TimberTowers: Advantages of wooden towers for wind turbines

Holger Giebel, Managing Director of TimberTower GmbH presents the unique advantages of the innovative wooden towers for wind turbines his company produces. The wooden tower leads to lower project costs, it is easier to transport, it is manufactured from renewable resources and it supports the regional added value. A timber tower bonds 400t of CO2 instead of releasing it. Read the whole interview to learn more about this innovative product.

IQPC: What is your company’s role in the wind industry?

Holger Giebel: TimberTower GmbH develops, erects and sells timber towers for multi-megawatt class wind turbines including the foundation.

IQPC: In a fast growing and developing market, like the wind industry, how is your company setting itself apart?

H.G.: TimberTower GmbH is the first company worldwide, who builds wooden towers for large wind turbines. The construction has many advantages: It leads to lower project costs, it is easier to transport, it is manufactured from renewable resources and it supports the regional added value.We can guarantee on the one hand highest quality with our experienced and specialized partners, on the other hand a minimum tower life cycle of 40 years with our procedure for durable conservation. With a tower height of 100m we save 300t of steel. Beyond that a timber tower bonds 400t of CO2 instead of releasing it.TimberTower GmbH is the first company worldwide, who builds wooden towers for large wind turbines. The construction has many advantages: It leads to lower project costs, it is easier to transport, it is manufactured from renewable resources and it supports the regional added value.We can guarantee on the one hand highest quality with our experienced and specialized partners, on the other hand a minimum tower life cycle of 40 years with our procedure for durable conservation. With a tower height of 100m we save 300t of steel. Beyond that a timber tower bonds 400t of CO2 instead of releasing it.

Interested in reading on? Find the complete interview HERE

Get more information about new tower concepts, tower interfaces and upcoming regulations on the 1st international conference Advances in Wind Turbine Towers!
  http://www.windturbine-towers.com/

The Innovation and Design of Rotor Blades for the Future

European renewable energy targets continue to fuel the wind turbine industry, with the development of the offshore market pushing the demand for even larger turbines. Some of the designs currently in use have rotor diameters in excess of 120 metres, and the blades are required to perform efficiently under extremely turbulent conditions.

Rotor blades can account for 20-25% of the overall cost of a wind turbine, so it is essential that the blades are efficient and provide long service with little maintenance, to ensure their cost-effectiveness. Manufacturers are constantly developing the production process as new methods and technology are integrated. The move towards mass production to meet the demand of the growing offshore market, and the opportunity to manufacture close to site, offers the potential to reduce the cost of rotor blades significantly.

Rotor blade design concepts

Aerodynamics is crucial in rotor blade design; in the past blades have been designed on the basis of aviation airfoils, but these airfoils are intended for plane wings which are placed under entirely different wind flow conditions to turbine blades (¹). Most blade manufacturers use their own customised design for turbine blade airfoils, and are continually developing the technology behind them.

The aerodynamic design of a blade dictates its width, thickness and twist. And the key challenge to manufacturers is to find a compromise between air flow and blade strength to optimise performance and efficiency. In pure terms of aerodynamics, the perfect blade design would see a blade which is thick, wide and very long. In reality, this is not viable as the blade would put far too much strain on the turbine, and could strike the tower upon rotation. The strongest type of blade would be one of a circular structure, but this is equally implausible as such a blade would have minimal lift, and would not be suitable for producing energy from wind power. These extreme examples indicate why it is so important to find the best balance between air flow and strength in blade manufacture to improve efficiency.

One of the world’s leading blade manufacturers, LM Wind Power, have sold over 130,000 blades equivalent to a capacity of 43 GW; and more than one in three wind turbines in the world is fitted with their blades (¹). They use several innovative design concepts to improve performance, and are at the forefront of glass fibre development to produce lighter more efficient blades.

One unique feature in the design of LM blades is the pre-bending process, which means the blades flex towards the wind once they are mounted and are not subject to loading (²). Clearance of the tower is essential in blade design, and the tip to tower distance is critical.

Interested in reading more about rotor blade design concepts? Find out more here.

References:

(1)  http://smart-blade.com/research/airfoil-design.htm

(2)  http://www.lmwindpower.com/Blades/About/Business%20area.aspx

All at sea – Grid Integration of Offshore Wind Energy

Offshore wind power is set for a strong future, not least in Germany where the phase out of nuclear power will see the country lose around a quarter of its generating capacity in the next decade. Germany is already leading the way in wind power on the continent with 27,214 MW of installed capacity and the government is looking to increase this figure further as it favours wind over other renewables.

