Human-powered air-compressor and energy storage system
solar.lowtechmagazine.com
solar.lowtechmagazine.com
The main thing I wanted to know from this article is how much peddling it takes to keep the tank filled, and I don't feel like he answered that: how long is a peddling session? If it's 5 minutes, that's about four and a half hours of peddling to fill the tank. If it's 15 minutes, that's about 13 hours. And how often does he empty the tank? How long does it take just to keep it topped up in an average week? Details, man! He must know this if he uses the thing.
I looked at the prices of 80-gal 200 PSI rated tanks online, and the conclusion is...not great.
It's going to run you roughly $1000, for which you can realistically buy a whole set of cordless battery powered tools AND an outlet-powered air compressor on top of that.
Or you can get a bunch of empty propane tanks for a few bucks and call it a day…
> There are many used air compressors for sale that have faulty motors or pumps, and are therefore quite inexpensive
And the pneumatic parts/equipment:
> An additional benefit of using compressed air for energy is the low cost of air tools. The current trend is pushing toward more battery powered equipment, so people are selling off their “outdated” pneumatic tools.
"In a rapidly changing world where inexpensive and reliable energy going forward is no longer a given"
In such a world a steam engine will give you more useful output for the same input - you could literally burn your food in the steam engine and get more useful work vs eating the food.
This kind of thing only makes sense in a world that has not invented steam engines, or at the minimum using an animal that can eat grass that you can't. (And even then burning the grass will give you more work.)
[1] https://physics.stackexchange.com/questions/46788/how-effici...
And they can burn the entire fuel, unlike a person who can only eat the choice parts and must waste large portions. (For example corn - the person can only eat the kernels, the steam engine can productively use the husk and the cob.)
Also, your 20% figure is for energy absorbed after digestion (they check via oxygen consumption), but digestion itself is wasteful - lots of usable fuel is not absorbed when someone eats, and is emitted as waste.
It's really not even close.
It's a problem also for comparing bicycles vs cars - even though they are heavier, cars are surprisingly efficient compared to the entire production process of delivering food to humans (lots of energy is used in the farm).
If I remember my figures correctly 2 people in a car is more efficient than 1 omnivore on a bicycle. And a single person in a car is more efficient (less CO2 emitted) than a carnivore on a bicycle.
(The car comparison depends a lot on what the person eats.)
I'm perplexed by the comment about "empty tanks." In these systems the tank is almost never empty because pneumatic tools are pretty useless below a certain pressure; you can't just use them until they're empty. The impact guns I've used became tonka toys around 40 psi or so, if that.
The compressor might get shut off for the night, and sure, there are some air leaks - but the next morning when the shop opens, it's not empty.
Maybe the reason this dude's compressor is eating him out of house and home is because he's got a bunch of leaks he isn't addressing...
"Empty tanks" is probably just shorthand for "pressure too low to run the tools".
I’m both cases, you need to stuff the same volume of additional air into the tank, but in the 80–100 case, the resistance to the stuffing is higher.
At least I think that’s how it works. Assuming spherical cows and an ideal gas.
Except that it's not, because when you compress air you heat it, and all the heat energy is gone. This is why compressed air is a terrible energy storage method.
The hotter you heat the air (higher PSI) the more energy you waste.
Good note on the heat. I’ll wrap my whole setup in a blanket to recover that ;)
Another way to see that is to consider two tanks at different pressures that are connected to each other, and ask yourself why air will flow from the higher pressure one to the lower pressure one.
A 7hp compressor delivers in the range of 1m3/min@6bar or roughly 35cfm@90psi. The output can vary a lot depending on how the compressor is optimized though. Air tool air use varies as well, a sand blaster or paint sprayer will have different needs. But an air tool like a disc sander or die grinder or air hammer or impact wrench will be in the 5cfm range or a little under .2m3/min. So for an hour of tool use the compressor needs to run for 8.5 minutes or 2 hours and 50 minutes of cycling.
