A revolutionary device that can harness energy from slow-moving rivers and ocean currents could provide enough power for the entire world, scientists claim. The technology can generate electricity in water flowing at a rate of less than one knot - about one mile an hour - meaning it could operate on most waterways and sea beds around the globe.

Existing technologies which use water power, relying on the action of waves, tides or faster currents created by dams, are far more limited in where they can be used, and also cause greater obstructions when they are built in rivers or the sea. Turbines and water mills need an average current of five or six knots to operate efficiently, while most of the earth's currents are slower than three knots.

The new device, which has been inspired by the way fish swim, consists of a system of cylinders positioned horizontal to the water flow and attached to springs.

As water flows past, the cylinder creates vortices, which push and pull the cylinder up and down. The mechanical energy in the vibrations is then converted into electricity.

Cylinders arranged over a cubic metre of the sea or river bed in a flow of three knots can produce 51 watts. This is more efficient than similar-sized turbines or wave generators, and the amount of power produced can increase sharply if the flow is faster or if more cylinders are added.

A "field" of cylinders built on the sea bed over a 1km by 1.5km area, and the height of a two-storey house, with a flow of just three knots, could generate enough power for around 100,000 homes. Just a few of the cylinders, stacked in a short ladder, could power an anchored ship or a lighthouse.

Systems could be sited on river beds or suspended in the ocean. The scientists behind the technology, which has been developed in research funded by the US government, say that generating power in this way would potentially cost only around 3.5p per kilowatt hour, compared to about 4.5p for wind energy and between 10p and 31p for solar power. They say the technology would require up to 50 times less ocean acreage than wave power generation.

The system, conceived by scientists at the University of Michigan, is called Vivace, or "vortex-induced vibrations for aquatic clean energy".

Michael Bernitsas, a professor of naval architecture at the university, said it was based on the changes in water speed that are caused when a current flows past an obstruction. Eddies or vortices, formed in the water flow, can move objects up and down or left and right.

"This is a totally new method of extracting energy from water flow," said Mr Bernitsas. "Fish curve their bodies to glide between the vortices shed by the bodies of the fish in front of them. Their muscle power alone could not propel them through the water at the speed they go, so they ride in each other's wake."

Such vibrations, which were first observed 500 years ago by Leonardo DaVinci in the form of "Aeolian Tones", can cause damage to structures built in water, like docks and oil rigs. But Mr Bernitsas added: "We enhance the vibrations and harness this powerful and destructive force in nature.

"If we could harness 0.1 per cent of the energy in the ocean, we could support the energy needs of 15 billion people. In the English Channel, for example, there is a very strong current, so you produce a lot of power."

Because the parts only oscillate slowly, the technology is likely to be less harmful to aquatic wildlife than dams or water turbines. And as the installations can be positioned far below the surface of the sea, there would be less interference with shipping, recreational boat users, fishing and tourism.

The engineers are now deploying a prototype device in the Detroit River, which has a flow of less than two knots. Their work, funded by the US Department of Energy and the US Office of Naval Research, is published in the current issue of the quarterly Journal of Offshore Mechanics and Arctic Engineering.

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Paul Eccleston, 12 Feb 2008, Telegraph.co.uk http://www.telegraph.co.uk/earth/3325082/Latest-microgeneration-technology-for-houses.html

Energy saving technologies are still in their infancy and may not provide all the answers needed to build zero carbon homes.

• Overview of technologies reviewed in the research

The warning comes in a new analysis of the microgeneration technology currently available to housebuilders.

The UK Government has told the building industry that all new homes must be carbon neutral by 2016.

With more than 25 per cent of Britain's energy output going on heat, power and light for homes housebuilders will be relying on cutting-edge technology to meet energy-saving targets.

But a joint report from the National House Building Confederation (NHBC) Foundation and the Building Research Establishments (BRE) warns there will be significant risks in using some sustainable techniques such as solar panels and wind turbines.

The research assesses the 11 types of technology available for new developments, including biomass, solar photovoltaic, air source heat pump and fuel cell technologies. It examines cost-efficiency and carbon saving benefits, with crucial factors like payback periods, seasonal variation, location and local authority planning requirements taken into account. In addition the research looks at the capability and costs of retro-fitting technologies where this is possible.

The Chief Executive of the NHBC, Imtiaz Faroohki, said: "This research emphasises the fact that there is no technological 'magic bullet' to renewable energy.

"What is made absolutely clear is that builders need to use the right technology for the right situation and this needs to be done on a case-by-case basis, otherwise they are unlikely to deliver on the three crucial measurements: carbon reduction, cost effectiveness and customer satisfaction.

