Научная статья на тему 'Dispersed renewable generation in the power supply system of an industrial enterprise: technical feasibility and economic effectiveness'

Dispersed renewable generation in the power supply system of an industrial enterprise: technical feasibility and economic effectiveness Текст научной статьи по специальности «Электротехника, электронная техника, информационные технологии»

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Ключевые слова
COST-EFFECTIVENESS / ENERGY POTENTIAL / INTEGRATION / POWER SUPPLY SYSTEMS / RENEWABLE ENERGY RESOURCES / SOLAR / WIND

Аннотация научной статьи по электротехнике, электронной технике, информационным технологиям, автор научной работы — Podkovalnikov Sergei, Polomoshina Marina

This paper is concerned with the possibility of using renewable energy sources for power supply to an industrial enterprise (a mechanical plant). We assessed the climatic conditions of the area and explored if it is possible to install renewable energy facilities (solar panels and wind turbines) at this plant. The assessment of climatic conditions in Irkutsk revealed that the use of wind turbines is not reasonable due to the weak wind activity in the city. However, this area has a relatively high potential of solar energy. The paper presents an in-depth analysis of the integration of solar panels into the power supply system of a mechanical plant. Their actual output depending on solar activity was calculated. Based on the area of the buildings roofs, the number of solar modules, inverters and other equipment pieces connected to them was calculated. The payback period of installed equipment was determined to assess the economic effectiveness. According to the assessment results, the economic effectiveness of their use is currently quite low. However, with the expected reduction in the equipment cost and an increase in electricity prices, renewable energy sources will become more cost-effective in the future.

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Текст научной работы на тему «Dispersed renewable generation in the power supply system of an industrial enterprise: technical feasibility and economic effectiveness»

Dispersed Renewable Generation In The Power Supply System Of An Industrial Enterprise: Technical Feasibility And Economic

Effectiveness

Sergei V. Podkovalnikov and Marina A. Polomoshina* Melentiev Energy Systems Institute of Siberian Branch of Russian Academy of Sciences, Irkutsk, Russian Federation

Abstract — This paper is concerned with the possibility of using renewable energy sources for power supply to an industrial enterprise (a mechanical plant). We assessed the climatic conditions of the area and explored if it is possible to install renewable energy facilities (solar panels and wind turbines) at this plant. The assessment of climatic conditions in Irkutsk revealed that the use of wind turbines is not reasonable due to the weak wind activity in the city. However, this area has a relatively high potential of solar energy. The paper presents an in-depth analysis of the integration of solar panels into the power supply system of a mechanical plant. Their actual output depending on solar activity was calculated. Based on the area of the buildings roofs, the number of solar modules, inverters and other equipment pieces connected to them was calculated. The payback period of installed equipment was determined to assess the economic effectiveness. According to the assessment results, the economic effectiveness of their use is currently quite low. However, with the expected reduction in the equipment cost and an increase in electricity prices, renewable energy sources will become more cost-effective in the future.

Index terms — Cost-effectiveness, energy potential, integration, power supply systems, renewable energy resources, solar, wind.

* Corresponding author. E-mail: polomoshina@isem.irk.ru

http://dx.doi.org/10.25729/esr.2019.01.0002 Received December 18, 2018. Revised March 19, 2019. Accepted March 26, 2019. Available online June 25, 2019.

This is an open access article under a Creative Commons Attribution-NonCommercial 4.0 International License.

© 2019 ESI SB RAS and authors. All rights reserved.

I. Introduction

In many developed and developing countries of the world, the share of renewable energy sources (RES) in energy balances is quite considerable and further increasing. The transition from conventional energy sources to renewable energy resources is gaining momentum and becoming increasingly global. According to the results of various studies, a gradual transition to renewable energy sources is expected in the near future. Despite the global trends, renewable energy in Russia is still in the early stages of development, although the formation of the renewable energy industry can have a significant positive impact on the Russian economy. For example, RES can foster the creation of new companies and jobs, and provide new opportunities for meeting the consumer loads in off-grid areas [1-4].

