Outdoor photocatalytic hydrogen production reports rates and efficiencies that look weak next to laboratory numbers, and the comparison is usually unfair in both directions. The difference is the light source: laboratory constants versus a spectrum, intensity and angle that change by the minute. Normalization is what makes field data meaningful.
Solar spectra shift with time of day and weather, the morning's red-rich light and noon's blue-rich light drive photocatalysts differently even at equal power. Intensity swings by factors across a day, passing clouds impose transients labs never see. And angle of incidence changes effective illumination of tilted or fixed receivers.
Measure irradiance at the reactor plane with a calibrated pyranometer (and for spectral sensitivity work, a spectroradiometer). Normalize production by integrated irradiance over the same window, photons in per joule of product out. Report solar-to-hydrogen efficiency with the measurement plane stated, and quote the intensity window, efficiency is not constant with intensity, and a fair comparison needs comparable windows.
Report: production rate and cumulative production; irradiance conditions (daily insolation, intensity range); reactor temperature; normalization basis; and controls, blanks establish the floor. Compare lab and field by re-evaluating the lab catalyst under a simulated solar spectrum matched to the field window, otherwise the ratio compares light sources, not catalysts.
The strongest field statement pairs the normalized efficiency with the availability record, efficiency on the hours it ran plus the hours it ran. A number with context is science; without it, it is weather.
See Perfectlight's outdoor solar systems and photocatalysis solutions.
