energy. [1] 3. Manually. Operator can adjust the second axis on regular intervals throughout the year. Therefore, all types of tracking systems described above provide the highest solar radiation ome on the surface of a solar panel. The main advantage of solar trackers is that the system can significantly rease the power output by up to 30-45% compared to fixed-tilt solar

2 2 B.BALZHINIMAEV, USAGE OF SOLAR TRACKERS IN PV SYSTEM, POSTER 2017 CONFERENCE panels in case of single axis tracking and additional 5-10% in case of dual axis trackers. But the constraint factor of usage of solar trackers is that the trackers are more expensive than their stationary counterparts, due to the more complex technology and moving parts necessary for their operation. Correspondingly the trackers require more maintenance. [2] To provide maximum efficiency the solar tracker should have not only high performance, but also mechanical resistance, accuracy and fixation of position even in adverse conditions. Whether solar trackers are beneficial and recommended is dependent on various factors, luding weather, installation location and definitely the cost of the system. Se the solar trackers can improve efficiency of all solar power supply system the question Are they worth it? is arising. So, the goal of the work is to decide whether usage of solar tracker is economically feasible or not. For this purpose, I will use a technique which allows to calculate the hourly flow of the total solar radiation falling to the Earth s surface at any angle to the horizon and oriented in any direction on any given day. Beside that the technique allows to calculate the total solar radiation at the angle which is perpendicular to the flow of oming radiation meaning that the solar panel tracks the Sun. 3. Calculation technique The figure 1 shows the diagram which is necessary for the calculation of oming solar radiation at any oriented plane. Fig. 1. Calculation diagram of oming solar radiation at any oriented plane [3] 1 vertical plane; 2 lined plane; 3 horizontal projection of a normal to an lined plane; 4 horizontal plane; 5 horizontal projection of sunlight; Z normal to a horizontal plane; n normal to an lined plane; S direct sunlight to Earth s surface; α- solar altitude; β solar azimuth angle; γ plane azimuth angle; Q angle of idence of direct solar radiation; s plane lination angle (tilt angle). For the calculation it s necessary to introduce the following terms: Angle of idence of direct solar radiation Q (rad) the angle between the direction of radiation on any surface and the normal to the surface; Declination δ (rad) the angular position of the sun at solar noon relative to the plane of equator (the value is positive in the northern hemisphere); Plane azimuth angle γ (rad) deviation of the normal to the plane of the local meridian; Solar altitude α (rad) the angle between the direction of the direct solar radiation and the horizontal projection of the sun's ray; Solar azimuth angle β (rad) the angle between the horizontal projection of the sun's ray and the direction to the south; Hour angle ω (rad) the angle that determines the angular displacement of the sun during the day. One hour corresponds to π / 12 rad of angular displacement. At noon, the hour angle is equal to zero. The hours before noon angle are considered as a positive values, in the afternoon negative. When the solar radiation coming on any lined plane is calculated, the three components of radiation balance is taken into consideration: Q = S D R (1) Where Q total solar radiation which is ident on the lined surface, W/m2; S direct solar radiation which is ident on the lined surface, W/m2; S direct solar radiation which is ident on the lined surface, W/m 2 ; D diffuse solar energy which is ident on the lined surface, W/m2; R solar radiation reflected from the Earth's surface W/m2. S = S ort cos (2) Where S ort solar direct radiation which is ident to the orthogonally oriented to the rays panel, W/m2; S ort So sin = sin c Where S 0 solar constant which is equal to 1395 W/m2; с dimensionless coefficient characterizing the degree of transparency of the atmosphere. Angle of idence of solar radiation on the panel at different angles to the horizontal plane is determined by formula: Where φ geographic latitude, rad; δ sun declination, rad; s - plane lination angle, rad. (3)

