How much energy can this produce?

[vipe21]

I am doing some research and I was wondering if someone could tell me how fast wind would need to blow into a fan to produce a decent amount of energy? Similar to wind turbines but on a smaller scale. Say if you had a wind turbine in a box that was idk... 4 feet high, 5 feet in length and 3 feet wide.


If the wind blew say, 50mph...how much power could that produce?