Although much of this is currently installed onshore, 24 offshore projects have been approved, bringing with them a generation capacity of 7,000 MW. Overall, Europe is expected to see its wind power capacity triple by 2020. This growth brings with it the need to future proof the transmission system, allowing it to cope with the intermittent nature of wind power, while also extending the distribution network to integrate the growing number of wind farms with greater generation capacity located in harsher environments further offshore.

Future Demands on the Grid
Germany is, of course, not the only country priming itself for future success in the offshore wind sector. Across the EU there are currently 100 GW of wind power projects at some stage of planning, according to figures from the UK's Department of Energy and Climate Change (DECC), and this is ushering a new era of greater collaboration in the distribution of electricity. Incidences in recent months in Germany, where wind output has been particularly high, has left providers paying to remove power from the grid. This is a situation the industry does not want to see but may increase as wind capacity increases. With this in mind, among other issues, the UK, Ireland, Sweden, Denmark, Germany, the Netherlands, Luxembourg, France, Norway and Belgium last year signed an agreement on the North Seas Offshore Grid Initiative. The distribution system would allow power to be transferred from one country to another through subsea cables, while also allowing offshore wind farms to be connected to the grid. The DECC sees the relationship between the countries as being synergetic, giving the example of the UK sending its wind power to Norway to power its hydroelectricity stations when there is a surplus, and Norway delivering power back when wind output is low.

Interested in learning more about this topic? Check out more articles here.

The requirements for wind turbines and services for grid code compliance

The advancement in offshore wind power technology has led to larger turbines and larger wind farms being deployed throughout Europe. Where previously wind farms had been thought of as single distributed power generators, they must now be considered as integral components of the overall energy supply system, and be subject to the same regulations as other types of power generation.

The European Wind Energy Association (1) estimates that by 2020 between 14.4% and 16.7 % of the EU’s electricity supply will be sourced from wind energy, both on land and offshore. The European Commission’s energy strategy for Europe (2) suggests that up to 12% of this will be supplied by offshore wind farms.

Due to the increase in the size of wind farms, and the requirement of Europe’s TSO’s (Transmission System Operators) to integrate them into the network, grid code compliance rules have been implemented to ensure that offshore wind farms contribute to the system, and behave in the same way as conventional generators. Before connection to the grid, wind turbines and wind farms must certify that they comply with regulations surrounding frequency dependant active power supply (frequency control), Voltage control – both steady state and dynamic, Voltage dependant reactive power injection and absorption, and fault ride through stability.

While the European grid as a whole must undergo rapid redevelopment to access and integrate offshore wind power, the responsibility of turbine manufacturers and wind farm construction companies is to ensure that their equipment, when connected, has a positive impact on the overall system.
Grid code requirements for wind turbines and wind farms

The European Wind Energy association is working towards the harmonisation of grid code compliance across Europe, and in late 2009 issued the first template for a generic grid code (3) format for wind power plants. The organisation is in continued collaboration with the EU and with Europe’s TSO’s to develop a fully continental-wide harmonised grid code.

Want to learn more about grid integration of offshore wind energy? Check out further articles here.

References
(1) http://www.ewea.org/index.php?id=196
(2) http://ec.europa.eu/energy/publications/doc/2011_energy2020_en.pdf

(3)http://www.ewea.org/fileadmin/ewea_documents/documents/publications/091127_GGCF_Final_Draft.pdf

New Health and Safety Standards in the Wind Industry

Shore wind energy is considered the most promising source of renewable energy to achieve the ambitious political target of 20% by 2020. In response, the offshore wind power industry is growing rapidly with a considerable number of large-scale projects on the horizon.

To realise these ambitious mega-projects, large numbers of highly skilled personnel is required. All wind developers are required to consider the risks that may arise in their projects during construction, operation, and final demolition. Risks can be accidents which happen when working on a wind farm.

Only recently, a wind farm worker was killed inside a wind turbine in Iowa.

The problem is: As the off/onshore wind energy industry is moving at such a pace, developers have had little time to consider the practical problems involved with these projects, but this is sure to be a crucial task if the industry is to establish a reputation of being a safe workplace.