3 POSTER 2017, PRAGUE MAY 23 3 The calculation of the amount of oming solar radiation in case of sun tracking is performed at the angle which is perpendicular to the flow of oming solar radiation, consequently the angle of idence of solar radiation θ is equal to 0. So by setting the angle to be equal to 0 the perpendicularity of Sun rays can be obtained. Estimation of the value of the Sun declination can be determined by the formula of Cooper: 284 N = 0 sin(2 ) (5) 365 Where δ 0= sun declination for the northern hemisphere; N serial number of day in a year, counted from January 1; Sun altitude is determined by the formula: sin = sinsin cos cos cos (6) Diffuse solar radiation coming to the panel is determined by the formula: 2 D = D hor ( cos 0.313(cos ) ) (7) Where D hor flow of diffuse solar radiation which is ident on a horizontal surface 1 Dhor = ( Q0 Qort )sin (8) 3 Reflected solar radiation ident on the lined plane from the Earth's surface R_ is negligible does not have significant effect on the total ident energy. Thus, using the formula given above, the total solar radiation which is ident on the panel in clear weather conditions at different angles of lination to the horizon can be calculated by this formula: Q (, s, = S (, s, D ( s, (9) Where φ geographic latitude, rad; ω hour angle, rad; γ the deviation of the normal to the plane of the local meridian, rad; N serial number of day for the year; S direct solar radiation, W/m2; D diffuse solar radiation, W/m2. k = 1 ( a 0.38n) n) (10) Where a empirical coefficient depending on the environment (land or sea) and on the latitude; n the number of clouds as a decimal (n = 0 - cloudless sky, n = 1 cloudiness). This number can be found on the basis of meteorological observations database. Thus, the total solar radiation falling on the panel lined to the horizon at an optimum angle in case of cloudy weather conditions can be calculated by using the following formula: Q D (, s, = S (, s, (11) ( s, k The panel tilt angle s varies from 0 to π / 2, where the angle of 0 corresponds to a horizontal oriented panel, and π / 2 to vertical oriented panel. Plane azimuth angle γ ranges from - π to π, where the angle of 0 corresponds to plane oriented to the south, π / 2 the south-east, π / 2 the southwest. It can be concluded that by setting the orientation of angles of the panel and using the above-mentioned formulas, the amount of ident of solar radiation for any given location and at any day and time of the year can be determined. Thus, by using above described technique it s possible to calculate the level of specific insolation for a typical day at a different weather conditions (sunny, cloudy or partly cloudy) for analyzed month. As a typical day it is recommended to take the middle of the month. Characteristics of cloudiness can be determined on the basis of meteorological observations database. 4. Case study To reach the goal it s necessary to introduce the object of investigation. At present time, there are only 156 meteorological stations remained in Russia which had been making continuous observations throughout the 20th century. In some regions (Arctic, the central regions of Siberia and the Far East), the density of meteorological stations is reduced by dozens. So it s one of the main reasons of inaccurate weather forecasting on our vast territory. In this work, the object of investigation is a meteorological station which carries out 24 hours regular observations. The weather station is designed for autonomous measurement and transmission of meteorological variables and is located in the remote South- East part of Russia - area with decentralized power supply. The exact coordinates of the object are degrees of north latitude and degrees of east longitude. The station has the following: a set of meteorological and hydrological sensors; the central point which performs the processing of information coming from the sensors; storage for results before their transfer; the creation of the codes; radio transmitting apparatus; power source etc. Apart from that the weather station ludes the following elements: lighting, computer, display board, surveillance, alarm, heating system. The maximum power of object is determined and equals to 1.4 kw. The annual energy consumption of the object is W con = 7744 kwh/year (where in winter period W con per day is equal to 26.9 kwh, summer kwh). The typical constant load diagram of weather station is presented below.

4 4 B.BALZHINIMAEV, USAGE OF SOLAR TRACKERS IN PV SYSTEM, POSTER 2017 CONFERENCE Fig. 2. Daily load diagram of weather station To power up the object the three technical solutions of power supply are suggested: Variant 1. Power supply system is on the basis of petroleum generator. The petroleum-based generator KIPOR KGE2500E with nominal power of 1.7 kw is considered as the main source of power supply. The fuelconsumption rate of generator is l/kwh. The same generator is considered as a backup source needed for reliable and uninterrupted power supply. Overall amount of fuel needed to cover annual energy consumption is equal to 3380 liters/year. Lifetime of the generator is operating hours (about 5.7 years). According to above described technique the amount of ident solar radiation falling on the plane area of 1 m2 for both variants was identified. For example, the data of solar radiation in January, April, July and October is presented in the table 1. Variants Jan Apr Jul Oct Fixed position of Q ins, panels kwh/m 2 /day Optimum tilt angle degree Panels track the Sun Q ins, kwh/m 2 /day Efficiency performance of rease by % Tab. 1. Amount of ident solar radiation It can be seen from the table 1 the amount of ident solar radiation that falls on the lined panel at the perpendicular angle is higher by about ~ 10% in winter period and ~ 43% in summer period. To calculate the energy produced by a solar panel, the formula below was used. W = Q ns panel ins (12) Where Q ins the daily average amount of solar radiation, kwh/m2/day; n - efficiency factor; S panel - working area of solar panel, m 2. Variant 2. PV system with manual changing of position of solar panels. The variant provides that the position of panels is fixed and lined at the optimum angle to the horizon every month. Taking into account the location and weather conditions of the object, petroleum-based generator is accepted as the additional source of power supply in the energy balance of photoelectric system due to inexpediency of year-round electric power supply from a photovoltaic station. Where large part of produced energy is provided by photovoltaic panels but the rest amount of necessary energy is covered by generator. The PV system consist of: 16 solar panels FSM 250M with 15.6% efficiency factor, inverter MAP PRO ; controller Midnite Solar Classic 150 MPPT, 12 accumulator batteries Delta GX and generator is the same as it was considered in the first variant. The total energy produced by PV system is 6897 kwh which covers of 75.9 % of required energy where 24.1% is covered by generator. In this case, PV system decreases the fuel consumption by 2530 liters/year (see table 2). Variant 3. PV system with two-axis solar tracker. This variant ludes solar tracker that allows to track the Sun in both coordinates (tilt angle and azimuth). In this case the system is differed only by added dual axis solar tracker D DUAL. Self-consumption of energy is taken into account. Here, the PV system covers of 75.9 % of required energy and allows to decrease the fuel consumption by 2657 liters/year. PV PV + tracker Total installed capacity, kw 4 4 Total energy production, kwh Coverage of required energy 75.9% 79.4% Share of generator production, kwh Number of working hours of generator Fuel consumption, l Tab. 2. PV system performance 5. Economic evaluation The investments costs were identified based on statistical analysis of current prices of equipment on the Russian market for Se the object is located in remoted area the installation and transportation costs of all power supply stations is estimated 20% of total price of the station. The other equipment luding protection and measurement devices, cables, supporting structures and monitoring systems is estimated as 15% of total price. Maintenance of different variants was obtained according to the interview with Russian solar energy companies. Degradation rate 0.73 % of PV panels is taken into account. Var. 1 Var. 2 Var. 3 Lifetime of project 25 years Discount rate 8.83 % Annual fuel growth rate 6.84 % Total investments, rub Maintenance of generator, rub/year Maintenance of PV, rub/year Cost of fuel consumption and transportation, rub/year Tab. 3. Economic data of variants

