It would easily be 4x more power if it were 8' high. If it is 2' high and 40w at 8' high it would 160w.

Carbon fiber aero tubing.

I can make one side of the triangle bag have a plastic frontal surface, or carbon fiber frontal surface.

So, make the triangle bag have a receiver for tubing parallel to the frontal surface area; carbon fiber tubing, perpendicular to the horizon.

And an attachable plastic surface area for improved aerodynamic efficiency of the air foil. I don't know what the part of a fixed wing is called at the back of the air foil where a fixed wing's top and bottom surface area terminate in a line. Really the best way to improve the power of this air foil is the improve the height of the air foil.

I was just thinking about a triangle bag that is also designed to be an airfoil for use in a tail wind and the in-frame triangle position.
My thinking started to become fun when I was thinking that the triangular shape gives the polyhedron three different frontal surface areas with three different lift/drag ratios.
The "cool design" feature would be that it just attaches to the seat post like those new bike packing bags that are already a part of bike packing. During the summer, how much gear do you actually need? I don't even need the capacity of a triangle bag and a sleeping bag in the handle bar bed roll. I just use a poncho for a bed sheet and a $10 sleeping bag with bungee cords. I want the triangle bag to replace the back pack I use for my clothes.

So, I would just choose one of the lift/drag ratios and attach one extra set of hardware for attaching to the seat post. The extra hardware is not worth the extra drag and mass if this is meant to be for capturing energy. The addition of frontal surface area would be less than 2m so it would be for use during strong tailwinds, and going fast.