Added at start:
To answer this question at the depth requested could require a few reams of paper and its own website :-).
- The original statement about repowering was somebody's simplificatioin of one small part of a complex ongoing process. The basis for the claim can be seen in various sources but it is arguably not justified as a pithy one line summary of the factors that drive Danish wind power installations in and leading up to 2000. Read on ...
The original "Energy 81" incentive set targets and these were adjusted along the way by agreement and negotiation between government and industry.
The refence in (2) below gives a reasonably blow-by-blow description of the timing and nature of major relevant incentives. Repowering is not mentioned per se but you can easily see where it might fit in to such a program, laden with incentives to do new better things, create jobs, meet increased performance targets etc. Note the electricity production support scheme described as "only for gas from 2000" - that sounds like a very major reason to get any qualifying wind turbine work completed BY 2000.
(1) This UK Tyndal Centre report gives a reasonable brief summary of the issues and processes and timetables involved.
The role of political uncertainty in the Danish renewable energy market.
Of significance is their comment about per turbine capacities. The original legislation was framed with both total megawatt capacity and turbine count targets in mind. The growth in per-turbine capacity was not anticipated originally and repowering was a consequence of the better economics achievable by obtaining more power (and energy) from a given site.
Their section 2.1 notes
The first target for the deployment of wind power is found in Energy 81: 60,000 windmills to supply 10% of electricity by 2000. In 1990 a program was introduced to build 100MW of wind (Gronheit, 2002).
In 1996 the government and utilities signed an agreement for the installation of
200 MW. Utilities were already responsible for a target of 1,500 MW by 2005.
However, at the end of 2000 almost 2,300 MW wind capacity had been already installed.
It is worth noting that in 1997 the number of turbines was under 5,000, i.e. far below the target introduced in Energy 81. The increased size of turbines had not been forecasted by the legislation.
In 1998 utilities signed an agreement to install 750 MW offshore wind turbine before 2008. According to government’s forecast, these turbines would generate 10% of the electricity consumption. The agreement is considered the first phase of a total 4,000 MW installation before 2030. According to reports from the Ministry of Environment, the capacity for offshore wind is 12,000 MW or 30-40 TWh in generation terms (DEA, 2002).
(2) Here is a summary of key Danish legislative steps along the way from about 1990. Note that it is not possible to with certitude fit any one action to a repowering spike in 2000, but the relationship of the various actions to what occurred is traceable in general terms. Denmarks's Green industrial development
Here is a subset of those with arguable relevance.
1993 Wind turbine obligations - utilities pay high rate (85% of consumer price) for electricity from wind, plus subsidies, plus CO2 tax rebate.
1994 Green taxes, including energy & transport taxes - positive results in terms of emissions, industry behaviour and technological development. Continually revised. €10bn revenue in 2000.
1996 Energy21 policy - set target for 20% consumption from renewables by 2003.
1996 Electricity Act, supporting the development of all renewable energy technologies ~ utilities forced to give priority access to RE and pay 85% of consumer price. Utilities set target of 1,500MW from wind turbines by 2005 (met end 2000, with 2,100MW installed). Target of 50% of primary energy use from renewables (79% of electricity) set for 2030.
1996-7 Number of Government 'Executive Orders' - provide subsidies of 15 to 30% of the construction costs for renewable energy equipment.
1997 - 1999 Introduction of policies to support the research and development of new products and processes, and the uptake of these by Danish enterprises. Development of a Green Jobs concept.
1997 Programme for clean technologies, targeting SMEs - focus on new processes till 2000, then new products 2000-2004. Subsidies for development projects, green labelling and life-cycle analysis & method development. €35m for 2000 to 2004 phase.
1997 Action plan for ecological reorientation of buildings - subsidies for the development of products and processes. €10m for 2000 to 2004 phase.
1998 Green Jobs Fund - financial support (subsidies) for the creation of new jobs concerning environmental protection, including in product and process design & development. €4m a year for 1998 to 2001. 1,000 permanent jobs created.
1998 Energy research programme - grants and subsidies for the R&D of new and future (green) energy sources. €90m from 1998 to 2003.
1998 Electricity production support scheme - grants (per unit produced) for electricity production from renewables, bio materials and natural gas. €720m from 1998 to 2003 -
scaled down and only for gas from 2000.
1999 Electricity Reform Act - RE subsidies transformed and introduction of green certificates.
1999 Programme to support energy efficient enterprises - aims to encourage the design, development and use of new methods & processes. €250m for 1999-2003.
(3) Danish EPA climate change paper Includes ...
(4) The 2000 peak is not overly pronounced here (Wikipedia )
The motivation is summarised in passing in Repowering of Wind Turbines: Economics and Optimal Timing - reference details at end of this answer.
The development of wind power utilization in Denmark has been characterized by strong public involvement. The first target can be found in Decree Energy 81: the installation of 60,000 windmills to supply 10% of the electricity demand by 2000, a target that had already been reached in 1998 with fewer than 5000 turbines (Agnolucci, 2007).
In the early 1990s, a second target was announced by the government, namely to build 100 MW of wind power capacity, while in 1996 the utilities and the government signed a target agreement to install 1500 MW by 2005. Indeed, at the end of 2000, 2300 MW had already been installed (Agnolucci, 2007).
2012 - Energy policy in Denmark
2006 - Global wind report
Wind power in Denmark - Wikipedia
Why wind power works for Denmark
Wind targets for Europe 2020, 2030
Note: The aim of repowering is to make better use of wind resources on existing sites. Older sites can be "fully populated" by turbines in the 100's of kW range such that no new turbines can be installed. By replacing existing turbines with fewer much larger turbines with much higher mean heights an increased amount of energy can be intercepted for the same site area.
The picture below is from Europe Replaces Old Wind Farms
The amazingly similar [tm] cloud formations indicates that this is a conceptual rather than actual "after" example:
- Photo-illustration: Bundesverband WindEnergie.
A wind farm at Simonsberg, in northern Germany, would produce more electricity with just a few large turbines than it does with many small ones.
FCN Working Paper No. 19/2011
Repowering of Wind Turbines: Economics and Optimal Timing
Sebastian Himpler and Reinhard Madlener
November 2011 Revised July 2012
Institute for Future Energy Consumer Needs and Behavior (FCN)
School of Business and Economics / E.ON ERC