One of the most complicated aspects of power sources, even renewable ones, is how to weigh up their environmental effects. Some advocates of new gas power stations claim they are 'environmentally friendly' because they cause less acid rain than oil or coal. This is a misleading statement, since burning gas releases carbon dioxide into the atmosphere just as other fossil fuels do.
Renewable sources have their negative effects, too, with China's Three Gorges hydroelectric project, for example, having been particularly criticised for environmental, social and economical reasons. So how does hydro compare with non-renewable forms of power?
Hydro already generates around a fifth of the world's electricity, but this represents only a quarter of the world's hydro potential. China, Brazil, Russia, Canada and the US have the largest resources.
Not all water sources are suitable, however, and developed countries such as the US, Japan, France and Germany have already exploited around three quarters of the available sources.
Similarly, Norway, Iceland and Canada are already using hydro as a major power source. Most unused sites are in undeveloped countries, giving a wonderful 'free' resource to fuel economic growth.
Besides China, large projects are planned or underway in countries including India, Brazil, Peru, Malaysia and Vietnam.
China has the largest available resources and is expanding its hydropower usage, aiming to exploit about 70% of the total available in 2020. The country has extensive experience of hydropower and is a clear example for demonstrating the source's good and bad sides. The Three Gorges has become a case for other countries to learn from.
CUTTING COAL RELIANCE
China started from huge coal resources, with this remaining the country's primary energy source for the next decades. China now burns more than a billion tonnes of coal a year. Most of the existing coal-fired stations were built during the Communist era.
The result has been serious air pollution throughout the country, with acid rain reported to affect 40% of China. The World Bank has estimated that air pollution costs $25bn a year in health expenditure and lost labour productivity.
As many as 700,000 people a year die from indoor air pollution caused by burning coal for heating and cooking. A quarter of all early deaths are caused by respiratory diseases.
New coal-fired power stations will be more efficient than their predecessors and produce fewer harmful emissions. However, they will still generate huge volumes of carbon dioxide. China's energy strategy emphasises self-reliance and in a commendable move to reduce its dependence on fossil fuels, the country is giving hydroelectric power somewhat of a regeneration.
The country actually had an oversupply of power during the economic difficulties in the late 1990s, but is now building new power stations at a rate of around two a week. Rather than relying exclusively on coal, China plans to fill the energy gap with hydropower and nuclear power, and in the future wind and solar.
China's exploitable hydroelectric resources have been estimated at nearly 400 million kilowatts. This is equivalent to annual power supply of around 2 trillion kilowatt-hours, making up around one sixth of the world's total. It is equivalent to over 50 billion tonnes of coal. The central government wishes to boost the capacity from around 100 to 180 million kilowatts by year 2010, rising to 300 million kilowatts in 2020.
As with coal, the country's hydroelectric resources are mainly concentrated in the more rural west. China has identified 13 large hydropower areas that together form two thirds of the economically exploitable water resources. All but one are in western China.
Around two thirds of demand, however, lies in the eastern coastal areas. Coal has in the past been transported to the east coast with all the fuel and pollution that involves.
More recently China has preferred transmitting the electricity itself, across ultra-high-voltage power lines. Such a network is also handy for transmitting hydroelectric power. China is therefore developing ultra-high-voltage power transmission lines for this purpose. A 1MV demonstration UHVAC connects the 650km from Shanxi to Hebei, and another 0.8MV UHVDC line connects the 1,500km between Yunnan to Guangdong. In this way, electricity can be transported over 2,000km.
A WORTHWHILE POWER SOURCE?
Hydro is generally thought to be one of the most effective and lowest-cost renewable resources. Water is free, fairly dense and, left to its own devices, tends to flow downhill. The energy in water is proportional to the flow rate and the 'head' of falling water. Hydroelectric stations are either run-of-the-river, or have a dam and reservoir.
