I was curious whether they talked about the practicality of the whole setup, and they do, e.g.
> Electric kettles that run on grid power are often very powerful and boil water in a matter of minutes or even seconds. Boiling water using a bicycle generator will take a lot more time, but it’s perfectly possible. We acquired a commercial 12V electric kettle with a vacuum insulated reservoir of one litre. During a test, boiling water for one cup of tea took slightly more than one hour at an average power production of 60W.
To be honest, although I realize it would be ridiculous, but if inverters were small and cheap, I would personally prefer having an exercise bike plugged into the grid. That way my exercise energy would at least be useful to someone, somewhere.
but if inverters were small and cheap, I would personally prefer having an exercise bike plugged into the grid. That way my exercise energy would at least be useful to someone, somewhere.
You'd likely never produce enough energy to offset the energy used to create the inverter.
Just to come up with a rough estimate, if the bicycle grid-tie inverter cost $200, and 25% of that cost is due to energy @ $0.10/Kwh, that's 500KwH of energy wrapped up in that inverter. If you produce an average of 100W while biking, that's 5000 hours of biking, or about 10 years of biking 10 hours a week.
It might be more practical if you could harness all of the bikes in a busy gym where you could get hundreds of bike-hours of energy a day.
(Ok, I made some pretty big assumptions here. First, I don't know how much energy goes into making a product or how much it costs, and it's not all electricity, there's diesel and natrual gas in mining and processing raw materials, etc).
(Edit: my guess is probably not too far off, a typical phone in 2008 had around 180MJ/50Kwh of embodied energy [1], so 10X that amount for a 10 or 20 pound grid-tie inverter might be in the right ballpark. Aluminum alone has around 200MJ/kg embodied energy so a 2 pound heat sink would account for around 50KWh of the embodied energy of the device)
I have a philosophical issue with the embodied energy critiques. Primarily, it is that individuals who are trying to push the world in a carbon free direction would also likely prefer that the goods that they consume also be manufactured using carbon free energy. In essence it feels like they are taking the blame for decisions made by our predecessors when they are the ones trying to fix those bad decisions. In a sense, the blame for the embodied energy belongs to the previous generation that chose to use carbon based energy, with the exception for individuals who are advocating for the status quo. In that case, they should be accountable for it (not that they would care anyways).
Additionally, these analyses rarely take into account positive second order effects. For example if someone puts solar panels on a northern facing roof in Canada, they are unlikely to ever realize a breakeven point, and the project might not offset the embodied energy of the system (and associated emissions). But that purchase means more revenues and jobs for the solar industry. And in turn that means more investment and more economies of scale.
Basically, if we want to transition to a carbon neutral world, it is going to require a lot of people investing/purchasing projects/goods that do not make sense economically and might not initially be carbon neutral after accounting for embodied energy. Without early supporters we can only rely on government subsidies (which we already do, but obviously not enough). I personally don't think the free market can solve climate change, but if it is going to have a chance, we are going to need a lot of people to make these types of purchases/investments.
Also, another thing to consider is that the inverters lifetime is going to be directly correlated to the operating hours. So if the OP wants to hook up his exercise bike to the grid (assuming it is legal in their area), and then down the road decides to get some solar panels, that inverter will work perfectly fine for that purpose and have minimal degradation.
You can't deny that it's borderline foolish to spend much more energy to build a device to save energy, even if you think it could be repurposed in the uncertain future. If we're going to be conscious about our (carbon/pollution/etc.) footprint in this planet, we have to make rational decisions about our consumption. It doesn't mean we can't have fun, we just have to waste less.
We are talking about a handful of hobbyists and tinkerers making DIY systems. If they substitute a weekend road trip with a weekend of tinkering with DIY power generation at home, the fuel savings would more than offset the embodied energy of the hardware in their project.
But if everyone on the planet started doing it, I might rethink my position.
These calculations are all kinds of silly. No one should be exercising in the first place if you apply this kind of logic since humans are terribly inefficient (~25%) and the western food mix takes many many kJ to produce one kJ of nutrition.
> Basically, if we want to transition to a carbon neutral world, it is going to require a lot of people investing/purchasing projects/goods that do not make sense economically and might not initially be carbon neutral after accounting for embodied energy.
