Is there out there tri -fuel 15-20kw stand by generator?

I am looking for the stand by large generator 15-20kw (to use all the power on one transfer switch). The problem is that stand by generator require large propane tanks (expensive to install). I would like to find a stand by generator that i could run off gasoline and use all of it available power. I think this would the most economical solution. In case of propane/natural gas the cost of propane tank installation is significant. The diesel stand by generators are significantly more expensive. So far I have found tri-fuel13kw portable generator that has several outlets. In this case not all the power can be utilized.