How to obtain the extra energy gain promised by bifacial technology

FuturENERGY September-October 2020

There has been an increasing trend in the use of bifacial solar panels over the last few years. The technology has already been assessed decades ago, but due to the high costs involved, it has failed to expand until this past year, when manufacturing processes have managed to optimise bifacial panels to compete with their monofacial counterparts. By shifting from one type of panel to the other, a solar generation gain of around 8-10% can be achieved. This percentage is known as bifacial gain and is conditioned by multiple factors. (By Javier Tamayo. Design Engineer, STI Norland).

Three basic parameters directly determine PV project bifaciality. In order of relevance, starting with the most important, these are:

  1. Amount of irradiance: the greater the amount of light received, the more electricity can be generated from the solar resource. Most of this captured irradiance comes in the form of direct irradiance, which is reflected on those areas of the terrain not affected by shading from the solar panels themselves.
  2. Albedo: defines the proportion of irradiance reflected from the ground. It depends on the type of terrain and varies throughout the year. As a reference, common sandy terrain has an average albedo value of 0.25.
  3. View factor: depends on the geometry and position of the irradiance-capturing surface (the panels), in relation to the irradiance-emitting surface (the ground). An analysis of the tracker choice is therefore paramount to ensure bifaciality adequacy. In other words, a thorough analysis of the extent to which the tracker panels capture ground-reflected irradiance is essential.