Ever thought of investing in greentech? The early stage ecosystem there is much less developed -- there are simply fewer investors participating. I think what's limiting them is mainly non-essential: a combination of forbidding myths about capital intensity + regulations + time to market, plus the science being trickier. Probably a lack of angels who became wealthy from the space is an issue too, but there is no shortage of angels who were formerly physicists, aerospace engineers, chemists, biologists, etc.

There are massive opportunities, and the capital cost & lead time, at least in the earliest stages, are not nearly so bad as people assume. Working on design and theory costs roughly as much as a web startup -- founder's living expenses, some time at a machine shop, a few sourced parts.

At least that's how it was for us.

I think that the valuations, if you look from afar, are can seem pretty staggering as well, but I think that burn rates can be made low with the right approach.