Gary_Gough

Math can save you time and effort. [Renewable Energy]

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Me doing a three page diatribe on various power sources and why you should be friends with your calculator ;)

Power.pdf

When planning a wind project, or really any energy project, there are a few simple reality checks that should come first. Topping the list “does the energy exist and will I capture what I need”.

A real world cautionary example. A group had built a whirly-gig to harvest wind energy, and had spent $250,000.00 on the prototype. They had found a salesman who had lined up investors to buy their device at cost. The investors had asked to install some monitoring equipment to see how the unit performed. The instrument tech. ( me ) asked the inventors what the expected peak power would be, so the instruments could be sized to handle more then maximum. The answer “that's a secret”, never a good sign. So all the information available was a glossy sales brochure with a picture. Visually enough information to get the size +/- 10% , with that there are no longer any secrets. What follows should have been done before so much as a bolt was purchased.

From the picture , the area the whole machine presented to the wind was 1200 square feet.

A good wind site in North America will get an average wind speed of 13 mph.

The energy of moving air is kinetic , early school physics E = 1/2 m*v^2 , so one cubic foot of moving air contains energy in proportion to it's mass ( air density ) and the square of it's velocity.

The amount of air moving past your system is directly the velocity, so power output becomes a cube of the velocity.

Long story made short , you can write out a simple formula;
Power = density * Area * Velocity^3 * (a Constant that lumps together all the conversion factors)

Assorted things to be aware of; that gives you the total energy going through the system, what you can actually get is much less. To start with, to harvest 100% of the kinetic energy from any moving mass you need to stop it. A wall stops the air very nicely, but unless that air gets out of the way, the first push is all you get. Enter the “Betz limit” theoretical max output is 56% of the air flow ( idea applies to water too for the same reasons ) in real life if you do much over 1/2 of that you are doing well.

So lets run the numbers and give this thing every benefit of doubt...

I'm used to metric so to start , 13 mph = 5.8 meter/sec , 1200 sq ft = 111.5 sq meters, air density at sea level 1.2 Kg / m^3

and our formula P= d*A*V^3 * .5 , or 1.2 * 111.5 * 5.8^3 * .5 = 13053 watts ( metric often has the units work out really easily ).

so 13 Kw but only 1/4 of the full structure is actually catching moving air so 3263.25 watts , and then there is that Betz limit and assorted frictional losses. Lets just say 33% as an optimistic number , so we are down to a little under 1100 watts.

In this case the sales people are telling investors that the machine will pay for itself and make a profit ... but 1100 watts at full retail is about 11 cents / hour or $79.20 per month.

Now if we treat this as a 10 year payback at normal interest rates , $250,000 at 4% works out to monthly payments of $2,531 .

So this thing will be about $2450 short of making payments on itself every month. Or , to break even it would need to be 1000% efficient as opposed to maybe 33% for a real unit. Actually the design would have more likely been closer to 15% but it was already pointless to spend more time refining the numbers.

Horror story, but anyone involved could have figured this out before they had built anything, and they really should have.

Before you start anything, figure out what you need, what you have and how hard it will be to convert. Mathematics is your best tool and spending a few hours, or days, thinking, can save years in wasted work. When in doubt ask someone who knows, paying them to tell you is still a bargain.

 

Now, in the real world allot of us like to have electricity. It's handy stuff , lights, radios, computers pretty much need it. Renewable options are sun, wind, wood fire, hydro, geothermal.

Very few of us have a stream with a large enough drop over our property to use hydro and the legal barriers can be a killer, but if you have it it's great. One of those largely wasted resources too. Lots of flood control structures that could power 20 or 30 homes and it's not even considered.

Wood fired.. great for intermittent use and if you are already heating with it, it's nearly free power for the taking all winter. Steam is efficient but dangerous, but there are alternatives like Stirling that don't involve risking your life.

Sun, is like real estate , location, location, location ... The closer you are to the equator the better it works, clear skies are very nice. So places like mountain ranges are ideal. For calculations 440 watts of energy / sq meter on a bright clear day at sea level. Southern locations need maybe three days storage and sized to about 6 times power use. If you live around 53 degrees north Lat. Figure a weeks worth of power storage for battery size and enough collectors to produce a day's worth of power in one hour ( yep 24 times use ). Up here we get 3 hours of sun on a clear day in late December and only 12 degrees above the horizon, so also not the full 440 watts due to more atmospheric losses.

