Efficient compressed air turbines/motors

[swbluto]

Back to harvesting the pressure? If air is so inefficient compared to water (and you don't have much elevation to play with, or ground water), why not use the excess solar to pump water into a tower? Then make a mini closed system hydroplant. If it's potable you'll always have great pressure in the shower too

Again as mentioned above, you can spend 10s of thousands of dollars on the tallest tower with the greatest sized tank at the top, and this stores the energy of a shoebox of 18650s, while wasting at least 30% of the energy it stores, and another 30% wasted on recovery.

Agreed. Towers are too costly. Holes seem to be a far more economical way of achieving height than towers, just due to the fact the ground largely forms the supporting structure instead of the tower's many (costly) wooden/metal beams.

But, now that we're started on this idea of pumping water...

What if we dug a 100' hole, and somehow created a large reservoir underground for water (I don't know how...), and then pumped water up and down?

Hmmm....

I'm starting to think a simple well might be able to serve the same function somehow...

And I could use a well for my future vineyard.

Now I need to figure out how to install water turbines in the well, to see if it's viable and at what expense.

Are wells really this large? They also make it look like the water table is 10-20 feet below the surface, I thought they were more like 200-300 feet in my area?

Starting to do research, it appears first water is almost always between 30-100', it's the aquifer that's usually 300+ ft. down in my area.

I suppose that's not too bad. Mounting the water tanks ontop of the house/structure/etc. might be an easy way to add some additional height. I'm not sure how much water will be necessary to store, however, assuming 50 feet water depth. It might be excessively much for the energy storage requirements of 5-10 kwh.

So, some straightfoward water storage calculations for 10 kwh, stored 50 feet above first water.

watthours = pounds*feet/2631.4

pounds = 2631.4*watthours/feet

pounds = 2631.4*(10,000)/50 = 526,280 pounds


gallon = 8.34 pounds

gallons = 526,280/8.34lbs = 63,103 gallons of water

Those water towers apparently hold 500,000 gallons. An "average" backyard swimming pool can hold 20,000. According to some guy, a 20ftx40ft swimming pool at 6 feet deep can hold 36,000 gallons. So, apparently I need equivalent capacity for two 20'x40' swimming pools for 10kwh.

The cheapest 1000 gallon water tank I've seen is $500, so 63,000 gallons would cost roughly $32,000.

I would think a possibly cheaper means of water storage is by digging a pond and lining it with plastic/similar. But, that does somewhat defeat the point of trying to keep the water as far above the water table as possible, lol.

Still, a 6ft deep 40'x40' pond looks like it should do the trick. Would have to increase the capacity a little to account for the lower height, so might be looking at 40'x50'. Not really sure if it's wise to push pond water back down into the aquifer? Seems like there could be some legal issues with the county on that one (Contamination of the aquifer).

And, I could get 10kwh of salvaged tesla cells for $2000? Starting to look appealing, lol.

 

[spinningmagnets]

The first water plant I worked at was for a small town, and they had wells that were 60 feet deep, and located about 100 yards away from a modest river.

The federal facility I am at now has 90 feet deep wells.

 

[swbluto]

Okay, so now I need to use this post to explore various compressed air containment schemes, and calculate their costs.

Failed propane tanks are on the investigatory list.

But, at this particular moment, I have to focus on my (paid) work, so tata for now.

------------

Okay, I'm back.

Here's ideas worthy of evaluation.

-Scuba tank, used
-Propane tanks that failed inspection
-Typical huge air compression tank rated for some low PSI, used
-PVC pipe
-ABS pipe
-Pipe buried underground
-Digging a hole and enshrouding the perimeter with some kind of cheap hermetic fabric/cover. The idea is that the cheap material would ordinarily burst due to expansion, but since the surrounding ground contains the shape and limits expansion, it's possible to pump it to higher pressures. Might need extra material to prevent puncture from sharp objects in the ground (Possibly a grid or mesh of some sort to separate the ground from the material.).

Okay, here's the hard calcs.... category by category.

SCUBA TANK OR HELIUM TANKS
-------------------------------------
Helium tanks are typically larger than scuba tanks, so let's look for those. They typically come in the 80 cu. ft. variety, the kind used by party shops for filling helium balloons.

I see one going for $170 and rated at a pressure of 3000 psig (Or 20.6 mpa).

