# Why are sports clubs (gyms) are load, not generator, on the grid?

1. Dec 19, 2006

### EnumaElish

Wouldn't an extraterrestrial looking at the sports clubs think that people must be working hard to supply electricity? That they are running on giant dynamos?

But isn't the reverse true, that sports machines consume, not generate, electricity?

Is it merely a symbol of affluence (that is, another case of private benefit vs. social cost)? Or is there a cost/benefit analysis that would justify the direction of the flow?

2. Dec 20, 2006

### Danger

You know, dude... I think that you have one hell of a good idea there. If all of the equipment in a typical commercial gym could be outfitted with generators, it would significantly lower the outside energy consumption of the facility. I can't see it being enough to cover all needs of the building, but is should certainly offset the amount needed from the grid.

3. Dec 20, 2006

### Staff: Mentor

The only piece of equipment I know of that generates electricity is the bikes and rowing equipment. It would be a pretty complex (not to mention expensive) undertaking to design other equipment to generate electricity.

4. Dec 20, 2006

### wxrocks

Yeah -- running to generate electricity would give an odd running stride. But I could see bikes, stair climbers, ellpticals, all generating. Your weight machines could also use a magnetic resistance instead of actual weight and generate electricity (like a hybrid car).

You could go further and capture excess heat from saunas and hot tubs and maybe get something out of it -- but I don't know how cost effective it would be.

5. Dec 20, 2006

### Janus

Staff Emeritus
We had a simular discusssion some time back. After factoring in losses, it probably works out that the energy generated by a person on a treadmill or other piece of exercise equipment would barely generate enough electricity to run a 100 watt bulb for that same time. Or put another way, they wouldn't even provide enough electricity to heat the hot water they'll use when they take the shower they'll need to wash off their sweat.

It might put a small dent in the Electric bill of the Gym, but after the expense of installing and maintaining the generating equipment, it would be a long time, if ever, before it paid for itself.

6. Dec 20, 2006

### Danger

Are you sure about those figures, Janus? I know of some people who hooked generators to stationary bikes so their kids would have to excercise in order to watch TV. I seem to recall that they got about twice as much watching time as they spent pedalling, which would indicate an output of around 200 watts. Those were fairly sedentary little yard apes, so I would expect that fit adults pushing themselves should be able to do a lot better.

7. Dec 20, 2006

### AlephZero

This link suggests 200-400 watts is about as much as you will get as a long term average. The peaks output is a lot higher. http://cadlab6.mit.edu/2.009wiki/index.php?title=Human_output_in_variety_of_situations

It would probably be cheaper to put a solar panel on the roof than modify the equipment, considering sunlight can generate up to 900w/m^2.

In any case, all the energy is converted to heat for free, so the power required for heating in winter is reduced already!

8. Dec 20, 2006

### wxrocks

Well, there could be some truth to the heat thing as well -- You know the Mall of America has no heating system. It is heated by body heat and the waste heat from the resturants is exchanged back into the mall itself. So perhaps we should look at the gym of the future as more efficient by thinking of some of these things.

9. Dec 20, 2006

### FredGarvin

The heating aspect is really the only thing I think you would get on the plus side of the energy balance. It doesn't take very many bodies working out to create enough heat. We keep the thermostat quite low in the winter during our workout classes.

10. Dec 20, 2006

### EnumaElish

Installment and maintenance are sunk investments -- they are there regardless, and do not matter when deciding the type of equipment being installed. Put differently, they are not asset-specific investments, where the asset is a sports machine of type "L" (Load) or a sports machine of type "G" (Generator). So, installment and maintenance are not part of the cost/benefit analysis for the specific purpose considered here.

Saying that the amount of electricity is small may be missing the point. Right now each sports machine is a positive load. Even if each machine were to break even in terms of energy consumption (net consumption = zero), it would be a net gain; because it would take some load off the grid.

I see Russ's point about R&D costs; are we stuck in another type of "VHS tape" or "Qwerty keyboard" phenomena (an inefficient solution too expensive to reverse)?

