In-stream tidal units convert the energy of tides and currents into power – a type of hydropower which has operated successfully for decades. No matter what you call it -- wave, in-stream tidal, river current, or hydro turbines; or where it sits -- sitting on the river bottom or suspended from a barge -- the technology has proven itself. What has remained more elusive is the much-needed transition from subsidies to commercial financing.
Concentrated solar power (CSP) systems are a great promise for renewable energy at scale. But they can use a lot of water, which is a problem since they tend to be located in places where water is scarce. Some concentrated solar technologies need to withdraw as much as 3,500 liters per Megawatt hour (MWh) generated.