Difference between "invest in" and "invest into" [duplicate]

Possible Duplicates:
Difference between “in” and “into”
When should “into” be used rather than “in to,” and vice versa?

Since solar power is theoretically the most efficient energy source on earth, shouldn't we invest more in harnessing it?

As I was writing the sentence above, I became uncertain as to whether I should write in or into, and thereby doubted whether I really understood the difference. Please explain.

Solution 1:

The following Ngram indicates that "invest in" occurs nearly 400 times more frequently than "invest into". Personally, I have always heard "invest in", never "invest into".

http://ngrams.googlelabs.com/chart?content=invest+into%2Cinvest+in&year_start=1800&year_end=2000&corpus=0&smoothing=3

Since usage ultimately defines language, I would not tend to fight "invest in" merely because of the current definition of "in". There are many examples of words having different meanings in different contexts; "in" is one of them.

Solution 2:

We always use invest in something and not invest into something. Checking both CALD and OALD shows no usage of invest into, though the latter lists invests on.