There are a number of issues relating to health and safety that need to be addressed as wind farms move further from the shore and also into deeper water. If the industry wants to attract the best personnel and earn a reputation as a safe place to work, vital to its long term success, health and safety issues will require detailed consideration.

An industry-specific specialised health & safety standard, best practices in terms of training and equipment, good information sharing practices as well as sound HSE strategies and emergency response plans are crucial for all phases from design, construction to maintenance and repair.

Learn more about health & safety standards at the Conference on HSE in Wind Power Development in December 2011.

Recognizing The Potential Of Wind Energy As A Viable And Profitable Source Of Energy Production

B oth government and industry are searching for the most efficient environmentally friendly and sustainable methods to generate energy. Society’s love affair with cheap power has had far reaching consequences including the over reliance on fossil fuels which has had negative impacts on climate, habitats, and the lives of millions of people around the world. Though wind turbines have been used in various forms for centuries, there is now a renewed interest in the potential they have for supplying a large amount of energy.

The ability to harness wind energy for power has been attracting a great deal of attention, especially in the US. The United States now produces more wind power than any other nation, and it is predicted that by 2030, around twenty per cent of the nation’s supply will be sourced through this technology. In 2009 alone, thirty nine percent more capacity was added by the US wind power industry. This industry holds a lot of promise and a great deal of potential, however there are also obvious problems that this sector faces.

There are two main concerns regarding renewable wind energy as a sustainable source of power production. First of these concerns is sustainability. As everyone knows, the wind does not always blow. For this reason, many governments are unwilling to invest heavily in the latest turbines as there is no guarantee that they will be efficient, especially for countries that rely heavily on the export of their natural resources as their main source of economic growth. Their argument is that there would still be a need to have back up systems in place to cover any periods when there is no breeze.

The second concern is a combination of location and cost of operating a large scale wind project. Typically, the places where winds blow the most consistently are fairly remote. For example, steady winds are usually located at the top of mountains, out at sea, and across remote plains.

This is a problem that is highlighted in Texas, the country’s leading state for producing wind-power. West Texas is where the speeds and gusts are most constant, specifically on the high plains and mesas, but these regions are a considerable distance from Houston and Dallas, and installing the necessary power and utilities are difficult and expensive.

There is a lot of interest in positioning turbines offshore, though this is more expensive than onshore, data indicates that the breeze out at sea is both stronger and more constant than onshore. Offshore wind farms do make it possible to create large scale wind power facilities close to large coastal settlements, without the need for costly and extensive overland transmission cables. Also, by positioning the turbines at sea, they are not the eyesore that they would be if installed on land.

Cost of repair and maintenance at these locations can also be costly. However, new technology has enabled wind farm operators to assess, detect and repair large wind turbines without extended downtime and exorbitant costs that result in loss of profit.

This means that the positioning of wind farms isn’t as much of a problem as curbing the current governmental  mindset that fossil fuels are a necessity. The cost of extracting fossil fuels is becoming more expensive on an annual basis, yet the demand from consumers is showing absolutely no sign of decline. Sustainable power may be the solution that keeps the economy buoyant in the coming decades.

With more efficient wind turbines being constructed on an ongoing basis, the prevalence of wind technology is only going to grow. The real trick is showing both government and consumer that wind energy is cost effective as not only an efficient long term energy production method, but viable source of revenue.


Copyright © 2011 Cory Sober - All Rights Reserved. Hyperlinked material remains the property of its respective owners.  by  Cory Sober

Drivetrain Concepts for Wind Turbines Conference to return to Bremen

Despite rapid technical developments for ever larger wind turbines, high failure rates, downtime and a lack of proven track record cause time-consuming and costly repairs. At IQPC’s 2nd Drivetrain Concepts for Wind Turbines conference from 17 - 19 October 2011 in Bremen, Germany, professionals from the wind turbine industry will come together to discuss the present and future challenges in the field.

