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Schleswig-Holstein, Germany's most northern state, is an early success story in community wind development, through a union of government support, faltering agricultural conditions and strong winds. Many wind turbines were installed in the 1990s and, after 20 years of operation, are ready to be repowered.

Hermann Albers, president of the German wind energy association, is one of the early adopters of wind projects, and also one of the first to repower. Two years ago, he dismantled his 11 Enercon 500kW E40 direct-drive turbines, and replaced them with four Vestas 112 3MW units. In doing so, the power production on site has more than trebled, from 14GWh to 50GWh a year.

"I installed the first turbines in 1993, and soon became interested in repowering because of fast developments in German wind energy," Albers says. It was only within seven years of installing his 500kW turbines that 3MW turbines became available.

During the installation of the first turbines, Albers learned a lot about planning a project, including how long the permitting system in Germany works. "It normally takes five years, or sometimes up to years, as it did on my farm," which is why he looked at repowering only a few years after the first site was finished.

Brave decision

Albers came into the wind industry when he took his family's struggling agricultural farm and set about installing a wind project on the land. "The perspective for the future was that wind energy would provide a secure income," he says. "It was clear we were on a very windy site, only 800 metres from the dykes on the North Sea." The proximity to the coast was, and still is, a constant reminder to the local population of the dangers of a rising water level and the need to cut CO2 emissions.

In 1991, Germany introduced its first feed-in tariff system, which guaranteed around EUR8.5/kWh. He was not the only farmer in the region to take advantage of this rate and invest in wind turbines, but most of his neighbours restricted themselves to one turbine. "In those days it cost EUR250,000-300,000 for one turbine," says Albers. "I had planned two to begin with."

But his plans grew from two to eight and then on to 11. His choice of turbine also changed as new models became available, ultimately selecting the brand new 500kW E40 from German turbine maker Enercon. "This was a major step for Enercon. The first 500kW turbine, the first with a 40-metre rotor diameter, and the first gearless turbine. We closed the plans in 1992 with this, and we installed them in 1993."

Difficult financing

Raising finance was difficult, even with the generous feed-in tariff. "I talked long with the banks. My capital only covered about 8-10% of the investment," Albers recalls. In the end, he could only proceed by mortgaging his farm to the bank. The initial plan was to repay the investment over 11 years, based on the turbines generating electricity 100% of the time. "We soon learned that was wrong, and so the financial plans were wrong too," he says, noting that it took two years longer to repay. "Money was difficult because of the output and the technology."

In the 1990s, nobody knew how long turbines would last, or what would be required in terms of maintenance to keep them running. Owners and bank managers thought that once the turbines were installed they could just sit back and watch them generating electricity for the next 20 years.

The reality was rather different. Albers had bought some of the first machines to come off the Enercon E40 production line, and both he and the new German company had much to learn. Albers estimates that for the first five months, the turbines were achieving only 40% of their potential. They had to change blades twice and had one complete generator exchange. With no maintenance contracts, it was expensive for both Albers and Enercon. "And a lot of sorrow at the bank," he adds.

"In the early 1990s in Germany we all had to learn - the manufacturers, the permitters, the banks the turbine owners," Albers says. "Twenty years later we know so much more, enough to make recommendations as Germany pursues the Energiewende, the post-Fukushima transition to renewables."

Raising finance has become easier as the banks now understand the concept of a wind farm. "Interest rates are about 2.5%, very much cheaper than 20 years ago when I had to pay 6%. This means we can take risk in a new project and new turbines."

Planning to replace the 11 smaller turbines with the four Vestas 3MW turbines was in all aspects other than the land rights, effectively a new project. The foundations, roads, substation and grid connections were all new, and while the site was the same location as before, the permitting rules have become more stringent. The biggest difference is in the improvements to bird and nature protection, and noise restrictions.

The visual impact of the new project is much reduced, moving from 11 turbines to four, although their hub height has more than doubled from 60 to 140 metres, and rotor length from 44 to 112 metre. But the turning speed has decreased. The Vestas 112 runs at only 15rpm, compared with 40rpm of the Enercon units, he says, creating a calmer feel around the site.

That must make a difference to his family, who live on the farm, and who have one turbine closer to a residence than would be allowed on land owned separately. "These ones don't make as much disturbance, but for us it is our business. It is not a problem for us," he says. "If you have pigs, you have a smell. If you have turbines, you have noise."

Noise was an issue for the neighbours, and using quieter turbines in relation to capacity was one of the reasons he could increase the project's size from 5.5MW to 12MW. This was not just caused by the more modern designs, but also by a vast improvement in the noise programmes available. "You use this software to feather the blades a bit, lose a bit of power capture - 1-2% maybe - and they are much quieter."

Operating the new site is in a different league, and consequently the bank can be more certain about the expected returns from the repowered project, at least in terms of energy generation. Not only is the estimation of wind available in Germany more accurate, but the software to check energy capture is much improved. "We are using software from the same company as before, but it is better now because it is more precise."

Contracts with manufacturers for repair and maintenance can establish the cost of operation, something that was not available when Albers first ventured into the business. The concept of full guarantee has revolutionised the industry as far as operators are concerned, he says. "Vestas is monitoring that the turbines are running over 97% of the time." That was not available in the early days. "In fact, I think my first wind farm was one of the reasons that Enercon began to look into starting up the long-term guarantee it now operates," he says.

Cost of operation

"Today the right view for operating a turbine is that you have to reinvest 50 or 60% of the initial investment to manage the operation and maintenance. For the first project I began to make a profit after 13 years, so for the last six years of the first wind farm's life I was earning," he says. "I hope the new wind farm will need around 13 or 14 years to cover the refinancing of the project, and then we will see if the turbines have more than 20 years running time. Maybe after 15 or 16 years we will want to start the next repowering project."

"We need to continue to produce more wind power, cheaply and for many people. The next generation of turbines will have bigger turbines, higher hub height, longer rotor diameters. In just two years manufacturers have gone from 112- to 130-metre rotor diameters. This will all produce more efficiency and reduce prices."

And the old turbines? "We sold them to Poland and Belgium. There was a lot of interest in 19-year-old turbines. And we used the money to help finance the rebuilding of the new site."

The future of repowering in Germany is now at risk, with a reduction in the feed-in tariff and more uncertainty in the future. For those who are considering it, in Germany or elsewhere, he says: "Only consider it if the finance has been paid off on the first site. Talk to the manufacturers to find the best turbines for your site, and tie down your maintenance contract."