This study examines the integration of renewable energy sources into the power supply system of a mechanical plant. According to the project, the plant is located in Irkutsk, and climatic features of the area are taken into account. The input data contain the layout of the plant, including the shops located on the territory of the plant, and a statement of electrical loads of the plant with detailed information about consumers. The renewable energy sources are considered as complementary power sources. The paper describes in detail the integration of renewable energy sources into the power supply system of a mechanical plant, and presents the assessment of their economic effectiveness.

II. ASSESSEMENT OF RENEWABLE ENERGY POTENTIAL

in irkutsk

Many regions in our country (and the Irkutsk region is no exception) are promising in terms of the use of renewable energy, especially the energy of the sun. This is confirmed by the fact that the level of solar radiation in Irkutsk (located at a latitude of 52 degrees north) reaches 1340 kWh/m2, which is a fairly good indicator. The data on

Fig.1. Layout of the mechanical plant shops

the amount of direct solar radiation falling on a horizontal surface under a clear sky in Irkutsk are given in [5]. The highest solar activity is achieved in June at noon in clear weather and it is 2.81 MJ/m2 per hour. The rest of the time, this activity varies depending on the season, weather and time of the day. Thus, the Irkutsk region has a relatively good potential for the development of solar energy, which means that the use of solar panels at the plant is relevant.

In addition, Russia has a huge potential for wind energy. The large territory of the country and a wide climatic diversity foster the development of wind energy. The main indicator of the wind power potential is the annual average wind speed. Despite the wide climatic diversity, the annual average wind speed in most of the Irkutsk region does not exceed 3-4 m/s [6]. When the speed is less than 4 m/s, the use of wind turbines is not advisable, since the speed required for the normal operation of most wind turbines is 10 m/s. Consequently, it was decided not to consider wind turbines in the study.

III. Conditions for the use of solar panels at a mechanical plant

In this section, we analyze the possibilities of using solar panels at a mechanical plant, with the view to meeting demand for electricity by environmentally friendly energy sources.

Solar modules will be mounted only on the roofs of the shops and other buildings because other possible places

for their installation in the territory of the plant can be occupied by access routes, warehouses and other facilities. The roofs of the buildings are assumed to be horizontal and, therefore, the roof area will be equal to the area of the building. In addition, placement of solar panels on the ground may be inefficient, since in this case, shadows from fences and shops located nearby may fall on the panels and decrease their effectiveness. Therefore, the installation of solar panels on the roofs of the shops will provide the maximum possible output. Figure 1 shows the layout of the mechanical plant shops, and the area of the buildings. There are two groups of buildings at this plant:

• energy-intensive production shops with their transformer substation;

• non-production buildings which consume much less power and do not have their own transformer substation. The solar panels are supposed to be mounted on

the entire surface of the roofs of industrial shops. This will allow installing as many solar panels as possible and covering a significant part of the electrical load. At the same time, we need to bear in mind that the power generated by solar panels must not exceed the power load of the shop in order not to feed excess power back into the grid. Daily load curves of the shops are taken into account for this purpose. Such a constraint is imposed not to break the existing relations in the electricity and power market when its participants have a certain established status of electricity consumer or supplier. Moreover, reverse power

Photovoltaic modules

Tl- ——r-r

- + - +

iu!==mi=Sj

Fig. 2. A scheme of solar panels connection to consumers

Table 1. Actual output of one solar panel depending on the hour of the day and the season in Irkutsk (Wh)

