True, I only included kJ equivalent because some countries use kJ on nutritional panels instead of Calories. Actual conversion rate of human energy stores to usable power is, at a guess, more like
Calories * 0.25 * 0.6 * 0.8 - dt
where t is time, d is the self-discharge rate of the battery, 0.6 is the efficiency of the generator, and 0.8 is the efficiency of the battery.
A fun toy. But a normal exercise bike already converts the energy to heat. This heat then warms up the apartment.
Of course, with electricity, a heat pump for heating or cooling could be used, which is more efficient. But it’s not like the energy remains unused with a normal exercise bike, as long as it is cold outdoors.
TLDR: It’s a great concept but it’s about 100× more exhausting than you imagine.
I absolutely love stuff like this, and I also love cycling.
However, there is a big caveat here: I’ve been cycling for years and know my own power output:
Output – Time Window – Heart Rate
1400 W* | 60 seconds | 208 bpm
385 W | 20 minutes | 162 bpm
148 W | 6 hours | 110 bpm
*(yes, I know. My thighs are larger than some people’s torsos and it scares me too)
That means that on average, around 13 and ½ hours of pedalling to charge this thing. (2 KWh is also worth $0.68¢ where I live at standard residential rates).
Pedal power is amazing for things like charging phones or powering small devices and computers though, or for something completely meta: Charging up a eBike or electric scooter (120W), to then use without pedalling later.
Which then begs the question – if our “human/person power output” is like 150 watts constant … and the sun provides 1.4 kW/m² of energy – why not just lay down a 150W photovoltaic solar panel ($89) in the sun and sip on some unsweetened iced tea instead?
Pedal power is amazing for things like charging phones or powering small devices and computers though, or for something completely meta: Charging up a eBike or electric scooter (120W), to then use without pedalling later.
Skip that step and get a chainless digital drive bike. Same concept but you charge it as you ride.
Haha, I wish – they call it the hour record for a reason!
I’ve got explosive short-term speed, but it doesn’t last, and I get dropped within 20 minutes, as my power output dips below the optimized pros who can do 400W constantly for entire Tour stages.
While what we can generate is negligible. If, for example you had these in all gyms, that’s generating something. Not a lot, but more than nothing. Also all houses should have batteries and being able to remove the cost of a phone charge from what you suck from the grid would be nice.
It’s a really good business idea that I’ve had more than once – a self sustaining “green gym”.
Members would leave their electronic devices in special hardened lockers, plug them in, and then go to work out, and the power from central battery bank would then charge everything that’s in the lockers.
I also had an idea for credit system where the more power you generated the cheaper your monthly bill/subscription would be for the gym (only a few bucks here and there), or some kind of perks, like a free t-shirt once a year if you generated over 1 MWh (1000 kWh) or whatever.
The power generated by such a place would probably be negligible but it would give people the same emotional high as other pro-social tasks.
I think the power output of the earlier commentor is probably for a “basic” fit person. But what about those huge bodybuilding hulks? How much is the power output when they’re pulling maximums for a day?
In the best scenario, there’d actually br extra electricity to sell back to the grid, and the gym might be free for some of the “power-users”.
However I think as the earlier dude points out, stable power output isn’t that high and probably way more reliable to just put down solar panels, and a whole gym worth of generative weight lifting equipment would probably cost quite a lot.
I saw a report on a gym with the idea that the exercise equipment would power the gym. It wasn’t a good business model. They brought the reporter in and only turned on some of the lights - they had to be super stingy with electricity to get anywhere near net positive energy generation.
It’s still unlikely to pencil out to do this given the opportunity cost of actually going through the effort of building, buying and connecting these things, to be honest.
I’m fascinated by the idea but it’s important to remain realistic.
Personally, I think the best application of this concept is probably direct use of the mechanical energy, without converting the energy to electricity at all. See the bicimaquinas-concept: www.mayapedal.org/index.en
One of the wonderful things about bicycles is how extraordinarily efficient they are - very little energy is required in relation to how much transportation work you get out of it. This works against us in the case of power generation, though - little power going in means little power going out.
There’s not enough focus on direct energy usage or storage in general. If you want thermal energy, collect and store thermal energy. If you want mechanical energy, use that directly (and I guess compressed air and hydraulic head count as mechanical energy storage).
What I think would be cool for an exercise bike is to just have a power takeoff of some sort. Lots of bikes use a flywheel already, but even if they didn’t, but you could hook up a PTO to a flywheel or a charger so that in a pinch, you could charge your phone or whatever. Probably wouldn’t want to use it if you had a better option, but nice to have in an emergency. Like those wind up flashlights.
If you look at the “about us” section on their site, I don’t see anyone with human performance expertise (though who knows if any of them are hobby cyclists with a huge depth of knowledge). The seat and pedal design is definitely geared more towards aesthetics than performance, too. I probably wouldn’t want to do more than a hundred watts on there.
I definitely appreciate that the portability and aesthetic quality is a major design consideration for them, though. I see this more as a battery pack that you can pedal, than a bike that stores power.
As it seems to double as a balcony solar inverter if you add some PV pannels the price seems to be not so bad. A 2KWh LiPO4 battery, charge-controller and inverter alone will cost you at least half of the asking price.
It’s not about saving money. It’s about using the energy that would otherwise not be used, and incentivizing exercise. If I could keep my phone charged from exercising, that would be cool. But yeah the price point is quite high.
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