Sky Model

Liu & Jordan

Liu, Benjamin YH, and Richard C. Jordan. "The long-term average performance of flat-plate solar-energy collectors: with design data for the US, its outlying possessions and Canada." Solar energy 7, no. 2 (1963): 53-74.

Liu, Benjamin YH, and Richard C. Jordan. "The interrelationship and characteristic distribution of direct, diffuse and total solar radiation." Solar energy 4, no. 3 (1960): 1-19.

Hay

Hay, John E. "A revised method for determining the direct and diffuse components of the total short‐wave radiation." Atmosphere 14.4 (1976): 278-287.

Hay, John E., and Donald C. McKay. "Estimating solar irradiance on inclined surfaces: a review and assessment of methodologies." International Journal of Solar Energy 3.4-5 (1985): 203-240.

Perez

Perez, Richard, et al. "A new simplified version of the Perez diffuse irradiance model for tilted surfaces." Solar energy 39.3 (1987): 221-231.