While most of us are accustomed to the sign in nearly every hotel room bathroom prompting us to reuse our towels to aid conservation efforts, millennials expect more when it comes to environmental awareness — and they want it without a price tag attached."For the millennial generation, it is important that destinations are both environmentally and culturally sustainable. 'How do we preserve a place, yet share it with the world?' said Scott Lee, principal at SB Architects, a firm that has designed Ritz-Carlton and Auberge properties. "For this generation, travel is part of an enhancement to their sense of self, so it is important to get that balance right."Sam Cicero, founder of Cicero's Development Corporation, a hospitality construction company, noted that while Gen Y expects this kind of attention to sustainability, they aren't willing to pay more for it. Cicero helps his hotel clients consider what they can do to be more environmentally conscious and also please these discerning guests. It's surprisingly beneficial not just to the consumer, but to the property as well. "It almost always saves the hotel owners money when they take a look at the big picture," he said.From alternative power sources to aluminum water bottles, here are what some hotels around the world are doing to satisfy Gen Y's need for green.See: Top Hotel Trends to Watch in 2015At an increasing number of hotels around the U.S., Tesla electric cars are becoming the main house vehicle used to escort guests around town. In December 2014, InterContinental Los Angeles Century City added a new Tesla house car along with on-site electric charging stations for guests.Wyndham Grand Rio Mar Beach Resort & Spa also added electric car parking spots with charging stations for guests as part of a recent multi-million dollar renovation. Visitors may also choose to navigate the resort in new, eco-friendly Yamaha golf carts.Water bottles are a modern hotel room staple, but their environmental impact may be the reason for their demise. While budget travelers may shy away from imbibing due to the often exorbitant fees (upwards of $5 per bottle), the environmentally-conscious may be just as reluctant. Several properties are striving to tackle this issue by reducing disposable water bottle usage.Guests of Hotel Terra in Jackson Hole, Wyoming, are offered aluminum water bottles, which they can refill at water stations and purchase at the end of their stay. Additionally, the hotel uses aluminum pump-bottles for bathroom amenities.Meanwhile, the Hilton San Francisco Union Square recently installed "hydration stations" in all three of its hotel towers and its health club, and removed plastic water bottles from guest rooms. Each hydration station, which is filled with water from snowmelt in Yosemite National Park, has a small counter that shows how many plastic bottles are eliminated from landfills. At the end of 2014, more than 35,000 one-use plastic bottles were saved at the hotel.See: 50 Best Hotels in the USAHotel Santa Fe is the first property to use smart grid technology from Stay.Solar, a solar-energy distributor firm, to power all of its guest rooms with renewable energy. Its system matches the power used in guest rooms with third-party-certified renewable energy that has been fed into the grid from existing and new solar installations. Hotel Santa Fe Managing Partner Paul Margetson noted that the program costs its guests nothing, yet addresses their concerns about environmental responsibility. He said they've had positive feedback from all ages, including millennials.Hotel Terra also uses solar, hydro and wind energy and has installed a combination of fluorescent light bulbs that use 75 percent less energy than traditional incandescent bulbs in many fixtures.A keycard energy management system at Hotel Skyler in Syracuse, New York, cuts energy flow to guests' rooms when they aren't present to reduce waste. For guests that want to power up while out of their rooms, two outlets remain charged.Many hotels are using recycled and repurposed materials in the building process and throughout the decor. For example, Hotel Terra used recycled tires for roof shingles, reclaimed lumber in lobby pillars, recycled glass in bathroom countertops and soap dishes, and recycled seatbelts in cafe chairs.When building the W Retreat & Spa, Vieques Island, builders repurposed two existing hotels already on-site. The W's main entrance is constructed with wood from those buildings' decks, and even the previous hotels' doorknobs were reused as coat hangers for guest rooms. Designers also reused local art that once hung in the previous properties.Some properties are not only open to these green initiatives, but they're actually giving guests a reward for helping Mother Nature. At the Los Suenos Marriott Ocean & Golf Resort, which is set in a 1,100-acre rainforest in Costa Rica, guests can plant an almond tree as part of the hotel's "Reforest the Rainforest" initiative. Almond trees, a habitat for the area's scarlet macaw population, were in decline after the area went through a construction boom. Hotel staff say some guests are so moved by the initiative, they sometimes return to visit their tree.And if the environmental incentive alone isn't enough, San Francisco's Hotel Abri offers guests some "green" to go green. Each day hotel guests conserve and decline to have their room cleaned and towels changed, they receive a $5 Starbucks gift card.See: How Hotels are Capitalizing on What Business Travelers Value MostAbout the author: Lyn Mettler is an Indianapolis-based freelance travel writer who blogs at Go To Travel Gal. You can follow her on Twitter @GoToTravelGal or on Pinterest.