A fog collector can be described in watts, watt-hours per kilogram or joules per cubic metre of air. Each unit answers a different question. Comparing devices requires knowing which electrical loads were counted, which water was counted, and how much air actually passed through the useful treatment region.
Ginters and Ginters’s 2026 hybrid prototype study reports approximately 38.3 Wh/kg. Its conclusion describes an approximate assessment using 8–10 W and a voltage-conversion efficiency range of 40–70%. The apparatus combines electrical collection, thermoelectric cooling and passive deposition; the reported average passive contribution is 19% of collected water. Its fog supply includes a fan. These details prevent treating the headline number as an independently metered, complete air-processing system specification.
Where the approximately 30 J/m³ example comes from
The unit conversion is straightforward: 38.3 Wh/kg × 3,600 = 137,880 J/kg. Suppose, purely as an illustration, air contains 0.2 g/m³ of liquid water and all of it is collected. Multiplying by 0.0002 kg/m³ gives 27.6 J/m³, often rounded to about 30.
That arithmetic is not a measured result from the paper. It assumes the water-specific energy transfers to the chosen fog condition, complete capture, and a denominator consisting of captured incoming fog droplets. A hybrid device that also condenses vapour requires a more detailed water balance. Different capture fractions, operating modes and electrical boundaries change the conversion. The example cannot establish that energy is unimportant or supply a universal acceptance threshold.
Measure the quantities a buyer would inherit
For a proposed product, define the complete electrical boundary before testing: the power supply, controls, required fans, cooling and other necessary operating loads. Integrate that power over the trial and divide by independently measured air volume: eair = ∫P dt / ∫Q dt. Bench fog generation should be recorded separately when it creates the test environment rather than forming part of the product.
For water recovery, report total collected mass and the additional mass relative to the passive baseline. Incremental energy per additional kilogram answers a different question from total energy per total kilogram. If the additional mass is indistinguishable from zero, an apparently precise ratio is not useful.
Visibility success and product advancement should therefore remain separate decisions. First establish a repeatable optical benefit. Then compare its measured energy cost with a buyer-derived ceiling for the intended service, using the same operating boundary.