Large shifts like that don’t occur from people wasting money they have left over after entertaining themselves, they occur because the new way is much cheaper and the old way can’t compete.
The current situation is like a fishhook with many barbs. You can't go back without ripping your skin to shreds, so even though it hurts almost as bad, to minimize damages you have to push forward, embedding more hooks into your already wounded skin, in order to get to the smooth part of the hook so you can push it out and be done with it.
Too many people get hung up on the idea of pulling out the hook (the current carbon-positive processes that we use) and not about the ultimately least painful and most successful way of removing the hook (pushing forward with pressure to transition to carbon-negative systems even if in the in-between time that causes more carbon to be released into the atmosphere)
We would generate a ton of carbon to build and roll out an EV replacement for every ICE vehicle on the planet, not to mention the extraordinary expenses of generating enough electricity and charging plants for them.
If that were done in an amazing single year by military force or something, it would be the year of the most carbon production ever on the planet.
But the centuries afterwards with the extraordinary reduction in Carbon Dioxides and Monoxides and other exhaust gasses would be worth it, right?
That's the plan, work over time, get better every day, little by little, don't worry about perfection, focus on drawing closer to good enough.
> You'd likely never produce enough energy to offset the energy used to create the inverter.
Even if you did, the energy going into the bike isn't usually green. It's very, very far removed from the sun, especially if you eat lots of beef. Even if you don't, lots of gas was spent to get your food to your mouth, so you'd be much better off just not wasting the calories.
This argument is only relevant if you weren't planning on exercising anyway.
If you were planning on exercising, any energy you feed back is completely "free," regardless of your food source (minus the embodied energy of the equipment you hook up, as above).
Why? Exerting yourself and pumping out the watts forces your body to adapt to that and become stronger. Certainly better than being "efficient" and letting your body adapt to being sedentary.
Depending on what you eat you could still be well below the average environmental impact of a resident of an industrial nation. If you're vegan/vegetarian then 4000 calories a day from beans would be far less impactful than a 2000 calorie diet of meat.
Fit people need to eat more. Muscle takes calories to maintain. You can't maintain muscles without exercise. Your body expects that you're running down prey on a periodic basis. If you don't meet those expectations not everything will work as it should.
Humans evolved to move around a lot. Avoiding exercise to save food will lead to a host of ailments. Sarcopenia is a hidden epidemic among older people in developed countries.
I'm surprised they even got it to boil. I would have expected the heat to escape faster than it's added before reaching the boiling point. That aside, 60 W * 3600 s = 216 kJ. With ideal thermal insulation, that would be enough to boil about 600 ml of water. If they only managed to boil enough for a single cup (~300 ml), that's a rather inefficient setup they're using.
Yeah I'd suspect slowly charging up a battery with the bike generator and then quickly discharging the battery to boil the water would be quite a bit more efficient.
If it takes an hour to charge the battery or an hour to boil the water, it still takes an hour. Based on the previous comment of generating 60W, how much battery charging will that do? I'm really asking as I don't have the info at hand to do the maths. I'm assuming choice of battery comes into play.
I think that what they are saying is, if we remove the heat losses from the 1 hour boiling time and instead boil it in a burst of 5 minutes using a battery you would need significantly less energy overall. As a result, using a battery instead of directly utilizing the bicycle's electricity, would take significantly less time.
Internal resistance of the battery would be a significant problem, you'd need a fairly sizeable battery, and most lithium ion cells have a maximum discharge rate of around 1-5C unless they're high-discharge-rate cells which are usually more expensive and lower capacity.
Using a vacuum flask would dramatically lower heat loss.
Some cheap lipo cells can get you a sweet 60-120C discharge rate with a pretty okay capacity. They are also widely available on the used market, usually sourced from EV batteries or energy storage packs. But yes, for the typical 18650/cylindrical li-ion battery, this wouldn't be especially feasible at all
> That way my exercise energy would at least be useful to someone, somewhere
What very few people (who haven't worked on grid modeling) realize is that injecting energy into the grid from random locations tends to make operating grids harder and more expensive, rather than making it easier by reducing load.