Run-of-the-river types are easiest to build and have least environmental effect. They can be built on small diversion weirs, but mainly depend on constant and fast-flowing water flow. Large projects use a dam and reservoir to smooth out the effects of water level fluctuations throughout the year.
Water flows through a channel called a penstock to the turbine (normally a Frances turbine), which spins to drive the generator. Water can be pumped up to the reservoir again during periods of low demand and be reused when needed.
Small projects have low costs, fast construction and little need to relocate people. The Chinese Government claims that its 40,000 small hydro projects (under 50MW each, a total of 40GW) benefit more than 300 million rural people, mainly in poor areas.
But there have been issues. Many of the projects have been criticised for poor planning, causing problems such as drying up of waterways, vegetation damage, soil erosion and flooding. Environmental Impact Assessments have often been neglected, even since China's national EIA law of September 2003. However, the State Environmental Protection Administration (SEPA) has begun suspending projects that do not meet EIA requirements.
Large hydroelectric projects are the most visible and have the most effects on the surrounding population. China is now planning another dozen or so large stations over the next 20 years with a capacity of nearly 100GW. The projects will be built on the upper reaches of the Yangtze River and two upstream tributaries.
The Chinese government has admitted that the Three Gorges Dam could provoke an ecological and environmental 'catastrophe'. It has already caused conflicts over land shortages, ecological deterioration from irresponsible development, erosion and landslides on steep hills around the dam.
Hundreds of thousands of people who live behind the dam may have to be moved, joining the estimated 1.3 million others who have been relocated or face possible 'geological disasters' along the shore. The reservoir shore has already collapsed in 100 or so places, with 36km of the shore having actually caved in. The landslides have produced waves up to 50m tall, and these slam into the rest of the shoreline, causing further damage and loss of life.
WEIGHING UP THE EFFECTS
The major negative effects of hydroelectric power are environmental (destruction of habitats) and social (forced displacement). Large dams raise underground water levels near the lake, which has large effect on the surrounding flora and fauna. Even for projects with reservoirs, there can be supply problems in summer when flow drops.
There can be other problems with reservoirs themselves, not just with hydroelectric stations. The latter have been found to emit methane, which is a stronger and more dangerous greenhouse gas than carbon dioxide. This problem can be virtually eliminated at the design stage, since the gas can be trapped and used for power generation with suitable dam designs.
It has been estimated that China could collect about 2.6 million tonnes of methane from dams to generate extra power – the equivalent of over seven months' worth of its natural gas imports.
These effects have to be balanced against the amount of electricity that hydropower stations generate. Hydro is potentially the cheapest form of power available. Payback times, the most important measure of energy saving schemes, are good, and hydro is ideal for baseload operation.
The relatively long construction times of large stations are balanced by low long-term costs and a long lifespan, even up to 100 years. With proper planning and design, hydropower stations can also help to conserve water, irrigate and provide flood control.
The key words are 'proper planning and design'. The major issue with hydroelectric power is the location of the reservoir; decisions must be backed by thorough and impartial Environmental Impact Assessments. Biodiversity must be considered since inappropriate placing and design can flood irreplaceable habitats and historical sites.
Site approval cannot be left to local politicians, who are often swayed by short-term concerns. People who are displaced have to be compensated, in a way that gives them a living rather than leaving them dependent on 'handouts', and affected people must also be properly compensated. There needs to be protection against corruption (which has drained the Three Gorges relocation funds) and other wastes of funds. The technology must be appropriate. When the power station size is related to national prestige, countries start making the wrong choices.
However, before criticising the Chinese schemes, the West's own power record should also be considered. China has taken a lead in hydroelectric and photovoltaic development that already puts the West to shame. It is also helping the developing world, Africa in particular, to develop its own hydroelectric resources.
China already suffers from severe droughts, floods, storms and water shortages. The predicted global temperature rise from continued use of fossil fuels can only make this worse. The sea rises that are expected if we continue to burn fossil fuels and the resulting worldwide flooding could make the Three Gorges Dam look like a mere puddle.