I cannot fathom how growing indoors is going to be more efficient, you need light, and where is the power for that light going to come from? Solar panels? Why not plant the crops outside and skip the losses?
This went unanswered. It's a good question. Unsurprisingly, the sunlight (approximate power 1kW/sqm) contains all wavelengths of visible spectrum plus infrared. But surprisingly, plants can only use a tiny part of the spectrum, I could throw in an example number of 10% (feel free to do a literature research on this; but it's on the right ballpark). OTOH, a solar panel is capable of utilizing the complete spectrum; the efficiency is calculated assuming this. LEDs are capable of producing just the narrow wavelength bands plants need (basically deep red and deep blue).
So even when you are losing a lot of energy in the light->electricity->light conversion, you are not only doing that conversion; you are also doing
wavelength conversion; so you can increase the
efficiency of the plants, by converting light plants can't use into electricity then back to light plants
can use.
Do the numbers; if a plant uses 10% of the 1kW/sqm, you have 100W/sqm in direct sun. Now if you convert 1kW/sqm using a 22% efficient solar panel, then use 60% efficient LEDs, of which the plant is able to use 90% of their spectrum, you end up with 119W/sqm.
So while you could quickly assume producing energy with solar panels then burning that in LEDs would be extremely wasteful and lossy, this isn't actually the case, the numbers are very close. Through the (slow but real) advances in LEDs and solar panels, the gap will widen in favor of the indirect solution, despite how ineffective it
sounds to laymen.
Even with similar efficiencies, there are additional benefits though. Electricity is a great and flexible energy transport medium (as used in large ships where diesel engines run generators, which supply power to electric motors, instead of massive drive shafts!). Similarly, you can place LED plant lights completely arbitrarily, for example, for vertical farming. It's way easier to provide optimal lighting than playing with large mirrors, light pipes, and so on.
Obvious advantage is that you'll be able to exactly control the energy used to grow the plants and you can sell any excess production to the grid for others to use. Decoupling the plant growth and sunshine is also great; electrical power is easily transferred thousands of kilometers with little loss.