The Next Wave

by Patrick McCully
Monday, March 8, 2010

A Bright Future For Hydro – Without Dams

A quiet revolution is underway in the world of hydropower. An emerging non-dam based hydro industry holds the promise of economically viable technologies that do not deplete resources or warm the planet, and do not wipe out species, ecosystems and cultures. With supportive policies from governments, non-dam hydro could become a key part of the world's energy mix over the coming decades, and could, as wind power already has, overtake big-dam hydro in terms of its share of new capacity additions.

A tidal turbine
A tidal turbine

Non-dam hydro comes in a diversity of forms. It includes all technologies to generate electricity using water without dams. The two sectors receiving the most attention are wave power and "hydrokinetic" turbines that capture energy from the flow of water in rivers, estuaries and ocean currents, and even irrigation canals and water supply and disposal pipes. (Hydrokinetic turbines are also referred to as "instream," "stream" or "free-flow" turbines. They should not be - but frequently are - confused with "run-of-river" hydropower which includes a dam, but usually not a large reservoir).

Not all non-dam hydro technologies may be benign and environmentally appropriate at all sites, but it appears likely that many of the technologies could be very low impact compared with dam-based hydro and other conventional generation technologies. While the output of river flow hydro will, like run-of-river dams, be reduced in dry seasons and droughts, tidal and ocean power is highly dependable and can help reduce the vulnerability of electrical grids to climate change.

Funding for R&D of non-dam hydro has been meager until very recently, but is now being rapidly ramped up from both public and private sources, especially in Europe and North America. "We're at the stage of needing to see which of these technologies works and whether they can be scaled up," said Neil Kermode of the European Marine Energy Centre, in a December interview with the BBC. "That requires steady investment. Look what the Danes did with wind: investments year after year paid off and now they earn billions in exports. There is huge potential - absolutely huge amounts of energy out there - in fact we don't know how much but it is epic."

Unconventional Potential

In January 2010, consulting firm Pike Energy published the most comprehensive assessment yet of global non-dam hydro potential and possible rate of deployment. Pike estimates that if the European Union and US continue to increase incentives for non-carbon energy, by 2025 the world could have installed 3,000 megawatts (MW) of river flow turbines, 4,000 MW of ocean current turbines, 57,000 MW of tidal stream turbines and 115,000 MW of wave energy. By comparison, current global installed large hydro capacity is around 770,000 MW.

It would be a heroic feat to achieve the Pike forecasts - it would mean adding in 15 years a quarter of what the big-hydro industry took more than a century to install. In any case, the numbers are necessarily speculative given that the technologies are only just being commercialized and the available resource is very poorly mapped. But the Pike estimate is an indicator of what could be done with each technology.

Hydrokinetic technologies include turbines that look just like underwater wind turbines built on the riverbed or hanging upside down from barges anchored in the river; barges with turbines like water wheels on old-fashioned paddle-steamers; "helical turbines" that look like the blades on a hand-pushed lawnmower; and, more experimentally, hollow cylinders placed horizontally across rivers that move up and down as the river flows past them.

Underwater turbine
Underwater turbine

There appear to be no significant engineering challenges to installing and operating free-flow turbines in rivers. Research and development efforts are focused on bringing down costs and ensuring that the turbines and associated facilities do not harm fish or other aquatic life. So far it appears that the environmental impacts of the technologies will be low, although as their use is scaled up it will be important that their cumulative impacts are carefully monitored and that they are sited to avoid environmentally sensitive areas and disruption to river navigation and recreation.

The drawback to river-flow technologies compared to conventional hydro is that the potential energy from a given volume of falling water, which is what is exploited by an old-fashioned dam-based plant, will always be far greater than the kinetic energy from flowing water. So the laws of physics dictate that non-dam systems can never extract as much energy from rivers as can dams.

The first river flow turbine to enter commercial operation in the US came fully on-line in August 2009. The small turbine, capable of producing just a tenth of a megawatt, and looking something like a household blower fan, hangs beneath a barge immediately downstream of a navigation dam on the Upper Mississippi River at Hastings, Minnesota. Initial monitoring reportedly shows that the turbine is almost completely safe for fish.

A 2007 report from the Electric Policy Research Institute (EPRI) estimates the US river hydrokinetic potential at 10,800 megawatts (around a sixth of the existing installed capacity at US big dams). A 2009 study for the National Hydropower Association by Navigant Consulting projected that with current incentives for renewables in place, 500 MW of hydrokinetic turbines could be installed in US rivers by 2025. With a clear policy commitment to this new energy source, 2,000 MW could be installed.