This applies to everything from bikes (which on balance won't really make any detectable difference, and certainly won't ever make an economically positive contribution vs the cost of hooking them up) to home solar panels. Getting paid grid rates to dump extra solar energy back into the grid is actually a (very inefficient) subsidy benefitting solar panel owners. If the grid charges you fixed 10c/kWh for power, and has to pay you 10c/kWh when you dump solar surplus onto them, they're almost certainly losing money on you, and it's probably making the grid less efficient.
Here's a good starting point if anyone is curious why grid-dumping isn't socially efficient. Once you understand how socially efficient power pricing works (e.g. LMP pricing), it's pretty straightforward. https://www.eba-net.org/assets/1/6/6._[Savitski][Final][165-...
Not if the added inefficiency totally consumes the added clean energy and needs further non-clean energy to sustain it. You could end up in a situation where taking energy from residential solar panels leads to burning more coal than if you hadn't done anything.
> To be honest, although I realize it would be ridiculous, but if inverters were small and cheap, I would personally prefer having an exercise bike plugged into the grid. That way my exercise energy would at least be useful to someone, somewhere.
The only thing it would do is fuck up the grid. Grids are not sewers, they don’t work by having randos throw shit into it. Human power is way too low and unreliable to be of any non-hyperlocal use.
While impractical and not cost effective, having a bunch of bikes connected to the grid and randomly producing power would have no more of an impact on the grid than flicking a 60W light bulb on and off.
As long as he uses a proper grid-tie inverter, there's no reason the grid couldn't absorb his excess energy. It wouldn't be cost effective for him, though.
There are commercially-available exercise bikes etc. that have inverters built in[1], though they're marketed to gyms who want to buy a fleet of them it looks like. I am skeptical it'd be practical, but it might not be a terrible idea if you were buying your first machine (and not replacing a perfectly good existing one).
Your exercise is already useful to you (and those around you): it keeps you healthier and reduces future medical cost expected by the society.
It sounds like a fun project, so I'm not arguing against that, but I don't expect it to "help the Earth" in any meaningful way. Considering the fossil fuel usage by modern agriculture (and all the energy spent on delivering the food to our mouths), the net climate impact of using "human energy" is probably worse than an electric kettle.
Generating a dirty sine wave which will power an appliance is fine, but that's not the goal here.
The goal is to generate a clean sine wave which will benefit the grid when applied to it. This is probably impossible at bike workloads, and is in any case quite a bit more of a problem than just throwing an inverter at a DC source and calling it done.
200W isn't a lot of power. Most microwaves are 1KW. You'll need an inverter that can do that at least to run a fridge constantly and a microwave periodically.
I think you'd be better off plugging it into a kettle or coffee maker. At one hour per cup that sounds like good exercise and having a goal sounds like good motivation.
Alright - this is mostly off topic, but I see this website pop up here fairly frequently, and I really really hate the battery level indicator.
I find it makes reading the actual content far more difficult than it should be.
I get that it's intentionally drawing attention to the fact that this site is solar powered, but it pulls my eye to the line literally every time I scroll.
I end up closing the tab out without finishing the article - it bothers me so much.
Personally - I'd really love to have an option to hide it. I'm completely down for showing it by default - but after a minute or two on the site, the novelty has worn off and I'd really rather focus on reading your content.
I had no clue what you were referencing. I'm using Brave, and I have it automatically turn on the 'Speedreader' mode. When I disabled it, I then saw what you are referencing. I know the other browsers also have a mode that gets rid of all the junk and lets you just read the articles. Maybe you should give that a try?
I'm impressed at the relatively high efficiency of the system. Pedalling at 150 watts and recovering 100 watts of electricity is higher than I would have expected from such a simple system.
I'm very curious how much better the system would perform if the flywheel were attached directly to the drive-train instead of via friction roller. In practice this might not give much higher efficiency, but I would guess that the chain and primary sprocket would wear out slower than a tire friction-running a flywheel.
(They mention that they don't do this because this because it would be harder to build. I believe that. But I'm still curious.)
I've done enough bike wrenching to have raised an eyebrow on that.