Energy calculator ----> http://www.tribology-abc.com/abc/thermodynamics.htm

It appears a typical 80 cu. ft. cylinder(rated for 3000psi) is actually around 10 liters. (The above calculator uses 'liters' where it's labeled '10-3 m^3')

293 Kelvin is about 70F.

Now is 'adiabatic expansion' or 'isothermal expansion' what we're interested in? Adiabatic simply means you let the gas freely expand, which is going to cool it down to a lower temperature. This is why a deflated balloon feels cold right after deflation. I believe ordinary turbines are considered adiabatic, because they do not convert the heat energy in the cooling of the gas as it expands(decompresses) into electricity. If they were able to convert the stored heat energy into electricity (At 100% efficiency), they would be considered isothermal.

So the calculator is telling me 194 kJ which is 194,000 J which is watthours = 194000joules/3600 = 53.89 wh.

As a side note, this calculator is telling me the fully decompressed gas will approach 64 Kelvin or about -344 degrees fahrenheit. It'll most likely not be that cold in a real turbine since the gases won't be fully decompressed by the end stage, but it will get pretty cold. -100F or -200F probably wouldn't be unrealistic internal temperatures towards the latter stages of the turbine.

Assuming 100% conversion efficiency, a typical 3000psi 80 cu. ft. cylinder stores 53.89 wh of energy. Assuming turbine/generator efficiency of 80% (90% efficient turbine, 90% efficient motor), that's 43.1 wh of usable energy. The price is $170/43.1wh = $3.95/wh or $3950/kwh.

I've done the calculations once with the HUGE compressed air tanks typically rated at 200 psi (For some reason, it seems once they get wider than a typical helium tank, they immediately lose the ability to hold 3000 psi), and they're even more abysmal, and that's not taking into account the sheer cost of shipping something huge like that by freight and installing it.

Now, next, failed propane tanks.

PROPANE TANKS
---------------------------------

Typical size of a large "residential propane tank" is 500 gallons.

http://supersave.ca/wp-content/uploads/propane-tank-sizes.pdf - This is telling me a 500 gallon tank holds about 1500 liters.

What kind of pressures can a 500 gallon tank attain?

I'm seeing various figures between 100-200psi, on manufacturers pages as well in various threads, so let's assume 200 psi.

200 psi is 1.379 ma.

According to the calculator, a typical 500 gallon propane tank could hold about 2719 kJ of energy, released during adiabatic expansion. Watthours = 2719*1000 joules / 3600 = 755 wh.

As a side note, adiabatic expansion would cool the gas down to 138K, or -211 F, so a little more manageable. I might expect a real turbine to reach around 0 to -100F towards the later stages.

Now, what is the going price for these things? I see one listing on craigslist in my area for $500, might negotiate down to for $400.

Assuming 80% turbine efficiency, the usable energy is 755wh*.8 = 604Wh, and the $/wh using my craigslist survey is $400/604wh = 66cents/wh, or $660/kwh.

If you find one that failed inspection, you might even get it cheaper.

Yes, it looks like the Amish were onto something.



PVC pipes
--------------------------------------




Digging a hole and lining it with a cheap hermetic material.
-------------------------------------

 

[liveforphysics]

Okay, so now I need to use this post to explore various compressed air containment schemes, and calculate their costs.

Is this towards the pursuit of masochism?

16kWh of premium cells for $2500.

http://m.ebay.com/itm/13-14-15-CHEVROLET-VOLT-LITHIUM-ION-FACTORY-OEM-BATTERY-16-KWH-PACKAGE-2013-2014-/222192094539?hash=item33bbae4d4b%3Ag%3ABx4AAOSwIgNXjn8d&_trkparms=pageci%253Af42d97fc-56ca-11e6-a299-74dbd1808b28%257Cparentrq%253A3ee564a31560a2b0b2ee5e01fffa554c%257Ciid%253A16

 

[swbluto]

No, it's more like "What if I can't buy batteries 8-10 years from now?". And, 16-20. And 24-30. And 32-40. And so on?

What if...

-America becomes like 13th century china, where the average american peasant can no longer afford luxuries like batteries.
-America engages in the largest civil war known to man, and lithium batteries becomes impossible to source.
-America gets the shiiit nuked out of them, finally getting the retaliation they thought they could economically and militarily suppress forever, but ended up becoming impossible when the military had to downsize following some economic cataclysm, and one its mortal enemies was hurting so badly (Due to the same global malaise), they decided it was due time to administer America's coup d' grace?
-I become permanently disabled.
-I find working in the sweltering heat to be as hard as anyone else, so I too become lazy as **** like everyone else in the gulf states, and subsequently become poor just like the rest of the destitute people who live in that area? (I suspect the poorest states in America are in that area, simply because working in the heat is too hard; and, that area is hot because it's near the warm waters in the gulf, constantly being heated by the equatorial sun, and lacking the same kind of oceanic circulation as the rest of the ocean due to the entrapping geography.)

