In our lifetimes (~40yrs), we will have to replace the 87% of the energy sources that are adding carbon to the carbon cycle[1]. That's ~450 Quadrillion BTUs (QBTU) per year[2]. No matter what, this will happen.
Do you know how much solar the US installed in 2012? 30 Gigawatts[3], which equals ~0.9 QBTU/yr. Even if solar eventually only amounts to 20% of the total fuel replacement (~90 QBTU/yr), that's a 100x growth in 40 years for an already huge industry. That's Internet revolution scale growth.
And that's only one industry. What about energy efficiency? There's so much opportunity for tech disruption there, and the ceiling is just as high as solar.
Why the hell are entrepreneurs (and investors) trying to make the next big app when the ceiling is so much higher in cleantech? The next Google will be an energy company.
[1] - http://www.eia.gov/todayinenergy/detail.cfm?id=11951
[2] - http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.cfm?tid=44&p...
[3] - http://cleantechnica.com/2013/12/24/npd-solarbuzz-predict-ma...
No one made money on solar itself because everyone made the rational decision to invest in it at the same time. That produced an oversupply, which meant less profits, but a very successful outcome in terms of supply.
That doesn't mean there aren't opportunities - just that they are hard to predict during disruption (what's new, right?)
The biggest reason I think more entrepreneurs don't enter the space is likely that the pain points are unknown to them. If you don't spend half your day manually downloading utility bills, you wouldn't know that there are lots of people willing to pay money to automate that process.
