Provided is a fluid flow energy harvester (10) comprising a crankshaft (12) and at least one vane (14) pivoted into a sail portion (18) and a crank portion (20) on respective sides of the pivot (16). Both portions (18) and (20) are operatively oscillatable about the pivot (16) when the crank portion (20) is operatively arranged facing into a fluid flow (22). The crank portion (20) is linked to the crankshaft (12) via a crank (24) so that operative oscillation of the vane (14) imparts rotational force to said crankshaft (12). The harvester (10) also includes a fin arrangement (26) which comprises a fin (28) arranged on, and configured to guide, the sail portion (18) of the vane (14) facing towards or in a direction of the fluid flow (22). The harvester (10) also includes a fin actuator (30) configured to control an orientation of the fin (28) relative to the sail portion (18), so that during oscillation of the sail portion (18), either a surface (32) of the sail portion or a surface of the fin (34) impedes the fluid flow (22) when a surface of the other is parallel to such fluid flow. In this manner, stalling of the vane oscillation is counteracted thereby facilitating continuous rotation of the crankshaft (12) during fluid flow (22).