The point is.... what if...

"Here today, gone tomorrow"

 

[swbluto]

Now, I really don't want to go on length about the evanescence of life, it seems the Japanese have beat the horse to death with that one.

But...

Once upon a time back in high school, I shared a physics AP class with mostly fellow Juniors and a couple of seniors.

Those seniors names were...

Gavin Radkey
Elise Imhoff

They stood out, because this was the last quarter for them and their grades didn't really matter at that point, and so they loved life, unlike us Juniors who still had a year to go.

Elise... oh dear Elise...

She was cool. Had something of a scatological way of talking about her, and I infer she loved her Jack Daniels, but totally loving life.

So, zoom to something like 3 years later. Next thing I know, on the way to school, I notice she was completely bald, tale tale sign of chemo treatments. I didn't know too much past that because I wasn't really in 'her circle', but she was once part of our fun-loving tight-knit class, so I felt like there was at least that connection. So, zoom like 6 years later, when I suddenly remembered her because of some random fact I discovered in my cancer research. I wondered what happened to her.

I found her Twitter account, oh, that's cool. I see a bunch of random tweets about silly, random crap. For some reason, it seems like she stopped posting to her accounts like 3 years ago and there's no obvious reason why, she didn't leave breadcrumbs in her feed. That's weird.

Oh, what, a google search and her name is in an obituary?! Wait, what, she died 2 years ago and I suddenly found out on a random remembering of her looong after I last saw her?

Crazy, dude. It hit. I remember reading that book on the "Children with IQs above 180", reading her research. Interesting insight into the lives of these people. For the most part, they seemed to be just like ordinary people. Except, for some reason, it seemed like half of them died in their 20s. I chalked it upto "It was a sign of the times", apparently stomach cancer was common back during the Great Depression due to the widespread consumption of pickled foods. Then... I found her obituary... and apparently it's not only been true during the 20s/30s, it's been true ever since. Now, I can point to her excess alcohol consumption and high processed food consumption and blame that to hell, but... man... there's something wrong with America. The Kuna, natives of panama, just aren't dying in their 20s from cancer. They're like the jellyfish, able to keep cancer away, and rates down to an astoundingly low rate of 9 per 100,000 per year (Compared to America's 130 per 100,000).

Anyway, back to my point. You can't assume things will stay the same.

 

[swbluto]

Okay, so now I need to use this post to explore various compressed air containment schemes, and calculate their costs.

Is this towards the pursuit of masochism?

16kWh of premium cells for $2500.

http://m.ebay.com/itm/13-14-15-CHEVROLET-VOLT-LITHIUM-ION-FACTORY-OEM-BATTERY-16-KWH-PACKAGE-2013-2014-/222192094539?hash=item33bbae4d4b%3Ag%3ABx4AAOSwIgNXjn8d&_trkparms=pageci%253Af42d97fc-56ca-11e6-a299-74dbd1808b28%257Cparentrq%253A3ee564a31560a2b0b2ee5e01fffa554c%257Ciid%253A16

Hey, pretty good find. I wonder how practical it might be to bury half of the cells deep underground (To keep cool) in a discharged state so that you could use them a decade later? Or, possibly, a couple decades later?

 

[Chalo]

I wonder how practical it might be to bury half of the cells deep underground (To keep cool) in a discharged state so that you could use them a decade later? Or, possibly, a couple decades later?

Lithium batteries are technological devices which are in the heart of their development cycle. Keeping today's batteries for ten years down the line, even if they could be preserved perfectly, will be a lot like having mid-2000s batteries today. A waste of time, in other words.

If the batteries don't have to propel themselves, and you want to have them available indefinitely, then nickel-iron is the way to go. I have no idea where you'd find those.

 

[swbluto]

I wonder how practical it might be to bury half of the cells deep underground (To keep cool) in a discharged state so that you could use them a decade later? Or, possibly, a couple decades later?

If the batteries don't have to propel themselves, and you want to have them available indefinitely, then nickel-iron is the way to go. I have no idea where you'd find those.

