At first I thought that you were talking about growing vertically, but you probably meant something like a green house? Beyond extending the growing season, what else do they do to increase yeilds?
Heat is what everyone thinks of, however that's only part of the equation.
More importantly they maintain higher air moisture level around the leaves close to the saturation point.
This allows the plants to keep their stomatas open longer. This keeps the photosynthetic pathways operating for more time during the day. More time = more carbohydrate = more production.
They are also usually watered by drip irrigation as well. Providing he right amount of water, not too much or too little, greatly increases a plants yield.
A high tunnel is a unheated/cooled greenhouse/nethouse that is popular in every country not stuck in the dark ages with their agriculture. They come in many sizes. For example 100m x 20m ones popular in the middle east and Australia. In southern Spain they built ones that cover 20ha or more. A few in Poland were my favorite. They used split pine rails to build them.
Thanks for the reply. I can see this being a great way to go for a dedicated farm, which this post is proporting to do, but I am not sure I would want a high tunnel in my yard. I am on the wild-yard side of things and have wildflowers planted along one edge of my property, a milkweed garden, etc. I like to be able to see things growing and am not sure how I would feel about the visual block. I guess you could make one with more long-term transparent sides, but that would cost more $$.
As it is, we often have too large of yeilds when our four 4x8 raised beds really get going. Our issue isn't yeilds, it's the narrow width of peek yeild along with a combination of what we grow (not shelf stable) and storage systems (the whole pick early, store so it won't ripen, and ripen on demand system).
AFAIK it not just speeds up plant growth, but also extends vegetation period. It means for example that you can plant/harvest from March-October, instead of May-August.
Depending on the location, they can add 3-4 more months of a growing window. So double cropping or staggered plantings for a longer harvest window becomes viable.