H. E. Khalifa, R. Dipippo and J. Kestin. “Geothermal preheating in fossil-fired steam power plants,” Pr°Ceedings of the 13th Inters°Ciety Energy Conversion Engineering Conference, Warrendale, PA, USA, 1978.
 Sargent & Lundy LLC Consulting Group, “Assessment of parabolic trough and power tower solar technology cost and performance forecasts,” 2003. http://www.nrel.gov/d°Cs/fy04osti/34440.pdf
 R. Dipippo, “Small Geothermal Power Plants: Design, Per-formance and Economics,” Geo-Heat Center Quarterly Bulletin, Vol. 20, No. 2, June 1999.