It might interest you two to know that in all of the official "Back to the Future" screenplays (available here:
http://members.lycos.co.uk/hillvalley/bttf1.htm,
http://members.lycos.co.uk/hillvalley/bttf2.htm, and
http://members.lycos.co.uk/hillvalley/bttf3.htm) the correct amount of power is only expressed numerically - ie, "1.21 gigawatts".