Looking at the nature of exits from the two sectors offers a clue. Medical technology start-ups were 50 per cent more likely than cleantech start-ups to return profits to investors through an early lucrative acquisition. But there is a dearth of large investors willing to buy cleantech start-ups, which therefore often end up as stranded companies — ones that have run up against the capital and time constraints of VCs in spite of their promising technologies. A new wave of public and private support will be required to reboot investment in cleantech Without a likely pathway to a profitable takeover and facing a long grind to win support for an IPO, the cleantech sector has outlived the patience of VCs unwilling to lock up capital for a decade or tolerate massive expenditures to scale up.