Main discussion points at the conference will include:

• Drivetrain solutions for next generation wind turbines – from gearbox to direct drive
• Achieving higher reliability, better availability and easier serviceability
• Assessing generator topologies for very large turbines for offshore wind power development
• Reducing drivetrain loads to avoid wear and fatigue in your mechanical components
• Identifying the key challenges in reducing the cost of energy (CoE) from wind power

In addition to the two main conference days, on Wednesday, 19 October, delegates can participate in interactive workshops to further their knowledge in the following areas:

• Generator systems for multi-megawatt wind turbines
• Mechanical requirements of wind turbine gearboxes
• High Temperature Superconductor technology for generators

Delegates will have the chance to discuss with experts first-hand the current challenges and developments in wind turbine drivetrains. Companies and institutions including Vestas Wind Systems A/S, E.ON Climate & Renewables GmbH, National Renewable Energy Centre, ABB Oy, the University of Manchester and Siemens Wind Power A/S have been invited to present their projects and expertise.

Further information, including articles, interviews and the preliminary program can be found at the website.

Drivetrain Solutions for Next Generation Wind Turbines

European renewable energy targets for 2020 and beyond demand that every aspect of the offshore wind turbine is scrutinised for best performance, reliability and cost-efficiency. The drivetrain, the generator and the gearbox account for 14% of failures per turbine per year, but cause 39% of all downtime for the same period.

The components, particularly in the gearbox, are subject to intense stress due to wind turbulence offshore, and are often the first parts to fail. Downtime at sea is much more pronounced, and improvement in the design of the drivetrain configuration will significantly reduce breakdowns.

The next generation of drivetrains under development include several innovative designs using direct drive systems, or hybrid systems. The trend towards direct drive is most prominent in the offshore market because of the need for greater reliability; but the challenge remains to produce a system which is light enough for the largest offshore turbines, yet cost efficient when compared with a conventional geared drivetrain.

Progression from current to future design
Wind turbines have previously used a gearbox to drive the generator, but it has always been considered a weak link. Extreme stress is placed on a gearbox by wind turbulence, and the need for larger gearboxes to service larger turbines offshore make the gearbox a vulnerable component. The cost of servicing an offshore turbine and the extended downtime has led to advances in direct drive technology, thus eliminating the gearbox and all associated failures.

Direct drive
With the generator rotating at the same speed as the turbine shaft in a direct drive system, designers have compensated by increasing the radius of rotation; using generators with a diameter of several metres. Larger generators would be needed for larger offshore wind turbines, and the problem facing developers is reducing the weight to make direct drive viable. Direct drive technology improves reliability, simplifies the nacelle assembly and helps to increase efficiency, but improvements must be made in cost efficiency and weight reduction.

Hybrid systems
Hybrid systems combine a simple and more reliable gearbox with a direct drive system. The hybrid concept has gearing at megawatt scale, but also has a large diameter generator. The nacelle has a more compact design, with the gearbox and generator giving a balanced geometry to the system. The image of the WinWind 3MW turbine below demonstrates the suitability to offshore applications, as the nacelle does not extend too far from the tower centreline.

Source:  WinWind

Future concepts
Progression towards 10MW and larger turbines requires lighter, more reliable drivetrains; and some of the technology being introduced and currently under trial will be examined in this section. It is not yet clear which type of drivetrain will best serve the wind energy industry long term; direct drive and hybrid systems will soon be joined on the market by new concepts in controlling the variable speed of the turbine.

Interested in learning more about Drivetrain Solutions for Next Generation Wind Turbines? Click here for many more relevant free whitepapers, articles, and podcasts.

Serviceability of drivetrains

The design and innovation of components and of the drivetrain assembly as a whole will lead to greater reliability, less breakdowns and less down time; but the turbines still have to be regularly serviced and maintained. Current data shows that offshore wind turbines run at an availability level of 97% on average. In practical terms this equates to four visits per year either for maintenance or repairs.

It is estimated that operation and maintenance costs could account for up to 30% of the energy cost, and manufacturers recently indicated that the cost of operation and maintenance is around £30,000 per turbine per year in the UK. The cost of offshore servicing is exaggerated by the cost of equipment, particularly vessels, as the price is driven up by competition from the oil and gas industry. Weather constraints can also affect budget and increase costs.

The current generation of wind turbines require servicing once every six months, and take between 40 and 80 man hours per year. Typically a major overhaul will be carried out every five years, and would need 100 man hours. Cancellations due to weather are estimates at 15% of service visits, so can have a significant effect on schedule and cost.

