Walmart, that bastion of imported trinkets from China and everyday low prices on way too much mayonnaise, surprised many people in the environmental community when it announced a plan last year to develop a sustainability index for every product on its shelves. Since when, we wondered, does Walmart care about sustainability? Most likely, since the company realized that being green provides a boost to the bottom line and (unlike Sam's Club layoffs of 11,200 employees) some good press. And apparently Walmart figured that out long before it announced the sustainability index. Here, we take a look at some of Walmart's (and Sam's Club's) lesser-known green initiatives.

All 12 of Walmart's high-efficiency pilot stores feature this massive roof-mounted refrigeration unit, which uses a closed-loop system to increase energy efficiency and reduce overall refrigerant charge by 90%. The unit also reclaims waste heat to provide hot water in restroom and kitchen areas. There's still a long way to go before this high-efficiency unit is rolled out in all Walmart locations--there are over 2,300 supercenters in the U.S. But nationwide, 70% of hot water used in Walmart and Sam's Club stores is generated using waste heat from refrigeration.

Walmart recently launched a design challenge to its consumer electronics suppliers: create packaging that attracts consumers and reduces environmental impact at the same time. HP won the challenge for its Pavilion dv6929 Entertainment Notebook, a model available exclusively at Walmart and Sam's Club. The innovative packaging replaces Styrofoam and cardboard with a protective messenger bag made entirely out of recycled materials. HP's design cut down on product packaging by 97%, and now the company can ship three laptops to a box. It's a boon for HP and Walmart--the electronics supplier saves cash on packaging, and Walmart gets to say that it is the exclusive retailer of HP's ultra-green laptop.

This dual-mode diesel-electric hybrid truck is, according to Walmart spokesman Kory Lundberg, the only Class 8 hybrid in existence. The ArvinMeritor hybrid has both mechanical and electrical propulsion systems. The electric motor drive is used when the vehicle is operating under 48 mph. Once the truck goes faster, the mechanical propulsion system kicks in to help with the electric motor until it reaches highway speeds, when the truck goes into pure mechanical mode. The electrical system steps up to provide additional power during hill climbing. In addition to its work at highway speeds, the engine also charges an on-board energy storage system that provides power to the electric motor when demand is high. Walmart hopes to roll out the truck to its fleets--a move that could ultimately help the company increase its fleet efficiency by up to 25%.

Speaking of trucks, Walmart plans to test 15 Class 8 trucks in the Phoenix, Arizona area--they run on reclaimed grease fuel made out of waste brown cooking grease extracted from Walmart stores. So instead of clogging up drains, the grease goes to good use. According to spokesperson Lundberg, the trucks "provide Walmart the opportunity to develop a closed loop solution for the waste cooking grease it generates in its stores and Sam’s Club locations." That, and the trucks could ultimately increase Walmart's fleet efficiency by up to 2%.

The Love, Earth line of jewelry, sold exclusively at Walmart and Sam's Club, features a tag that allows consumers to trace the jewelry to its mine of origin. Consumers can go to the Love Earth Web site, type in the tag number, and receive information on where the metal in the jewelry came from before landing in a retail store. By the end of the year, Walmart is aiming for 10% of its jewelry to achieve the company's sustainability criteria and standards. Whether those standards are high enough, however, is still in question. Australian mining company Rio Tinto, one of the companies involved in the Love, Earth line, has been blamedfor environmental destruction and crimes against humanity resulting from a military blockade motivated by civilian resistance to one of its mines.

Walmart offers its own line of organic cotton baby clothing, George Baby Organic, as part of an effort to appeal to green-minded parents. The clothing isn't much more expensive than regular baby clothing because, according to Lundberg, "We don't think people should have to choose between a sustainable product and a product they can afford." Other green-themed baby products at Walmart include Parent’s Choice ORGANIC Infant Formula and Gerber Tender Harvest organic baby food.

Walmart probably isn't at the top of most people's lists for locally-grown produce, but the company partners with hundreds of growers across the U.S. as part of its "Locally Grown at Walmart" program. It's a project that has saved the company lots of cash. The stores used to source peaches from only a few suppliers, for example. Now Walmart buys over 12 million pounds of peaches from 18 different states--a change that has saved 672,000 food miles and 112,000 gallons of diesel fuel. The total freight and gasoline savings combined equal more than $1.4 million. And that's just for peaches.

Sam's Club used to have a hardware aisle, but customer demand triggered the chain to replace it with a Home Efficiency Center that features CFL and LED lightbulbs, efficient appliances, Energy Star washers and dryers, and even high-efficiency toilets that use minimal water. The aisle started out in 9 California-based Sam's Clubs in 2008--now it's in all of them.

The 3,564 solar panels on top of Walmart's Santa Ana, CA store provide between 20% and 30% of all energy needed by the facility. Walmart currently has 29 facilities with solar panels--27 in California and 2 in Hawaii. "We do a power purchase agreement with vendors," Lundberg explained. "They own and do maintenance on panels and we just buy the power. We can get power for at or below what we'd pay for traditional energy."

The so-called "Super Sandwich Bale" is a cluster of recyclable trash (loose plastic, plastic hangers, office paper, aluminum cans) sandwiched between two layers of cardboard. In the past, items contained in the bale were tossed into the trash because they are hard to collect for recycling. Now the bales go to a materials recovery facility where individual pieces are separated out for recycling. All in all, the bales have stopped 182 million pounds of plastic, 18.9 million pounds of plastic hangers, 12.4 million pounds of office paper, and 1.3 million pounds of aluminum from going to landfills.