WATER BUDGET OF AN ENERGY CANOPY

Abstract:

The United Nations Food and Agriculture Penman-Monteith equation FAO56 is the standard method for modeling and determining evapotranspiration from a variety of managed landscapes. A canopy and the plants growing under it together form a microclimate which alters the evapotranspiration. Common examples include canopied forest, orchards, vineyards, traditional field crops or a solar energy canopy. An open question is: do these equations apply to other built canopies (e.g. solar panel arrays) and the ecosystems that live below them?

The shade provided by the panels reduces water demand by plants and the transpiration of the plants cools the local microclimate increasing the efficiency of the solar panels. Understanding the mechanisms behind the formation of this microclimate increases our ability to understanding and predict the evaporation and transpiration of plants under the panel. Among other factors, the degree of shading of the solar panel canopy and the amount of water available at the soil surface affect the evaporation process.

We initiated an experiment to determine whether FAO56 Penman-Monteith is applicable to model the evapotranspiration of plants growing under a solar panel canopy in July of 2019 at the North Willamette Research and Extension Center in Aurora, Oregon, USA. The data collected are used to confront the FAO56 ET estimates with measurements of actual ET below the solar panels.