Hours Month

I II III IV V VI VII VIII IX X XI XII

0-1

1-2

2-3

3-4 1.5

4-5 8.1 14.8 9.6 1.5

5-6 10.3 30.2 39.8 33.9 19.2 1.5

6-7 6.6 37.6 58.3 70.1 65.6 43.5 17.0 1.5

7-8 8.9 30.2 70.1 90.7 104.0 104.0 77.5 50.9 22.9 0.7

8-9 9.6 37.6 67.9 104.0 126.1 139.4 137.9 115.1 81.1 50.9 14.8 5.2

9-10 28.0 62.0 101.8 135.0 162.3 171.9 166.0 146.8 115.1 78.9 39.8 19.2

10-11 43.5 82.6 124.7 162.3 190.3 194.0 188.8 169.7 141.6 104.0 60.5 33.9

11-12 54.6 94.4 137.9 177.0 203.6 207.3 201.4 179.2 154.9 112.9 70.1 43.5

12-13 54.6 94.4 137.9 177.0 203.6 207.3 201.4 179.2 154.9 112.9 70.1 43.5

13-14 43.5 82.6 124.7 162.3 190.3 196.2 188.8 169.7 141.6 104.0 60.5 33.9

14-15 28.0 62.0 101.8 135.0 162.3 175.6 166.0 146.8 116.5 78.9 39.8 19.2

15-16 9.6 37.6 67.9 104.0 128.3 143.1 137.9 115.1 82.6 50.9 14.8 5.2

16-17 8.9 30.2 70.1 92.2 105.5 104.0 77.5 48.7 22.9 0.7

17-18 6.6 37.6 60.5 70.1 65.6 43.5 17.0 1.5

18-19 10.3 31.7 39.8 33.9 19.2 0.7

19-20 8.1 14.8 9.6 1.5

20-21 1.5

21-22

22-23

23-24

Diurnal 271 571 938 1393 1747 1896 1815 1505 1124 742 372 204

Monthly 8409 16007 29063 41750 54143 56872 56282 46619 33710 23014 11138 6344

Yearly 383350.93

Table 2. The results of calculation of solar panels area

Shop # Sshop, m2 S, m2

1 285 312.6

2 3222 3352.18

3 4880 5361.03

4 2560 2813.37

5 4268 4688.95

6 2290 2377.9

7 1067 1172.24

8 2134 2344.47

9 1280 1406.68

10 1494 1641.13

11 3841 3889.34

12 4723 4962.97

13 2788 3063.45

flows may require changes in the relay protection and automation organization in the power supply system of the plant, in the supply substation, and in the grid itself. Thus, the shops with low electricity consumption and non-production buildings should be equipped with a limited number of solar panels to meet the above constraint.

With a decrease in the power supplied from the grid due to the power received from solar panels, the previously selected transformer capacity, cable carrying capacity and switching devices were not revised. This slightly worsened the economic effectiveness of solar panels, however, was necessary because solar energy is unpredictable, it cannot be considered as firm and, therefore, it requires full redundancy. In this case, the grid plays a role of such a backup source. On the other hand, due to the connection of the solar panels to the centralized grid, it was decided not to use electric power storage for solar panels as an additional backup source. This will significantly reduce the cost of solar systems.

To synchronize and connect the solar panels to the power supply system of the plant we use grid-tie inverters. Grid-tie inverters are devices that convert DC voltage from renewable energy sources to AC voltage. They have a distinctive feature - the presence of synchronization of the output voltage and current with a stationary network. Thus, the grid-tie inverter converts direct current from solar panels to alternating current, with the appropriate values of its frequency and voltage phase for the connection with a stationary network. In our study, we use a three-phase inverter. In contrast to single-phase inverters, three-phase inverters evenly distribute energy received from solar panels between phases. In the case of three single-phase inverters, the output power of each inverter will fluctuate depending on the output of the solar panel connected to its input. If the power of solar panels is different and /or each solar panel is oriented or lit differently, then, accordingly,

the power supplied by different phases will be different [7].

Figure 2 illustrates the basic principle of connecting solar modules to a grid-tie inverter, and the joint operation of the inverter with a centralized grid.

IV Calculation of the actual output of solar panel

To perform further calculations, we selected solar panels "Sila Solar" with an installed capacity of250 W each [8]. These panels has a quite good output at a relatively low price in comparison with the panels of other producers.