And NHBC Foundation chairman, Nick Raynsford MP, said: "Leading builders and developers have stepped up to meet the challenge of creating zero carbon homes, but much more needs to be done to achieve real carbon and cost savings for consumers.

"The report is a first step in helping the house building industry comprehend the risks and issues associated with building zero carbon homes. With strict requirements set out in the Code for Sustainable Homes, Energy Performance Building Directive and building regulations, new technologies are crucial to their success."

"The generation of energy using wind, water and alternative fuels is still in its infancy for mass-scale housing developments. The NHBC Foundation is supporting builders in the complex task of analysing and selecting the most suitable and cost-effective systems appropriate to each development to provide a whole generation of homeowners with efficient and well-designed housing."

Mark Clare, chief executive of Barratt Developments, one of Britain's biggest builders, said: "The NHBC research is an important step forward and it is clear that much more needs to be done to ensure that there are reliable and cost effective technologies available. We are determined to drive the environmental agenda forward to ensure that the right solutions are available for our customers."

A Review of Microgeneration and Renewable Energy Technologies is the most recent in a programme of sustainability research projects by the NHBC Foundation, you can download a copy at the NHBC Foundation website.

Overview of technologies reviewed in the research

• Biomass systems
• Solar photovoltaic systems
• Solar hot water systems
• Wind power systems
• Ground source heat pumps
• Air source heat pumps
• Absorption heat pumps
• Small-scale hydroelectric systems
• Micro combined heat and power systems
• Renewable combined heat and power systems
• Fuel cells

Biomass systems

In general biomass in the domestic sector almost always refers to wood fuel, which is only sustainable if it comes from renewable forest sources. Biomass systems can have high levels of efficiency, typically 60-80 pre cent in ranges, pellet stoves, log stoves and log boilers.

Biomass does require care in installation, maintenance, siting and also requires a sufficient amount of space to store the fuel which generally has to be bought in bulk. In areas which are designated as smokeless zones not all systems will be suitable, although modern systems generate considerably less smoke than their older counterparts.

Key facts:

Carbon savings: 4.5 Tonnes per year for a three-bedroom 1950s house
Typical costs of system and installation (retro-fit): £6,000
Typical costs of system and installation (new build): £6,000
Cost effectiveness - simple payback: N/A (capital expenditure exceeds savings)
Typical lifetime: 25 years

Solar photovoltaic systems

Photovoltaics (PV) work by converting the sun's energy into electricity using roof-mounted panels. Cheaper units convert some 5 per cent of solar energy into electricity and more efficient, and more expensive units, convert up to 18 per cent of energy received into electricity.

Power output depends on the type of materials used in construction and the amount of sunlight received. The maximum output from PV systems is in the summer, but the maximum power usage in the home is in mid-winter. Energy from these systems can be sold back to the National Grid.

Key facts:

Lifetime energy, carbon and cost savings (20-year useful life) per kWp (peak Kw output): If all electricity is consumed within the household, the money saved @ 8.5p/kWh is close to £1,360
Typical costs of system and installation (retro-fit): £6,000 per kWp
Typical costs of system and installation (new build): £5,000 per kWp
Cost effectiveness - simple payback: Currently a system cannot generate sufficient energy over its lifetime to repay its cost
Typical lifetime: 25-30 years at rated output, after which performance deteriorates

Solar hot water systems

These systems used the sun's energy to heat water for use in the home for washing and other domestic uses, they do not usually heat the home itself. The two standard systems are "flat plate" and "evacuated tube" and both are normally fitted onto roofs.

Flat plate systems use a dark plate in an insulated box to transfer energy into the water system. Evacuated tube systems are more expensive and sophisticated, using metal strip collectors in vacuum tubes but have the advantage that smaller panels are needed.

In the summer months, these systems can provide 90 per cent of the hot water needs of a typical home.

Key facts:

Lifetime energy, carbon and cost savings (30-year useful life): Fuel/energy displaced 60,000-75,000 kWh; CO2 displaced 12 tonnes (gas) or 30 tonnes (electricity); Gas @ 1.5p p/kWh around £1,000; Electricity @ 8.5 p/KWh around £5,700
Typical costs of system and installation (retro-fit): £3,000-£7,000
Typical costs of system and installation (new build): £1,000-£4,000
Cost effectiveness - simple payback: Eight to 20 years depending on fuel displaced, conversion efficiency and fossil fuel/energy price escalation.
Typical lifetime: 30 years

Wind power systems

These work by converting the wind energy into an electrical output which can be used in the home after passing through a suitable inverter unit. Care must be taken in installing these systems to ensure the home can bear the loads generated by moving turbine blades.

