Development of High Spatial Resolution Solar Radiation Maps for Hawai';i

Surface solar radiation data are important for a wide variety of applications in natural sciences, engineering, agriculture, human health, and alternative energy.. However, the availability of accurate surface solar radiation measurements for these applications is often limited. In lieu of observations, models can be used to simulate time and space variations in solar radiation. For places such as Hawai';i, with extreme topographic relief, useful simulations require high spatial resolution and a parameterization capable of representing sharp spatial gradients in cloud cover and terrain shading effects. The purpose of the study presented here was to develop digital maps of the mean diurnal cycle of direct, diffuse, and global solar radiation for each month at 250 m resolution for the major Hawaiian Islands. The model used to develop the maps combines clear-sky solar radiation estimates with satellite-derived cloud cover to produce estimates of all-sky solar radiation. The clear-sky model used spatially-dependent estimates of atmospheric constituents based on ground elevation, surface characteristics, and terrain effects. Cloudiness patterns were estimated by fusing high temporal resolution Geostationary Observational Environmental Satellite (GOES) data with high spatial resolution Moderate Resolution Imaging Spectroradiometer (MODIS) data. We use measured solar data from 32 ground stations across the islands for model development and validation. These sites represent locations on six of the eight major islands and cover a vertical elevation gradient of 1.5 to 2290 m.