Wind Farm Repowering

Wind farm repowering programmes are underway in more mature wind markets such as Germany to repower older wind farms with new turbines.  Repowering is a cost-effective way of re-using existing brownfield sites (which are typically the best sites, having been the first to be developed) through the use of larger and more efficient turbines.  Site output can be increased materially as a consequence of increased capacity and/or improved capacity factors arising from the use of more efficient and higher hub height turbines.

A 2-MW wind turbine coming off the production line now with a rotor diameter of 80 metres can generate four to six times as much electricity as the 1-GWh annual yield of a 500-kW wind turbine with a 40-metre rotor built in 1995[1]. For example, in Germany in Schneebergerhof in the Rhineland-Palatinate region, Juwi has replaced five Enercon E66 1.5-MW turbines with five 7.5-MW E126 machines, amongst the largest operational wind turbines in the world today. These generate more than six times the power of the old turbines — around 20 GWh annually instead of 3 GWh[2]. Because the original sites already have permits in place, plus the local community is usually supportive and well-accustomed to having a wind farm in its vicinity, the permitting process time in many countries for repowering is considerably easier and shorter than for new greenfield sites.

Growth in wind turbine power

Most of the global cumulative wind power nameplate capacity has been recently installed, but a sizeable percentage — nearly 17%, or 73,957 MW — was at least 10 years old in 2015.[3] One consequence of this technology’s aging is reduced performance. According to some experts, wind turbine load (or capacity) factors decline markedly with age. A 2014 study from the UK’s Engineering and Physical Sciences Research Council of load factors recorded for 282 onshore wind farms in the UK between 2002 and 2012 found that wind turbines lose 1.6% (±0.2%) of their output per year, with average load factors declining from 28.5% when new to 21% after nineteen years. The Council noted that the trend is consistent for different generations of turbine design and individual wind farms.

Global installed base of wind power 2000 – 2015[4]

Typically, the cables installed to transfer power from the wind farm to the grid were specified at double the maximum power output of the original turbines installed; clearly, with an increase of up to six times output through re-powering, many existing cables will have to be replaced. This represents a major opportunity for CTS with its characteristics of low loss, potential to transmit power at lower voltages and its ability to be buried over greater distance than conventional AC cable.

Based on the latest internal company test data[5] from the Type III cable, the Company has modelled the following benefits of using CTS as opposed to conventional cable in typical wind farm re-powering scenario, where there is a    4-turbine wind farm installed approximately 15 – 20 years ago with turbines of say 800kW output. These turbines are replaced with 4 new turbines of 2.8MW output, i.e. upsizing the aggregate capacity of the wind farm from the original 3.2MW to 11.2MW (all subject to securing new planning consents, lease extension, grid connection capacity, etc). The cable to the grid injection point will have to be replaced in any case because the original cable will typically have been specified at double the peak power output (i.e. c.6.4MW). After re-powering, the installed capacity has roughly trebled, rendering the original cable obsolete.

The tables show that using CTS instead of conventional cable for that one 4- turbine wind farm could permit potential delivery, using a 30% utilisation factor,  of an additional £17.22m of revenues at UK retail price of £0.15 per kWh over the projected 20-year life of the turbines. CTC may be more expensive to produce as the copper strands are coated with dielectric. On the relatively short lengths produced for testing, the dielectric coating added 20% to the material cost of the conductor only. All other elements (sheathing, production costs etc.) remain the same. In large scale production, the incremental cost of CTS over conventional cable is expected to be in the range of 5% – 10%. Further analysis of this is ongoing.

Before re-powering (assuming 30% utilisation)

After re-powering (assuming 30% utilisation)

Taking the German market as an example, it is clear to see why re-powering is such a strong growth area. In 2016 there were 1,624 new turbines added to the German grid of which 238 were for re-powering projects. The average distance from turbine to grid injection point in Germany is estimated at 10 kms.

Onshore wind installations in Germany – turbine size

Share of re-powering in German wind farm market and number of new turbines installed


[1] Renewable Energy World website

[2] Electric Power website, January 2016

[3] Global Wind Energy Council website

[4] Global Wind Energy Council website

[5] NOTE: not yet verified by NPL