The actual power of solar panels averages 75-85% of its rated power. This depends primarily on climatic factors, as well as the angle of inclination (the angle between the horizontal plane and the solar panel) and the orientation of these modules to the south (for the northern hemisphere). Solar panels achieve the highest efficiency when they are directed to the sun and their surface is perpendicular to the sun's rays. Solar panels are located on the roofs of the plant shops in a fixed position; therefore, they are not at a right angle to the sun's rays throughout the day. In this case, the tilt angle of the panels is selected so as to ensure that they are at right angles to the sun's rays during the longest time possible.

The optimum mounting angle of solar panels is chosen depending on the latitude of the area. In the city of Irkutsk, located at a latitude of 52 degrees, the optimum tilt angle is 36 degrees [9].

In this case, the solar panels located on the roofs of the shops are assumed to be south facing. As is seen from Fig. 1, such a geographical location of the panels provides the minimum deviation from the southern direction. With the deviation from the southern direction assumed to be equal to 5 degrees, the power output of solar panels is maximal [10].

To calculate the actual output of one solar panel, we use the formula [10]:

E = -

I-V■k ■ k

U

(1)

E - actual output of one solar panel, Wh;

I - amount of solar energy falling on a horizontal surface, kWh/m2 (it is given in Table 1 with conversion to the specified units);

V - rated power of one solar panel, W (it is given in the technical characteristics of the solar panel "Sila Solar" 250 [6]);

ko - correction factor depending on the tilt angle of solar panel and the deviation from the southern direction

Table 3. Energy produced by solar panels of shop No.2 (kWh)

Months

I II III IV V VI VII VIII IX X XI XII

Diurnal 565 1189 1954 2899 3637 3949 3778 3133 2341 1545 774 424

Monthly 17508 33327 60512 86928 112730 118413 117184 97065 701188 47918 23191 13208

Yearly 798175.78

o

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Table 4. The calculated data on solar panels of the shops

Substation Shop Design power, kW Number of panels, pcs. Rated power of solar panels, kW Generated power, MWh/year

#1 2 1431.08 2082 520.53 798.18

#2 7 1247.313 728 182.02 279.12

#3 3 1266.936 1845 461.13 707.1

#4 3 1248.182 1485 371.33 569.4

#5 4 2764.521 1747 436.86 669.88

#6 9 1147.897 874 218.43 334.94

#7 8 1830.188 1456 364.05 558.23

#8 11 1174.512 2416 603.93 926.08

#9 12 2789.062 3083 770.65 1181.71

#10 13 1737.349 1903 475.69 729.43

- 1 10.84 25 6.25 9.58

- 6 189.36 250 62.5 95.84

- 10 26.74 100 25 38.34

- 5 206.43 490 122.5 187.84

Total 18483 4620.87 7085.65

(it is taken from [9] according to the panel tilt angle and the deviation from the southern direction); k - loss factor (it is assumed to be equal to 0.94 and includes losses associated with an increase in the panel temperature, with shading and pollution of solar panels, losses during the period of low solar radiation, and losses in shunt diodes); U - solar radiation intensity at which solar panels are tested, kW/m2 (it is given in the technical characteristics of the solar panel "Sila Solar" 250 [8]).

Formula (1) is used to calculate the actual output of solar panels. The calculation data are summarized in Table 1.

The calculation results indicate that the highest output of one solar panel will be achieved at 11.00-13.00, in June. The rest of the time, the actual power of one module will decrease in proportion to a decrease in the amount of direct solar radiation.

v Calculation of energy Parameters of solar panels

The plant layout (Figure 1) indicates the geographical location which is taken into account to make the solar panels face south. Table 2 shows the dimensions of the plant buildings. Since the solar panels are fixed at an angle, their area will increase (comparing to underlying surface of the shop roofs), which will allow mounting more panels than on a horizontal surface.

Table 5. The equipment cost

Equipment Price, thousand rub. Quantity, pcs Cost, thousand rub.

Sofar 11ktl 3- phase photovoltaic grid-tie inverter 120 394 47280

Cable Solarflex PV1-F NTS 10 mm2 0.19 11820 2246

Solar panels "Sila Solar" 250 W 9.1 18483 168195

Total 217721

The area of solar panels given their tilt angle is calculated by the following formula:

S = 0.9—1— • b (2)

cos a

l - building length, m; a - solar panel tilt angle equal to 36°; b - building width, m;

0.9 - coefficient taking into account the area of technical passages for the maintenance of the solar panels.

