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274 Managing Global Warming

plants. Improved hydrological forecasts combined with advanced optimization
models are likely to improve operation and at the same time respect new environmen-
tal constraints and multipurpose use of the water. New improved optimization
methods and software will need to be further developed for better coordination with
other renewables, where hydropower could have a key role in the balancing and grid
stabilization as the percent of variable generation capacity in wind and solar plants is
increasing.
A few interesting areas where new technology is under development can be men-
tioned. This selection is mostly based on the chapter “Prospects for technology
improvement and innovation” in reference [1] and on the Hydropower Development
book series [5,6,9,10].

8.5.1 Extending operational regime for turbines
Hydropower turbines, running at fixed speed, have traditionally been optimized for
operation at a “best point” defined by speed, head, and discharge. Operating outside
this best point (different head and/or discharge) will usually lead to considerable
reduction in efficiency and reduced power output. Large hydropower turbines are
now close to the theoretical limit for efficiency in a small region near the “best
point,” but may still be improved for more flexible operation outside this region. This
is illustrated in Fig. 8.2, which shows typical efficiency curves for different types of
hydro turbines [6]. The application of “Variable-speed” turbines offers advantages in
the form of greater flexibility in handling such situations, with higher efficiency as a
result.

8.5.2 Utilizing low or very low head—Unpowered dams

Most of the existing hydropower projects were developed in times with lower energy
price, where projects with low (<15m) and very low (<5m) head were not econom-
ically feasible. Most such low head projects were excluded from hydropower potential
mapping, for the same reason. Therefore, existing data on hydropower potential for
low head sites are probably not complete and sometimes completely absent.
As an example, mentioned in reference [1], in Canada a market potential of
5000MW of low head hydropower plants was recently identified. In many countries,
there is a large untapped potential for producing electricity from irrigation dams, pro-
vided low head turbines can be developed at low cost.
There is probably also a large potential for increasing generation by refurbishing
and upgrading existing HPP. Many of the existing hydropower plants are >40years
old, and there is a significant potential to increase efficiency and capacity. This poten-
tial is not included in Table 8.3. A recent study in Norway based on 20 refurbishment
projects of 30- to 60-year-old plants revealed that the generation increased by 23% on
average due to increased capacity and efficiency [11]. Similar results were found in
studies in United States under the Hydropower Vision project [12]. Here, it is stated
that it is possible to increase hydropower capacity from 101GW today to 150GW in
2050, a large share of this from sites previously not considered useable.