This is very interesting. Natural sunlight pumps in about 1000 W max per square metre normal to the sun's direction. At the surface, it'll be lower at higher latitudes. You also need water, nutrients, heat and ventilation. On the surface, depending where you are, you'll get some or all of these for free!
Underground, you need to provide sunlight, warmth, water, nutrients and ventilation. Can you do this at less cost underground?
The Clapham example is somewhat of a cheat in that they are providing microgreens. A lot of the energy - probably about half, going into the crop comes from the seed, so they probably only need half the amount of light energy per hour compared to growing a crop to maturity. Also for microgreens, about 7–14 days is probably total time from planting till harvest. The same area will then give you 30–50 harvests per year. That's probably profitable.
I've not done the sums, but I suspect the economics might be more tricky for growing 'staples', e.g. wheat, corn, potatoes, rice, cassava etc., which provide calories in the diet as opposed to a bit of garnish.
It's an interesting concept nevertheless, and I suppose very topical when people are thinking about sending rockets to Mars.
www.bbc.co.uk