The calculation data for the shops are summarized in Table 2.

The data from Table 1 are used to calculate the annual output of electricity produced by solar panels. By multiplying the data from the Table by the number of solar panels placed on the roof of the shop, we obtain the power and energy for a particular shop. Further, we calculate the total energy generated by solar panels of the shop for a year. Table 3 demonstrates an example of the calculation of power and energy of solar panels of shop No. 2 depending on the day and time of the year. From this Table we take the total value of the generated energy for the year. This value is necessary to calculate the economic effectiveness of the solar panels. The number of panels for each shop and the rated power of the entire solar system for the shop are also calculated. The calculation results are presented in Table 4.

vi. Selection of auxiliary equipment

The Sofar 11KTL 3-phase solar inverter is used to convert DC to AC and to synchronize solar panels with the power supply system of the mechanical plant [11]. The maximum power of one inverter does not correspond to the power of the connected panels, consequently, it is necessary to calculate the number of inverters required for solar panels for each shop.

The Sofar 11KTL-X grid-tie inverter allows connecting up to 48 solar panels with a capacity of 250 W each [12]. For the production shops, where solar panels occupy almost the entire area of the roofs, the number of solar

Table 6. The calculation of NPV indicator (thousands rubles)

Period (year), Т Capital investment , CI Cash inflows, CIn Cash outflows, CO Cash flows, CF NPV

0 150 227,40

1 - 20 909.75 6 009.09 14 900.66 -136 430.49

2 - 21 327.95 6 009.09 15 318.86 -123 297.04

3 - 21 754.51 6 009.09 15 745.42 -110 797.82

4 - 22 189.60 6 009.09 16 180.51 -98 904.66

5 - 22 633.39 6 009.09 16 624.30 -87 590.44

6 - 23 086.06 6 009.09 17 076.97 -76 829.06

7 - 23 547.78 6 009.09 17 538.69 -66 595.40

8 - 24 018.73 6 009.09 18 009.64 -56 865.35

9 - 24 499.11 6 009.09 18 490.02 -47 615.74

10 - 24 989.09 6 009.09 18 980.00 -38 824.33

11 - 25 488.87 6 009.09 19 479.78 -30 469.78

12 - 25 998.65 6 009.09 19 989.56 -22 531.65

13 - 26 518.62 6 009.09 20 509.53 -14 990.34

14 - 27 049.00 6 009.09 21 039.91 -7 827.07

15 - 27 589.98 6 009.09 21 580.89 -1 023.88

16 - 28 141.77 6 009.09 22 132.68 5 436.44

panels connected to one inverter is 48. For the rest of the shops, where the panels cover only part of the roof area, for even load distribution we calculated the number of the panels to be connected to one inverter (Table 5).

Knowing the inverter input power and voltage, we calculate the current for the system of solar panels. According to the calculated current, we choose a cable produced by HELUKABEL Company. This is Solar flex PV1-F NTS with a cross section of 10 mm2 and an ampacity of 40 A [13]. The length of the cable running from the solar panels to the inverter is estimated at 30 meters. The total cable length is calculated by multiplying the number of inverters by the length of the cable from the panels to the inverter. The results of the above calculations are given in Table 5.

vn. calculation of economic effectiveness of solar systems

Previously, we selected all the necessary equipment for mounting solar panels. In addition to the solar panels, we chose all the necessary auxiliary equipment. Below, Table 5 presents input and calculated data on the cost of this equipment. The cost of mounting is assumed to be 15% of the equipment cost [14]. Thus, the total capital cost of the entire system will be equal to 250379 thousand rubles. According to the calculations made earlier (Table 4), solar panels produce energy equal to 7085.65 MWh per year.

This is 27% of the total plant electricity consumption. This amount of energy is saved owing to dispersed renewable generation system (in other words, the power consumed by the plant from the grid is reduced by this amount).

