To cite package 'solaR' in publications use:

Oscar Perpiñán (2012). “solaR: Solar Radiation and Photovoltaic Systems with R.” Journal of Statistical Software, 50(9), 1–32. doi:10.18637/jss.v050.i09.

Corresponding BibTeX entry:

  @Article{,
    title = {{solaR}: Solar Radiation and Photovoltaic Systems with
      {R}},
    author = {{Oscar Perpi{\~n}{\'a}n}},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {50},
    number = {9},
    pages = {1--32},
    doi = {10.18637/jss.v050.i09},
  }