Most morning talk shows have daily segments on what is trending — meaning what is popular currently.  A better word for these rapid changes in taste would be fad — for market research, a trend is established over time and will encourage a change in behavior. 

1) Trends are established via the use of statistical tests to establish a change in behavior — a lot of evidence that establishes a pattern over time.

2) A trend is established using consistent methodology

3)  The analyst must be able to draw a statistical line using unbiased data gathered through consistent methodology (history is important)

4) Rigorous statistical tests must be used

5) Most important, a change in behavior must become apparent through statistical means not anecdotal evidence — for market research, circumstantial evidence is not enough!

Utility scale (multi-megawatt) solar:  An established trend

Residential Solar Leases:  Trending, not yet a trend

Community (group buy) Solar:  Beginning to trend

Power Purchase Agreements for solar: An established trend

Tender bidding for Solar: Trending, not yet a trend

Crowd funding for solar installations:  Not even trending yet

Crowd funding for solar manufacturing: Not even trending yet (would also be very dangerous)