Renewable energy is energy that comes from natural resources, like sunlight and wind that are replenished at a faster rate than they are consumed.
Houston signed a two year agreement with Reliant Energy to buy more than 140 million watts of renewable power.
Laura Spanjian is Houston's sustainability director.
"I am charged with reducing emission, and so anything we can do to reduce that electricity useage, reduce the impact of the electricity useage is great. And buying renewable power not only decreases the cost of renewable power over time, it also supports the development of new renewable generation."
She says Mayor Annise Parker is trying to reduce the city's emissions in a number of different ways.
"And purchasing renewable power is a significant way to help us continue to reduce our emissions. We just reviewed data that shows that since 2007 & the last five years — the City of Houston reduced our emissions by 26 percent. So we are on the right track and we just want to continue."
Luke Metzger is director of Environment Texas, a statewide, citizen-funded advocacy group that strives to protect air, water and open spaces. He commends the effort underway here.
"We definitely applaud Mayor Parker and the city for making these investments. And this is getting some national attention and that's important I think, for not just the symbolic value, but Houston's already been taking steps to invest in clean energy with one of the largest electric vehicle charging station networks in the country, some of the strongest energy efficiency standards, and now, regaining the title as the largest purchaser of renewable energy for city operation."
He says switching to a more environment-friendly existance is sometimes not that easy.
"Historically, investing in clean energy has been a matter of cost, but wind prices right now are incredibly competitive with natural gas prices, so it's become easier than ever to invest in clean energy. And not only do you get clean air, but you are able to show leadership by making these investments. It shows the world that it's doable."
The purchase of renewable energy to cover half of the city's electric demand makes Houston the largest purchaser of renewable energy in the country.