Many models for estimating solar irradiance exist and there are still more software packages utilising these models. The majority of these models simply look at total irradiance and do not consider the influence of the spectral distribution. More sophisticated models use a single standard spectrum for the whole year. This distribution insensitive approach introduces errors since photovoltaic cells are more sensitive to some wavelengths than to others.
For my masters degree I developed a wavelength sensitive model that calculates the solar energy in high resolution across the spectrum. and recalculates it as the atmosphere changes across the the and throughout the year. My model also calculates the physical characteristic of a P-N junction photovoltaic cell. These two parts of the model form a powerful unison and can calculate the electrical yield form a photovoltaic cell where the effect of the atmosphere as well as the effects of the photovoltaic cell are taken into account.
This model is working well and gives excellent results; however is still a rough prototype stuck together with the software equivalent of duct tape. I would like to change this into a fully-fledged software tool for the use of both science and industry.