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Magacin investicija

Solar panels on the roof of warehouse


Project task

Examine the profitability of installing solar panels on the useful surfaces of the roofs of buildings in Tamnave East Field. For this, I use the free web application SPAC that I developed to help calculate gain from solar for homeowners.

But, the application received a slightly larger range of use than the original intention. To begin with, I started with the standard SE1 questionnaire.

The project task:  Examinations  for assessing the potential for the installation of photovoltaic power plants on the roof surfaces of  EPS (Electric Power Serbia)  buildings

Branch: Open mine facilities Kolubara Tamnava East Field

Power Plant: Place:  Warehouses and workshops

Infrastructure and the overall plan of examined objects

Solar panel application (SPAC) use for warehouses

Solar panels example calculation for the roof of the halls

The use of solar in Serbia is calculated by the SPAC application for the   large cities and surrounding , specifically in Serbia for cities Niš and Belgrade. The SPAC application works on the principle of processing statistical weather conditions (cloudiness). The standard initial query for this case requires data that we normally use in the SPAC application. It includes the branch, the power plant, the town, and the facilities in the town. All buildings are equally oriented to the south-southeast. Given that they are approximately the same height and more than 6 meters apart, there is no possibility of them creating shadows on each other in winter. The workshop buildings have annexes, but they are lower and subject to the influence of the shadow of the main halls. That is why they were not taken into consideration. For all buildings, only half of the roof is counted, and that is the one facing the favorable side (south-southeast).

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WG object coordinate Object type Roof dimensions for solar panels Roof slope Roof type Commentr
14 29` 49``
20 15` 5``
1-Investments warehouse 74x10.8 South South-east 16 deg. Trapezoidal roof sheet Writing shadow tree south side
14 29` 49``
20 15` 5``
2-Spare parts warehouse 62x10.3 South South-east 16 deg Trapezoidal roof sheet Writing shadow tree east side
14 29` 49``
20 15` 5``
3-Mechanical workshop 58x6.99 South South-east 16 deg Trapezoidal roof sheet No shadow obstacles
14 29` 49``
20 15` 5``
4-Elektro radionica 46x6.99 South South-east 16 deg Trapezoidal roof sheet No shadow obstacles
14 29` 49``
20 15` 5``
5-Buldozerska radionica 40x7.28 South South-east 16 deg Trapezoidal roof sheet No shadow obstacles
solar panel installation facility survey form

Infrastructure and the overall plan

Halls that will be taked into account are :

  • Investments Warehouse 
  • Spare parts Warehouse
  • Mechanical workshop
  • Electrial workshop
  • Buldozers repair workshop

These objects were chosen because of their favorable orientation and the small number of (surmountable) obstacles. As you can see from the picture, all the objects have a mostly clear view from east to west. Exceptions are minor obstacles: a tree near object 1 on the south side and object 2 on the east side. Buildings 4 and 5 have annexes that are lower than the parent buildings and are subject to greater shadow influence. They are therefore unsuitable for the installation of solar panels, so they will not be considered.

Objects 4 and 1 from example

Object A1[mm] A2[mm] A3[mm] A4[mm] Roof slope Roof length [mm]
1-Warehouse inv. 8190 5360 10430 74000 15.18 10807
2-Warehouse sp.part 7670 5440 10100 62000 12.45 10343
3-Mechanical workshop 7550 5440 6670 58000 17.55 6995
Electrical workshop 7550 5440 6670 46000 17.55 6995
Buldozers workshop 9830 7830 7000 4000 15.95 7280

All measurements were made with a laser range finder from the ground, and then the unknown quantities were calculated. The useful lengths of the roof and nagba are calculated from the measured data according to the following formulas:

The working principle of the SPAC application and an example of calculation

After defining all the dimensions, we will approach the calculation of the electricity gain by introducing solar with the help of the SPAC version 1.27 application. The SPAC application takes into account the calculation of the angle at which the sun’s rays fall on the solar panel (incidence angle) for every hour of the year and then collects, averages, and multiplies the data with the statistical cloudiness coefficient for each month. Statistically processed data are for larger cities in the northern hemisphere (Asia, Europe, North America, and North Africa). For the forecaster, we use the European version of the application, which can be found at the following link:

Entered parameters for the calculation of the roof of the investment warehouse (object no 1 in our case). Because the slope angle is dependent on the roof, it is impossible to set up the ideal angle of the roof.

