Hydropower

Hydropower

1. Introduction

Hydropower is the largest renewable resource used for electricity. It plays an essential role in

many regions of the world with more than 150 countries generating hydroelectric power. Asurvey in 1997 by The International Journal on Hydropower & Dams found that hydro supplies
at least 50 percent of national electricity production in 63 countries and at least 90 percent in 23
countries. About 10 countries obtain essentially all their commercial electricity from hydro,
including Norway, several African nations, Bhutan and Paraguay.
There is about 700 GW of hydro capacity in operation worldwide, generating 2600 TWh/year
(about 19 percent of the world’s electricity production). About half of this capacity and
generation is in Europe and North America with Europe the largest at 32 percent of total hydro
use and North America at 23 percent of the total. However, this proportion is declining as Asia
and Latin America commission large amounts of new hydro capacity.
Small, mini and micro hydro plants (usually defined as plants less than 10 MW, 2 MW and
100kW, respectively) also play a key role in many countries for rural electrification. An
estimated 300 million people in China, for example, depend on small hydro.

2. Capacity and Potential

There is vast unexploited potential worldwide for new hydro plants, particularly in the
developing countries of Asia, Latin America and Africa while most of the best sites have already
been developed in Europe and North America. There is also upgrading potential at existing
schemes though any future hydro projects will, in general, have to satisfy stricter requirements
both environmentally and economically than they have in the past.
As shown in Table 4 the world’s gross theoretical hydropower potential is about 40000
TWh/year, of which about 14000 TWh/year is technically feasible for development and about
7000 TWh/year is currently economically feasible. The last figure fluctuates most being
influenced not only by hydro technology, but also by the changing competitiveness of other
energy/electricity options, the status of various laws, costs of imported energy/electricity, etc.

Until recent years there has been less than 100 GW (about 350 TWh/year) of new hydro capacity
under construction at any one time, equivalent to less than 15 percent of the capacity in
operation. The figure has now risen, reflecting China’s vast construction program, which
includes the 18.2 GW Three Gorges Project, now in its second phase of construction. Most new
hydro capacity is under construction in Asia and South America. China has by far the most, with
about 50 GW under way. Brazil has largest resources in world (800,000 GWh/year) of
economically exploitable capacity and Norway depends almost entirely hydro for its electricity
needs.
Hydropower continues to be the most efficient way to generate electricity. Modern hydro
turbines can convert as much as 90 percent of the available energy into electricity. The best fossil
fuel plants are only about 50 percent efficient. In the U.S., hydropower is produced for anaverage of 0.7 cents/kWh. This is about one-third the cost of using fossil fuel or nuclear and onesixth
the cost of using natural gas. Hydro resources are also widely distributed compared with
fossil and nuclear fuels and can help provide energy independence for countries without fossil
fuel resources.
There is also significant, widespread activity in developing small, mini and micro hydro plants.
At least forty countries, particularly in Asia and Europe, have plants under construction and even
more have plants planned. China, Brazil, Canada, Turkey, Italy, Japan and Spain all have plans
for more than 100 MW of new capacity.

3. Small Hydro

Small-scale hydro is mainly ‘run of river,’ so does not involve the construction of large dams and
reservoirs. It also has the capacity to make a more immediate impact on the replacement of fossil
fuels since, unlike other sources of renewable energy, it can generally produce some electricity
on demand (at least at times of the year when an adequate flow of water is available) with no
need for storage or backup systems. It is also in many cases cost competitive with fossil-fuel
power stations, or for remote rural areas, diesel generated power.
Small hydro has a large, and as yet untapped, potential in many parts of the world. It depends
largely on already proven and developed technology with scope for further development and
optimization. Least-cost hydro is generally high-head hydro since the higher the head, the less
the flow of water required for a given power level, and so smaller and less costly equipment is
needed. While this makes mountainous regions very attractive sites they also tend to be in areas
of low population density and thus low electricity demand and long transmission distances often
nullify the low cost advantage. Low-head hydro on the other hand is relatively common, and also
tends to be found in or near concentrations of population where there is a demand for electricity.
Unfortunately, the economics also tend to be less attractive unless there are policy incentives in
place to encourage their development.

4. Environmental and Social Impacts

Although hydroelectricity is generally considered a clean energy source, it is not totally devoid
of greenhouse gas emissions (GHG) and it can often have significant adverse socio-economic
impacts. There are arguments now that large-scale dams actually do not reduce overall GHG
emissions when compared to fossil fuel power plant. To build a dam significant amounts of land
need to be flooded often in densely inhabited rural area, involving large displacements of usually
poor, indigenous peoples. Mitigating such social impacts represents a significant cost to the
project, which if it is even taken into consideration, often not done in the past, can make the
project economically and socially unviable.
Environmental concerns are also quite significant, as past experience has shown. This includes
reduction in biodiversity and fish populations, sedimentation that can greatly reduce dam
efficiency and destroy the river habitat, poor water quality, and the spread of water-related
diseases. In fact, in the U.S. several large power production dams are being decommissioned due
to their negative environmental impacts. Properly addressing these issues would result in an
42
enormous escalation of the overall costs for producing hydropower making it far less competitive
then is usually stated. As many countries move toward an open electricity market this fact will
come into play when decisions regarding investments in new energy sources are being made. If
the large hydro industry is to survive it needs to come to grips with its poor record of both cost
estimation and project implementation.

5. Conclusions

Hydropower is a significant source of electricity worldwide and will likely continue to grow
especially in the developing countries. While large dams have become much riskier investment
there still remains much unexploited potential for small hydro projects around the world. It is
expected that growth of hydroelectricity will continue but at a slower rate than that of the 70’s
and 80’s. Thus, the fraction of hydroelectricity in the portfolio of primary sources of energy,
which is today at 19 percent, is expected to decrease in the future. Improvements and efficiency
measures are needed in dam structures, turbines, generators, substations, transmission lines, and
environmental mitigation technology if hydropower’s role as a clean renewable energy source is
to continue to be supported.