Wind is also location dependent, that lovely forest that makes wood heat so easy can also mean not much useful wind. If you do have a good location though , a 20 foot diameter prop. Should handle a 600 watt constant load including storage losses for charging / discharging batteries. Note that the prop. Should be designed for a design wind speed and rotation rate. Also remember that velocity cubed factor. A 26 MPH wind = 4 time the energy, 39 is 8 times, 52 is 16, and 65 is 32 times, so the stresses build fast. That nice tame 1 Kw generator has to handle 32 kilowatts in a moderately strong storm.

A hot spring would be great, much like hydro few of us will have it.

If you think you can bike your way to energy independence, a human produces apx. 100 watts constantly, Olympic class athletes can do an extra 150 watts for a marathon. So the bike can recharge your cell phones and run an energy efficient computer and some lights if you don't mind the workout ( about 25 watts ). Two hours of hard pedalling will charge a battery enough for a 5 minute microwave run , or ten minutes of making toast. But you will be in great shape after a couple of weeks :-) .

Now some handy resources.

http://www.ajdesigner.com/phpwindpower/wind_generator_power.php#ajscroll real world power calculations for wind, will also ball park hydro if you assume “air” of 1,000 Kg / M^3 .

http://bekkoame.ne.jp/~khirata/academic/simple/simplee.htm Stirling engines. Undoubtedly I'm pushing outside of the limits on this calculation but try standard air pressure ( 0.1 Mpa ) 1000000 cm3 swept volume, 60 degrees C on the hot side and 20C on the cold. Use air. Looks like a 4' by 4' by 12' engine could power a small house from warm air , and radiate into the house too. One of those “when I have free time” projects :P

http://solardat.uoregon.edu/SunChartProgram.html free chart of where the sun will track for anyplace on earth. I also like this for passive solar heating calculations. Put the windows and awnings in the right place and you can have heat in the winter, cooling in the summer and no operating costs.

http://www.turnkeyips.com/assets/steam_temperature_pressure_table.pdf Steam chart, this is mostly so you'll know to treat this stuff with allot of respect. At a reasonable working pressure of say 150 PSIG , the steam is at 365 degrees F. A leak beside your arm would cook the arm before you figured out why it felt cold ( nerves are gone before you have a chance ). Now if you understand what you are doing ( take a course, get your steam papers ) this is how every coal and nuclear plant converts heat to power. A conservative design and an outdoor firebox could work well and you could still use the coolant from a condenser to heat a house. Just keep anything live at a safe distance and have lots of safeties.

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Okay um.. best pdf on renewable energy I've ever read. Love your writing - so clear - and the math is so very appreciated.

Often you'll see people talk about this kind of stuff without any numbers and I have to wonder if it really works. This is probably the best breakdown summary of the different kinds of renewable energy I've ever read as well.

Thank you so much for posting!

 

If I could just make one request - could you copy and paste the contents of the pdf into a comment/post in this thread - just in case some might have trouble viewing PDFs or anything like that (though this day and age that shouldn't be the case!). Wouldn't want anyone who might like to read this valuable information to go without being able to do so. Insightful as hell!

Also I'm really excited that we now have a renewable energy guy on the forum. :) So much to learn from you!

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Okay um.. best pdf on renewable energy I've ever read. Love your writing - so clear - and the math is so very appreciated.

Often you'll see people talk about this kind of stuff without any numbers and I have to wonder if it really works. This is probably the best breakdown summary of the different kinds of renewable energy I've ever read as well.

Thank you so much for posting!

 

If I could just make one request - could you copy and paste the contents of the pdf into a comment/post in this thread - just in case some might have trouble viewing PDFs or anything like that (though this day and age that shouldn't be the case!). Wouldn't want anyone who might like to read this valuable information to go without being able to do so. Insightful as hell!

Also I'm really excited that we now have a renewable energy guy on the forum. :) So much to learn from you!

