Free Energy

Here is an interesting claim. 24 hours of energy for 1 hour of pedaling a bike. Can it be true? Well, no but lets have a look at the figures.

I an a regular at the gym and always start with 20 minutes on the rowing machine which shows how much energy I use in kcal. Working quite hard I can do 200 kcal of work in 20 minutes. 1 kcal is the energy required to raise the temperature of 1 kg of water by 1°C which is 4200 J. I therefore do 840 kJ of work in 20 min which is a power output of 700 W. Converting the energy to kWh gives about 0.2 kWh if I could keep this up for an hour I'd produce 0.6 kWh

So, how much energy does an average house hold use? According to shrink that footprint a European household consumes about 4000 kWh per year that's 11 kWh a day. However this device is being marketed in India where the consumption is 900 kWh per year or 2 kWh a day. So my rowing would only supply about 1/3 rd of the daily usage.

The photo shows the bike powering some appliances let's take a look at that.

18 light bulbs probably 10 W each = 180 W
iPad 12 W
iPhone 5W
Fan 15 W

That's 212 W so easily achievable with a bike. To keep these devices running all day would require 5 kWh of energy so my hour of high intensity rowing wouldn't be enough. What would you get for my 0.6 kWh? Approximately 2 light bulbs and an iPhone (which of course wouldn't need charging all day).

One thing is for sure, you can't get more out than you put in (first law of thermodynamics), in fact you can't even get out what you put in (second law). When I use the rowing machine all my energy goes to do work against friction and air resistance, ending up as heat. So the best way of using my energy would be to put me in a room that needs heating. Hmm, this could be my new job, the problem is the pay is lousy at 15 cents per kWh that would be 2 dollars a day.