Sub-Saharan Africa, where more than three-quarters of the population is without electricity, will soon be lit up — or that’s the promise of governments building a host of new hydroelectric schemes across the continent. These projects are an attempt to keep up with the rising power demand from Africa’s economic boom. But the trouble is that, like the boom, the power seems destined to benefit only small industrial and urban elites. For the rest of Africa’s billion inhabitants, this investment looks unlikely to further UN secretary general Ban Ki-moon’s goal of “sustainable energy for all.”

The Congo River in central Africa — the world’s second-largest river after the Amazon — is the latest focus of the rush to harness the continent’s rivers for generating electricity. On May 18, the government of the Democratic Republic of the Congo (DRC) announced in Paris that it was initiating the first phase of the world’s largest hydro scheme on the river’s majestic Inga Falls. At these falls, downstream from the capital Kinshasa, the massive Congo’s entire flow of 42,000 cubic meters a second cascades down a series of rapids, falling 100 meters within a 15-kilometer stretch.

South African hydro-engineer Henry Oliver has called Inga Falls “one of the greatest single natural sources of hydroelectric power in the world,” and his fellow engineers have long dreamed of tapping these waters to power an Africa-wide electricity grid. Two small schemes built in the 1970s and 1980s, known as Inga I and Inga II, are largely moribund, victims of the DRC’s wrecked economy and long-running civil war.

The completed project on the Congo would be twice the size of China’s Three Gorges dam.

But the idea was revived a decade ago, when world leaders pledged a New Partnership for Africa’s Development (NEPAD). Now it is Chinese construction companies — including Sinohydro, the world’s largest dam builder — who are in line for the contracts.

The first phase, dubbed Inga III, will on its own generate more power than Africa’s current largest hydroelectric-dam, the High Aswan on the Nile in Egypt. Construction should begin in 2015 and will cost at least $8.5 billion. The energy is mostly destined for South Africa, 3,000 kilometers away, where energy utility Eskom has promised to take more than half the capacity of 4,800 megawatts (MW).

But the project’s eventual aim, the DRC’s water and electricity minister Bruno Kapandji Kalala told the Paris meeting, is even grander. The completed project would be almost ten times larger than the initial phase, making it twice the size of China’s Three Gorges hydro-scheme, currently the world’s biggest. It will tap the Congo with 50 separate riverside electricity generating units, each the size of a large conventional power station.

The treaty signed between DRC and South Africa pledges both countries to the $50-billion development, along with extensive transmission lines to a planned southern African supergrid. The project’s promoters say it could one day supply power to half a billion people across the whole of Africa. But the logistics of constructing a distribution to more than a handful of urban centers would take many decades and dwarf the cost of building the hydroelectric works, and nobody has suggested where that money would come from.

There is, it has to be said, an environmental case for the Inga Falls scheme. The Congo River’s flow is so strong and so constant that its enormous power can be extracted without a large dam to store water. With no large reservoir, the “run-of-river” scheme will flood little land, thus saving rainforests, reducing the need to move people, and limiting greenhouse gas emissions from rotting vegetation. Unlike many dam projects in rainforests, it will be a genuinely low-carbon source of energy.

The Inga Falls project is only the latest of a rush of giant hydroelectric dams across Africa. They include the recent completion of the 250-MW Bujagali dam on the Nile in Uganda, which has flooded a much-loved local falls; a 300-MW Chinese dam completed in 2009 in Tekeze canyon at the headwaters of the Nile in Ethiopia, which at 185 meters is one of Africa’s highest; and the 120-MW Djibloho dam completed last year on the Wele River, which now supplies 90 percent of the electricity in tiny Equatorial Guinea.

Ethiopia’s Grand Renaissance Dam on the Blue Nile will shortly supplant the High Aswan as Africa’s biggest.

But these are small fry. This week, Ethiopia diverted the flow of the Blue Nile while it constructs the 6,000-MW Grand Renaissance dam on the river near the border with Sudan, which will shortly supplant the High Aswan as Africa’s biggest. And Ethiopia is just completing the 1,800-MW Gibe III dam on the River Omo. The latter was a favorite of the former prime minister, Meles Zenawi, who defended the project against Western criticism in 2011 by saying: “We want our people to have a modern life and won’t allow [them] to be a case study of ancient living for scientists and researchers.”

That may be. But critics both inside and outside the country say the scheme, which will also provide irrigation water, will wreck the lives of a quarter-million pastoralists and divert so much flow that it will halve the size of Lake Turkana, the world’s largest desert lake, in neighboring Kenya. Some call the project a repeat of the Aral Sea disaster in central Asia half a century ago.

Yet Ethiopia is undeterred. It is East Africa’s water tower and the source of 80 percent of the Nile’s flow. With an economy growing by more than 8 percent a year, analysts say mountainous Ethiopia seems bent on tapping all its rivers before they reach other countries. Besides powering its own industrial drive, it plans on exporting power to its neighbors. To that end, it has set up the Eastern African Power Pool, an intergovernmental authority promoting the transmission of power across the region, linking Ethiopia to Kenya, Tanzania, Eritrea, Uganda and Sudan. The first phase, a high-voltage link between Ethiopia and Kenya, which has World Bank funding, is set for completion by 2019.

