Hydroelectric dams come with their own environmental collateral, crop-based ethanol turned out to be far from sustainable (and in some cases worse than fossil fuels), and the dream of the hydrogen economy remains elusive.

But newer and greener technologies are in development within the renewable energy sector, which is already seeing big growth in wind farms, solar power towers and other forms of clean energy. Here are five of the emerging cleantech trends you won’t want to miss.