Grains will be the last thing to change and that won't be for a very long time. Also you have to take into account increased yields, faster grow times, lower f

Grains will be the last thing to change and that won't be for a very long time. Also you have to take into account increased yields, faster grow times, lower fertiliser, pesticide, herbicide and tractor fuel costs. Your sanity check is way off. Solar panels only get about 22W/m^2 though out the year on average and they're more efficient than plants. Second the maximum plants can use is about 100W/m^2 and that is at maximum midday strength. Now lets take into account varying intensity of sunlight, growing seasons, leaf orientation, gaps between plants and other factors and your energy requirements are much lower. Research is still being done but most plants grow very well with the full red spectrum and 10-20% of the blue spectrum. This vastly reduces the energy required.