Current issues in terrestrial solar radiation instrumentation for energy, climate, and space applications

Uncertainty in terrestrial solar radiation measurements of a few watts per square metre (1 W/m(2) to 2 W/m(2)) is needed to validate estimates of the Earth's radiation balance derived from satellite data. The characterization of solar energy resources for renewable energy technologies requires simil ar accuracy for economical technology deployment. Solar radiation measureme nt research at the National Renewable Energy Laboratory addresses calibrati ons, operational characteristics, and corrections for terrestrial solar rad iation measurements. The characterization of field instrument geometric and thermal responses contributing to radiometric errors is described, togethe r with correction schemes reducing the uncertainty of broadband irradiance measurements from tens of watts per square metre to a few (+/- 2 W/m(2) to +/- 5 W/m(2)). Such improvements in accuracy reduce the time and labour req uired for detecting and quantifying trends in terrestrial solar radiation a cid possible changes in the Earth's radiation budget.