Wednesday 1 September 2010

Human Powered Gym- Part 2

In Part 1 we examined the use of cardio machines (specifically a exercise bike) to generate electricity to power various items in the gym.
The conclusion of Part 1 was that a normal gym goer could power the machine, charge his phone and maybe power a light or two. Alternatively, he could power the machine and the stereo system.

That's for one person. What about if we have loads of machines, with some being used by people at a certain time, and others not (i.e a gym)?
Let's take the gym I go to as an example. It's a relatively small gym, with 6 upright bikes, 2 recumbant bikes (which I will regard as equivalent for the energy-generating purpose), 8 treadmills, 6 cross-trainers and 4 rowing machines, along with various weights machines and free weights.

If all of the bikes are used at the same time (they never are, but let's assume) then the total power being produced will be 56 x 8 = 448W.                                  [This 56W value comes from Part 1]

 However, I reckon that on average only about half of the machines are used at any one time. This means that we have half the power (224W) to use.


This will be just about enough to power the 4 machines (80?W), light up some of the gym (assuming 4 20W fluorescent tubes, 80W), power the music system (which is probably more than 30W as there are quite a few speakers- 50W?) and charge any gadgets the users want to (maximum of 8W).

Hang on, I hear you cry- what about the other machines?



Weights Machines: These are a bit tricky, as they are linear (i.e they go up and down, not round and round). Conceivably, you could use the same method as a rowing machine (you pull a handle and a flywheel spins). However, there is a major problem, brought to my attention in this forum post by andyfence. It basically says that weightlifting (generally) is a two way exercise- lifting the weights, and lowering the weights. Obviously, the weights end up in the same place after the exercise, so there is no net energy gain from weightlifting. What is actually happening is that you work to lift the weights, and on the way down the weights do work on your muscles. So, it is not really possible to produce electricity with weights machines.

Treadmills: At the moment, almost all treadmills are powered (i.e require power to operate). There are also self-powered treadmills, but these are usually either very old or "for the home" as they can be folded away easily (as they dont require a heavy motor). Interestingly, they are also cheaper. It is conceivable to produce energy from this method, but it presents many more difficulties than the bike and cross-trainer, so hasn't been tried out to the same extent. If anyone has any numbers or accounts of people generating power using a treadmill, please comment it below- I couldn't find any such examples with a quick online search.

Cross trainers: These provide a bit more hope, as they can already be self-powered (like this one). As you can see from the picture in that link, the user does turn a wheel (the lighter grey circle on the back part of the machine), and so power can be generated in the same way as for the exercise bike. I am going to claim that it is possible to produce the same amount of power using a cross trainer as a bike (56W). Again, if anyone has any concrete studies or accounts of this, please do comment.

So, with my (small) gym, there are 8 bikes (an average of which half are being used, producing 224W) and 6 cross-trainers, of which also about half are being used on average (producing 3 x 56 =168W), a total of 392W. So all in all, we could power the machines (7 machines, so 7 x 20= 140W) the lights (10 x 20= 200W) and the sound system (50W?).

However, in my gym at least, there is also a air conditioning system and 4 tvs working all the time. This means that unless power usage at the gym is also cut down (turning tvs off, using efficient heat pumps for air conditioning), the people working out at a gym will not be able to power it.
The above usage does not include gadget charging- I know this is not a feature of gyms at the moment, but with ever more powerful gadgets, it is more likely we are going to want to recharge them, unless major changes in battery technology occur.

Speaking of batteries, how are we actually going to get the power from the machines to whatever they are powering? The concept gyms from part 1 (this one and this one) use batteries to store the energy produced by the people. This seems like a good option, and to be honest there aren't that many other good ways of storing energy- it's one of the big problems for electric cars. Other options are flywheels, producing hydrogen or water reservoir (although this is a much larger-scale option). The efficiencies of these four methods are:

Batteries:                ~90%                         (wikipedia)
Flywheels:      up to 90%                           (wikipedia)
Hydrogen:           50-60%                          (wikipedia)
Water:                  ~75%                           (wikipedia)
I am not taking the figures above as absolute fact (as they are from wikipedia), and they will vary system to system.

The wikipedia page on grid storage is quite good, although it is referring to much larger amounts of energy than our little gym. I will not discuss energy storage in detail here, but I may well in a later blog post. For now, I suggest you look at that wikipedia page if you are interested.


However, I will say this about hydrogen:
It is important for people to realise that hydrogen is not a fuel- it is simply a way of storing energy, just like a battery. It also remains to be seen whether the "hydrogen economy" is going to become a reality. I am personally divided on my opinion about it- if the energy used to produce it (from water, H2O) is produced by excess renewables energy, then it's brilliant. However, if it is produced by burning fossil fuels (oil, gas etc) then it is not a solution at all.

 Economics_______________________________________________________________

I'm not an economist, and I'm not going to pretend to be one. All I'm going to do is work out the money saved by the gym by installing power generating exercise machines vs the cost of installing that equipment.


Money saved:
I put my postcode into this site and looked at the results. The average cost was about 8p per kWh (or 9p for specifically green electricity). I am very aware that these results are for a home, and I was also taking the "general" cost, not the "first X kW". Any more accurate energy costs would be appreciated. Note that kWh is a unit of energy (kilowatt-hours)- this is explained here.
Before we continue, we need to work out the energy saving. Remember that power is the energy produced per second. In other words: using a 1W device for 2 hours uses the same energy as a 2W device for an hour.
My gym is open from 8am til 10pm (interestingly, it is changing hours to 4pm-10pm due to lack of membership). It is busiest in the early evening, 5-9 or so, and is pretty empty the rest of the time. I am going to assume that it is, on average, half full for the 14 hours it is open. That's probably a bit ambitious, but let's assume.
The machines which produce energy were the cross-trainers and the bikes- the others are too difficult to produce a significant amount of energy at the moment. The value derived above is 392W. For the sake of calculation, I am going to assume that we can produce that extra 8W from somewhere, possibly the rowing machines. So we have a value of 400W produced by the gym. This is equal to 0.4 kW (as 1000W = 1kW)
The energy produced in the working day of 14 hours is simply 0.4 x 14 = 5.6 kWh.
By the prices above, this is a saving of about 50p. Over a year, the saving is  50p x 365 = £182.50.

The costs:
The cost of a new exercise bike or cross-trainer varies wildly, and there is likely to be a bulk discount for these machines. I am going to assume a cost of about £200 each. The system of generators and batteries will also be expensive, but there is no documentation about prices (that I could find anyway) as these products are not yet widely available.
Even with just replacing the 8 bikes and 6 cross trainers, (a total of £2800), it will take 16 years or so for the power produced to pay back the cost of these machines. This used gym machine site suggests that gym equipment is replaced every 3-4 years or so- I'm sure that the machines would change over the 16 year period too, and most gym users won't want to be using very old equipment.

Conclusions_________________________________________________________________

It seems, then, that from a money point of view, the Human Powered Gym concept is a non-starter. It would cost more to put in the equipment than would be recouped by energy production in a reasonable amount of time. This doesn't mean that the concept would not be successful, however. At the moment, at least, people are very concerned with "doing their bit to help the environment". Many people would therefore rather go to a gym where you are "helping out" by producing energy and the amount of people on the internet posting on various concept gyms articles shows that this is a problem in many people's minds. Unfortunately, though, most gym managers will be worrying about the bottom line above all else, and if the process will not produce money, it's not going to be implemented in the major gym chains.

Pity, eh?

No comments:

Post a Comment