Photovoltaic Array Power Density (Capacity per Square Metre of Array)

This formula says how much direct-current capacity a solar array packs into each square metre of ground it covers: the array's dc rating $P_{dc}$ divided by the area $A$ of the array. The answer depends on which area and which capacity are counted, and the page fixes both. The area is the array footprint, the outline around the panel rows, and not the fenced site, which is larger because of roads, buffers and substations. The capacity is the dc rating at standard test conditions, not the ac power the inverters export, which is lower.

The United States Geological Survey's large-scale solar photovoltaic database (USPVDB, version 4.0, April 2026) publishes both numbers for every ground-mounted plant of 1 MW or more: the capacity in megawatts dc and the area of the array boundary in square metres. The 752.1 MW dc Topaz Solar Farm in California covers 12 480 866 m², which is 12.48 square kilometres of arrays, so $p$ is 60.26 W/m². The database lists its ac capacity as 585.90 MW, a reminder of how much the choice of capacity matters. Skyline, in Illinois, has 6.5 MW dc over 96 477 m², which is 67.37 W/m². Run backwards, 60.26024 W/m² over 12 480 866 m² is the 752.1 MW dc, and 752.1 MW at that density needs 1 248.0866 hectares.

Handbooks often quote the inverse, the land needed per megawatt. A figure of 1 hectare per megawatt is 100 W/m², and 2 hectares per megawatt is 50. The density is not a constant of the technology: rows set far apart to avoid shading, and trackers, lower it, and panels of higher efficiency raise it. Ong and colleagues (2013) give land use per megawatt, weighted by capacity, for the plants of their day, and van Zalk and Behrens (2018) review and compare power densities across renewable and non-renewable generation.

The density is a ratio of capacity to area, not the energy a year brings. The yield page takes the dc rating on to energy with the peak sun hours and the performance ratio. Watts per square metre of a lit floor are a different thing with the same units.