In an interview with German business magazine Capital, Rannou said having to file for bankruptcy, just months into his tenure, is one of the worst things any company CEO faces.
Rannou now has the benefit of hindsight, so does not place blame on Senvion's previous management for why the company suffered.
However, Rannou told Capital the manufacturer should have looked for third-party investment earlier.
"I don't think a medium-sized manufacturer like Senvion would be able to survive on its own in the long-run," he said.
"The wind industry has an ever-increasing need for capital, it costs hundreds of millions of euros to develop a new offshore platform. Would Senvion have been able to do that? No."
Rannou also questioned the need for so many western OEMs and said the industry needs consolidation.
Rannou stopped short of fully blaming the dramatic downturn of the German onshore wind market for Senvion's financial woes — "bankruptcy has a whole cocktail of causes" — but said the problems in the manufacturer's domestic market had "ultimately pushed us as a company over the fence".
He said the company could have seen that issues were coming earlier and changed strategy by not relying on Germany for the majority of its business.
"We know how volatile politicians can make decisions. Therefore, a company must always be prepared for different scenarios.
"The large dependency on the German home market with a sales share of around 65% was a big mistake for Senvion. Senvion started to internationalise the business too late," he told Capital.
Senvion is currently in the process of selling "selected onshore wind assets", intellectual property and service operations to Siemens Gamesa Renewable Energy, in a €200 million deal agreed in October.
The rest of the company remains up for sale.