Capehart, B. L. ., Salas, C. E. ., Turner, W. C. . and Parker, S. A. . (2003) “N EW C ERTIFICATION PROGRAM AVAILABLE FOR DISTRIBUTED G ENERATION AND COMBINED HEAT AND P OWER P ROFESSIONALS”, Distributed Generation & Alternative Energy Journal, 18(3), pp. 71–80. doi: 10.13052/dgaej2156-3306.1833.