Introduction

During my initial days, I took part in the development of a large wind park in India called ‘Vankuswade’. Now carries a total 259 MW capacity, on the hilltop stretching 21 km at Satara district in India. Those days the site was populated with 263 numbers of 350 KW turbines.

Would it have been a site with 263 numbers 2.1 MW turbines of the same make, the wind park capacity would have six-fold higher. The principle of repowering is based on this very opportunity.

Wind Park
Image by Gordon Johnson from Pixabay

A little bit of Back Ground

You may recall that the “world’s first” machine to convert wind energy to electricitywas built in 1887. Since then, this technology is continuously evolving in this field.

India tested an 8 KW prototype in the year 1961. And today majority of the supply is of 2/2.1 MW capacity. A 3 MW is on the way.

Globally, wind turbine technology development is progressing at a rapid pace. Today,multi-megawatt turbines are plenty available. Even a turbine as big as 20 MW is under making.

Rotor diameter and tower height ( hub height) are also increasing to capture more energy making less windy sites viable. The rotor diameter of modern turbines is increased up to 140 meters, comparing to 80 to 100 meters in the old turbines. Hub heights have also increased from 53 meters (of older days) to 160 meters.

I can recall the first 2 MW turbine introduced in India (manufactured by me) was with an 88-meter rotor dia. And now the same machine is having a 97-meter rotor dia. with an increased hub height of 120 meters. 

Today’s advanced turbines provide better availability (up to 98 per cent) and improve the capacity utilization rates to 30–40 per cent at lesser operation and maintenance costs.

repowering tower
Image by Hans Linde from Pixabay

What is Repowering

Wind turbine repowering means replacing old & smaller machines with modern large turbines; to harness more energy from the wind at a comparatively lesser cost. 

In cases, it is also done by replacing or retrofitting some components that can improve the performance.

The aim always is to increase energy production from the same wind park at an acceptable levelised cost. The extended life of the wind park comes as a bonus.

Since 1961, a couple of thousands of wind turbines have been erected across the country. A big chunk of them is also of sub MW capacity and have already crossed their designed life span.

Today, India has a total of 38.8 GW of installed capacity and, at least one-fifth of these turbines may have been halfway through their life span.

The fact is that, along with ageing, the load factors of the turbines decline. Consequently, performance reduces. A study done by a UK university reveals that a wind turbine loses 1.6 per cent ( ± 0.2 per cent) of its output per year due to ageing. And at the age of 19, its average load factor declines from 28.5 per cent to 21 per cent.

So why not go for replacing these old machines with higher capacity wind turbines?

Repowering Options

Lifespan extension: It means reconditioning the vital parts and elective replacement of the control system for better reliability & efficiency in performance.

Partial replacement: It is like installing a new and improved drive train and rotor along with peripheral components. Worldwide this method has been practised for some time.

The limitation of this process is that we cannot mount longer blades on a smaller hub beyond an extent or cannot put a 2 MW drivetrain on the top of a tower designed for a 350 KW machine.

Complete replacement: It is nothing but the complete dismantling of the older one and erecting a higher capacity new turbine at that location.

Whatever the case may be, repowering aims to get improved turbine performance and better revenue. GE said they could increase annual energy production by 20 per cent and turbine availability by 1.5 per cent after repowering.

Global Repowering At A Glance

Denmark and Germany are the global pioneers for repowering. Since 2001, in Denmark, 70 per cent of the older wind turbines were repowered. The government has backed this initiative with a power purchase incentive.

Germany also did the same thing. The country amended its Renewable Energy Sources Act in 2004 to support repowering.

In the USA since 2017, GE alone has done repowering of more than 2500 wind turbines covering 4 GW of capacity in 40 wind parks across the country.

NextEra, another large power utility company, has repowered its 60 per cent fleet in the past five years. In the last year, it has done 1.5 GW of repowering. And has a plan for 2 GW this year.

repowering blade
Image by Marco Federmann from Pixabay

India’s Wind Scenario

India has a target to create a wind energy capacity of 140 GW by 2030. The country is lagging; the wind power sector is ailing. For the last four years, yearly capacity addition was less than 2 GW consistently.

There is even no visibility that India can attain the asking rate of 11 to 12 GW capacity addition year on year till 2030.

Repowering of older wind turbines can boost some generation capacity in this situation.

Until 2000, most of the wind turbines installed in the Indian market were 500kW or smaller. As a result, major windy sites are now occupied by these smaller turbines of about 3 GW total capacity.

According to an estimate, a total of around 3 GW capacity of these smaller wind turbines has filled up the majority of high wind sites limiting the energy harnessing potential of the parks. When we extend the range up to 1 MW & below, this estimate comes to around 10.5 GW.

Replacement of all these sub MW machines — with turbines of 2 or 3 MW size — can add 30 GW extra in the renewable portfolio without much problem. India has a manufacturing capacity of 10–12 GW of wind turbines per year to feed this demand.

Why Nothing Moving?

It is unfortunate that despite declaring the repowering policy in 2016, India couldn’t start any activity so far due to various commercial and execution related hurdles.

The first one is ‘transmission connectivity’. The connection of older turbines is to 11 kV lines at various states of the country. I have seen this, particularly in Tamil Nadu.

To take up repowering projects, first, these transmission infrastructures are needed to be upgraded. Who will bear the cost of up-gradation? It is yet to decide.

The second one is ‘ Legacy PPA’. The tariffs in old PPAs are very low to justify the investment for repowering. On the other hand, ‘Discoms’ and captive off-takers will prefer to stick to the old tariff till it expires.

After installing bigger wind turbines, it would be complex to reorganize the ownership and capacity share of new turbines and the piece of land owned.

The third one is ‘ ownership of land & turbines’. If we take an example of the ‘Vankuswade’ site, there are multiple owners and, some of them own even only two, three or eight turbines of 350 kW size.

After installing bigger wind turbines, it would be complex to reorganize the ownership and capacity share of new turbines and the piece of land owned. It will call for renegotiation and a new lease or sell agreement with multiple owners. Again a complex task.

The fourth one is ‘waste disposal’. The process will generate a considerable volume of non-biodegradable waste. How to handle it in an environment-friendly way? So far, the practice in India is to use it for landfills. But this practice won’t be sufficient to support mass repowering.

Probable Solutions

A new business model protecting the interest of all stakeholders would potentially solve the problem.

The extra energy generated due to repowering could be sold to new buyers at a revised tariff while honouring existing PPAs for Discoms and old buyers.

Installing a “Special Purpose Vehicle (SPV)” to manage the ownership of projects (post repowering), distribution of equity ownership and revenue sharing in an appropriate proportion etc., could also help.

Conclusion

Repowering is a must-do for India. It offers a practical way to free the windiest sites (occupied by old & smaller machines) for bigger & advanced turbines, thus increase energy production capacity extending the wind park life.

The commercial viability of repowering projects is proven in the EU & the USA. So India need not be hesitant to invest.