Copy and paste don't seem to work into this for me. so I'll try inserting it in .txt

Power.txt

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Copy and paste don't seem to work into this for me. so I'll try inserting it in .txt

Power.txt

Thats a fantastic bit of math. I do find (much like Elise) that a lot of the discussions concerning energy generation tends to be a bit light on the specifics in terms of viability which is a damn shame. Good job Gary!

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Thats a fantastic bit of math. I do find (much like Elise) that a lot of the discussions concerning energy generation tends to be a bit light on the specifics in terms of viability which is a damn shame. Good job Gary!

Thanks. Yeah I see way too many articles that not only leave out any analysis, but are often nearly pure fantasy. A square meter solar panel on the roof is not going to be enough to run all the things most people are used to ( conversion efficiency is getting better, but still < 25 % , so if the roof pitch is exactly lined up with the sun you are still under 100 watts charging )  ideal place , say San Cristóbal de las Casas  and that would give you 50 watts full time. Enough to use LED lights and run a laptop computer, maybe even an "all fridge" but you run out of energy fast. Normal house uses about 1 Kw averaged out over the day. So in an ideal place you still need 20 panels and a about 36 KwH of usable storage if you want to use a bit more, like freezer, water pressure system, washer, dryer, microwave, kettle, toaster, it all adds up. One other thing I notice is far too many purists, one solution for everything. Mixing sources and using the local resources can cut down costs. Batteries are expensive, so it's nice to have some "on demand" power generation. The power companies like "base load" sources like dams, renewable isn't always the easiest that way. 

One idea I've seen for hot water looks interesting, but again finding hard numbers is proving challenging. Manure and straw.. Water filled pipes / hoses in a large enough compost pile. Write up I saw was a camp using a 12 ft. pile to provide water for showers. It would have been nice if the author had put a water meter on the flow and recorded the input and output temperatures as opposed to " enough hot water for 24 campers". The article was enough to be interesting, and at the same time not enough to be able to predict how useful it really is. I really should get together with someone with enough livestock to try this one out :) If a pile that can make 500 watts isn't too huge then that has just reduced the need for batteries by at least 1/2 and maybe even eliminated them. There is "base load" slow, constant and 24/7 . I really want numbers. Showers, on the other hand, is almost a waste. Short, intense and intermittent use. I welded an old gas water heater onto a steel barrel ( as the chimney ) and we had unlimited hot water showers at a tree planting camp. A couple of arm loads of fire wood and that kept it going for all the time needed. Peak use power, not base load.

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Alright! I figured out a way to copy and paste, and so added it to the original post up at the top.

And upon re-reading - I have a question (sorry if this sounds silly and is very basic!): How on earth do you collect the power from wood fire? I actually didn't even know that was a good way to collect energy before you posted your PDF!

A square meter solar panel on the roof is not going to be enough to run all the things most people are used to ( conversion efficiency is getting better, but still < 25 % , so if the roof pitch is exactly lined up with the sun you are still under 100 watts charging )  ideal place , say San Cristóbal de las Casas  and that would give you 50 watts full time. Enough to use LED lights and run a laptop computer, maybe even an "all fridge" but you run out of energy fast. Normal house uses about 1 Kw averaged out over the day. So in an ideal place you still need 20 panels and a about 36 KwH of usable storage if you want to use a bit more, like freezer, water pressure system, washer, dryer, microwave, kettle, toaster, it all adds up. One other thing I notice is far too many purists, one solution for everything. Mixing sources and using the local resources can cut down costs. Batteries are expensive, so it's nice to have some "on demand" power generation. The power companies like "base load" sources like dams, renewable isn't always the easiest that way.

Omg you have no idea how useful this comment is!

I had no idea that the numbers were that low (50 watts full time!) even in the most ideal location.

And that is a really really good point about diversifying into different types of energy. I think people typically get overwhelmed with trying to set up many different kinds, or like to have "matching" things or something along those lines and that's probably why. But it's honestly a terrible idea to put all your eggs in one basket anyway - which preppers should especially know.

Anyway - again, I am so glad that we now have a renewable energy guy that I can ask all my silly questions to ;)

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Alright! I figured out a way to copy and paste, and so added it to the original post up at the top.

