POWER December 2015 - 8

Ethiopia Begins
Generating Power from
1.87-GW Gibe III Hydro
Plant
Ethiopia's generation capacity got an immense
boost as operations began at the
1.87-GW Gibe III hydroelectric power
plant in the middle reach of the Omo River
basin this October. The plant-Ethiopia's
largest-is the third in the Gibe-Omo hydroelectric
cascade, which includes the
184-MW Gilgel Gibe and 420-MW Gibe II,
both upstream of Gibe III. Two additional
plants downstream, Gibe IV and Gibe V,
are planned by state-owned utility Ethiopian
Electric Power Corp.
According to Salini Impregilo, an Italian
firm contracted to build the $1.6
billion project, the plant comprises a 249meter
(m)-tall roller-compacted concrete
(RCC) dam-one of the highest in the
world-and an open-air power plant with
10 Francis turbines. It is expected to produce
6,500 GWh per year (Figure 1).
Salini Impregilo designed and built the
plant and the gravity dam, along with a
surface spillway. It also carved out three
diversion tunnels, two twin pumping tunnels,
two intake structures, two horizontal
tunnels, four vertical wells, and two
distributors. Consulting engineering firm
Studio Pietrangeli performed the feasibility
study, designed the plant, and provided
technical supervision during construction.
Construction began in July 2006. For
Salini Impregilo, many of the challenges
in building the dam came from logistical
hurdles, specifically because the site-
about 450 km southwest of Ethiopia's
capital, Addis Ababa-is so remote. Access
to it required building an airport, a
120-m span bridge, 75 km of new national
roads, and 40 km of project site roads. The
firm then needed to provide workers with
housing, sanitation, health, and recreation
facilities.
Then, when crews began foundation
excavation, they encountered hot springs
that required interception. Later, crews
discovered that locally sourced Ethiopian
cements were unsuitable because of variability
in quality and intermittent supply,
leading the government to step in to open
up the importation of special high-quality
cement. And because the RCC dam is one
of the highest in the world and the site did
not offer ideal conditions for the project,
special design solutions were required.
Despite those geological issues as well as
complex financial problems, the plant was
completed within nine years.
With a rainy season that lasts three
to four months, mountainous Ethiopia is
etched with large river gorges that have an
1. Steep undertaking. The Gibe III hydroelectric plant on the Omo River in Ethiopia features
a 249-meter-tall roller-compacted concrete dam, one of the highest of its type in the world.
The remoteness of the site, the narrow gorge where the dam is located, the height of the dam,
and challenges in sourcing reliable materials required unprecedented solutions to get the plant
built. Courtesy: Studio Pietrangeli
overall hydroelectric potential estimated
at around 160 TWh/year. This country with
a population of 94.1 million and a booming
economy has ambitious plans under its
Growth and Transformation Plan to become
a regional renewable energy hub in powerstrapped
East Africa. The Gibe III project
added much-needed capacity to the country's
total installed 2.3-GW base.
By 2037, Ethiopia aspires to have a total
capacity of 37 GW (a 1,500% increase) and
become a major power exporter. Acknowledging
that the feat will require massive
investments, the government is committed
to increasing private sector participation
to expand its grid and to reform tariffs to
allow for full-cost recovery.
-Sonal Patel, associate editor
" Revolutionary " Grid
Connection for Offshore
Wind Turbines Unveiled
Siemens, the only provider of direct-current
(DC) offshore wind connection projects,
in October unveiled a potentially
game-changing technology that it says
enables cheaper and simpler grid connection
of wind turbines miles off the coast.
The DC technology presented at the
National Maritime Conference in Bremerhaven,
Germany, consists of a platform
housing the transmission equipment that is
80% more compact than the conventional
large central converter platforms used to
convert DC into alternating current (AC)
for transmission and distribution. The new
compact design neatly holds diode rectifier
units (DRUs)-replacing conventionally
used air-insulated transistor modules-the
transformer, the smoothing reactor, and the
rectifier in one tank.
If a number of smaller platforms can
be built, a DC cable can connect several
of them sequentially in a wind farm and
then route them to an onshore transformer
substation, the company explained. Typically,
two DRUs (each with a transmission
capacity of 200 MW) are installed on one
platform. Up to three of these new platforms
can be connected to each other to
create an offshore grid node that replaces
collection platforms in the wind farms-
essentially creating a link that can connect
up to 1.2 GW of offshore wind capacity to
the mainland (Figure 2).
And that could result in cost savings
and more efficiency compared to conventional
platforms: " The volume of the plat8
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