Bifacial solar cells now hold more than 90% market share, and their origin traces back to the efforts of Antonio Luque around 1976. There were, admittedly, earlier precedents with designs very different from the one that dominates the market today: Mori’s patent describing contacts on faces perpendicular to the light-incident surfaces, interdigitated back-contact cells (which have limited bifaciality), and developments from the Soviet space program, which barely crossed international borders given the Cold War context. But before the efforts of Luque and his collaborators, the term “bifacial” did not exist in photovoltaic scientific literature. Who deserves the credit matters less than understanding the sequence of events, because our present is not inevitable — it is the consequence of historical anecdotes and accidents. Everything could (and perhaps should) be different.
In 1979 Luque founded the Instituto de Energía Solar (IES), and in 1981 he created, jointly with Javier Eguren, a company that became the first to commercialize bifacial panels. Isofotón would go on to become the seventh-largest company in the international solar market, before the European solar industry was nearly wiped off the map by China’s rise as an industrial super-power.
Luque’s initial motivation stemmed from the need to lower the cost of solar energy, and his imagined solution was to illuminate both faces of a bifacial cell using a parabolic reflector, maximizing the power generated per cell. But more influential than Luque’s original idea turned out to be a proposal from another IES member, Cuevas: using the rear face of bifacial panels to capture light reflected off the ground. The simplicity of this alternative, combined with the technical difficulty of Luque’s original proposal, led Cuevas’s idea to become established as the new paradigm for bifacial technology. But it can be argued that Cuevas’s idea, despite having contributed to the consolidation of bifacial technology, also had a pernicious effect — contributing to the abandonment of riskier but higher-potential ideas based on symmetrically exploiting both faces of bifacial cells. All our actions, even when driven by the best intentions, carry an increase in entropy and certain pernicious effects. Perhaps the understandable concerns of investors about short-term results were also harmful, later leading Isofotón to abandon bifacial technology along with its highly advanced n-type cell technology — an architecture comparable to modern PERT cells (though with less effective surface passivation than what Martin Green’s group would later develop). After this setback in Isofotón’s strategy, the market remained dominated by p-type and monofacial technology for over four decades, until the technological superiority of n-type and bifacial cells finally prevailed commercially.
The IES — with Eduardo Lorenzo playing a particularly prominent role — also played a decisive part in building the first photovoltaic power plant with horizontal-axis trackers, which was also the first solar installation in Europe, and the second in the world, to reach 1 MW, following the Carrizo Plain disaster in California: a failed experiment in the use of reflectors that also significantly shaped the direction of solar technology.
Perhaps the time has come to reimagine new ways of harnessing bifacial technology. May we have the strength to choose the steeper and less traveled path, following the example of Luque, Sala, Lorenzo, Eguren, Araújo, and so many others. Forty years later, Isofotón’s bifacial panels are still working on the IES rooftop, and the memory of what happened continues to inspire us.
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