We have all aprameters, so let s start calclulation

Example for Object No. 1 Data from the table

When we start the application, we enter the following parameters:

1 place: Belgrade, Serbia, 2.Roof slope: 15 degrees;

3. Orientation: 16 degrees deviation from the south axis (south southeast).

The width of the roof has been calculated at 10.8 meters, and the length has been measured at 72 meters. It is necessary to check the “Roof” option. We do not change other options. ,

It is also necessary to choose a solar panel. In order for it to fit as well as possible into the width of the roof (10.8m), we will have to do some calculations. After reviewing the panels that have a price (marked in red) and that are currently affordable to buy, I decided on

Trina Solar TSM 390 DE 9C07 power 370 Wp. Panel dimensions are 1754 mm by 1096 mm. It can fit six solar panels across its width. Now that all those parameters have been entered by clicking on the calculation button, we get theoretical and practical result

The results

Then we have a results page. There are tables of angles and irradiation in display.  We will skip all that because we are interested in a concrete practical calculation, which can be found at the end in the “Real data estimation” section.

Calculation of the ideal angle and realistic calculations of the obtained energy for a given panel configuration, inclination, and orientation in accordance with the geographical position

The packing of the panels fits good. The degree of utilization of the roof is over 90%. In total, it fits 6 panels per width times 67 rows per length of the roof, or 402 pieces. The total theoretical maximum power is 156780 W.

Choosing an inverter and entering the electricity price

In order to continue the calculation, it is necessary to enter this information. We select the inverter from the list offered. It is preferable to choose the one that has a given price for the calculation of the total investment. We choose the inverter according to the power of the panel. We will choose different inverters of different powers for the sake of experimentation in the future.

It is very important to choose a realistic electricity price for the calculation. The price of electricity varies, but for these examples, I adopted a lower tariff in the blue zone, which is 9   dinars per kW converted into 0.086 US dollars.

It remains to select the “Report” button to get the final report.

Final Report: 

The window “Final Report” is very simple and provides only the most important data that is most interesting: the total number of inverters, annual production, and the total cost of investment in panels and inverters, which make up about 90% of the costs. In our case, it amounts to:

Total investment of 108218 USD.

Expected annual profit: $12,131

This further means that the investment would pay for itself in nine years.

Calculation for other facilities and conclusion

For other objects, the calculation principle is the same as for object 1. When choosing panels, we will pay attention to dimensions and price. The following table shows the results.

No Object 2 Object 3 Object 4 Object 5
Panel type JA JAM 54S30 400 W ZN Shine ZXM6-NH 370 W ZN Shine ZXM6-NH 370 W Panasonic EVPV360 360W
Panels summary 5x55=270 6x32=192 6x25=150 6x23=138
Panel utilization rate % 82.56 88 86.7 86.18
Chosen inverter Solar Edge SE 6000 12kW Growat MOD 4000 TL3-XH/DC 8kW Growat MID 50KTL3-X2 75kW Growat MID 36KTL3--X2 54kW
Inverters summary 9 9 1 1
Maximum Power [W] 108 000 71 040 55 500 49680
Investments costs [$] 93 237 60 196 44 920 38 494
Expected annual production [kWh] 95 933 64 398 50 311 45 887
Expected annual profit [$] 8 250 5 538 4 326 3 947

At this  experimentation, I used different panels and inverters. For example, for the first three cases, I chose commercial inverters in order to get a less favorable investment price. For facilities 4 and 5, I chose a high-power industrial inverter to get an optimal result.

It can be concluded that the repayment period for the chosen configuration is more or less the same and amounts to 9 to 10 years. However, it should be take into account,  that the roofs are quite flat,” so that they deviate from the ideal by about 15 degrees. This type of roof, as I mentioned earlier, is ideal for the summer months, also for cloudy weather (when they collect only diffuse radiation).
A roof leveled in this way has extended the time od pay off  for 2 to 3 years compared to the classic installation of solar panels of solar power plants : south orientation, and ideal tilt angle. So it amounts to 9 to 10 years instead of 7 is result.

 But this is not a problem because, as is known, solar panels have a guaranteed service life of 16 to 25 years, i.e., until drop to 86%  capacity after 25 years of work.
It should also be noted  that the SPAC application is designed to work as a consumer calculator and not as a program for making serious projects, but it doesn’t bother him for the calculation of solar investments.

Note The reference prices for the equipment are taken from the website  A1Solar Store

Miroslav Mitić

Mechanical engineer and programmer for 25 years. Solar energy expert

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