It's based on the now famous(!) Munty design, which you can read all about on here. (See page 3 for a good example without beans, page 4 for one with beans growing - gorgeous!). You may not see any similarity at first, but the principle is the same: the open side of the structure faces south and the beans grow towards the light. As the beans grow they are supposed to dangle down from the underside of the slope, making them easier to see and pick. I will post another picture when the beans have climbed to the top, so you can see whether it works!