Single Venetian blind sail generator

Once reached end of location, blinds open to let air through and sail pulled back to origin. During operation it pulls a cable that runs an electric generator or mechanical storage (such as a flywheel, compressed air or compressed magnets).

Benefits: Slowly moving parts, no need for special permits and no worries about birds. On building tops can catch a vast amount of wingspan with a very small imprint and small need for infrastructure investment.