I am going to finish the 2nd year of my PhD and have been working in a field which is not the major research area of my PI. He promised there will be industrial involvement and collaboration with other professors so I agreed to work on this field, thought I have only a little bit background in the area. However all of these promises have just not been fulfilled (I did try to find collaborators myself as well). As nobody in my group is working in this field and my PI is not particularly knowledgeable about it, I feel isolated and helpless. Meanwhile, I am attracted to a field in which my PI is an expert, and several of my colleagues actively work on it. 

I have mentioned this problem to my PI and he agreed I can get trained about the field which I am interested in, while continuing to work on the field I originally worked on. Recently I have found my 2-year results within my original field of study are invalid, and there are fundamental errors in it.

After learning the new field in which my group is much more active and becoming knowledgeable on it, I really feel passionate and motivated about this. It is a more difficult field but I am determined to spend time on it. As I am halfway into my PhD, **how should I convince my supervisor that I should switch my research field to an area in which our group is more active and knowledgeable, while abandoning my initial field completely? I am not trying to avoid solving the problem I faced in my initial field and would not like my PI to feel that is the case.** I just think working on my initial field here in my group is pointless as nobody is knowledgeable on it, nobody knows what I am doing so nobody is able to give me genuine comments, and most importantly, **I am not enthusiastic about it**. However I know my supervisor would like to develop this field as it is more commercially viable. I need to admit I am not genius in this field and can't just work on my own without any proper supervision. 

Any opinion is welcome. 

PS: I would not like to change my supervisor. This would be the last resort.