Cool. I see a few suppliers based out of Europe at http://www.ebay.com/sch/i.html?_sacat=0&_nkw=nickel+iron+battery&_frs=1 . They appear to be marketed towards the wind/solar crowd, that's a good sign.

Eyeballing it, it looks some are going for 60-70cents/wh at >10kwh?

I wonder about the quality of their manufacture. Not a huge market, not a lot of reviews.

I suppose I could get a couple for testing, and just go with the lithium option for now, and just hope I have the means for replacement down the road.

 

[liveforphysics]

Iron nickel has massive self discharge, and vent corrosive hydroxide compound vapors that consume whatever they share a room with. They also need regular maintenance, as like lead acid the way they balance is through consuming water.

They also have commonly ~10% charging losses and ~10% discharging losses.

Comparatively, a Tesla/Volt/Leaf pack will need nothing and store energy at >99% efficiency and discharge energy at >99% efficiency. By the decade or two later when they need replacement, batteries that will out live your own human body will be plentiful and cheap.

 

[nicobie]

I am so tempted to buy that Volt battery pack add about 6kW to my solar and tell my electric utility to FO.

 

[swbluto]

I've updated the compressed air storage tank cost calculation post. I've evaluated helium tanks, large compressed air tanks, and used propane tanks so far. Used propane tanks are looking pretty darn competitive at 66 cents/wh. Helium tanks are out of the running at $3.90/wh and huge purpose suited compressed air tanks are worse, considering their transport and install costs.

I'll take a second look at them, however. I think some might be rated at 200 psi, just like the propane tanks, and they can be notably larger.

hmmm... I'll just jot it here...

2200gal 137PSI $1250

OKAY, that's about the only one that's larger than a 500 gallon propane tank at this time on ebay.

So the size is 2200/500 = 4.4x higher.
The psi rating is 137/200 = .685x lower
The price is $1250/400 = 3.125x higher

.685*4.4 = 3.01x overall more air, 3.125x higher price = not a deal compared to used 500 gallon propane tanks.

 

[Chalo]

Iron nickel has massive self discharge, and vent corrosive hydroxide compound vapors that consume whatever they share a room with. They also need regular maintenance, as like lead acid the way they balance is through consuming water.

Sure, and they're heavy and not widely supported. But they're the only batteries that will outlast the house they are intended to power.

I think it's best to use better performing batteries, and replace them as they are used up and as even better options become available. But for a paranoid post-apocalyptic self-sufficiency scenario, which seems be what the OP is getting at, nickel-iron has the longevity and simplicity to match.

I think it's overwhelmingly unlikely that battery longevity would be an issue in a SHTF situation, because some other crisis or solution would intervene long before then.

 

[swbluto]

I can't seem to find information on the cycle life of these buggers. Seems to be some kind of secret...

Well, found this:

The Changhong NF-S series NiFe

cell is adaptable to a wide range

of depth of discharge (DOD). The

number of cycles vary with DOD

required. The lower DOD is, the

more number of cycles are. The

number of cycles reach thousands

during shallow discharge, while it

can only reach hundreds of cycles

during deep discharge.

And, I thought I would be paying extra for a "forever battery", lol. Seems to be identical to lithium, cycle life wise.

That propane tank compressed air tank idea is looking good. Now, the idea of a -100F air coming out the turbine's outlet... I just have a feeling that might cause something I'm thinking of putting in there to break. And, this isn't -100F of dry air, it's humid air that's been compressed. I'd suspect there'd be frost towards the output or similar.

It'd be nice if I could store that heat created during compression, and use it during decompression. That would also, hypothetically, let me achieve the "isothermal expansion" energy capacity which is like 3x higher than the adiabatic expansion's energy capacity.

I suppose I could heat up the propane tank prior to discharge to around 200F, but it just seems like that would possibly significantly reduce the net effective energy recovered since energy is being spent on heating the propane tank. And, all those thermal losses to the environment during the operation of the turbine, seems like it could be significant at 200F.

 

[liveforphysics]

The Volt cells reach >~40,000 cycles of shallow DOD (50%).

Even from an apocalypse prepper perspective, the turbine has exotic parts to rebuild it. Volt cells are found ubiquitously (at least in California).

 

[Punx0r]

What's the deal with a propane tank that's failed its safety inspection? Corrosion?

 

[nutnspecial]

https://permies.com/t/9902/wind/Windmill-air-compressor-electric-generator

Here's some more info swbluto. Interesting stuff!