Obstructions such as trees and other buildings will reduce the efficiency of these systems and wind energy is not uniform across the country so not every region in the country can gain maximum benefits. The maximum output from wind energy systems is in the winter, which coincides with the maximum power usage in the home, but there can be prolonged periods of winter calms due to high pressure atmospheric systems.

Energy from these systems can be sold back to the National Grid and can also generate income under the Renewable Obligation Certificate (ROC) scheme, depending on output.

The Renewables Obligation (RO) is the UK's policy for increasing the contribution of energy from renewable sources to fulfil the EU Renewables Directive. The RO requires licensed electricity suppliers to source a percentage of their sales from eligible renewable sources.

This percentage increases each year, starting at 3 per cent in 2003 and reaching 10.4 per cent by 2010. Each mWh of renewable electricity generated is accompanied by a Renewables Obligation Certificate (ROC) and energy purchased from microgeneration and renewable systems can accrue towards this whilst, in return, generating an income for homeowners using renewable technologies.

Key facts:

Lifetime energy, carbon and cost savings (20-year useful life): Electricity generated 40,000 kWh, CO2 displaced 17,200 kg. If all the electricity is consumed within the home the money saved @ 8.5 p/kWh is around £3,400
Typical costs of system and installation (free-standing): £3,000 per kW capacity
Typical costs of system and installation (building mounted): Typically £1,700 for a 1kW system
Cost effectiveness - simple payback: A well-sited, 50 per cent grant funded 2.5 kW turbine could provide a simple payback within about15 years.
Typical lifetime: Up to 20 years with maintenance and a mid-life overhaul

Ground source heat pumps

Increasingly popular and in use in Scandinavian countries in particular in recent years, these systems work by taking low level retained heat from the ground and boosting it for use in heating the home and water for domestic use.

Working in a similar fashion to fridges these systems are best suited to provide a constant, lower level, of heating without sharp peaks in temperature such as is required by under floor heating systems.

Because of the way in which heat is extracted, normally through a network of coiled piping, ground area may be a factor in the ability to install these systems. These systems are highly efficient, delivering 300 per cent-400 per cent efficiency against 86 per cent typically seen with condensing gas boilers.

Key facts:

Carbon savings: Typically 250 kg per year for a small two-bedroom dwelling.
Typical costs of system and installation (excluding internal heat distribution system): £6,000
Cost effectiveness - simple payback: Eight to 15 years
Typical lifetime: 20-25 years for the heat pump and up to 50 years for the ground coils.

Air source heat pumps

These operate in a similar fashion to ground source heat pumps but use the ambient air temperature to generate heat within the home. Unlike ground energy systems the air temperature input for air source systems can vary greatly both seasonally and daily and the systems are not suited to cold winters. These systems can be highly efficient delivering up to 250 per cent seasonal efficiency.

Key facts:

Carbon savings: Typically 180 kg per year for a small two-bedroom dwelling.
Typical costs of system and installation (excluding internal heat distribution system): £6,000
Cost effectiveness - simple payback: Eight to 15 years

Absorption heat pumps

Instead of using electricity, absorption heat pump systems use another heat source such as natural gas to compress the refrigerant. Otherwise they are similar in operation to ground or air source heat pumps.

Key facts:

Carbon savings: Compared with a condensing gas boiler operating at 85 per cent seasonal efficiency these systems would deliver approximately 60 per cent greater carbon savings.
Typical costs of system and installation (excluding internal heat distribution system): £7,000
Cost effectiveness - simple payback: Eight to 15 years

Small-scale hydroelectric systems

These rely on a constant flow of water to generate electricity using a turbine system. Power outputs will vary seasonally with flow rates and the systems may not be suited to all domestic situations because of the cost of installation against the power generated.

The capability to generate electricity is also increased by the size of the vertical distance the water falls, know as the "head". Greater heads tend to generate more electricity. Planning issues may mean that it is not always able to obtain permission to install hydro-electric plants. The majority of energy created by these systems is typically sold back to the National Grid.

Key facts:

Annual energy, carbon and cost savings per kW installed capacity (60 per cent capacity factor): Electricity generated around 5,300 kWh with 2,300 kg of CO2 displaced.
Typical costs of system and installation for 100 kW system: Low head - £115,000-£280,000; High head £85,000-£200,000.
Cost effectiveness - simple payback: For a 100 kW system operating at 60 per cent capacity capital costs of around £200,000 with £30,000 in maintenance are typical. The lifetime yield is around 4,800,000 kWh sold @ 5p/kWh to the National Grid and with ROC income @ 4.5 p/kWh of around £216,000 would mean an approximate payback period of 15 years.
Typical lifetime: 30 years

Micro combined heat and power systems

This is an emergent technology that is being suggested as a direct replacement for the boiler in domestic use. These systems generate electricity as well as heating the home and providing hot water. Primarily the systems generate heat, but also incorporate a heat recovery system combined with electricity generation, typically using a Stirling engine system.

