What "efficiency" are you questioning? Solar farms can generate electricity for a fraction of the cost of coal and cheaper than the cheapest fossil fuel or nuclear plants on a levelized per MWH basis. How is that not "efficient" in any universe?
By efficiency, I mean comparing all the costs associated with having a solar farm, including real estate taxes, an interest rate representing opportunity cost of land and equipment, system maintenance, installation labor, accounting and management, insurance or an amount reflecting risk of damage from a variety of sources, and depreciation with the cost of simply paying for electricity as provided by a utility company. If the actual cost of solar is more than what you could by a ulility per kilowatt hour, I would deem solar as inefficient.