RE:RE:Solar Alliance signs contract for Tenn. solar project $$$$$$They don't often put the dollar figure in the news release because it is commercially sensitve information that their customers don't always want them to share. A good rule of thumb, however, is that it costs anywhere from $1.20 - $2.00+ / watt to install. So for a 500 kW system, more than $500K but less then 1mil. Not bad at all!