What you need is two gears on the flywheel, rather than one, a gear rather than a friction wheel on the generator, and some way of tensioning the second chain which you run between them. This isn't the kind of harder to build that should stand in the way, although I will grant that the single gear was already on the wheel and changing that does involve, well, changing that.
This gets ~10% efficiency back, which for a generator is huge. It's probably the only efficiency gain left, other than a gear cassette to optimize power to a target voltage.
I'm wondering if the energy loss through the tensioning and/or internal gears is at all significant.
Instead, would it make sense to have a heavy flywheel, a fixie gear, and a way to slowly ramp up the power draw, so the power draw itself is the "gear" that allows you to go from a hard-to-start heavy wheel to a smoothly-running wheel?
> I'm impressed at the relatively high efficiency of the system. Pedalling at 150 watts and recovering 100 watts of electricity is higher than I would have expected from such a simple system.
It doesn't seem very surprising that motion can be converted to electricity at 66% efficiency. Normal power plants[1] can convert heat to electricity at 64% efficiency. It'll be much more interesting to see the end to end efficiency of this, ie. how many calories were consumed compared to electricity were generated.
A well-trained athlete can achieve about 33% efficiency in terms of calories used (not 'consumed' - we're talking about energy coming from glycogen and fat, in addition to whatever is eaten. The human digestive system can only process a couple hundred calories per hour before it starts diverting blood flow to the digestive system, which impairs athletic performance significantly.)
He claims 100W steady output but I'm sure more is possible.
One advantage of the bike over a rower is you can be doing other things at the same time, like reading a book, or tapping on a phone or keyboard. On a rower ,only passive activities like listening to music or watching a screen are realistically possible.
Leg muscles are the largest and most powerful in the human body and it's pretty easy for them to exhaust the body's aerobic capacity.
The number of muscles involved is not a limitation for longer duration power generation. There's aerobic capacity, but also glycogen and oxidative (fat) energy pathway efficiency. Experienced endurance athletes usually have quite high oxidative energy capacity/efficiency.
These sorts of projects are silly because even a decent average adult male will struggle to make 100-150W for an hour.
You're absolutely right that projects like these are silly as anything more than a fun tinkering exercise, but that 100-150W number is a low estimate. I'm fairly small and out of shape and can produce 180W for an hour. In-shape amateurs can do better than that.
Still not enough to be even remotely practical as a generation method, but substantially more than 100-150W
Leg muscles are the most powerful in he body, but they are not used to the extent on a bike as they are on a rowing machine. Additionally, they extend the work done by the arms and back, ie the work is not just the sum of the individual muscle movements, but the combined action.
Yes, it is silly and the author intimates that in the OP and the article I linked too, but I don't think meaningful power generation is the point of the exercise.
BTW a decent average male should be able to do 100W easily for an hour. I'm a (not particularly powerful) rower in my 50s and can easily sustain 150W for an hour, ie circa 120W accounting for generator inefficiencies.
150W is a pretty good workout sustained for an hour. Humans can do what, maybe 1000W or so at peak? Non-athletes, I mean. But nobody is putting out 1000W for very long. I'd have guessed that over an hour 75W-100W is more realistic. I recall playing around with a bike generator at the local power plant about 30 years ago and it was hard to keep a regular light bulb lit for any length of time.
I like to bike, but am just an amateur. My ftp is ~280W, which is what I can sustain for a long time without accruing too much lactic acid. I've held 200+W for hours. Just to give a baseline. A heavier person could probably do even more.
A track cyclist can reach 2000+W bursts, but they are freaks.
> Humans can do what, maybe 1000W or so at peak? Non-athletes, I mean.
1000W is “trained biker sprinting”.
> I'd have guessed that over an hour 75W-100W is more realistic.
The mechanical output which can be maintained over a work day is generally estimated around 75W. So accounting for losses 100We for an hours is realistic but vigorous effort.
One kiloWatt-hour of electricity costs around $.24 in my state. If you can output 100 Watts for 1 hour, that’s .1 kWH. Do it every day for a year that’s ~36 kWH, or about $10 in electricity.
One thing I think that could be changed here is a different storage medium. For example, flywheel storage instead of batteries, or compressed air storage, instead of batteries. Since batteries can't be charged faster than a certain rate, it creates a limitation. Of course, compressed air is only so useful and not so efficient to turn into electricity but, still an idea.
