I have been told that idling the Sprinter for an extended period of time is a bad idea due to "black death". The main application of the second alternator is to run the house AC and charge the house batteries while driving. The front AC does a reasonable job of cooling the cab area, but my wife found that riding in the rear of the van warm in hot weather without the house AC running.So your planning on using the sprinter engine as a generator motor?
I expect the solar panels to charge the house batteries while boondocking during the summer enough to support the fridge and evening LED light with some HF radio use.
It is interesting to note that Road-trek in their new eTrek conversion uses a similar, second engine alternator and advertises it as an engine-generator. I guess time will tell if their vans have the black-death issue if the Sprinter engine is used in that fashion.
Hein -- sorry about highjacking your thread. Over to you ...