A US gym has installed specially-adapted exercise bikes that recycle energy generated by people as they work out.
The Green Microgym in Portland, Oregon, aims to be a carbon neutral exercise facility through the use of solar power and human-generated energy from clients as they pedal and run.
"The big challenge has been finding the right equipment and adapting the technology," says Adam Boesel, the gym owner.
The science behind generating electricity from gym equipment is not new. For decades people have been using dynamos on their bikes to power the front and rear lamps. Generating power in a gym setting is based on the same principle.
"If you think about a gym, almost all of the exercise equipment has a spinning wheel, and if you can spin a wheel you can make electricity, just like a windmill makes electricity," explains Mr Boesel.
The gym has teamed up with a Texas-based company, Henry Works, which is in the process of developing what it has dubbed the Human Dynamo.
The device connects several exercise bikes with a battery that stores the energy generated as people pedal. External appliances, such as a TV set or a lamp, can then be plugged into the box, to utilise the power.
If you figure 100 watts per machine and you have 40 machines, that is 4,000 watts
Mike Taggett, inventor of The Human Dynamo
The exercise equipment generates DC power. The Human Dynamo uses an inverter to convert it into AC, which is required by domestic appliances to work.
"A lot of gyms have large spinning group exercises with 30 or 40 or 50 people exercising at the same time - and that's a perfect environment to use a machine like this," explains Mike Taggett, who invented the Human Dynamo.
"Everyone is working extra hard and you have a lot of people doing it at the same time, and a machine like the dynamo, if you figure a 100 watts per machine and you have 40 machines that's 4,000 watts.
"In a club that doesn't have high air-conditioning requirements, for example, they would definitely be powering the whole gym, during that time period."
Connecting to the grid
The challenge for the future is developing a mass storage system for the electricity. The most efficient way is channel it into the grid operated by a local utility company. The system is already used to integrate solar generated power with the electricity supply system.
"We are working on a new generation technology which we call fire wheel which is a really interesting way to connect the power directly to the grid, says Mr Taggett.
"Most utilities now have net-metering types of agreements for solar use or if you have wind turbines or something like that.
"So it would be a matter I think of notifying your local utility company that you have this human power fire wheel equipment installed."
The downside, for gym owners, is that the system requires a significant amount of capital to install energy-generating equipment.
"We've actually thought about it for years," says George Comalli, owner of Giants Gym, a large workout facility, also in Portland.
"We've always thought it was one of those things that the technology was probably out there somewhere, but was it cost effective?"
In a tight economy, the cost of harnessing human energy may be too high a price to pay for some. The challenge for the companies that supply the new generation of environmentally friendly exercise equipment is to make it affordable.
Inside the green gym
But Adam Boesel's gym is forging ahead. The facility also employs energy saving practices such as switching TV sets off and powering down exercise equipment when it is not in use. The frugal use of electricity alone saves the gym over 50 per cent on energy costs. Solar panels on the front of the building generate about a third of the electricity the gym needs to operate.
"We need to understand how much it takes to run light bulbs and all of the things that we take for granted, especially here in the United States," says Mr Boesel.
"We waste so much energy and by starting this gym and really being focused on energy conservation, there are so many things that I've found that are very easy for people to do to save energy."
The goal is to have the gym run solely on the energy it generates.
"Especially in these times, the ability to at least make some small impact on improving the future of not only this country or the community, but really the world…is a really motivating factor for people right now."
"I think in 20 years it's going to be standard for all gyms,' adds Mr Boesel.
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