Considering the fact that the electricity price for industrial enterprises with a power consumption above 10 MW in the Irkutsk region is equal to 2951.22 rubles/MWh, including value added tax (as of August 2018) [15], the cost of electricity saved will be 20911.31 thousand rubles/ year.

Preliminary estimates show rather low economic

effectiveness of the solar systems. This limits severely investor's activity in financing such projects. However, it should be borne in mind that the price of solar panels has decreased by almost 90% over the past ten years [16] and such dynamics of falling prices will continue. It is predicted that by 2030 the price of solar panels will fall by an average of 40% [17]. Not only the cost of solar panels, but also the cost of inverters and other equipment will be reduced [18].

Apart from the reduction in the equipment cost, another important point is a prospect of an increase in electricity price. Thus, according to the data presented in [15], the cost of electricity for industrial enterprises with power consumption above 10 MW in the Irkutsk region has increased by almost 20% (excluding inflation) over the past ten years, and the annual increase in electricity prices has been about 2%. There is no reason to believe that this trend will not continue in the future. Thus, we calculate the effectiveness of solar panels with a 40% reduction in the cost of equipment, and an increase in the price of electricity by 2 % per year. This will allow us to estimate the potential for the growth of the cost-effectiveness of solar panels.

For the analysis of the effectiveness of this project, we calculate such an indicator as Net Present Value (NPV) according to the formula:

n cf

NPV = £-- CI

t=1 (l + r)

CF = CIn - CO

(3)

(4)

CFt - cash flow in time t;

CI - capital investment;

r - discount rate (it is taken to be 8%);

CIn - cash inflows;

CO - cash outflows.

CIn is the cost of electricity from the centralized grid substituted by solar panels. CO is the maintenance cost of the panels. CI is the cost of the panels themselves and their

installation. The results of calculations according to the above formulas are presented in the Table 6.

NPV was calculated taking into account the reduction in capital costs for equipment and the rise in electricity prices noted above. It reached a positive value in 16 years after the implementation of the project, which is much more cost-effective than the implementation under current conditions.

The achievement of more favorable conditions for such integration is real in the coming decades, as the dynamics of rising electricity prices from traditional energy sources and the reduction in the cost of solar panels themselves, due to the emergence of new technologies, contribute to this.

viII. Conclusion

The paper is concerned with the possibility of using renewable energy sources to partially replace the electric power received by a mechanical plant from a centralized grid. For this purpose, we considered the possibility of using solar panels and wind turbines. The assessment of the climatic conditions shows that the use of wind turbines is not reasonable due to the low annual average wind speeds, consequently, their installation is not considered. At the same time, with the increased solar activity in the studied region, the use of solar panels for power supply to the plant is relevant. The specific feature of the shop buildings design enables a sufficient number of solar panels to be mounted on the roofs, which will make it possible to cover a significant part of the shop load during the daytime.

The total number of solar panels and the amount of energy generated by them were calculated. To exclude the possibility of feeding surplus electricity back to the grid, the number of solar panels on the roofs of non-production buildings was reduced.

The expected growth in the price of electricity and further steady decline in the cost of equipment for solar systems will significantly increase their economic attractiveness. Moreover, it will stimulate the integration of solar panels into the power supply systems of consumers in Russia.

Acknowledgement

The study has been conducted in the framework of the Research project of Siberian Branch of the Russian Academy of Sciences № AAAA-A17-117030310447-3.

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Cf Sergei V. Podkovalnikov, Ph.D., Head | of Laboratory at Melentiev Energy , Systems Institute SB RAS. His research interests are the effectiveness of interstate electric ties and interconnected power systems, electric power industry ^ development, liberalization and organizational structures in the electric power industry, mod-eling of electric power systems and markets.

Marina A. Polomoshina graduated from Irkutsk Tech-nical University. She K», «.1 is a master student in electric power i^A systems and researcher at Melentiev Energy Sys-tem Institute SB RAS. Her research interests are re-newable energy | sources, power industry development and interstate electric ties.

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