There is also a small, but useful, potential for "conduit hydro" - kinetic turbines installed in pipes and irrigation canals. The beauty of conduit hydro is that it has almost zero environmental impact. The California Energy Commission estimates that the state has the potential to generate 255 MW from existing pipelines and canals. In neighboring Nevada, wastewater from Las Vegas will soon be flowing through two 8 MW turbines on its way from a new treatment plant into the reservoir behind Hoover Dam.

Since 2005 the water piped down from a nearby mountain reservoir to supply Bogotá has flowed through a 13 MW hydro project. Areas with extensive canal irrigation networks such as the Indus valley in Pakistan and the plains of northern India should have considerable conduit-hydro potential.

A Sea Change

Worldwide, the bulk of hydrokinetic power potential - and investor interest - lies not in rivers and pipes, but in tidal streams and ocean currents. Navigant Consulting predicts that over the next 15 years the US could see the installation of 250 MW of ocean current power (all from the Gulf Stream flowing past the southern tip of Florida); and 400 MW of tidal stream power. With improved policies, three times more ocean current power could be exploited, and ten times more tidal power. Marine hydrokinetic power is particularly attractive as currents and tides are very predictable and reliable.

Extracting energy from the seas does pose unique challenges given the harshness of the ocean environment, the remoteness of some of the best sites, and the expense of building reliable infrastructure to bring power from the project to the shore. The potential for these technologies, however, is extremely high and the challenges are mostly ones that engineers are already familiar with in other contexts (e.g., installing and maintaining offshore oil platforms, and delivering power from offshore wind farms).

Seagen, the world's first commercial tidal stream turbine, was installed in 2008 near the narrow mouth of Strangford Lough, a coastal inlet in Northern Ireland. (It's an appropriate location for this first - Strangford Lough is also the site of the world's oldest excavated tidal mill, built by 8th century monks to grind their grain, showing the venerable history of tidal power technology). Seagen has a capacity of 1.2 MW, enough to power 1140 Ulster households.

Strangford Lough is legally recognized as an "Area of Outstanding Natural Beauty," and the impact of Seagen is being closely monitored. So far there have been no reports of significant harm to the marine environment, and as the structure is mostly submerged it has little scenic impact. The same technology is slated to be installed next in a 10.5 MW project off the coast of Wales, and the company behind it is now exploring the potential of the Bay of Fundy off Eastern Canada, site of possibly the world's most powerful tidal current.

Voith Hydro, one of the world's largest suppliers of conventional large hydro turbines, is testing a new tidal turbine design in Korean waters and is an investor in a plan to build "the world's first tidal current power park," a 600 MW project in Jeollanam-do Province.

While tidal current technology appears likely to be very low impact, the same is not true for the better-established tidal barrage schemes. A tidal barrage is essentially a low dam across an estuary. Tidal barrages can generate very large amounts of power, but can cause seriously harm estuarine ecosystems by changing their salinity and sediment flow patterns, blocking passage for fish and marine mammals, and flooding coastal mudflats which have major wildlife value, especially for shore birds.

The British government is currently studying options for a major barrage in the Severn estuary between England and Wales. One of the options under serious consideration is a 8,600 megawatt power plant that could supply more than 4% of total UK electricity generation. Most of the large UK environmental groups oppose this megaproject. 

Wave of the future

Britain and Ireland have one of the world's biggest concentrations of wave power potential. The resource is sufficient to supply 16% of the UK's electricity. The UK Carbon Trust estimates that up to 2500 megawatts of wave power plants could be installed across Europe over the next decade. EPRI estimates that by 2025 the US will have installed 900 megawatts.

The world's first offshore wave farm to enter commercial operation is the Pelamis "sea snake." The initial Pelamis scheme, installed off the coast of Portugal in 2008, had three floating cylinders made of hinged segments, each with a capacity to generate 750 kW. The scheme, however, had a tragically short life. Its cylinders sprang leaks and had to be towed off for repairs only two months after its deployment.

The company behind Pelamis is now working on a second generation machine. In December 2009 they announced a joint venture with Swedish utility Vattenfall to build a wave project off the Shetland Islands in the North Sea, up to 20 megawatts in size.

Brazilians have a joke that theirs is the country of the future ... and always will be. For years, wave and tidal power similarly seemed to be on the verge of a breakthrough into the big league of power sources, but for technical and cost reasons failed to meet the promise. Today, concerns over climate change and a sharply rising tide of political support for renewables, coupled with steady technological progress and investor interest, mean that the future has finally arrived for the new hydropower.