I know this is way off-topic but in Calum’s YouTube video about British Intelligence in Gibraltar he mentions a pedal-powered generator which was the primary source of power for the agents working deep inside the bunker.
It's not very high, obviously: energy is conserved and humans are not particularly efficient in converting food into energy. It's also not very effective: the article itself mentions that boiling the water for a single cup of tea took almost an hour at 60 Watts. Imagine how long you'd need to pedal to power a microwave with this, or a clothes dryer. Each of those would need at least 10x more power, so you'd be looking at 10 hours of pedaling for a single load of laundry. At that rate it's quicker to just do away with electricity entirely and wash your clothes by hand.
It could be useful in an emergency situation where you have more food than electricity though, or if you really really need something small that can only work on electricity like a HAM radio.
For a washing machine especially, the inefficiencies of turning mechanical energy to electrical energy and then back are going to be be pretty bad. If you could work out gearing to spin the tub mechanically, it might be better, although the back and forth motion of agitation isn't something I'd know how to do. Pumping the water and spin dry should be relatively simple, although getting enough speed for effective spinning may be a challenge.
> although the back and forth motion of agitation isn't something I'd know how to do
A smaller wheel linked to a larger wheel, where the smaller wheel is driven by the bike. As the smaller wheel spins, the linkage will move back and forth. If the second wheel is sufficiently larger, it won't be rotated enough on the push stroke for the pull stroke to complete a rotation, and will oscillate instead.
This still assumes, however, the perspective that a spinning tub is ideal. It's convenient when you're starting with rotational motion, like with a motor. But if we're looking for the most efficient way a human could power it, I'd suspect moving the clothes across a washboard with a static tub is way more efficient. It also has zero moving parts, outside of the human itself.
Mechanical washing machines were a thing before ww2. You might be better off finding one in an old barn and replacing whatever it uses (likely a crank) with a PTO you can link to a bike. Adapting a modern washing machine would likely be quite a bit more difficult.
a bit perhaps. but the drum is always connected to a belt that has a motor on the other end. and a washing machine is full of metal framing which you can drill and screw stuff to.
the hardest part would perhaps be to reenact the water cycle?
Honestly as long as it remains human-powered I don't see a lot of value to be gained. Humans just don't generate a lot of raw power.
The quickest way to improve this system would probably be to attach it to a set of wind turbine blades or a waterwheel, but "how to build a very poor wind turbine" is not nearly as catchy as a blog post title.
I think they made the right choice in designing it around providing an adjustable mechanical resistance.
As it's primary goal is for working out and charging cell phones I think it's best compared to a normal workout bike, which outputs all of the energy as heat (and sound).
Sure, the usable energy is minimal, but it's higher than zero and it can meaningfully top up your smaller electronics devices.
If I were to create such a system today I would take advantage of an inexpensive (~$10-$20) MPPT (maximum power point tracking) solar controller to regulate the unruly DC output of the generator or rectified alternator. It will sweep the input voltage/amperage to find the maximum power production for a given power source. These devices will automatically charge either a 12v or 24v battery and also provide several 2a USB ports for device charging.
Reminds me of the toaster challenge video[1] where Robert Förstemann, German track cyclist, powers a 700 Watt toaster for over a minute on an exercise bike. Absolutely insane.
The main reason I want a bike generator is to power my laptop, so that if I'm going to be sucked into web browsing regardless, I'll at least have to get some exercise in the process.
I guess the more sensible option would just be to use a bicycle to get around. Simply because with the car you require most power just to get the car moving, not so much the person inside.
> Electric kettles that run on grid power are often very powerful and boil water in a matter of minutes or even seconds. Boiling water using a bicycle generator will take a lot more time, but it’s perfectly possible. We acquired a commercial 12V electric kettle with a vacuum insulated reservoir of one litre. During a test, boiling water for one cup of tea took slightly more than one hour at an average power production of 60W.
To be honest, although I realize it would be ridiculous, but if inverters were small and cheap, I would personally prefer having an exercise bike plugged into the grid. That way my exercise energy would at least be useful to someone, somewhere.