Farming solar energy in the Fens

Something else I saw from the train last week was a field given over to harvesting sunshine.

Yes, you say, isn't that what all crops do? Indeed, but here, between Ely and Cambridge, is a vast array of photovoltaic panels, angled to catch the maximum amount of sunlight and generating electricity. Except at night.

I'm uncomfortable about fertile fen farmland being turned over to this non-food product. Couldn't the panels have been erected on a brownfield site, say, or on top of a former landfill site?