It's the largest of its kind in the world, and it's happening right here in central Wisconsin.
The 15th Annual Energy Fair kicked off Friday in Custer. Visitors checked out the 200 exhibit booths and 11workshops that educate those interested in renewable energy.
"It's really an exciting event for us because these are people who care about the planet. They care about renewable energy and once a year we all come together in one place," says Tehri Parker of the Midwest Renewable Energy Association.
Parker says the fair expects to draw around 15,000 people this weekend, and some will come from as far as Australia and Germany.
Exhibit booths range from hybrid cars to solar-powered fans. There's also an area for kids to build renewable energy products.