And upon re-reading - I have a question (sorry if this sounds silly and is very basic!): How on earth do you collect the power from wood fire? I actually didn't even know that was a good way to collect energy before you posted your PDF!

Omg you have no idea how useful this comment is!

I had no idea that the numbers were that low (50 watts full time!) even in the most ideal location.

And that is a really really good point about diversifying into different types of energy. I think people typically get overwhelmed with trying to set up many different kinds, or like to have "matching" things or something along those lines and that's probably why. But it's honestly a terrible idea to put all your eggs in one basket anyway - which preppers should especially know.

Anyway - again, I am so glad that we now have a renewable energy guy that I can ask all my silly questions to ;)

Well, the best way to go for fire -> power in terms of safety is pretty much a Stirling cycle. http://stirling-tech.com/ these guys say they make a 5 hp engine. In theory directing the exhaust from a clean burning fire ( catalytic wood or forced draft ) at the hot end of the unit should work. You'd want to put some automated controls on airflow and really without technical specs this is guesswork. I usually don't like sales sites that don't give a price and I really like to see enough tech. data to know what it takes to attach it to the real world. Oh well. If you ask a sales guy a significantly detailed question they'll usually panic and let you talk to a techie. Different motivations, the sales guy wants to keep you talking and push anything he can even if it's useless, the techies like to make things work. In fairness there are a few sales people who actually understand their own products, real gems when you find them. 

Stirling engines used to be all over the place, one of the early electric fans was a stirling with a resistive electric heater to power it. That was a company that already made stirling fans trying to adapt to the new power source. Here is a kerosene powered fan  http://www.stirlingfans.8k.com/  similar stuff was made in USA and with the advent of electric power they added an electrically heated version for a short while. Electric motors are so much better for this application that the stirlings lost that competition. 

Other options, I did mention steam. That's fairly easy to do, boiler on top of, or after, a firebox ( thick, high pressure steel pipes usually ) and live steam going to a turbine or reciprocating steam engine, output from it to a condenser and a small pump to push the condensed water back into the boiler. Most places will let you build your own, but selling boilers brings a flock of lawyers and inspectors, somewhat justified as a failure is dangerous. I've worked in a 900 megawatt plant and the rule is, no one goes near the boiler while it's running. 

Low temperature differential collection is a really under developed field. But that could be done with a water jacket , open to atmosphere so not likely to explode, and water taking the heat to an engine. Side benefit is that can also be your hot water supply and heat distribution system to radiators.

Stirling cycle can do this, but as the differential drops you need to adapt to less gas expansion and lower output or larger engines. Quick course in Sterling cycle.. Fist start thinking in Degrees Kelvin, Celsius or Fahrenheit will just confuse things. A classic Stirling engine needs a heat source around 540 degrees K and a sink into 270 K  Using pressurized helium as a working gas you can make a compact and very efficient engine. The hot gas will be double the volume of the cool gas, so two cylinders offset by 90 degrees and running pistons on a common drive shaft can transfer gas back and forth while the volume doubles and halves. Heat one cylinder and cool the other so that the gas is in the hot cylinder at max expansion and in the cool one at min and you have an engine. Add a regenerator ( basically a heat sponge to absorb and release heat between the cylinders ) and you can have very high efficiency. Now the reason to think in K , double the temperature, double the volume. Thinking in C or F and it just looks like arbitrary numbers. Now on to less obvious designs , if you don't have as high a temperature source you can still harvest energy, for instance water boils at 373 K , so hot water at 370 for a source and ice water for a sink ( 273 K ) will give an expansion of 1.35 times instead of double. ( 370 / 273 , isn't that easy? B|  ) so if you can change the angle between the cylinders until the max volume is 1.35 times the min, you still have a running engine. Of course less energy, the end case is no temperature difference, 180 degrees between cylinders and no energy output ( worse friction loses so it just sits there ).

Now the bad parts, a small engine means very high pressures for energy production ( think 5,000 PSI ) so for simplicity and safety the engines tend to be huge. Air isn't a great gas, Hydrogen is much better , but there is that Hindenburg factor. Energy output is also limited by how fast you can move heat through the system. As the heat has to enter, and leave, transferred through something that will also be a limiting factor ( think larger again ). 

