Bifacial solar modules: A test project for the future of technology

GOLDBECK SOLAR claims to be the best supplier of solar systems in Europe.

The EPC company from Hirschberg is also constantly developing the technology with its partners. For example, with a large-scale test of bifacial modules at the solar park in Akadyr, Kazakhstan. The results provide a basis for the comparability of the new technology.

Akadyr solar park, Karaganda, Kazakhstan

Even the ancient Egyptians recognized the enormous potential of the sun and, for example, aligned their doors so that the hot midday sun did not additionally heat up the living space. Nowadays, thanks to the technical developments of modern times, solar radiation is now used specifically to generate electricity and heat. An alternative to environmentally harmful and risky energy generation methods. The French physicist Henry Becquerel laid the foundations for solar technology almost 200 years ago. The silicon solar cells used today to generate solar power were developed on this basis and can now be found on numerous roof surfaces. GOLDBECK SOLAR also uses the modules for its numerous solar projects around the world.

Akadyr solar park with 76 MW

However, the development of solar modules is far from over. GOLDBECK SOLAR is constantly involved in the further development of technical solutions. When expanding the project in Akadyr, Kazakhstan, the EPC company was therefore happy to take the opportunity to test bifacial or double-sided modules. Kazakhstan is a popular country for solar projects due to its vegetative and climatic conditions. For GOLDBECK SOLAR, the Akadyr solar park was therefore not the first project in Kazakhstan. The solar expert already carried out the construction of the first plant, which was built in 2019 and commissioned with an output of 50 MW. With the award of the contract for the second construction phase, GOLDBECK also took on the expansion of the solar power plant in the Kazakh region of Karaganda by a further 26 MW. The project expansion was completed in June 2020, meaning that the entire Akadyr plant now has a total capacity of 76 MW. The technical specifications for the second construction phase were optimized for the use of bifacial modules. Over the next year, GOLDBECK SOLAR intends to test the efficiency of the bifacial solar modules and use this to provide sound information for the future development of the technology.

The flags of Kazakhstan and Germany in front of solar modules

Lack of experience with bifacial solar modules

Bifacial or double-sided solar cells have been tested for some time. Researchers hope that this will lead to more efficient solar modules. This is because the double-sided modules should absorb the light on both the front and the back. This increases efficiency in several ways. On the one hand, the bifacial solar modules can capture direct sunlight at the front as well as indirect radiation at the rear in front of diffuse reflective backgrounds such as light-colored sand. On the other hand, with standing elements, the wandering solar radiation can be used throughout the day. This results in a higher energy yield from the solar modules. Although double-sided modules have been on the rise for a good year now, demand is still relatively low – especially in Europe. This is due to the fact that many people still lack experience with this new technology and there are often no concrete application examples. In addition, experts have still not been able to agree on standardized data and test procedures. Planners can therefore rely almost exclusively on manufacturers’ forecasts. However, there is still no real comparability between projects that have already been implemented. The actual cost-effectiveness is also still questionable.

However, there is already greater interest in bifacial solar modules in some regions of the Middle East and Asia. This is mainly due to the fact that large ground-mounted systems are being built in desert-like regions in these regions. The project in Akadyr is also one of these.

Creating greater comparability

The geographical and climatic conditions in Akadyr were ideal for GOLDBECK SOLAR to test this type of module. With the test facility in Akadyr, the Hirschberg-based EPC company is also pursuing the goal of achieving a better basis and greater comparability between bifacial solar cells and standard modules. In this way, GOLDBECK SOLAR is already looking to drive forward further development in the solar industry. In the Akadyr project, the use of bifacial cells and the installation of six 630 kVA inverters did not result in any changes to the configuration from an electrical point of view, but the angle and height of the substructure differed due to the alignment with the double-sided modules. Due to the different tilt angles and heights, the primary aim is to observe how these affect the efficiency of the modules and where the optimum lies.

