Wednesday, November 25, 2015

Can you power for one day your house with the exercise from one hour bike ride?

A friend just posted this video in FB, from Billions in Change. I can't agree more with the philosophy of this group of inventors, but in the video/website, they claim to have developed a bike where pedaling for one hour would produce electricity for your home for the whole day. So, I had to check if this was close...
  1. Pedaling for one hour at a very good pace, say vigorous spin class, burns about 1000 calories (this is no average person). These are actually 1000Kcal, or ~1kWh. Let's assume that all that energy is stored in the battery, i.e., 100% efficiency.
  2. An average US household consumes about 30kWh/day. Of course, one can expect US to be a big consumer, so, checking around the world we find that the average would be 9.5kWh/day while a country like India you would still need about 2.5kWh per day.
  3. Just to run a energy efficient refrigerator, it would take 1kWh every day.  
So, we could qualify the wording as quite an an exaggeration. One probably would need a few strong family members to get there :)... But as I said, I do appreciate their intentions...

Nevertheless, taking this a step further, what if the cost of the bike went simply into solar power? Say that the fancy static bike was about $500. Just a number although we know you can get much cheaper... How much solar power you can buy with that? Based on this 2012 article (price is probably much cheaper now) the installed cost of solar panels was between $7-$9 per watt. So, $500 would give you about 80W of solar power. Considering that you don't need to have a family of athletes and that many of the poor countries are in areas of long sun hours, it seems plausible that the more traditional solar panels would do at the very least the same job for the same cost.

Actually, after I wrote this I found a more recent source of information. Claims that the solar system once installed (in Q3 2013) is about half the above price ($4.72/W) with most of that going to installation, permitting, etc... which traditionally would be much cheaper in lower income countries. In fact, the panels alone were $0.7/W!

Conclusion, it is very likely that dollar for dollar, solar would beat by now the above invention. Nevertheless, the bike is a reliable source (you get the electricity when you need it) and certainly healthy. :)

Comments welcome!! :)

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