I mentioned a 12 foot long 4 foot square engine, that's the numbers I get for a 1 hp engine with air at atmospheric pressure as a working gas, room temperature heat sink and hot water ( about 70 C ) in. On the bright side you could build it out of wood and canvas with a central section of scrap aluminum as a regenerator radiators either side of that for heat transfer and a chain drive with idlers to adjust the phase angle between end pistons. Will also need a huge flywheel as it will run around 40 RPM.

For the adventurous Rankine cycle engines don't have to be steam. You could use say R290 refrigerant as a working fluid ( also called propane ) or R717 ( ammonia ), of course the need to have a very tight gas seal is obvious.  That's probably the system I'd choose to try for that compost pile power source idea. Prob. don't want the pile beside the house, so make something small and just run a cable back. If it's chicken coop output it's already got ammonia. Both flammable gases and ammonia used to kill people back when home refrigerators used it ( Albert Einstien and Leo Szilard patented a sealed electric pump to try and fix that, too noisy as it turned out but so reliable that they are used in nuclear plants ) so outdoors is the best choice to play with these.  

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I usually don't like sales sites that don't give a price and I really like to see enough tech. data to know what it takes to attach it to the real world. Oh well. If you ask a sales guy a significantly detailed question they'll usually panic and let you talk to a techie. Different motivations, the sales guy wants to keep you talking and push anything he can even if it's useless, the techies like to make things work. In fairness there are a few sales people who actually understand their own products, real gems when you find them. 

This is probably the most accurate depiction of the sales/tech divide I've seen penned, lol. So very true!

 

Stirling cycle can do this, but as the differential drops you need to adapt to less gas expansion and lower output or larger engines. Quick course in Sterling cycle.. Fist start thinking in Degrees Kelvin, Celsius or Fahrenheit will just confuse things. A classic Stirling engine needs a heat source around 540 degrees K and a sink into 270 K  Using pressurized helium as a working gas you can make a compact and very efficient engine. The hot gas will be double the volume of the cool gas, so two cylinders offset by 90 degrees and running pistons on a common drive shaft can transfer gas back and forth while the volume doubles and halves. Heat one cylinder and cool the other so that the gas is in the hot cylinder at max expansion and in the cool one at min and you have an engine. Add a regenerator ( basically a heat sponge to absorb and release heat between the cylinders ) and you can have very high efficiency. Now the reason to think in K , double the temperature, double the volume. Thinking in C or F and it just looks like arbitrary numbers. Now on to less obvious designs , if you don't have as high a temperature source you can still harvest energy, for instance water boils at 373 K , so hot water at 370 for a source and ice water for a sink ( 273 K ) will give an expansion of 1.35 times instead of double. ( 370 / 273 , isn't that easy? B|  ) so if you can change the angle between the cylinders until the max volume is 1.35 times the min, you still have a running engine. Of course less energy, the end case is no temperature difference, 180 degrees between cylinders and no energy output ( worse friction loses so it just sits there ).

That is so cool! And very well explained. I don't think I would've understood this concept if it were explained to me by most anyone else. Feel like tomorrow I will try looking up some videos to see this in practice.

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math.....

 

we meat again ¬¬

 

awesome .pdf!

No shit right? Effing math..... and I even understand most of what is being discussed.

The other thing to remember, aside from the physics and mathematics of the thing which are constant, is that as with all technology this may be completely out of date in the next 6-12 months. Fortunately, that is mostly a very good thing, especially with some of the solar cell efficiency changes that seem to be coming.

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Yes the new solar cells have even managed to pass one theoretical limit ( 14% ) by figuring out how to capture more then one frequency ( colour ). Nice bit of work there. Just saw an article go by claiming 1Kw / sq meter ( which is true, for full spectrum, in orbit ). It doesn't hurt to know some common values, helps sort out wishful thinking from useful ideas.

As much as better efficiency, lower costs per panel is great too. If I can buy 2 panels at 20% , for the cost of one old one at 13% , then I've got 3 times the energy to play with :-) . Guess I should mention I've designed instrument packages for remote use, which was motivation for spending the time on this. Same info also applies to things like ham radio repeaters on remote elevations. Solar beats running in a power line at some of those. 

