Scaled-up windfarms: unexamined costs

Sunday 27th May 2012
Horns Rev Windfarm, 10 miles off Denmark http://www.windtaskforce.org/profiles/blogs/problems-of-maine-offshore

The offshore wind energy industry is being urged to develop "mega-projects" co-operating to improve its supply chain, if it is to cut costs sufficiently to compete with other large-scale power generation sources, according to management consultancy Accenture. But the advise makes no mention of European Geosciences Union (EGU) concern that before exploiting the energy solution of offshore wind turbines, oceanographic and atmospheric community must “sit down and have a serious discussion on what the influence may be, before [large scale] wind farms are built.”

In a report being launched at the All-Energy renewable energy conference in Aberdeen reports The Herald  consultancy Accenture said that capital investment costs in the wind industry need to fall by between 30% and 50% if it is to rank alongside other technologies such as gas-fired turbine. Accordingly the industry needs to look at ways of reducing ongoing operating costs and generating higher revenues, according to the report Changing the Scale of Offshore Wind.

The report authors – Accenture's lead consultant for clean energy (L2R) Melissa Stark and MauricioBermudez-Neubauer, its lead consultant for offshore wind – wrote: "The capacity of mega-projects is significantly larger and, in many cases, an order of magnitude greater than any wind farm currently in operation.

"The emergence of such mega-projects brings about the potential to significantly drive down costs in offshore wind development. Indeed, there is ample proof in the energy industry that increasing project size is a substantial driver of cost reduction."

The firm defines an offshore wind mega-projectS as one with a capacity of <800MW or more estimating more than 70% of planned mega-projects worldwide will be in the UK with SSE and Fluor's Firth of Forth development, ScottishPower's Argyll Array and EDP Renovaveis and Sea-Energy's Moray Firth plans.



The report argues the cost of offshore wind power has to fall to around £100MW/h from between £149 and £191  to compete with other energy sources.  "With this scale of cost-reduction requirements, even an industry-wide implementation of leading practices in today's scale of offshore wind farms [100MW to 300MW] would not be sufficient to drive down costs to make offshore wind competitive with traditional power generation technologies." the report said.

Merely implementing current best practice would cut costs by up to 20%. "Such savings still fall short of the important reductions required to make offshore wind competitive." Hence the quest for scale thorugh mega-project with no apparent attention to mega-project environmental risks.

Savings according to the report  couldcome from better risk-sharing, more efficient contracting; cost-effective geological surveys; competition putting downward pressure on prices; investment in improving supply chains; larger turbine size; and more specialised vessels  to speed up installation.

Accenture also warns of a potential "bottle-neck" in the supply chain because demand for turbines in Europe has been limited. "Offshore wind projects have ..been employing technologies, processes and business models adapted from the onshore industry, rather than designed for the very different offshore marine construction and operations environment.

"The turbine supply chain needs to transform … by the order of magnitude changes in turbine demand that mega-projects will bring about."  And  industry is "stalemated", with supplier and developer each expecting the other to take the risks.

It might be the saving grace needed to really explore that unexamined other cost that is  large offshore wind farms could have ecosystem effects on ocean circulation patterns, temperature structures, and nutrient cycling, reports Physicist Today 

The European Geosciences Union (EGU) General Assembly in Vienna dedicated several sessions to climate change and the need to reduce society's dependence on fossil fuels. Offshore wind turbines are one solution, but as Norwegian Meteorological Institute's Göran Broström  urges that the  oceanographic and atmospheric community needs to “sit down and seriously discuss what the influence may be before [large scale] wind farms are built.”

In 2008 Broström made a case that large wind farms significantly affect nearby wind speeds. A wind speed of 5–10 m/s may generate ocean upwelling and downwelling velocities of more than 1 m/day near the turbines.

Upwelling draws nutrient-rich deep water toward the surface changes the temperature structure and availability of nutrients in the wind farm vicinity potentially leading to changes in local ecosystems.

“The biggest wind farms as of today are close to the coast so the impact on the ocean is difficult to see,” he says. Currently operating small wind farms mean ocean circulation effects might not be detectable.

Generating strong horizontal shear in the wind stress via atmospheric convection; shear leads to surface divergence and convergence in the upper ocean so circulation and an upwelling pattern are engendered by the wind farm.

Ekman transport which explains the theoretical state of circulation if water currents were driven only by the transfer of momentum from the wind explains these changes. Variable winds mean that Ekman transports are not uniform and that they lead to convergence and divergence of surface currents. Water uplifted from below balances the urface divergence at the turbines.

MODELLING THE DYNAMICS 

Elke Ludewig used the Hamburg-Shelf-Ocean-Model, which simulates oceanic, coastal, and sea-shelf dynamics, in a sensitivity study on the effects of a proposed wind farm.

Germany plans to harvest 8700MW worth of wind energy in the North and Baltic seas, building the equivalent of 20 offshore wind farms with a total of 80 turbines.

“The [farm] width is more important than the density of the wind mills,” says Broström and suggests that upwelling and local current changes would be noticed at 3- 4km2 wind farms.

A small wind farm of 12 turbines, rotor diameter 80m rapidly leads to upwelling and downwelling zones in North Sea conditions. The circulation change affects an area 160 times as big as the wind farm itself, key results being a change of a few millimeters in sea level and a tilt of the thermocline.

“We're still checking the dynamics,” says Ludewig. Next simulations of the North Sea will include investigating local climate and whether it becomes warmer or colder. The results will help to analyse ecosystem effects and reef development within the wind farms.

Permission to build wind farms is granted by national authorities, but proposed mechanisms for ocean circulation and ecosystem change, based on solid theoretical ground, have not been masured for verification.  Broström adds another caveat. “Different wind farms may interact, giving rise to a combined influence that is greater than their own influence.”  

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