Wind resource can significantly vary in countries each year but remains “very predictable” on a global scale, according to a new study whose authors suggested developers and investors should build geographically diverse portfolios to avoid being stung by quiet years in one region.

“Within a given country, the production of a wind farm can differ significantly from one year to another, up to 25%, due to the variation of the wind resource,” said Habib Leseney, CEO of Eoltech, the French wind and solar resource assessment consultancy that published the study.