Vertical bifacial photovoltaic systems – Innovative applications with enormous potential for agriculture

​veröffentlicht am 10. August 2020

 

Vertical bifacial photovoltaic (PV) systems are double-sided solar cells in which the modules are not tilted as usual, but placed vertically. Due to their bifacial features, they can not only achieve higher specific energy yields and relieve the grid, but can also be used variably thanks to their specific orientation. Especially in combination with agriculture, this offers a wide range of possibilities.

 

The technicalities

In our last article we discussed bifacial solar cells as an innovative PV system model.

Bifacial PV modules differ from conventional solar modules in that the full-rear contact of the module is replaced with a fingerprint contact. As a result, the solar cell can also use light that hits the rear of the module to generate electricity. This also increases the efficiency of the module. The extent to which the yield gain will increase depends largely on albedo, the reflectivity of the surface underneath the module. The brighter the surface underneath the module, the higher the yield gain generated by the rear side. Thus bifacial PV modules can achieve a yield gain of between 5% and 15% p.a. under German weather conditions.¹

The possible areas of application of bifacial PV modules have recently been further developed and one technology in particular could turn out to be future-oriented and therefore deserves special attention: vertical bifacial PV systems.

 

Most common is the east/west orientation of the modules.

This installation method offers some advantages compared to the conventional layout. On the one hand, the production profile changes. Due to the specific orientation of the module, power generation peak is not reached at midday, but in the morning and afternoon. As a relatively large amount of energy is thus generated in the morning and in the evening, the spot market price tends to be higher. This reduces the cannibalisation effect.² Complementary power generation can thus also relieve grids to a certain extent.

 

The vertical orientation effectively prevents snow from depositing and helps avoid the accumulation of dirt.

The construction of vertical bifacial PV modules also involves some challenges, though. Firstly, a possible mutual impact between the PV system and agriculture and the greater need for land should be taken into account. Secondly, because of albedo, the yield depends on the developed area and this fact should be taken into account in planning. Furthermore, the higher market value achieved thanks to the complementary generation profile of the modules can only be used in the PPA segment, but not under the EEG market premium model.

Examples of application

The biggest advantage compared to conventional PV installation methods is the minimal land use. This enables implementing new usage concepts such as solar fences, noise barriers or novel agro-PV systems. The combination with conventionally inclined PV systems (so-called hybrid systems) also offers the possibility of installing a relatively large PV generating capacity with a relatively small need for grid connection.

The installation of a vertical PV system at the boundaries of existing power plants has economic potential due to possibly simplified approval processes and low connection costs.

Because the installation of vertical PV modules requires less space, the used area can basically be used for dual purposes. The row spacing of at least 10m (to avoid shading) allows under certain conditions cultivating land on the same area. Thus, the higher specific demand for land in PV projects becomes a secondary issue. The fact that there is no competition for land with food producers is a big plus, especially in the narrative of public authorities. This could convince even critical decision-makers and win sustainability-oriented municipalities as regional partners.

In financial terms, this novel technology will involve higher investment costs than conventional systems, since vertically mounted bifacial modules are not a widespread standard product yet. Lease costs highly depend on the negotiated price and may be lower despite higher specific demand for land. At least part of these additional costs is compensated by the dual use of the land, lower specific grid connection costs and higher specific PV yields.

 

Because land not subsidised under the EEG support scheme can be used here, the higher market revenues have an additional positive effect. In addition, vertical bifacial PV systems and hybrid systems are often advantageous due to the generation profile of PV systems optimised for self-consumption. Overall, given the usual strong dependence on electricity revenues and investment costs (the lease costs play a rather minor role), the profitability is comparable to that of conventional PV systems.

This should be analysed on a project-specific and case-by-case basis.

From an agricultural point of view, this technology offers a wide range of options for use. In addition to the use of grassland for e.g. livestock farming, it also enables field cultivation. As modules give additional shade, particularly suitable is the cultivation of beets or potatoes, which may be grown even in partly shaded areas. It is only important that the minimum distance between rows is ensured and that plants do not shade any modules.

Because vertical PV modules do not influence the distribution of precipitation, only some water savings can be expected in combination with the shade provided.

 

Market overview

Currently, some research facilities and only few companies in the German-speaking countries are more intensively involved in the implementation of projects concerning vertical bifacial PV systems. These are often project developers who also offer custom-made products. Suppliers of bifacial solar systems purchase panels for their construction in the same manner as all suppliers of vertical PV systems. 

Below is a list presenting a selection of bifacial module manufacturers and vertical PV installation manufacturers/project developers from the German-speaking countries:

Bifacial module manufacturers (selection):	Vertical PV installation manufacturers/project developers:
​Canadian Solar LG Electronics LONGi Solar Solarworld Trina Solar Yingli Green Energy JinKo Solar	​Next2Sun (project developer, BoS manufacturer) Kohlhauer (noise barriers) Elektrotechnik Leitinger Photovoltaik GmbH (project developer) HilberSolar (project developer) MaxSolar (project developer)

Support and financing

There is currently no special approach under remuneration or licensing law for vertical bifacial PV systems.

Accordingly, a building permit should be obtained as part of the standard approval process after the area has been appropriately designated in a development plan (Article 30 et seq. of the Federal Building Code [BauGB]).
Any legally guaranteed remuneration and connection to the grid are handled within the framework of the Renewable Energy Sources Act [EEG] (Article 16, Article 19 et seq., Article 37 et seq., Article 48 et seq. EEG 2017) depending on the size of the system and on areas that meet the area-related criteria for support.

Because the land area is only additionally used for PV electricity generation and this does not restrict agriculture to any significant extent, a separate, simplified approval process for such PV systems would be desirable and conceivable, but it is unfortunately not yet in sight. In terms of sustainable agriculture, which is increasingly being postulated by many stakeholders, support would also be a positive factor for farmers themselves. They would not only benefit financially but would also be positively perceived by the public.

 

Conclusion

So far, only few projects involving vertical bifacial PV systems have been implemented compared to other countries. The costs of the systems are in some aspects (especially investment costs) higher than those of conventional PV systems, but are offset by lower costs or higher revenues in other areas (higher specific electricity generation, lower specific lease costs, electricity marketing revenues, lower specific grid connection costs). The wide range of possible applications, the dual use and a generation profile that is attractive in terms of self-consumption speak for considering this type of a power plant when acquiring land and planning the system layout. Sustainability-oriented municipalities can be an ideal partner for project development and land acquisition.
 

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¹ Fraunhofer ISE: „Maximum Yields and Greatest Reliability with Bifacial PV Modules”

² With an increasing production of e.g. solar power, the price of electricity on the stock exchange falls; this effect intensifies as the installed capacity increases, so that PV systems reduce their own market price according to the current market principle

 

 

 

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