The ROI exists - Goldman, Walburg, etc all have billions invested. Most solar developers are private companies. A lot of the oil giants have been investing in these developers to diversify. The issue is not whether this asset class generates a return, but rather is it available to non-institutional investors. Diversification normally preserves wealth - we tend to recommend our investors to allocate 5% of their portfolio in this asset class - its not correlated and annuity generating). Full disclaimer - I'm a co-founder at renewables.org.