Key facts:

Carbon savings: Carbon savings are as yet not fully proven under laboratory conditions but suppliers of systems estimate savings of 1.5 tonnes of CO2 per dwelling per year with a cost saving of approximately £150 per dwelling per year.
Typical costs of system and installation: Approximately £500 greater than for a condensing gas boiler
Cost effectiveness - simple payback: Estimated at three-five years.
Typical lifetime: Untested but estimated to be similar to condensing gas boilers

Renewable combined heat and power systems

In essence these are exactly the same as micro combined heat and power (CHP) systems, but they rely on renewable fuel sources such as biofuels and biogas. At present the only renewable CHP system operating in the UK is run on a community rather than household scale. The potential CO2 savings and the benefit with regards to addressing fuel poverty may make these systems an ethically and environmentally attractive option in the future.

Fuel cells

The chemical energy stored in gaseous fuels such as hydrogen, methane and propane can be converted directly into electricity by fuel cell technology. Although each cell has no moving parts, to be effective several cells are required, which must be wired in series, and the resultant generator unit can be quite complex and incorporate fans, pumps and control valves.

Efficiencies of more than 80 per cent have been achieved in experiments with fuel cells, with power consumption for related equipment such as fans and pumps being relatively low. However, systems currently on test only offer 30 per cent efficiency, which means they may be best suited as CHP systems because of the heat they generate when operating.

Key facts:

Lifetime energy, carbon and cost savings: Not yet available
Typical costs of system and installation: Prices of commercially available systems are not yet available
Cost effectiveness - simple payback: Unknown as yet as cost of systems is unavailable at present.
Typical lifetime: Projected at 20 years with some replacement parts required during the lifetime.

Phil McKenna, New Scientist, 22 November 2008,

http://www.newscientist.com/article/mg20026836.000-plumbing-the-oceans-could-bring-limitless-clean-energy.html

FOR a company whose business is rocket science Lockheed Martin has been paying unusual attention to plumbing of late. The aerospace giant has kept its engineers occupied for the past 12 months poring over designs for what amounts to a very long fibreglass pipe.

It is, of course, no ordinary pipe but an integral part of the technology behind Ocean Thermal Energy Conversion (OTEC), a clean, renewable energy source that has the potential to free many economies from their dependence on oil.

"This has the potential to become the biggest source of renewable energy in the world," says Robert Cohen, who headed the US federal ocean thermal energy programme in the early 1970s.

This has the potential to become the biggest source of renewable energy in the world

As the price of fossil fuels soars, private companies from Hawaii to Japan are racing to build commercial OTEC plants. The trick is to exploit the difference in temperature between seawater near the surface and deep down (see diagram).

First, warm surface water heats a fluid with a low boiling point, such as ammonia or a mixture of ammonia and water. When this "working fluid" boils, the resulting gas creates enough pressure to drive a turbine that generates power. The gas is then cooled by passing it through cold water pumped up from the ocean depths via massive fibreglass tubes, perhaps 1000 metres long and 27 metres in diameter, that suck up cold water at a rate of 1000 tonnes per second. While the gas condenses back into a liquid that can be used again, the water is returned to the deep ocean. "It's just like a conventional power plant where you burn a fuel like coal to create steam," says Cohen.

The idea of tapping the ocean's different thermal layers to generate electricity was first proposed in 1881 by French physicist Jacques d'Arsonval but didn't receive much attention until the world oil crises of the 1970s. In 1979, a US government-backed partnership that included Lockheed Martin, lowered a cold water pipe from a barge off Hawaii that was part of an OTEC system generating 50 kilowatts of electricity. Two years later, a Japanese group built a pilot plant off the South Pacific island of Nauru capable of generating 120 kilowatts.

In the first flush of success, the US Department of Energy began planning a 40 megawatt test plant off Hawaii. Then in 1981, the funding for ocean thermal technologies began to dwindle. It dried up altogether in 1995 when the price of oil began to drop, eventually falling below $20 a barrel.

Now rising fuel costs have revived interest in this neglected technology. In September, the Department of Energy awarded its first grant for ocean thermal energy in more than a decade, giving Lockheed Martin $600,000 to develop a new generation of cold water pipes.

Cohen believes this could eventually lead to 500 MW OTEC plants on floating offshore platforms sending electricity to onshore grids via submarine cables, and factory ships "grazing" the open ocean for power.