5 POSTER 2017, PRAGUE MAY Results For the economic evaluation of the variants the net present value (NPV) technique is used. The values of minimum price on electricity produced of considered variants will be compared between each other. The calculation is made by means of Microsoft Excel. Variant 1. Generator Variant 2. PV system Variant 3. PV + tracker NPV, mil. rub Min. price, rub/kwh Tab. 4. Results Take into account the indicators presented in the table 1 we see how trackers can rease the amount of ident solar radiation compare to the fixed position. Despite that fact, the economic performance of solar trackers is not attractive to compare with PV without tracker, though the difference between values is not significant (see table 4). But both these PV cases are better than the generator variant due to operating costs of generator such as maintenance and fuel consumption, especially, in remote areas where the costs for services are higher by 40-60% depending on the distance to the object. 6.1 The sensitivity analysis In this work the sensitivity analysis is based on such important inputs as: discount rate, investment costs. The analysis of the investments cost is shown in the figure 3. The prices of all used devices in the PV systems can be changed. A few years ago the photovoltaic panels have been passing developmental revolution. The decrease in price of solar panels can be the reason of price reduction on all equipment associated with solar energy, especially accumulator batteries. As for generator variant there is only small influence. According to figures presented above the figure 4 shows that as long as the discount rate reases the NPV value decreases. Such a strong dependence of NPV on a discount rate the wrong estimations of the discount rate can bring a significant impact to the results. That s why it s very important to choose a proper rate. 7. Conclusion There are few powerful factors which have influence on the results performed in the table 4. First factor, solar trackers require more maintenance due to the more complex technology and moving parts. Second, the performance of solar trackers in the winter period when it s really needed is not sufficient to satisfy energy requirements of the object. The third factor is today s cost of solar trackers which is significantly high. In some cases the price of trackers can exceed the price of PV system itself. But to compare with the generator variant both PV systems have advantage results. Because of implementation of PV, system reduces both fuel consumption and the working hours of generator. The solar panels decrease working hours of generator by 6489 hours in the variant without tracker and by 6816 hours in the variant with solar tracker thereby decreasing the maintenance of generator and extending its lifetime. Based on the results of this paper it can be said that usage of solar trackers at present time is not economically efficient, but usage of PV systems to provide energy is the primary way of development of energy supply systems for isolated consumers. Fig. 3. Dependence NPV on investment costs References [1] A. A. TARAN and A. V. LOHMANOV, Sistemy slezheniya dlya solnechnykh elektrostantsiy - Tracking systems for solar power plants, Eng. Acad. Don state Agrar. Univ., pp , [2] B. WICHERT, PV-diesel hybrid energy systems for remote area power generation A review of current practice and future developments, Renew. Sustain. Energy Rev., vol. 1, no. 3, pp , [3] B. V. LUKUTIN, I. A. PLOTNIKOV, Sistemy elektrosnabzheniya s vetrovymi i solnechnymi elektrostanciyami - Power supply systems with wind and solar power, pp , Fig. 4. Dependence NPV on discount rate

6 6 B.BALZHINIMAEV, USAGE OF SOLAR TRACKERS IN PV SYSTEM, POSTER 2017 CONFERENCE About Authors Badma BALZHINIMAEV, was born in Ulan-Ude, Republic of Buryatia, Russia. Currently, student of master s double degree program between Tomsk Polytechnic University and Czech Technical University in Prague.