INTRODUCTION
The sun is the only significant source of energy to the earth. Received entirely as radiation, this energy is subsequently converted, so that at any time and place, an original quantum may appear in anyone of several diverse forms. Thus, with respect to the energy encompassed in the day-to-day climate at a given place and time, solar energy may appear as the latent heat of vapor, the advected heat of air masses, radiant energy from sky and terrestrial objects, and unconverted solar radiation arriving as direct beams. The unconverted solar radiation in the form of direct beams, is a very important form that is dominant in the hydrologic processes of evaporation, transpiration, snow ablation, as well as in the growth and succession of vegetation.
The total flux of energy to a site at any given time is difficult to measure, and now only the flux of radiant energy alone can be measured readily at a point. However, this flux varies so widely over most land surfaces that point measurements are of limited value. The spatial heterogeneity in the radiant flux is due to the variation in solar beam irradiation caused by variations in the inclination of the earth's surface with respect to beam direction. Within a geographic region subject to uniform atmospheric conditions, irradiation from the sky is fairly uniform, regardless of surface inclination. However, the total sun and sky irradiation varies widely with surface orientation and slope. The variation of direct beam radiation varies in time with atmospheric condition and path length, the combined effect of which can be estimated.
Systematic long-term measurements of solar and terrestrial radiation in India using calibrated and maintained instruments as per international standards was started in the year 1957-1958. The radiation laboratory of the India Meteorological Department, Pune, serves as the radiation center for India and monitors 25 specifically selected sites, which form the national radiation network. Of these 25 stations, 13 (principal stations) are equipped to monitor continuous records of global and diffuse solar radiation, and measurements of direct solar radiation are done at regular intervals in addition to the recording of sunshine. In the remaining 12 stations (ordinary stations) a minimum program is carried out of continuous recording of only global solar radiation in addition to the recording of sunshine. Apart from these parameters, all stations maintain continuous records of other meteorological parameters such as temperature, relative humidity, rainfall, wind speed, and wind direction.
Goa and Mangalore represents a principal and an ordinary station, respectively. Meteorological observatories at Karwar, Honnavar, and Shirali record only climatological parameters. In order to assess the solar potential in the coastal belt of Uttara Kannada, we have adopted an empirical method. With this empirical relationship (based on radiation and climatological data at Goa and Mangalore), we estimate global radiation (GR in kWh/m2) for Karwar (with 37 years of climatological data), Honnavar (with 50 years of climatological data), and Bhatkal (Shirali, with 15 years of climatological data)