Lockheed's first goal is to get a test facility up and running. The company has got together with Makai Ocean Engineering of Waimanalo, Hawaii, to build a 10 to 20 MW plant, most likely off Hawaii, that it hopes to have up and running in the next four to six years. The plant - including a 1000-metre pipe some 4 metres in diameter - would feed electricity to the island's energy grid via submarine cables.

While Lockheed gears up for its test facility, a plant for the US military could come online even sooner. OCEES International, based in Honolulu, is finishing designs for an ocean thermal facility to be built off the island of Diego Garcia in the Indian Ocean, which is home to a major US military base.

The plant would provide 8 MW of electricity and would also power the desalination of 1.25 million gallons of seawater per day. OCEES says it could be up and running by the end of 2011.

At the moment Diego Garcia is powered entirely by diesel fuel, and base commanders see ocean thermal as a means to energy independence. "It's a strategic military installation in the middle of the Indian Ocean," says Harry Jackson of OCEES. "They don't want to rely on others to provide their power."

"I think OTEC has the potential to develop sufficient power output much quicker than wave buoys or tidal power would," says Bill Tayler, director of the US navy's Shore Energy Office. "It would take a lot of buoys to produce 8 to 10 MW of power. We're looking at them all but have our hopes on OTEC."

Still, both teams will have to work out issues such as how to connect the floating, bobbing platforms to fixed submarine power lines. Heat exchangers will have to be designed in a way that prevents excessive buildup of algae, barnacles and other marine organisms that could clog the system.

If these test plants are a success, larger, commercial-scale plants could transform the energy equation on Hawaii, where nearly 77 per cent of electricity is generated by burning oil. "It will be the major energy game changer for our state and elsewhere in the world if we can get OTEC working well at the 100 MW level or larger," says Lockheed collaborator Reb Bellinger of Makai Ocean Engineering.

But scaling up won't be easy. "A 100 MW plant might have a pipe 30 feet in diameter suspended 3000 feet. That's not a small challenge. You've got this huge structure vertically suspended. You've got a lot of stresses and strains from current, from the movement of platform on the surface - how you are going to anchor it and install it?" asks Bellinger.

Smaller designs have already run into trouble. In 2003, Indian engineers building a 1 MW ocean thermal plant attempted to lower an 800-metre cold water pipe into the ocean from a barge in the Bay of Bengal only to lose the pipe in 1100 metres of water. A new pipe met the same fate the following year. "Both times there were some winch problems and it fell to the bottom of the sea," says Subramanian Kathiroli, director of India's National Institute of Ocean Technology. "I don't think we will ever be able to go beyond 5 to 10 MW with present knowledge," he says.

Yet the technology will have to be scaled up if OTEC is ever to make a significant impact on the green power market. Hans Krock, who has worked on OTEC designs for the University of Hawaii, the US Department of Energy and others since 1980, says he's tired of testing. "Pilot tests have been done," Krock says. "It's not a matter of design, it's a matter of getting the economics right."

Krock, who founded OCEES in 1988, recently left to start Energy Harvesting Systems, a firm with ambitious plans to build a 100 MW OTEC plant off the coast of Indonesia. The electricity it generates will be used to produce hydrogen, a green fuel that could be used to power zero-emission vehicles. Krock says he has funding for the $800 million plant and it could be up and running within two years, once building contracts are finalised.

For Cohen, who has also waited decades for ocean thermal to come into its own, such a large plant seems overambitious, especially as it is coupled with the production of hydrogen, whose distribution structure is still largely undeveloped.

"Scaling up so quickly could be risky," warns Cohen. "I'd like to see us move fast on ocean thermal but I think we have to be careful."

Lake Ontario helps Toronto chill out

As governments and private companies around the world look to capitalise on ocean thermal energy, an offshoot of the technology is already up and running. Instead of trying to harness cold, deep water for electricity production, the city of Toronto in Canada uses water from the bottom of Lake Ontario to cool its buildings. Makai Ocean Engineering of Waimanalo, Hawaii, recently helped construct the city's cold-water air conditioning system that will save 60 megawatts of electricity when it is fully connected to buildings in the city's centre. The system works by pumping water at a temperature of 4 °C from a depth of 80 metres and then sending it to buildings within the city via three pipes, each5 kilometres long. The cold water is then used to cool air.Makai is working on a similar cold-water air conditioning system for Honolulu in Hawaii. "Ocean thermal energy is the big prize, but cold-water air conditioning can play a major role in cutting energy needs, and it can do it today," says Reb Bellinger of Makai.

From issue 2683 of New Scientist magazine, page 28-29