This is good for low hydraulic head scenarios(basically, where the water doesn't have that much room to fall). With this system you can install it even if water only falls 2 feet, whereas more traditional turbines might need 6-10 feet

Yeah but that just means there's less power there to begin with, so not really economical or useful.

I think that's an over simplified view of it.

You can imagine a world where the efficiency of a more traditional turbine setup (measured in watts/$ including amortized capital and operating cost) scales down badly as hydraulic head decreases, and in fact is scales more poorly than the amount of power available.

What you're left with are scenarios where there's room for you to perform more efficiency than a traditional turbine if you can somehow get different scaling characteristics.

The economic viability becomes even more complex once you start considering things like what type of distribution you're dealing with.

Questions like, is it more efficient overall to have more distributed, but less efficiency generating sources, with reduced distribution costs, or have fewer more efficient generating sources with increased distribution costs.

I'd agree that in more of North America and Western Europe, this probably doesn't make sense. But there's still lots of places where the cost of hooking up to the grid is substantial.

I don't think that's necessarily true. Couldn't you make up for it on volume? I can picture scenarios where you'd have a lot of water falling a small distance and it would be more convenient to install something like this than to use a site with a lesser amount of water falling a larger distance.

Absolutely. The potential power is _water mass/sec * head height * g_ - more water volume is just as valuable as more head height.

Actually, looking at that calculation, I wonder how much the fact that this turbine doesn't introduce cavitation (bubbles) affects the efficiency. The water would be more dense, which would theoretically improve output... no idea if enough to worry about, though.

Less power sure, but it's still untapped power.

It looks like it provides enough power for a few households even with a fairly small version of it. Could be useful in some places.

It doesn’t require as much of a vertical difference between the input and output.

Having just read the linked article, it says smaller scale and that fish can safely get through.

With large scale dams there is also huge environmental impacts and displacement of the local population. You have to form a sizeable reservoir lake etc. They also take considerable time to build.

It's essentially the same, just applied to the particular case of smaller height difference and low pressure.