NASA Challenge - Can we win this? - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: October 11, 2012, 01:10:11 pm
content: Now this is a serious question.NASA has announced a challenge for an energy storage system requiring very high efficiency. Can we win this thing?I believe that if we (this forum) has enough expertise and stand a good chance to win it provided we can organize ourselves. There is a1.000.000$award if we can pull it off. Even if we do not participate it is still a good exercise for the gray matter.Details:Quotehttp://www.nightrover.org/rules-regulationsOr check the PDF below for the rules and specs

author: Unknown
author_rank: Unknown
timestamp: October 11, 2012, 03:02:22 pm
content: Here is one method winch might work:Normal Li-ion batteries reach energy densities of up to 250 W.h/kg. The point of the exercise is to invent some voodoo magic to boost this past 300 W.h/kg. Considering that lunar night is as cold as -177 C and the day (in the test) is as hot as +25 C the voodoo seems obvious: Use the thermal mass of the batteries to store additional energy during the day. Allow this energy to escape during the night by placing a stirling engine between the hot batteries and the cold environment. A miniature free piston stirling engine might do the job nicely.A good thing about flating piston stirling engines is that they have no rotating or sliding parts therefore no friction. Also they are completely hermetic so operating them in space is easy.Here is one that NASA prepared earlierntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080012733_2008011106.pdfSo what do you think?

author: Unknown
author_rank: Unknown
timestamp: October 11, 2012, 04:26:51 pm
content: Here is what it might look like:

author: Unknown
author_rank: Unknown
timestamp: October 11, 2012, 05:28:15 pm
content: No takers ?Anyway, lets do some maths:Specific heat of a Li - ion battery is roughly 1000J/kg*K. In other words to raise the temperature of 1kg battery 1 Kelvin we need to apply 1000 Joules of energy.Lets assume we have 90kg battery at 25*C temperature. If we take this battery to an environment which is as cold as -177*C i.e. temp. diff. of 202*C. Therefore to reach thermal equilibrium, 18.18MJ of energy must flow from the battery to the environment until thermal equilibrium is reached. Assuming ballpark efficiency of 40% for a good stirling engine we have 7.2 MJ energy available for recovery.Assuming a normal energy density of 0.90MJ/kg this approach gives us extra 0.09 MJ/kg10% increase already !!edit: 10% is without taking into account the self heating of the battery during charge and discharge which work to our advantage as well.

author: RCMR
author_rank: Frequent Contributor
timestamp: October 12, 2012, 02:10:46 am
content: Fail I'm afraid.Lithium cells have a fairly narrow range of temperatures over which they can deliver their rated capacity.When they get hot -- they fail.When they get cold -- their capacity drops dramatically.It'll be swings and roundabouts using your proposed strategy and I'm afraid you'll lose a *lot* more than you gain :-(

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 12, 2012, 02:38:40 am
content: Interesting challenge. thanks for the contribution HalAnother problem with the stirling engine is how do you do the heat transfer in a vacuum?It might be very cold but how is the external reservior going to change temperature at any useful speed?According to wikpedia there are other Lithium Chemistrys that have the required Wh/kg. Such as Li-SOCl2 @ 500 wh/kg.I don't know how practical any of these are.The other one that sprang to mind was hydrogen fuel cells. Again I don't know how feasible these would be.

author: Unknown
author_rank: Unknown
timestamp: October 12, 2012, 03:53:17 am
content: Quote from: RCMR on October 12, 2012, 02:10:46 amI guess I was hoping that the 60% inefficiency of the stirling cycle would work out somehow to prevent the batteries from getting to rock bottom temperature. Stirling engine is perfectly capable of extracting thermal energy even if the battery is dead but there is no use in that - it won't be able to meet the power demand alone. So might as well cut-off once the batteries are empty. Some other chemistry perhaps?Quote from: HackedFridgeMagnet on October 12, 2012, 02:38:40 amIn vacuum all heat transfer to the environment is radiative. If you want to cool something you expose it to the deep black space, it radiates infrared light and cools down. Works very well because deep space is only 4*K above absolute zero.Looked at the other lithium battery types but most of them are lab experiments or protected by a patent thicket, no hope of getting some.Hydrogen is ruled out by the requirements. No permission to outgass. No hazardous substances allowed inside test chamber.

author: Unknown
author_rank: Unknown
timestamp: October 13, 2012, 03:45:31 am
content: It seems like an Aussie company is halfway there alreadyhttp://en.wikipedia.org/wiki/Zinc-bromine_flow_batteryhttp://www.redflow.com.au/docs/assessment__zinc_bromine_battery.pdf

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: October 13, 2012, 06:08:46 am
content: Not all sweet in the land of Redflow.RedFlow puts expansion on hold, cuts Brisbane workforcehttp://reneweconomy.com.au/2012/redflow-puts-expansion-on-hold-cuts-brisbane-workforce-44649

author: Unknown
author_rank: Unknown
timestamp: October 13, 2012, 02:34:01 pm
content: Quote from: HackedFridgeMagnet on October 13, 2012, 06:08:46 amUgh! Overzealous startups and their worldly naiveté... Well If I was them I'd be trying to pull a much needed public stunt out of this.

author: sacherjj
author_rank: Frequent Contributor
timestamp: October 13, 2012, 03:50:02 pm
content: I wonder if NASA currently provides heat to their Li power pack or just use charge/discharge thermal inefficiency and insulation?