Animal waste such as fish heads and chicken fat may be the newest source of green energy. - 

Jeremy Hobson: Something fishy is going on across the pond. Private companies in the U.K. are going to power some of their store with leftover food. Maybe some day old fish -- seriously.

In today's Mid-day Extra, the BBC's Romi Levine reports from London.

Romi Levine: Here in the United Kingdom, retail giants like Walmart and grocery store chain Tesco are turning garbage into green energy. They're taking food waste, mostly unwanted stuff like fish heads and chicken fat, and they are converting that into electricity. Yes, it's green, but the companies are also doing it to save money. There's a landfill tax in the U.K. -- a hefty fee for companies that send their waste to the public dump. And by burning their garbage and turning it into electricity, Walmart and others can avoid that tax.

Caitlin Shepherd, co-founder of the food waste advocacy group This Is Rubbish says moves toward sustainability are commendable but she questions the humanitarian intentions.

Caitlin Shepherd: This 'waste not' mentality is certainly not contained to the United Kingdom or even Europe.

Bloomberg New Energy Finance says $18.2 billion have been invested globally in waste-to-energy initiatives in the past five years.

In London, I'm the BBC's Romi Levine for Marketplace.