Some quick replies to previous comments: -The amount of pedaling needed to keep the tank topped off depends on the amount at which air is emptied from the tank. -A steam engine powered design would be cool to see, but not currently in my skill set. Steam power might also prove challenging in an indoor environment. -The total cost to build this machine was roughly $1000USD in parts, but I could have lowered the costs considerably by sourcing more used components. I also bought some parts to try that were updated to an improved design. I did just score another 80gal tank for $20USD, so the deals are out there if you take the time to look for them. -The pedaling effort is easiest when the tank is empty, and gets progressively harder as you build pressure. -The air system has no noticeable leaks, and I monitored tank pressure closely for a few weeks with no measurable pressure loss. -Energy will not get cheaper.
https://www.usinflationcalculator.com/inflation/electricity-...
Reliability is a little less of a given, but it's not unreasonable to expect grid operators to seek to continue making profits.
There's nothing wrong with exercising design skills to address living without reliable (or any) electricity. If nothing else, it's a hobby and keeps your mental juices flowing. If such bad times never happen, you still get the benefits that come with such projects. If they do happen, such skills can become invaluable. And there are many parts of the world where the reality is that something like this could be practically useful right now.
If you're really worried, buying a bunch of backup/spare parts in case we do lose global supply chains seems like a far more viable solution. If you're really that worried about losing access, there are steps you can take, like buying copper plates and photo-resist to make your own, really shitty solar cells, from "scratch", or buying 18650 lithium ion batteries and a 3d printer (along with a plastic recycler) to print your own tool batteries from renewable plastic. If bad times never happen, then what of what practical use is it to know which wild plants in my area are edible and which ones are poisonous, or which storage unit has 10 years worth of MREs inside?
People are free to invest time and money in whatever hobby they want, and in case of global (or local) calamity, my prepper friend is my going to be my first stop. I just personally don't believe it's an especially useful hobby, any more than, say, my hobby of Lego building, which has super useful practical applications in my daily life as a Duplo builder for my nephews.
> just buy a couple hundred watts of consumer-grade available solar [...]
For my own disaster preparedness, this is exactly what I've done. And I use it when I go car camping. But, as you point out, it's not exactly cheap so is less suitable for parts of the world that are more likely to suffer from infrastructure breakdown (or are lacking the infrastructure entirely).
But there's also an undeniable appeal to knowing how to accomplish things like high pressure air when you don't have electricity at all.
> If bad times never happen, then what of what practical use is it to know which wild plants in my area are edible and which ones are poisonous
I think that there's great value in knowing things like this even if it's not of practical use to you. Like knowing how to sew & repair clothing even if you never need to make your own clothes. It's amazing how often knowledge in one domain can give you insight into solving problems in other, completely unrelated domains. The more in your mental hopper, the better.
> I just personally don't believe it's an especially useful hobby
Sure, depending on what you mean by "useful". I think that all hobbies are useful in some form, even if that use is just exercising your brain.
Most mechanics use battery tools these days. Impact drivers for all but the biggest stuff, with handheld drivers having enough torque to work on a lot of suspension components easily, and there are even electric ratchet drivers now with sufficient torque for a lot of smaller stuff under the hood that require little more space than a hand ratchet, and no room for swing needed.
Battery tools are faster, quieter, easier to control. The system scales linearly in capacity, charging speed, etc. Add two mechanics to your shop where you're only using air? You're looking at thousands of dollars to upgrade a compressor, maybe a tank too.
If you're concerned about still being a mechanic when you lose power, put a solar panel on the roof, attach it to a MPPT solar charger and a couple of car batteries you recycle from customers' cars, and have an inverter ready to switch on if you need it.
What mechanic has the energy to pedal this thing just to work? What mechanic does so little work with their tools that the system can be infrequently refilled by a guy taking an hour or more to fill the tank?
This is at best useful for a shadetree mechanic and the article is fetishizing low-tech BS with no practicality. Replacing a 7hp compressor that was chewing up his electric bill...with something he pedals? If it was chewing up his electric bill, then there's no way he could replace it by pedaling.
