As the world transitions to an energy model based on renewable sources, new challenges are emerging in how we manage the electricity grid. One of the most well-known—and visually striking—is the so-called “duck curve”. Coined in 2012 by the California Independent System Operator (CAISO)1, the term refers to the shape taken by the net electricity demand curve over the course of a typical day. Net demand is defined as the total electricity demand minus solar generation.
A clear example of this phenomenon can be seen in a graph from California on October 22, 2016, a sunny day with low and steady wind generation. Around midday, solar power production (green) peaks, significantly reducing the amount of electricity that needs to come from other sources. When subtracting solar generation from total demand (white), we obtain the net load (shown in purple)—the remaining energy that must be supplied by non-renewable sources. However, solar output drops sharply just as demand peaks in the evening, increasing reliance on fossil fuels. This net load curve (purple) resembles the profile of a duck, giving the phenomenon its name, and represents a great challenge for electrical systems.
This trend is clearly mirrored in electricity prices. When solar generation dominates — for instance, around midday on a sunny day — the grid is flooded with excess power, supply outstrips demand, and prices collapse to zero or even turn negative. In contrast, as solar output is scarce when demand peaks earlier and later in the day, energy prices surge. The reason is simple: non-renewable sources, which ultimately set market prices, must recover their costs during the few hours they operate; those limited windows of production need prices high enough to keep them economically viable. The effect becomes more pronounced on sunny days with low demand, such as holidays or weekends, and is even more challenging in isolated or weakly interconnected power systems, as is the case in parts of southern Europe.
Between 2010 and 2020, the cost of photovoltaic technology dropped by an average of 15% per year. This sharp decline fueled a global installed capacity boom, which expanded at roughly 25% annually over the same decade. If this growth trajectory continues, solar PV could emerge as the world’s leading energy technology within the next 10 to 20 years. Yet the rapid build-out of solar has also intensified the so-called “duck curve” — a pattern clearly visible in Spain’s electricity spot prices over time.
This phenomenon poses an increasing threat not only to the economic viability of conventional solar power but also to the broader energy transition at a societal level. The main risk of the so-called “duck curve” is that it creates frequent periods when electricity prices drop close to zero—or even turn negative—significantly reducing the market value of solar energy and undermining the profitability of conventional photovoltaic plants. This has major implications: expanding solar capacity is essential to reduce reliance on fossil fuels, yet that expansion is only feasible if solar power remains economically viable. This curve is becoming increasingly common in many countries and regions with a strong solar presence in their energy mix, such as Spain, Germany, France, Italy, Belgium, and many states across the U.S.
Graph inspired by Julien Jomaux
In this context, the need is not just for renewable energy that’s cost-effective, but for one that delivers truly valuable power. VectHor embraces exactly this approach: an innovative solution that combines vertical bifacial solar panels with optically engineered reflectors. Together, they maximize solar capture throughout the day, boosting both output and the market value of the electricity produced.
On their own, vertical bifacial panels are highly effective at capturing direct sunlight during the early morning and late afternoon, precisely when demand tends to rise and conventional horizontal or low-tilt panels produce very little. Thus, as shown in the chart —which compares the actual output of VectHor systems (green) with that of fixed-tilt installations oriented 20 degrees south (white) on a spring day in 2024— VectHor generation (green) peaks both at sunrise and at sunset, aligning with the typical electricity price peaks (purple) observed over the course of a standard day. However, they do have a limitation: because they face east and west, they generate very little energy at midday. And while the goal is to reduce the midday solar surplus and reinforce generation during critical demand hours, it’s still essential to maintain a reasonable level of production around noon to ensure a balanced generation profile —particularly in winter, when electricity prices remain high throughout the day.
This is where the reflectors come in, allowing VectHor to operate as a solar tracker without moving parts. Thanks to these elements, energy production at noon is not nearly zero—as it typically is with vertical panels without reflectors—but instead, as shown in the graph in green, remains steady, reaching levels comparable to those of a conventional fixed tilted panel (white). Positioned on both sides of each panel and designed with patented optical geometry, they redirect sunlight onto the panel surface throughout the day, enhancing its exposure and enabling a more stable and demand-matching solar output. This allows for the capture of sunlight at times when electricity prices are highest, leading to substantial energy and economic savings.
- California Independent System Operator (CAISO) (2013). What the duck curve tells us about managing a green grid. Available in: https://www.caiso.com/Documents/FlexibleResourcesHelpRenewables_FastFacts.pdf