Substantial investment is being put into the development of more reliable drivetrain systems, to reduce the amount of maintenance. One area of development is computer controlled monitoring systems to react to faults, or highlight potential failures that can be rectified before they cause complete breakdown. SCADA (System Control and Data Acquisition) systems transmit signals and alarms between the turbine and the onshore control centre. Minor faults can be resolved remotely from the control centre, while more serious problems can be diagnosed early to reduce down time.

Summary
Wind turbine drivetrains (read also more here) as a concept, and at component level are undergoing rapid development. As one of the most significant contributing factors to the down time for wind turbines each year, the drivetrain is being revolutionised; along with the wind energy industry as a whole. It is unclear at this stage which technology will prove most suitable for mass production in the long term, so planning an operation and maintenance routine is a fluid process that must evolve with the design of each new system. As wind farms venture further out to sea in search of higher winds, so the turbines will increase in size, and may even exceed 10MW. The drivetrain solutions to suit that next generation of wind turbines will require their own custom maintenance plans.

Thousands of wind turbines will need to be installed over the next ten years if European energy targets for 2020 are to be met. This increase in volume of maintenance will change the landscape of the operation and maintenance sector of the wind energy industry. The cost of servicing is already at a very high level, because it requires specialist equipment, highly trained technicians and is reliant upon weather conditions.

Better reliability of the components within the drivetrain and longer service intervals built into design, can reduce the frequency of visits and cost of maintenance. Computer monitoring systems should also be utilised to relay detailed information back to the control centre, but also used interactively to diagnose and repair faults. Automated maintenance, such as filter changes, can be implemented into design to make the turbine as ‘self sufficient’ as possible.

The next round of development across Europe will see several wind farm installations, and much of the new technology being developed will be utilised to make this generation of wind turbines more economic and efficient; some of the innovations will be on ‘trail’ under very real conditions. To minimise the cost surrounding breakdowns and repairs due to unreliable components, strategies to improve the reliability and serviceability of drivetrain systems should be implemented, and should be seen as a vital part of the design process.

INTERESTED IN LEARNING MORE ABOUT THIS TOPIC? 2nd Drivetrain Concepts for Wind Turbines  Don't miss the "2nd Drivetrain Concepts for Wind Turbines" Congress, taking place 17-19 October 2011 at the Swissôtel Bremen, Germany. --> DOWNLOAD THE FREE BROCHURE

Question Time with Mark Riemers - Managing Director of SPT Offshore

Mark Riemers, Managing Director of SPT Offshore, gives insight into his company’s work and the challenges and benefits involved with self-installing wind turbines.

What is SPT Offshore’s specialty?  

We are an offshore contractor specialised in suction pile foundations/anchors and self installing platforms. See for details http://www.sptoffshore.com/

You’re currently working on a project involving self installing wind turbines - Which situations are these systems suited for?  

The SIWT concept is suited for 99% wind farms in deeper water, say starting at 20m up to 60m and for the larger turbines say 5MW and bigger. The suction piles are suited for most soil conditions (99% in the North Sea and Irish Sea), i.e. in sands, clays, layered soils, etc. 

What are the greatest challenges in such systems?  

We have a wide experience in oil and gas where we have successfully designed, fabricated (in most case) and installed >400 suction piles in shallow (5m) up to very deep waters (1,200m). The Offshore Renewable business is, however, still slow in adopting our technology, because of the lack of knowledge around suction piles. We are working hard to make the technology also accepted for this sector and we will be successful sooner or later. 

What are the benefits?  

No noise underwater, plus no special offshore construction equipment (crane vessels and jack-ups) is needed for installation, just a flat barge, tugs, suction pumps and jacks are needed and obviously land cranes to assemble the SIWT in the harbour. We therefore incur fewer weather risks as our ONE piece foundation and WTG installation requires limited work offshore compared to the traditional techniques. 

When do you see offshore wind turbines becoming economically viable? What does the future have in store?  

In 5-10 years, I see that subsidies will no longer be required.  

Mark Riemers will speak about "Self Installing Wind Turbine (SIWT): An innovative foundation concept for wind turbines" at the IQPC Conference Offshore Foundations for Wind Turbines.  Find more information here.

INTERESTED IN READING MORE ABOUT THIS TOPIC? Visit our Download Center for more Articles, Whitepapers & Interviews --> VISIT THE DOWNLOAD CENTER HERE

How loud is a Wind Turbine?

