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Renewables & efficiency - Aug 18

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Scientists explore how the humble leaf could power the planet

Alok Jha, The Guardian
It is one of evolution's crowning achievements - a mini green power station and organic factory combined and the source of almost all of the energy that fuels every living thing on the planet.

Now scientists developing the next generation of clean power sources are working out how to copy, and ultimately improve upon, the humble leaf. The intricate chemistry involved in photosynthesis, the process where plants use sunlight to convert water and carbon dioxide into sugar, is the most effective solar energy conversion process on Earth. And researchers believe that mimicking parts of it could be the ticket to a limitless supply of clean power.

The untapped potential for using the sun's rays is huge. All human activity for a whole year could be powered by the energy contained in the sunlight hitting the Earth in just one hour. Harnessing even a small amount of this to make electricity or useful fuels could satisfy the world's increasing need for energy, predicted to double by 2050, without further endangering the climate.

Most solar power systems use silicon wafers to generate electricity directly. But although costs are coming down, these are still too expensive in many cases when compared with fossil fuels such as coal, oil and gas. Scientists are keen to develop more efficient and cheaper alternatives sources of energy.

...According to James Barber, a biologist at Imperial College London and leader of the artificial leaf project, if artificial photosynthesis systems could use around 10% of the sunlight falling on them, they would only need to cover 0.16% of the Earth's surface to satisfy a global energy consumption rate of 20 terawatts, the amount it is predicted that the world will need in 2030. And unlike a biological leaf, the artificial equivalent could be placed in the arid desert areas of the world, where it would not compete for space agricultural land...
(11 August 2009)



Raising Wind Turbine Output With Longer Blades

Matthew Wald, New York Times
A basic problem for wind turbines is that the wind often dies down. As a result, they produce far less electricity than if the wind blew constantly, at full speed.

...One major turbine manufacturer, Siemens Energy, is trying to increase the proportion of potential energy that the wind harvests — by making the blades longer. The new machines, by Siemens, all use the common three-blade design. But a new Siemens turbine has a rotor diameter of about 330 feet, rather than one with a 305-foot diameter.

The “swept area” — the circle of air from which the machine captures energy — is therefore about 18 percent bigger.

When the wind blows strongly the longer blades make no difference, because the size of the turbine’s generator is unchanged. At moderate speeds, the output goes up. At 17 miles an hour, for example, Siemens says that the larger blades produce about 7.5 percent more electricity than those with smaller blades. They do not spin faster, but they extract more energy from the passing air...
(11 August 2009)



How a wind farm could emit more carbon than a coal power station

Fred Pearce, the Guardian
Let's be clear: Britain needs wind turbines. Lots of them. But just about the worst place to erect them is on top of peat bogs, which are huge stores of carbon that can easily leak carbon dioxide into the air when damaged by the inevitable roads or drains.

So there are serious questions about the green credentials of plans to build Europe's largest onshore wind farm on 187 square kilometres of thick peat on the Shetland Islands. The fate of the £800m project will be decided by the Scottish government in the coming weeks.

More than half of the wind turbines in Scotland are on highland peat. This is not sensible. Scottish peat bogs hold three-quarters of all the carbon in British ecosystems – equivalent to around a century of emissions from fossil fuel burning.

Apart from water, peat bogs are largely composed of huge volumes of saturated, undecayed plants. A single hectare typically contains more than 5000 tonnes of carbon, ten times more than a typical hectare of forest. But any disturbance leads to lower water levels and to the peat drying, oxidising and releasing its carbon, says biochemist Mike Hall of the Cumbria Wildlife Trust.

...One of the big risks for any construction on peat bogs is that the disrupted drainage will cause whole hillsides of waterlogged or dried out peat to slide and eventually oxidise. Such a peat slide happened at a wind farm at Derrybrien in Ireland in 2003, probably cancelling out all the benefits of building the wind farm.

Peat slides are a regular feature of the Shetland bogs. An independent technical assessment for the company raised serious issues, finding 54 problem areas.

But that hasn't stopped Viking's environmental statement from stating that the risk of a slide, even in a worst-case scenario, is zero. It blandly states: "It has been assumed that measures have been taken to may [sic] limit damage so that C losses due to peat landslide can be assumed to be negligible."
(13 August 2009)
Sent in by EB contributor billhook, who writes:
If one wanted to distract people from campaigning for effective alternatives to fossil energy supplies, then Onshore Wind power offers remarkable advantages -

- it is exemplary in its unpredictable intermittency of output, thus needing either huge storage capacity or huge 'splinning reserve' fossil energy capacity -
- it is exceptional in its industrial intrusiveness on the UK's wildest and most lovely landscapes, thus neatly splitting the green movement down the middle, with realos staunchly pointing out that there are far better resource options still awaiting development, while fundis parrot the developers' slurs of 'NIMBY' and urge the further gutting of local planning democracy -
- it is unique in worsening the antipathy between the movement and the majority rural population, directly encouraging the latter's denialism and actual support for a return to the mining of British coal and submission to the nuclear option -

Offshore Windpower, as distinct from 'Inshore' and 'Onshore' versions, is of course quite another matter, but it has yet to attract any serious R&D funding. Surprise, surprise.

Regards,

Billhook

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