In West Africa, Guinea has plans to dam the River Niger upstream of the river’s inner delta, a wetland jewel in neighboring Mali that is the size of Belgium. That, say hydrologists at the NGO Wetlands International, threatens the livelihoods of some 1.5 million people on the delta.

In southern Africa, work started earlier this year on damming the Batoka Gorge for a 1,600-MW scheme downstream of Victoria Falls on the Zambezi River, which forms the border between Zambia and Zimbabwe. And China’s Export-Import Bank has agreed to help fund the 1,500-MW Mphanda Nkuwa project further downstream on the same river in Mozambique. The Mphanda Nkuwa scheme is also a run-of-river project that will not flood much land. But critics say it will nonetheless be very damaging because it requires a new management regime at the upstream Portuguese-built Cahora Bassa dam that will scupper efforts to restore the ecology of the lower Zambezi delta.

The World Bank, after years of avoiding big dam schemes because of environmental concerns, is back on the case.

One reason for the rush to build is that the World Bank, after years of avoiding big dam schemes because of environmental concerns, is back on the case. For instance, it is expected to join the African Development Bank, the Development Bank of Southern Africa, and others in funding Inga Falls.

Meanwhile, Chinese banks and construction companies are keen to get involved, because China wants power to run its growing portfolio of African mines. And the Chinese are less squeamish about environmental downsides than Western aid agencies. Chinese companies recently finished a 1,250-MW scheme in Sudan on the Nile at Merowe, which displaced 15,000 families and flooded a 174-kilometer section of the fertile Nile valley. And they are busy in Ghana damming the Bui Gorge to create a reservoir that will flood a quarter of the Bui National Park.

With financing unlocked, dam builders at the International Hydropower Association this month met in Kuching, in the Malaysian province of Sarawak, to herald an “upsurge in hydropower development” in Africa and elsewhere. But they could not drown out protests from local indigenous communities against dam building in the rainforest-rich Malaysian province.

And the dam industry’s cheerleading was in contrast to a meeting in Bonn, Germany, attended by 500 water scientists from around the world, which agreed that “tens of thousands of large dams” were damaging the flows and ecosystems of most of the world’s great rivers, flooding large areas of fertile river valleys, and displacing millions of people. The scientists’ meeting ended with a declaration that mismanagement of the world’s water resources could “trigger irreversible change with potentially catastrophic consequences.”

All countries face choices about balancing short-term economic growth and protecting their natural resources. But the difficulties for promoters of hydroelectric dams are complicated by the joker in the pack — climate change. Parts of Africa almost certainly face major change to rainfall and river flows in the coming decades, with important threats to the sustainability of hydro schemes.

The Intergovernmental Panel on Climate Change (IPCC) has reported the Zambezi as being at special risk, with an anticipated decline in rainfall across its catchment of 10 to 15 percent. Richard Beilfuss, a hydrologist at the University of Wisconsin—Madison College of Engineering and the University of Eduardo Mondlane in Mozambique, says none of the studies for the 13,000 MW of dam projects currently proposed on the Zambezi analyze the risks of changing river flow.

Critics say giant hydro schemes are the wrong kind of development for a largely rural continent.

But critics say that giant hydro schemes — whatever their environmental credentials, and whatever the risks from climate change — are the wrong kind of development for a still largely rural continent that lacks power grids to distribute large amounts of centrally generated energy to its inhabitants.

While the DRC talks of sending the power from Inga Falls across Africa, it remains likely that the mass of the Congolese probably won’t see any of it, since their country has no national power grid to deliver it to them and no plans to develop one. The main beneficiaries within its borders are likely to be the copper mines in the southern province of Katanga.

Critics contend the Inga Falls plan, like many other big hydro schemes on the continent, runs counter to the aims of the UN’s Sustainable Energy For All initiative, which is being promoted by secretary-general Ban Ki-moon. It aims to unlock investment for connecting 1.3 billion people to electricity by 2030, while doubling the contribution of sustainable sources of energy to world supplies.

But, says Rudo Sanyanga, the Africa director of the California-based environmental group International Rivers, there is little likelihood that mega-schemes like Inga Falls will democratize access to power. In the Congo, where only 9 percent of the population has access to the electricity grid, he says, “Grid-based electrification is not a realistic option… Billions of dollars in aid for the energy sector will once again bypass Africa’s rural poor.”

The money should be spent on decentralized power systems using solar and wind energy along with small-scale hydro schemes, says Sanyanga. “Like cell phones in the telecom sector, they can revolutionize the lives of the poor that have been bypassed by the centralized landlines and the electric grid systems.”

Building grid systems is essential to getting the power to people who need it. Most countries have created national grids for their people, before devising international links to export power. In Africa, it seems to be the other way round. For most of its citizens, Africa looks likely to remain a dark continent.