Because wind turbines are such a great source of clean, renewable energy, they’re usually greeted with a great deal of enthusiasm. Especially since the catastrophe in Japan, wind energy is on everyone's mind again.

Google Search Results for wind and wind energy has been rising since March - but what about those complaints about the complaints of local residents on aesthetics and noise levels.

Apparently the noise of wind turbines can be heard within a mile of the blades. Is this so? How noisy are these turbines?


The closest that a wind turbine is typically placed to a home is 300 meters or more. At that distance, a turbine will have a sound pressure level of 43 decibels. To put that in context, the average air conditioner can reach 50 decibels of noise, and most refrigerators run at around 40 decibels.


At 500 meters (0.3 miles) away, that sound pressure level drops to 38 decibels. In most places, according to Keith Longtin of GE Global Research, background noise ranges from 40 to 45 decibels, meaning that a turbine’s noise would be lost amongst it. For the stillest, most rural areas, Longtin says the background noise is 30 decibels. At that level, a wind turbine located about a mile away wouldn’t be heard.

For a complete run down of louder-than-a-fridge but quieter-than-a-blender context points, check out the graphic below.

Click on the image to see a larger version.

Are you interested in Wind and Renewable Energy? Visit the following conference website for more information on the topic area. Also visit the Download Center for free articles and whitepapers, complimentary presentations and interviews. E/E Systems for Wind Turbines 11-13 Mai 2011 in Bremen

How does Wind Energy work? Infographic

How is wind energy actually harvested? How does this whole system work? Take a look at this great Infographic created by Column Five Media.

Click on the image to see a larger version.

Ever wonder how wind power works, start to finish?
This detailed infographic:

• explains how the power is harvested, from gust to grid;
• lists the world’s largest wind farms;
• elaborates on the world’s installed power capacity;
• pegs how much the infrastructure costs per plant;
• details how much the entire industry is worth.

Data for the admittedly complicated infographic is pulled from Greenpeace.org, ReinforcedPlastic.com, the American Wind Energy Association, the 2009 World Wide Energy Report, Biowatch.com and (gasp) Wikipedia.org.

Are you interested in Wind and Renewable Energy? Visit the following conference websites for more information on the topic area. Also visit the Download Center for free articles and whitepapers, complimentary presentations and interviews. E/E Systems for Wind Turbines 11-13 Mai 2011 in Bremen Offshore Foundations for Wind 4-6 Juli 2011 in Bremen

Wie genau entsteht Strom aus Wind?

Wie genau entsteht eigentlich Strom aus Wind?

Dieser Beitrag auf YouTube von TecTVChannel als Teil der Jugendportals technik-welten zeigt wie aus Luft und Wind Strom erzeugt werden kann. Schauen Sie rein:

Quelle: YouTube

SIE MÖCHTEN MEHR WISSEN? Erfahren Sie jetzt mehr zum Thema Wind-Energie. Besuchen Sie die Wind Energie Konferenzen: E/E Systems for Wind Turbines 11-13 Mai 2011 in Bremen Offshore Foundations for Wind 4-6 Juli 2011 in Bremen

Germany Could Be Powered Mostly By Wind

The blog http://www.energyrefuge.com/ has published an interesting post about wind power in Germany:

A report on Nasdaq this week said that Germany could produce 65% of its electricity with onshore wind if wind farms were erected on 2% of its total land. The statement was made by industry group Bundesverband WindEnergie (BEW), based on a commissioned study.

The study says wind power alone could not meet baseload power demand (due to wind’s fluctuating output), but BEW President Hermann Albers said during a recent conference that onshore wind power could replace all of Germany’s nuclear power plants, and that combined renewable energies
can replace nuclear power and some coal-fired power plants.

The study calculates that Germany’s wind power potential could reach 198 gigawatts, which would produce 390 terawatt-hours. The nuclear industry’s output was 140 terawatt hours in 2010.

In the wake of Japan’s nuclear disaster, Germany has been the most pro-active country in putting nuclear plans on hold and unplugged seven older nuclear power stations.

The latest figures show that Germany’s wind power capacity was 27 gigawatts at the end of 2010. Bavaria in the south of the country has the biggest wind potential, currently underused with a production of only 500 MW installed capacity.

(Source: http://www.energyrefuge.com/blog/germany-could-be-powered-mostly-by-wind by APasolini)