Quote:
Originally Posted by oli63ro
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Q:
Energy conversion efficiency of compressed air would be much less compared to the traditional flooded batteries. This means the size of panel array must be increased to generate the same amount of power drawn from a battery.
Do you have any cost analysis/comparison between a battery system vs compressed air system for residential use? I'm interested to know and I hope I can get rid of costly batteries. Maybe steel reinforced concrete will work as a tank also.
A:
1)Compressing air has usually 15% efficiency. Heat is the difference. Usually the heat generated can be converted back to energy (the Stirling engine 50% efficiency, gas turbines), or can be used for home use (air or water heating) so overall efficiency increases. More the thermodynamics of this tank has special properties allowing (for the moment in theory) thermodynamic systems with more than 65% efficiency.
2) Using conventional batteries means paying more for replacing batteries than for grid electricity (Pb batteries should be replaced after 500 cycles, lithium after 2000-3000) How much do you pay for gasoline on 100 miles. An air car needs 3$ compressed air. No pollution, it cleans the air (dust from air condenses in the tank and can be eliminated locally) and other advantages can be obtained. I'm writing an e-book on the subject (hope to have time to explain all the thinks I've found).
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Please correct this where I have it wrong:
- 15% efficiency from compressing air (waste heat used for other things, but not for compressing air)
- 3$ of compressed air will get an air car 100 miles. Where I live, 3$ is about 30 kw-h. At 15% efficiency, that's 4.5 kw-h of energy put into the air tank, which would be too little to move an air car for 100 miles.
- that does not take into account the efficiency of the air motor, the drive train, etc and measure power delivered to the road. I guess we can ignore that part for now.
You mention that an electric car has more cost for replacing the batteries than for the electricity purchased from the grid. I don't have experience with that (I'm sadly not driving electric as yet), but that sounds reasonable to me.
Here are the numbers that I'm using. The pack I've sized (from web site information) for my project is around $10,000 for a 15 kw-h pack that should give my converted 5000lb Chevy S10 a range of about 30 miles of highway travel. If the battery pack lasts 5000 cycles or something like 8 years (charging twice a day, once at work and once at home), it will have been charged with 5000 * 15 kw-h (worst case) * 0.10/kw-h (present price in my area) and that would cost $7500. If it only lasts for 2000 or 3000 cycles, the batteries would cost double what the electricity cost (my apologies for assuming constant costs on the electricity). I've left out the efficiencies of the charger, the batteries, the drive train - these are all percentage losses that add up ... but the discussion so far is not at that level of detail.
By way of comparison, how much does your proposed tank system cost (up-front capital cost - I am assuming that you have a prototype), to compare to the $10,000 in my example above? Please include the compressor as well, with the water knockout filters, air drying equipment, etc. I know nitrogen is liquid at 1000 bar, not sure about air.
What does it cost to certify your proposed tank (the regulators can take a long time to decide - again, I assume that you have this taken care of), to compare to no cost listed above as I am not aware of a certification required on batteries in mobile use. And how often would the tank need to be tested? (I would assume 5 years without further research or evidence) My propane tank is regulated as portable equipment and costs me $25 every 5 years to trade it in - I could pay them to certify the same tank, but that would be more. The SCOTT airpack that I use as a volunteer firefighter costs something to certify ... not sure how much since I don't pay for it ... and I think the test that it is sent away for is called a hydro-test, it's done every 5 years. The Scott Airpack is only rated at 100 bar. A 1000 bar certification for mobile use - I would expect to cost more.
And what would it cost to drive - 30 miles in my example above, but I'll take costs for 100 miles or any other data you may have and scale it to make the comparison work. $3 of electricity does not appear to work out to 100 miles as listed above.
If we're to compare costs, in my opinion, all of the costs should be identified and quantified. My example above comes in at about $4 per day for the battery pack ($10,000 / 2500 days) and $3 for the electricity (1.50 per charge, 2 charges per day) for a total of $7. This compares well to the 7.5 liters of gas I use to drive to work and back each day, at 1.25 per liter. And that ignores the advantages of no oil changes, filter changes, other reduced maintenance, and spending less time at a gas station (which I currently list as priceless)
If I use your numbers, worst case, of 2000 cycles. $10,000 / 1000 days is $10 per day. Still $3 for the electricity * 1000 days = $3000. $13 per day - how does that compare to your air tank solution. Does it take less than $3 of electricity for your air tank solution?
If you've filed for patents then you have put a lot of time and effort into the analysis, the documentation process, and the red tape that is involved ... likely lawyers as well ... so you must have some 'example numbers' that you are planning to show investors, venture capital people, etc. Please post them for us to critique.
I'm trying to evaluate your claims as posted. If your system is $3 per day compared with $7 for my proposed system - I will gladly switch technologies. But I'm having problems with the math.
By the way, even as a newbie, you can post a link like this:
www dot my-patent-is-here dot com
We can't click on it directly, but it has worked for others in the past.
I look forward to further information.