The biggest bottleneck with alt. energy is still storage. Mostly we are dealing with either diffuse sources, or unpredictable, or both. So storage for use on demand is a must. Lots of trade offs though. High density also means hazards. For instance lithium metal batteries have much better energy density then lithium ion, but are prone to internal shorts after cycling, which leads to localized hot spots, then general overheating and then burning lithium. If you've ever dealt with burning magnesium, you'll have an idea what that's like. ( smother with sand, if you apply water, it strips the oxygen, burns even hotter and releases incandescent hot hydrogen. ). Aluminum antimony salt batteries are impressively cheap, scale up nicely, self heal and would be great on Venus but they do need to be heated ( to melting temperatures ) here. Still at power grid scale, promising idea.

Geothermal has some storage use here. Too many installations are treated like wells, at first you get allot of useful heat, but unless you are very lucky and have a hot spring ( may redefine luck as that also usually means seismically active ) you need to know the average rate of ground heat is apx. 0.1 watts / square meter. That doesn't make it useless, but when there is plentiful heat the ground supply should be replenished. Ice is a good insulator, so once the ground field freezes the energy flows drop fast.

Slight aside, was thinking about stirlings a bit and looking at my inventory ( also called eyesore junkyard in polite society ) About 6 spare VW Rabbit engines at least 4 under 300,000 km .. so ran the numbers on a 1.6 litre Stirling engine designed for 60 degrees C temperature difference. About 1 kW using air at 600 PSI for a working medium. Hydrogen would be much better but.... Anyhow , a nicely balanced piston block, low stress ( as a diesel they do apx. 14 kW so this is light loading ). Do need to see how the water jacket would work with the heads replaced with flat steel and 4 regenerators running between 2 blocks. Chain drive between. But as long as the water flows can be made to work, this looks like something worth trying.

 

Way off topic, but not sure where to place it.... Scam alert.  I got a bunch of links to pretty web sites to crowd fund an energy project recently. The resource is real ( ocean currents, Gulf stream etc. ) so they could point out how much it would power if harnessed ( it's huge ). Then it got silly. They have a 3 panel system with shutters closing for 1/2 rotation, on a vertical shaft, on top of a pillar. Claim is "simplest, safest system, best efficiency".  Once again, look at the system and run the numbers... The shutter design doesn't make sense for the same reasons we don't make windmills the same way. Only optimised for speed and rotation along one vertical line, unlike a propeller. Huge number of moving parts and wear points. Under water it will fill up with debris. even a small unit will exert tons of force on it's mounting. No mention about how it gets anchored , serviced, or connected to land. This is pretty pictures, a system that anyone can look at and say " yes, that will spin" and a way to ask for money. It may be honest, in which case no one will become rich, or it may make a few people rich at the cost of everyone else. Anyhow avoid this if you see it.

 

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I should mention lithium ion batteries and Canada. If you charge a Lithium ion battery when it is below 0 Degrees C , the chemistry changes and what you get is a lithium metal battery after charging. Another problem is there is a thermal fuse in the battery packs that opens at about 105 C. It's a safety feature ( Shut down current before it catches fire ) closed boxes in direct sunlight ( car trunk ) can get that hot ( more likely in southern US ) so you might have several batteries all fail for no obvious reason, at once. Anyhow, get them to room temp before charging and be aware of their limits.

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Way off topic, but not sure where to place it.... Scam alert.  I got a bunch of links to pretty web sites to crowd fund an energy project recently. The resource is real ( ocean currents, Gulf stream etc. ) so they could point out how much it would power if harnessed ( it's huge ). Then it got silly. They have a 3 panel system with shutters closing for 1/2 rotation, on a vertical shaft, on top of a pillar. Claim is "simplest, safest system, best efficiency".  Once again, look at the system and run the numbers... The shutter design doesn't make sense for the same reasons we don't make windmills the same way. Only optimised for speed and rotation along one vertical line, unlike a propeller. Huge number of moving parts and wear points. Under water it will fill up with debris. even a small unit will exert tons of force on it's mounting. No mention about how it gets anchored , serviced, or connected to land. This is pretty pictures, a system that anyone can look at and say " yes, that will spin" and a way to ask for money. It may be honest, in which case no one will become rich, or it may make a few people rich at the cost of everyone else. Anyhow avoid this if you see it.