The configuration of the inverters was as follows:

Inverter no. 1:
1530 module / 435 Wp / standard monocrystalline / 30° / 0.8m ground clearance
Inverter no. 2:
1530 modules / 435 Wp / bifacial monocrystalline / 30° / 0.8m ground clearance
Inverter no. 3:
1530 module / 435 Wp / standard monocrystalline / 30° / 1.2m ground clearance
Inverter no. 4:
1530 modules / 435 Wp / bifacial monocrystalline / 30° / 1.2m ground clearance
Inverter no. 5:
1530 module / 435 Wp / standard monocrystalline / 25° / 0.8m ground clearance
Inverter no. 6:
1530 modules / 435 Wp / bifacial monocrystalline / 25° / 0.8m ground clearance

Sophisticated floor structure for bifacial solar modules

For the ground-mounted structure, the project managers focused primarily on creating a system design that would maximize the bifacial gain. To achieve this, the shading effects on the rear of the modules had to be avoided. The Sigma IIST Bifacial Fixed Tilt System from Mounting Systems was exactly the right solution to meet these requirements. This is because it is extremely adaptable and enables a fully customized design. For the Akadyr project in particular, this meant that the tilt angle and ground clearance of the system were set high. On the one hand, this was to adapt to the local environment and, on the other, to maximize the bifacial gain of the vertically arranged modules. The module rails were positioned along the half-cut module junction box spaces in such a way that shading on the rear of the modules could be avoided. Due to the different substructure configurations in the test area, which are mounted with both standard and bifacial modules, it was then possible to carry out a direct performance comparison. This made it possible to calculate the exact gain of the bifacial cells and the effect of ground clearance and angle on the solar energy yield.

Extensive data collection

In addition, each area should have secondary class pyranometers that measure not only the direct light on the front side, but also the diffuse light on the back side in order to obtain data on the irradiation and the diffuse light. The information obtained in this way can then be put into context with the measured energy production. The back pyranometers are positioned in the middle of each row of modules so that they also measure the difference in light intensity on the top and bottom rows of the system. The various measurements will ultimately make it possible to obtain all the necessary data to make a well-founded assessment of the success of the test project. However, it will not be possible to completely reduce all uncertainties with simple monitoring instruments. One example is the shading of the bottom row. If you compare the light measured on the back of the modules with the output of the front area, you can expect a higher gain in the upper rows, as more diffuse light could reach the higher modules while the rest is shaded. Based on the final measurement data, GOLDBECK SOLAR will be able to technically improve the installation so that such losses are reduced to a minimum.

Challenges of bifacial modules mastered

With the test project in Akadyr, GOLDBECK SOLAR wants to create a solid evaluation basis for the future use of bifacial modules in various conditions. The solar plant in the Kazakh region of Karaganda is well suited to the fact that the very low vegetation in summer does not massively change the albedo. At the same time, the winter with almost five months of constant snow allows a detailed analysis of the effect of albedo on the gain offered by bifacial modules compared to standard modules.

Nevertheless, there is one major challenge for the project in Akadyr. With temperature fluctuations from -50°C to +50°C, the climate is a key factor that had to be taken into account when planning and installing the system. To solve this problem, a specially designed thermal expansion joint was built into the substructure. In this way, the steel parts and rails have enough space and flexibility to avoid any damage to the components and ensure bifaciality.

Currently unique project

With Power Plant Akadyr, GOLDBECK SOLAR has created a unique opportunity to compare the performance of single and double-sided modules at different tilt angles and clear heights on an individual inverter basis. This is because the solar power plant is currently the only known system of this size that can do exactly this. In a year’s time, it will be possible to obtain the first comparative results, taking into account additional parameters relating to temperature and environmental conditions in summer and winter in Kazakhstan. GOLDBECK SOLAR wants to live up to its claim of being the best solar supplier in Europe. To this end, the company is constantly investing in technical analyses of the various components used in its own solar systems in order to be able to offer its customers the best possible technical solutions based on constant analysis and research over a period of 20 years. The plant in Akadyr is just one of many projects that the solar expert has already carried out over the past two decades. However, the testing of bifacial solar modules at the Akadyr site certainly makes the project one of the most exciting.

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