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In general, hydroelectric power is derived from the height
through which water falls. When we build a dam, we are
doing the equivalent of bringing two points along the river
close together, to create some desired height.
Think of it in terms of the basically gentle slope of a
Points A and B along the length of that
riverbed, with B being downstream of A. If we drew a
horizontal line from A to B, how high above B would that
line be located? Well, when we build a dam at B, the
water-level behind the dam is exactly that horizontal line
connected to A.
So, it can now be understood that we don't actually need to
build the dam! Instead, let's put a large Tunnel Boring
Machine at Point B and set it to dig horizontally toward
Point A. Once we are beneath Point A, we bore vertically
to connect to the upstream part of the river. Now all we
need to do is put a turbo-generator into the bore-way, and
we will be generating hydropower, exactly as if we had
built a dam at point B.
There are some advantages and some disadvantages to
this Idea. The main disadvantage is that we won't want to
send the whole river down the borehole at Point A --but in
terms of a dam, essentially the whole river does generate
power at Point B. The two main advantages are that fish
are free to swim the whole river (we merely need screens
to keep them from going down the bore hole), and that we
can build these borehole hydropower systems all along the
length of the river, without any need to look for special
places to put them (like high canyon walls are needed when
building a dam).
I would like to think that the net effect is, we could
actually generate more total hydropower from this dam-
less system, along the length of a river, than from the
normal damming system. To be determined, of course!
AKA Run-of-the-river hydroelectricity
[scad mientist, Apr 23 2014]
||Very, very baked I'm afraid. Quite often implemented as simply laying a pipe adjacent to (or even in) the flow.
||For the microhydro projects around where my folks live, there are very strict regulations on what percentage of a river can be diverted - any noticeable change to the environment is verboten, so dams are right out.
||But it's not just tiny systems that do this, I'm sure you're aware of Dinorwig power station? They dug a tunnel between two lakes, and placed all the generators underground.
||Nope, never heard of Dinorwig before.
||You also missed the bit where dams act as a
battery, allowing the storage and controlled
release of power. Where I live has a major dam
and canal system to provide for power to (now
obsolete) textile mills. Roughly speaking, they
would use twice the river's flow for 12 hours, and
then shut down for 12 hours. Without the dam,
that would not have been possible.
||There's also the fact that the major purpose of
most dams is not power generation. Hoover Dam,
in the US, was primarily built for flood control and
irrigation. Power generation is a significant
bonus, but not the primary purpose.
||Many, many rivers in the world do not run at full strength
during the year. In Maine, for instance, a turbine sluice
without a dam above it would only work for a few weeks
each spring and autumn, when everyone's up to their tits in
floodwater and nobody dares to plug in the toaster anyway.
||Yes, very baked, but if you are going to be copying
someone, you can do worse than Nicola Tesla, as this
is the way Niagara Falls is done.