My 30cfm compressor is 45db. Basically noiseless. You can easily have a normal conversation with it running. The air itself makes more noise than the compressor. It is happy with any duty cycle from 0-100%. Maintenance interval is about every 5 years. It produces oil free air. I can use it for breathing air (spray finishing) and not worry about things as much (I have proper gas sensors on that part anyway but it's nice to know i won't get poisoned by oil in some fashion)
I pay for this in efficiency. A oil sealed rotary screw would be about 30% more efficient (maybe a little more) but have some carry over and be about 65db. Not hugely noisy but still.
My pneumatic sanders have much lower vibration (30-40%), are quieter, smaller, weigh a lot less, and are essentially maintenance free. They can be repaired easily if I ever need to because they are very simple devices. The mechanism lends itself well to really good dust collection.
As a result They are much nicer to use than even the nicest electric festool and mirka sanders (I have both). The electrics are massively improved over two decades ago but still.
I don't woodwork or metalwork without mask or ear protection at all times so even if they were noisier I'd be fine.
The air drops are set up to be convenient from anywhere in the shop.
All that said, I do agree with the rest and the main point- for most people, battery is a better bet. I use what I do for convenience and comfort, not for cost or effectiveness.
There are times using air is just a better way of doing that than batteries.
Air tools are not maintenance free. They all require oiling devices inline, or regularly being oiled, and that oil gets into the shop and coats everything; you're also breathing that shit into your lungs. That's why in a lot of mechanic's shops, everything is greasy. Pneumatic tool oil.
You can buy a lot of batteries, tools, and chargers for the cost of installing a hard line air system. That still doesn't address the annoyance of the air hose, which is even worse than electrical cords - less flexible and heavier.
Hardline air system is ... not a significant cost? You make it sound like it's 10k.
Most shops are using a couple hundred feet of 1" copper, which has gone up in price but it's not that expensive. It would have been wildly cheap a decade ago (6 bucks a stick vs 20)
200ft of 1" copper is, at shitty prices, 200-250 bucks. Fittings for drops another 100 or whatever.
Time to solder it is annoying for sure, but you could press it if you want.
You could also go aluminum pipe systems, etc.
I've spent way more on battery based festool sanders (500-600 a piece) and drill/drivers than i did on hardline for the shop. The pneumatic tools were much less expensive as well. So i definitely disagree there.
Oil gets everywhere in anything working on metal, no matter what. I don't think that is avoidable - it definitely isn't fixed in any way by battery tools. I don't know a mechanic shop of any sort, battery or air based, that isn't a greasy oily mess. Battery tools require maintenance too. Heck, lots of mine want to be oiled regularly which is annoying without in-line oilers.
Your hate of air cords is more than mine - they seem equally as annoying as electrical cords. I can easily make well organized ceiling drops of electrical or air that keeps them out of the way.
If your shop is just running cords all over the place (as plenty of small operations do), it's, at least for me, equally, annoying whether they are electrical or air.
I guess we will just disagree.
I'm using scroll compressors, which are very quiet. Smaller versions are used in your HVAC system (assuming you have one).
Even basic ones are 49-50db. https://www.powerexinc.com/industrial/air/enclosed-scroll-sy... You can do better.
Most people's experience is with piston based reciprocating compressors, which are quite loud. 80+db.
Or little pancake compressors, which are the same.
Most shops move towards rotary screw because they need higher cfm than even 2 stage reciprocating can provide.
But I try not to be too knee-jerk critical! Because I am glad someone is doing the work of trying experiments to look at outside the local maximum of our current technology.
I'd think that an infrequently-used air compressor would be a fantastic place to use electricity from peak solar generation. That kind of thing seems closer to a sustainability local maximum than using human power.
Seeing as you need exercise anyway to stay healthy, it might as well be doing something useful.
With uBlockOrigin blocking all Javascript by default, there is no "email popup".
Myabe its there and I missed it.
https://solar.lowtechmagazine.com/2022/03/how-to-build-a-pra...
Well worth a read!