Thanks for the interesting information and thanks for this scam alert. I will be sure to keep an eye out for it.

Your summary of different battery types will come in extremely handy once we finally start looking into renewable energy for ourselves (probably will be a few years, but still good to know this stuff as groundwork!)

I should mention lithium ion batteries and Canada. If you charge a Lithium ion battery when it is below 0 Degrees C , the chemistry changes and what you get is a lithium metal battery after charging. Another problem is there is a thermal fuse in the battery packs that opens at about 105 C. It's a safety feature ( Shut down current before it catches fire ) closed boxes in direct sunlight ( car trunk ) can get that hot ( more likely in southern US ) so you might have several batteries all fail for no obvious reason, at once. Anyhow, get them to room temp before charging and be aware of their limits.

Did not know this at all - thank you for mentioning it!

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What would be the likelihood of venting with the large scale lithium ion? I know most likely the safeguards work spectacularly well, but anything that can go wrong eventually will go wrong and in a full house, or larger, scale situation that could be especially catastrophic. 

Speaking of batteries, I have to check my NVIDIA Shield tablet when I get home as 88k of them are being recalled due to battery overheating issues. Apparently several of them have gotten hot enough that they have damaged floors. And I just remembered that not only did I upgrade the Android version this morning, I also left the device on the charger.............

Edited by William
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Well Li-ion are normally totally sealed and don't out gas at all. All bets are off if they overheat. Here is a product safety sheet http://data.energizer.com/PDFs/lithiumion_psds.pdf  and lots of information on this site http://batteryuniversity.com/learn/article/lithium_ion_safety_concerns 

Personally my first concern would be shorts and fires. In a large installation I'd want to consider a controlled storage space, probably with fire break gyproc walls and ceilings, a fuse on each battery and smoke alarms. Of course that goes for pretty much any battery bank. 

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Want to light up a 6.2 volt LED with a 1.5 volt source?  https://en.wikipedia.org/wiki/Joule_thief That's the real use for this circuit, and it does a fine job. You can also use it to charge Li-ion button cells or a super cap from a minimal voltage source ( playing with a peltier cell and one of these, I could light a LED intermittently ). There are highly efficient variations using charge pumps to harvest electronic noise to power a bit of circuitry. ( That 60 Hz hum that is pretty much everywhere that has grid power, can power nano watt loads wirelessly ). If you want to play , the electronics from a disposable flash film camera will give you everything you need. Be careful salvaging, these can store a painful charge for several hours disconnected from the original single AA battery. In use they make a 2,000 volt pulse to initiate a 350 volt discharge, with a few amps, through a zenon flash tube. Nuf said? The total amount of energy is still low due to it being a very brief pulse. If anyone is interested I can show how to build a 100,000 watt UV laser that will run off of AA batteries, one pulse every few seconds, duration 10 nanoseconds.

Now the silly parts. An unfortunate number of the alt energy crowd have latched onto Joule thieves as "free energy" because a low voltage gets turned into a higher voltage. ( so if you feed the output of one into another, and charge a battery to run a fan, and use another fan backwards to make electricity to feed into the first Joule thief ... This was an actual proposition I was given, and after three hours of me explaining exactly how each conversion lost energy it ended with veiled threats to have me "hexed". No kidding ) 

Here is the pertinent math . Power = voltage * current  .

Notice power is what we want , converting voltages higher allows us to use things that need the voltage to run, but in raising the voltage we get less current ( and lose a little power as heat. TANSTAAFL )

Broader application, when you see a "demonstration" of free energy showing voltages without also showing current, it is a) meaningless b) either a deliberate attempt to deceive or a total lack of understanding. So when you see a motor running on a 12 volt battery, spinning a generator, putting out 14.7 volts  and running back into the battery. That's missing the point that you will be drawing more power from the battery then you will return from the generator. Yes it runs, until the battery is discharged. Same applies to all systemic attempts at perpetual motion , be it electronic, magnetic, gravity or mechanical. Unless you feel it's worth your time to explain why the device "almost works, we just need to make a few improvements" isn't going to happen, I'd suggest saying "that's nice" and going for coffee.

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