Agri-tech & precision
Agrivoltaics with biological integration
The physiological basis of agrivoltaics: photosynthetic light saturation, why shading costs less yield than it costs irradiance, and how panel geometry becomes an agronomic design variable.
Agrivoltaics looks like a compromise — sunlight split between a panel and a crop — but its basis is not compromise, it is non-linearity. The photosynthetic light-response curve saturates. A leaf of a C3 crop — wheat, potato, lettuce, most vegetables — gains almost nothing above roughly 500–1000 µmol of photons per square metre per second, while clear-sky summer midday delivers about 2000. Light beyond the saturation point does not become biomass: it is dissipated as heat, spent on transpiration, and under heat and water deficit it drives photoinhibition and stomatal closure. Take that excess with a panel and you lose irradiance without losing the proportional share of yield.
The caveat is compulsory. Saturation is a leaf-level property; a whole canopy, with its shaded lower layers, responds to light far more linearly. So the real crop response to shading is always smaller than leaf physiology promises — and always larger than zero.
Microclimate under the array
The second mechanism is hydrological. A panel cuts incoming shortwave radiation and with it leaf temperature and the vapour pressure deficit at the surface; evapotranspiration under the array falls and topsoil moisture persists longer. In a dry summer this can be a net yield gain — the sheltered plant never experiences the water stress that the open-field control does. In a cool, wet season the same mechanism runs the other way: light and thermal time are short, and slower canopy drying raises fungal pressure. The sign of the effect is set by the site’s climate, not by the installation.
The metric used is the land equivalent ratio: relative crop yield plus relative electricity output compared with using the same area separately. Values above one mean the combination beats separation. The Fraunhofer ISE trial at Heggelbach, Germany, reported an LER of roughly 1.6–1.7 in the dry 2018 season, when potatoes under the array outperformed the control.
Geometry is an agronomic variable
The ceiling is crop-specific. Shade-tolerant and leafy crops, berries, forage and pasture tolerate 20–30% shading with little loss; cereals in a favourable climate lose roughly in proportion. That leaves genuine design freedom, because the shading fraction is set by layout rather than by installed capacity. Widely spaced rows on tall supports, vertical bifacial panels oriented east–west (which give a morning and an evening generation peak and shade very little at midday), and trackers steered on agronomic rather than purely electrical criteria are all ways of distributing the same annual shade differently across the day and the season.
The practical limit is structural, not physical: the clearance needed for machinery and the foundations that take land out of production push the cost per installed watt well above a ground-mounted plant. Agrivoltaics therefore pays where land is scarce, or where the second harvest is water saved — not merely where a field happens to be free.