Last edited: Dec 20, 2006
11. Dec 20, 2006

### Q_Goest

I'd have to agree with Janus. From what I've seen, the average person isn't going to generate more than 100 watts, but for the sake of arguement, let's make it 200 watts. That's 1/4 hp, quite a bit to maintain for any significant amount of time for the average person.

Now let's say the bike has a 50% utilization rate over a 10 hour day. That's 200 watts for 5 hours, or 1 kw hour. That amount of energy is worth about $.07. In a year (365 days) that's$25 worth of electricity.

Note also the time the generator is spinning is about 1800 hours. A typical low cost generator isn't going to last more than 2000 or 3000 hours, so you need a much better, industrial grade generator to get the 50,000 hours you'd need to make it worth while. They'll be much more expensive.

For \$25 a year, you're looking at something on the order of 20 year payback (about 36,000 hours of operation) without considering interest. There are much better ways of spending that money.

And that's exactly right. The amount of heat energy during the winter is going to have considerable value. That energy is taken out of the room as electricity where it could otherwise be used as heat. That pushes the payback period out much farther than the 20 years.

12. Dec 20, 2006

### brewnog

Setting aside the cost issues (and back-of-envelope calculations show me that the juice just isn't worth the squeeze), it'd be a technical nightmare to set up things like treadmills and rowing machines to supplement the conventional power supply in terms of frequency synchronisation. You'd just never get it to work.

Turn off some light bulbs instead, that'd be far more beneficial. Or cancel your gym membership and go cycling in the park instead.

13. Dec 20, 2006

### Staff: Mentor

That is only true if the cost is close to the same, and it clearly would not be for anything other than the machines that already have generators on them. Both the first-cost and the maintenance would be greater for other equipment with generators.
Well, the energy generated affects the cost-benefi analysis...

14. Dec 20, 2006

### Staff: Mentor

Depends on how big the TV is.

I'm in reasonably good shape (though not very big) and I don't ever generate more than 150W, if the bike is to be believed.

15. Dec 20, 2006

### Staff: Mentor

Good analysis. And when you start talking about putting linear induction generators on weight machines, the first-cost goes through the roof. And that doesn't even begin to deal with the difficulty in gathering together all that poor quality power and trying to get it to the grid (brewnog's point).

16. Dec 20, 2006

### wxrocks

You could also approach this from a grid stabilization perspective. There was a PopSci article talking about having plug in hybrids where the car would be an electricity storage device as well to supply short term surges in power demand and would charge suring lower points of demand -- thus allowing generation to run more steady state. Perhaps Gyms could provide the same -- store up power in the winter to be used to cool the gym in the summer... Just an idea.

17. Dec 20, 2006

### brewnog

You're not going to be able to generate enough electricity from gym equipment to power the lights, let alone enough to store it all up and cool the place in the summer!

I'm all for thinking outside the box, but do the numbers yourself. Failing that, trust the people who have already done the numbers.

Last edited: Dec 20, 2006
18. Dec 20, 2006

### EnumaElish

This proves you've never been old enough or poor enough. Electric trolleys had a flywheel system attached to brakes; as the car decelerated it changed from load into generator (put juice into the grid). AFAIK the new hybrid cars have a similar flywheel that converts heat into electricity to be stored. But the trolleys did the same thing at the grid level.

Last edited: Dec 20, 2006
19. Dec 20, 2006

### brewnog

Right, and just how much energy do you reckon a treadmill-driven flywheel is going to store? Then, how do you propose you rectify that to 50/60Hz, phase it, and synchronise it with the grid, whilst providing suitable backup for when the customer stops running, and ensuring that the demanded load swings are not imposed on the customer? Oh, whilst ensuring that this is all economically viable of course.

Modern hybrids do not have a flywheel which "converts heat into electricity". They just use a combination of conventional and electric propulsion, and some use some regenerative braking. A ten-tonne tram decending a hill is a far better prospect for such technology than a rowing machine. Do the numbers...

20. Dec 20, 2006

### EnumaElish

If they don't, then they should, just like the old trolleys (except the trolleys were connected the grid).