 

[swbluto]

I'm looking into the Tesla battery longevity. It appears they're designed with a 10 year calendar life and would decline to 80% with 50% DOD in 5000 cycles. Since the salvaged batteries are typically 3 years old and have 1000 cycles on them, I'm guessing they probably have about 7 years and 4000 cycles left until 80% of original capacity. But, for my uses (upto 10kwh, usually less.), I'm guessing I would be more realistically expecting 15 years and 7000 cycles left, so about 15 years of life. Not shabby - I might even be able to bypass the lead acid batteries and run directly off the lithium, if only the Renogy MPPT charge controller was designed for Li charge voltages. Oh, what am I talking about? Just hook up as many dc-dc converters as needed to get the 24V from the lithium and bypass that lead. The lead should last forever if it's never used.

I still like the idea of designing a home turbine, but with a charge efficiency of 20-30% (Most of it is lost as heat as the air cools down in the tank), a battery seems more sensible for a relatively limited amount of excess solar being harvested. And, it's true, compressors break and turbines need maintenance, while a battery, properly used, should be good to go for a long time.

I still want to evaluate the other forms of compressed air storage, however. Leave no stone unturned.

 

[swbluto]

Okay, let's evaluate the idea of lining a hole with cheap material and pumping air into.

Let's take your common 55 gallon trash bag.

Under normal circumstances, if you just inflated it as is, it'd be probably expand and blow up at 15-25 psi. But, if you dug a hole and lined a hole with it, it wouldn't be capable of expanding so it'd be hypothetically possible to pump it to higher pressures.

What kind of pressures? I don't know.

I just know that you don't want it to be /too/ low, because than that severely reduces the efficiency of the turbine.

Let's say 50 psi.

Digging a hole = free;
Appropriate Lid (Make it out of sheet metal) = $5
Plastic liner = free (effectively)

Using the Energy calculator ----> http://www.tribology-abc.com/abc/thermodynamics.htm

Using .3447 bar(50 psi), 55 gallons is 208 liters.

The adiabatic expansion energy contained therein is 53.2 kJ or 53,200J/3600 = 14.77 Wh.

Assuming an average turbine efficiency of 70% to account for the lower operating efficiency from the lower pressures involved, the usable wh is 10.339 wh.

The $/wh is $5/10.339 = 48 cents per watthour

Now, if we could achieve higher pressures, that'd push the $/wh figure even lower, but I think the better question is if 50 psi could even be reliably attained with a trash bag encapsulated by the ground. I haven't experimented yet, to know.

I think a more pressing limitation is the amount of holes needed for 10kwh. At 10wh/hole, it appears I'd need 1000 holes in the shape of a standard 55-gallon trash can.

-----------------------

Now I need to evaluate storage via PVC pipes.

I wish I could just /go/ to the store and look and see what's available, but you see, goddamn 20century infrastructure means I need to be paying my monthly tribute to the insurance feudal lords to make that happen, and there just seems to be something extremely lopsided with a $70/month insurance bill and $4/month gas usage.

And, it appears Home Depot and Lowe's haven't gotten on the "Let's make all our inventory available online" like Walmart has. I hope that changes soon? Like, good good man, this is the 21st century.

PVC pipes
-----------------------------
I'm just scanning the home depot website.

Volume = pi*r^2*L = pi*(diameter/2)^2*L

diams
--------------

2"
--------------
5 ft. - $15.75

capacity(in^3)=3.14*((2/2)^2)*(5*12) = 188.4"

$/in = .0836

1.5"
---------------
5 ft - $8.63

capacity(in^3)=3.14*((1.5/2)^2)*(5*12) = 105.975"

$/in = .0814

1.25"
-------------
5 ft - $7.70
capacity(in^3)=3.14*((1.25/2)^2)*(5*12) = 73.59"

$/in = .1046

2 ft - $2.61
cap=3.14*((1.25/2)^2)*(2*12)=29.43"
$/in = .0887


It appears the 1.5" variety has the most bang for our buck, so 105.975 in^3 = 1.737 liters. 130psi= .896 mpa.

1.8 kj => 1800j/3600 = .5 Wh.

Assume turbine efficiency of 80%, usable is .4wh.

The $/wh = $8.63/.4wh = $21.575/wh

Whoever thought PVC pipes were a good idea for storing compressed air is an idiot. I guess it might be OK for certain kinds of low energy air tools, but not for electricity generation.