Hydroelectric power is one of the oldest and best established sources of renewable energy, and world hydropower capacity has been growing at a steady rate of about 3% a year since the 1960s. The bulk of hydropower is generated on a large scale using water stored in dams. But, lately, smaller-scale run-of-river hydro schemes have been gaining traction in many developing countries, especially in rural areas.
Hydropower constitutes the world’s largest source of renewable electricity, contributing nearly 16% of total electrical power generation in 2011.
Last year, global hydro capacity grew by 25 GW, or 2.7%, to about 970 GW. China accounted for almost half of last year’s new hydro capacity, while Vietnam, India, Brazil and Canada also brought significant new capacity on line. Beijing plans to boost China’s hydro capacity from 212 GW last December to 300 GW by 2015.
China already leads the world hydro generation capacity rankings with a 22% share, followed by Brazil, the US and Canada, each with 8%, and Russia, with 5%. These five countries, therefore, boast half of the world’s hydropower capacity.
In terms of generated electricity, hydropower contributed an estimated 3 400 TWh in 2011, with the top contributors being China (20%), Brazil (13%), Canada (11%) and the US (10%). A total of 160 countries generate hydroelectricity, mostly in modest amounts. But several countries obtain a large portion of their electricity from hydropower, including Paraguay (100%), Norway (95%), Ethiopia (88%), Brazil (86%) and Venezuela (68%).
Several key advantages explain the prominence of hydropower. First, although large-scale hydro requires large initial capital outlays for dam and turbine construction, the operating costs are relatively low, since there is no feedstock cost. Second, hydro plants have a long life span – typically over 50 years.
Third, hydro plants at dams have a built-in energy storage facility, which allows hydro to be both a baseload power source and a backup for intermittent renewables like solar and wind. There is now about 130 GW of dedicated pumped-storage capacity globally. Fourth, there are no carbon dioxide emissions during operation – although dams may release methane gas – a potent greenhouse gas – from rotting vegetation.
The energy return on energy invested (EROI) ratio for hydropower is highly vari- able, depending on the location and size of the reservoir, with estimates ranging from 11:1 to 167:1. For the majority of large schemes, the EROI ratios outperform most other energy sources.
As with everything, however, there are some downsides to hydropower. For one thing, dams can be very damaging to the local and downstream environments and sometimes displace whole communities – as in the case of China’s gargantuan Three Gorges dam.
Some hydro plants are affected by seasonal rainfall, leaving countries vulnerable to power shortages in the dry season. Droughts linked to climate change have already reduced hydroelectric power generation in many countries around the world, as river flows have become weaker or more erratic.
At present, only a few countries are invest- ing in new large dams with hydropower facilities, led by China and Brazil. Global investment in small-scale hydro grew by nearly 60% in 2011 to $5.8-billion, according to the Renewable Energy Network. Manu- facturing capacity for hydro equipment is limited to a few large economies.
The prognosis for hydropower is reason- ably good, especially for developing countries. There is considerable scope for expansion of small-scale and microhydro turbines, which can be very efficient, although this would be mainly for rural areas. Brazil added 433 MW of small-scale capacity (less than 30 MW) in 2011. India has 3.3 GW of small-scale capacity.
It has been estimated that one-third of the global potential for hydropower is already being used – mainly in the industrialised countries. The greatest scope for new large-scale hydropower lies in Africa, where a lack of finance and, in some cases, political instability have thwarted its development. In recent years, Chinese banks have begun making loans for dam construction in Africa, and Chinese companies are often contracted to do the construction.
The single greatest prospect – at least from a potential energy perspective – is the long-awaited Grand Inga power scheme, in the Democratic Republic of Congo (DRC). An estimated 40 GW of hydropower capacity remains untapped after decades of adverse political conditions. Exploitation of this energy source – which is mooted to provide power to consumers as far away as South Africa and Europe – will depend on the construction of costly new transmission grids running through numerous countries. The South African government recently renewed negotiations over the Inga project with its DRC and Southern African Power Pool counterparts.
Hydropower will continue to play a vital role in the mix of renewable energies in the decades ahead as fossil fuels continue to deplete and countries move to mitigate climate change. Pumped storage, in particular, should see strong growth in tandem with intermittent solar and wind power.