Much of India's early wind capacity sits on some of its best sites. Turbines of 225 kW to 1.5 MW were installed in Tamil Nadu, Gujarat, Maharashtra, and Karnataka from the 1990s onwards, at hub heights of 30 m to 80 m. Replacing them with modern machines on 120 m-plus towers and much larger rotors can multiply the energy from the same land, and MNRE policy has encouraged repowering since 2016.
For the owner, the lender, or a buyer, the question is not whether repowering produces more energy. It is how much more, with what confidence, and which assumptions could make the new P90 wrong.
1. Start from what the old fleet actually produced
A repowering site has an advantage a greenfield site does not: years of SCADA data. Wind speed at the nacelle, power output, availability, and curtailment records show how the site really behaves, including in monsoon and non-monsoon seasons.
That data has limits. Nacelle anemometers sit behind the rotor and need a transfer function, old turbines may have been derated or poorly maintained, and records are often incomplete. The assessment has to clean the data and explain every exclusion before it is used to calibrate anything.
- Use SCADA to check the long-term wind climate from the met mast or reanalysis, not to replace it.
- Compare actual production with the original EYA to see which assumptions were too optimistic.
- Separate grid curtailment and availability losses from wind-driven shortfalls.
2. Shear to the new hub height
The biggest single change in a repowering project is usually the hub height. Moving from 50 m to 120 m or more means extrapolating the wind speed well above most historical measurements. Shear in India varies strongly by season and time of day, and a single annual shear exponent can overstate the wind at the new height.
The most reliable approach is a new measurement at or near the new hub height, using a tall mast or a LiDAR, correlated against the existing long-term record.
3. Wake works in both directions
Repowered turbines have larger rotors and are fewer in number, so the internal wake pattern changes completely. They also sit among neighbours that may not be repowered for years. The wake model needs to include existing neighbouring turbines, and ideally test a case where those neighbours repower too, because that would change the wake the project receives.
4. Grid and land constraints
A repowered project often has more capacity than the original grid connection was sized for. If the evacuation capacity is not upgraded, part of the extra energy is lost to curtailment. Land rights, setbacks, and turbine spacing on fragmented landholdings can also limit how many larger turbines fit. These are not wind questions, but they belong in the energy case because they change the net yield.
5. What the lender will test
- Whether the long-term wind climate is consistent with what the old fleet produced.
- How the hub-height shear was established, and how much uncertainty it carries.
- Whether neighbouring wake and future neighbour repowering are included.
- Whether grid curtailment is treated as a loss rather than hidden in availability.
- Whether IEC 61400-1 suitability has been confirmed for the new turbine at the new positions.
A repowering EYA that answers these questions directly usually moves through lender review faster, because the technical advisor can see the evidence rather than ask for it.