Designing photovoltaic parks with bifacial panels
Elvan presents the new fixed base for photovoltaics BIF2V, specially designed to maximize the performance of projects using Bifacial panels. With a small price difference from the conventional base, thanks to the innovative design of the base, you can take advantage of >99% of the active back surface to increase the production of the installation up to 20% (in combination with other interventions, e.g. the appropriate configuration of the reflectivity of the soil – albedo, etc.). On this occasion, we present a report with guidelines for the optimal design of photovoltaic parks that use bifacial panels.
Photovoltaic technology is constantly evolving, thanks to the very intensive research and development carried out worldwide. Although there are several technological innovations available, bifacial panels seem to be steadily gaining ground in the market and it is certain that their market share may rise to 60% in the next decade. Of course, any technology to establish itself in the market must be able to be financed (“bankable”). According to a BloombergNEF survey, more than 80% of PV market executives believe that installations with bifacial panels are “bankable”.
Given that bifacial panel technology will dominate the market, it is very important to understand how to design a bifacial panel project to maximize its performance and what the returns are to expect. We start with the factors that affect the performance of such a project.
Given that bifacial panels generate energy from both sides, it is of primary importance that both sides of the panel receive the maximum amount of light. It is therefore necessary to list and understand all the factors that affect the amount of light that reaches both sides of the panels.
These factors are:
- Soil “reflectivity” (albedo)
- Ratio of front / back surface power (bifaciality)
- Ground Coverage Ratio (GCR)
- Front free height of base (Clearance)
- Special base design
We will now consider each of these factors separately:
1. «Reflectivity» of soil (albedo)
A panel produces electricity when light falls on it. While the front side of the panel has sufficient direct exposure to sunlight, the back side absorbs light reflected from the ground. So it is very important that the ground on which the photovoltaic park will be installed has the maximum light reflection. The ratio of light incident on the ground to light reflected back is known as albedo. It is obvious that each soil has its own albedo.Thus a soil with improvement (eg white coating) has a higher albedo than a dark colored soil without improvement. The increase in efficiency due to the installation of bifacial panels is proportional to the albedo of the soil and with soil improvement the efficiency increases. A park installed on sand (albedo 50 %) can have a yield increase of 16 % and this increase can reach up to 25 % if the ground is covered with a white film (albedo 85 %).
2. Front / back surface power ratio (bifaciality)
Although the first point of contact of the light is the ground, the next is the back side of the bifacial panel. In bifacial panels there is another factor known as the front/back surface power ratio (bifaciality). This means that the back side of the panel does not produce the same power as the front. This property is not a defect of the bifacial panels but their natural property. Different bifacial cells have, depending on the type of wafer and the technology used, a different front/back surface power ratio (bifaciality). For example:
3. Ground Coverage Ratio (GCR)
The location of a solar park also has a very large effect on its performance. It is very important to allow the light to reach the ground so that we have the necessary reflection on the back of the panel. And this is exactly where the Ground Coverage Ratio (GCR) plays a very important role. The Ground Coverage Ratio (GCR) is defined as the ratio of the length of the panels to the distance between the rows of park tables. It essentially gives an indication of how sparsely the panels are placed within the park. A high Ground Coverage Ratio means densely placed tables / panels and thus reduced profits from the installation of Bifacial panels.On the contrary, a low Ground Coverage Ratio of around 20% means that we allow enough light to reach the ground and therefore to the back of the panel, but on the other hand the area required for the installation of the park increases exponentially. It is therefore necessary to achieve a “golden ratio” between the area required and the energy produced by the park. A ratio of 40 to 50% is optimal.
4. Front free height of the base (Clearance)
Beyond the Ground Coverage Ratio (GCR), the front free height of the base has a very significant effect on the profit from the installation of bifacial panels. Front clearance is defined as the distance from the ground to the lowest point of the Panel. If the panels are placed at a large, but reasonable height, the light that falls on the ground, therefore also on the back side of the panel, increases the performance of the park. Of course, every increase in height also means an increase in the loading of the system from the wind, due to higher wind pressures, so a more robust construction is required.This results in an increased base cost. ELVAN’s design department, after taking into account the limitations of the Greek Town Planning Regulation and all cost factors, concluded that a front free height of the base of 1.2 m. is optimal.
5. Special design of the base
The last factor that plays a special role in increasing the performance of a park with bifacial panels is the special design of the base so that:
- that the maximum amount of solar radiation falls on the ground
- to minimize the shadows of the metal parts on the back of the panels.
This is exactly what the new, specially designed base for bifacial panels, ELVAN’s BIF2V base, achieves.