Page 315 - Managing Global Warming

Hydropower 275

With increasing energy demand and price, and improved technology for such low
head projects, one can see a growing interest in technology development. At
extremely low head also hydrokinetic technology may open up new possibilities, since
it can extract energy directly from moving water, in the same way as wind turbines
extracts energy from moving air.

8.5.3 Fish-friendly hydropower plants

Dams and hydropower plants may create obstacles for fish migration and reduce
access to important rearing and spawning sites, and reduce or eradicate fish
populations. Safe passage for fish is therefore a major concern in environmental anal-
ysis of hydropower projects [9,13]. There are two main categories of technology
development, for upstream or downstream migration:
Upstream migration: Fish ladders for upstream migration, combined with flow release and
adaption in operational regime to minimize problems when migration actually occurs. Other
common devices include bypass channels and fish elevators. In some cases, small correc-
tions at culverts and weirs can improve the situation and increase upstream migration.
Downstream migration: The main objective here is to avoid fish entering into intakes and tur-
bines. New technology for such avoidance systems under development is based on screens,
acousticcannons,light(strobeandlaserlight),andcontrolofflowdirection.Ifitisnotpossible
to avoid fish to enter the turbines, new type of turbines (“fish-friendly turbines”) may mini-
mize the risk of injury or death on passing fish. Some turbine manufacturers claim that the
turbines may have good efficiency and still allow 90%–100% of the fish to pass safely.

8.5.4 Tunneling and underground power plants
Tunnels and rock caverns are important construction elements in many large-scale
hydropower projects: headrace/tailrace tunnels, access tunnels, powerhouse, surge
shafts, power cables and ventilation shafts. In Norway, nearly all large-scale hydro-
power plants have been built underground since 1960. In 2002 there were 500 under-
ground hydropower plants worldwide, about 40% of these were then found in Norway
[10]. An example showing an underground powerhouse is shown in Fig. 8.3. Typical
layout of tunnel system and rock caverns is shown in Fig. 8.4. Tunneling technology
has evolved from traditional drill-and-blast technology to the use of full-face tunnel
boring machines (TBM), increasing speed of tunneling and lowering cost.
Today, there is also an interesting technology development for “microtunnels” that
can be used to replace pipes and penstocks for small hydropower plants (<1.5m diam-
eter), avoiding completely overground work and disturbance in the nature. This tech-
nology has been being developed and tested in Norway and is now used successfully in
an increasing number of small hydropower plants [14]. Another potentially important
use of such microtunnels could be for transmission power cables, avoiding power lines
through environmentally sensitive areas.
The use of underground power stations combined with tunnels to transport water
gives high flexibility in locating power plants and makes it possible to build efficient
systems, superior to traditional systems with surface powerhouse and open-air