Standard or bifacial modules – what’s the difference?
03/06/2021
Not so long ago, solar module manufacturers were engaged in a protracted positioning struggle to make their mark in the standard solar panels market. While investing all their energy and finances in the search for opportunities to improve their efficiency, they hoped to achieve promising developments that would open the way to the conquest of the PV market. It turns out that such an innovative idea already exists – these are bifacial solar panels.
Developed back in the middle of the last century, they didn’t manage to come into common use and for a long time existed as a theoretical model and a small number of exhibition samples. The reason is that their increased, but still limited efficiency would not provide a significant gain in production profitability compared to monofacial panels.
The real prospects for launching bifacial modules into production appeared after the release of a new solar cell manufacturing technology – PERC. The first tests showed a significant advantage in the efficiency of bifacial panels over their monofacial counterparts.
Today, there is no doubt that bifacial modules increase electricity generation. However, in order to make an informed decision in the choice between standard and bifacial modules, it is necessary to have more complete and accurate information on both the advantages and disadvantages of each. Keeping in mind that cognition comes through comparison, let’s have a closer look at the characteristics to consider.
Efficiency
Efficiency is one of the main parameters of solar panels, which in standard conditions (immediately after assembly) is determined only by their design features. For monofacial modules, this parameter varies between 10-20%. The use of bifacial panels allows an increase up to 20-30% on average – their efficiency can reach 27%. Considering various other factors, which include weather conditions, these values can vary significantly from the given, both upward and downward.
It should be noted that nowadays the efficiency criterion is no longer the decisive one. Today, the most successful modules on the market are those that can claim the best ratio between total cost of their production and operation and the amount of energy generated during their lifetime. In other words, modules that produce the cheapest electric power. To calculate this ratio the LCOE (Levelized Cost of Energy) indicator was developed. [1]
Given the importance of external factors and solar modules characteristics for the LCOE calculation, it is useful to compare these criteria.
Power
The first most obvious advantage of bifacial modules in terms of power, all other variables being equal, is up to 25% gain in power due to the additional usage of reflected light to generate energy on the back side of the module.
The cost of projects based on bifacial modules, with a given power and performance, will be lower than for monofacial modules due to the reduced number of modules required. Accordingly, fewer modules will require less space, which is quite important when the cost of land is high.
Weight
The use of a glass coating on both sides increases the weight of bifacial modules by an average of 5-8 kg compared to standard modules. This may make them a little more difficult to install, but it is not
an obstacle during operation. The slight increase in the cost of installation work does not have a significant impact on the LCOE value.
Longevity
The life span of both monofacial and bifacial solar modules depends largely on the degradation rate of the photovoltaic cells used in them and is close to 30 years. However, we should not forget about the influence of natural factors. Here, bifacial modules have a clear advantage. The use of tempered glass to cover the front and back side eliminates the negative effects of UV. Additionally, the transparent structure prevents excessive heating of the cells, which has a positive effect on longevity. The absence of an aluminum frame (for frameless modules) eliminates the risk of corrosion. In general, the increased resistance of bifacial modules to natural factors increases their service life.[2]
Mounting Features
Unlike standard modules, projects using bifacial modules will require additional engineering calculations:
- correct module placement, taking into account shading, row spacing, surface reflectivity, and height above ground level;
- power generated by the back side of the module;
- module inclination angle that will provide maximum efficiency for a given location;
- power of inverter equipment.
The practical application of the results of these calculations will certainly lead to higher module installation costs, affecting equipment costs and the overall cost of the project upward. However, the benefits of a significant increase in power generation far outweigh the magnitude of these costs and ultimately contribute to a reduction in LCOE.
Influence of natural factors
In terms of efficiency and productivity, bifacial modules have an undisputed advantage over standard solar modules under adverse environmental conditions. They are able to provide sufficient energy generation even in low light (morning, evening) and scattered light conditions (fog, low cloudiness) thus enabling their usage in all climatic zones.
Another advantage of bifacial modules compared to standard modules is the lower temperature of the cells [3]. That feature provides minimal performance degradation during hot weather. In this case, sunlight passes freely through the transparent cell without heating it up. In monofacial modules, the light hits the opaque back side and heats it up, increasing the temperature of the cells.
Use of tracking
Both monofacial and bifacial modules can be additionally equipped with tracking devices, which allow changing module position for maximum illumination. But, while standard panels performance increases insignificantly, bifacial modules with uniaxial tracking can achieve an increase in power output of up to 35%. This design provides a significant reduction in LCOE and it can be effective in most parts of the world.
Design
It should be also noted that there is not much room for creativity in the usage of the standard solar modules constructions (house roofs, balconies in high-rise buildings, adjacent areas). Whereas bifacial modules are much more effective in this regard. Being transparent, they can be widely used as original coating elements, for example, for gas stations, open and closed passages between buildings, terrace roofs in country houses and other modern design solutions. They are even used as
noise barriers along railroad tracks.
Conclusion
A comparative analysis shows that bifacial modules are superior to standard modules in many respects, which explains their rapid success in the PV market. In 2020, their market share was already more than 25%, contrary to the ITRPV (11th edition) forecasts, which estimated a maximum of 15%.
Such rapid market expansion became possible largely due to the results of independent testing conducted by various companies, which confirmed the declared parameters, including the increased energy yield and efficiency of bifacial modules compared to monofacial ones.
Leading world manufacturers continue to master this segment, investing significant financial resources in research and development aimed at reducing the cost, eliminating known shortcomings and improving efficiency.
It is safe to claim that if the current trend continues, bifacial modules will take the leading position in the market in the near future and become the preferred choice for large projects in the solar power industry.
[1] https://www.e-education.psu.edu/eme801/node/560
[2] X. Sun, M.R. Khan, C. Deline, M.A. Alam, Optimization and performance of bifacial solar modules: a global perspective, Appl. Energy 212 (2018) 1601-1610.
[3] M.W.P.E. Lamers, E. Ozkalay, R.S.R. Gali, G.J.M. Janssen, A.W. Weeber, I.G. Romijn, B.B. Van Aken, Temperature effects of bifacial modules: hotter or cooler? Sol. Energy Mater. Sol. Cell. 185 (2018) 192e197.
