NASA Challenge - Can we win this?

[HLA-27b]

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 a 1.000.000$ award if we can pull it off. Even if we do not participate it is still a good exercise for the gray matter.

Details:

The Night Rover Challenge is the latest in a successful series of Centennial Challenge competitions from NASA's Office of the Chief Technologist.

Leading researchers and entrepreneurs are being challenged to create the best energy storage system that allows a simulated lunar rover to operate through the sheer darkness of the lunar night while exceeding a minimum of 300 wh/kg.

Systems will be tested through two rounds of trials:

    Phase 1: Ambient Trials: storage systems must operate through two lunar cycles (~2 months), providing adequate power to meet a simulated lunar mission profile.
    Phase 2: Lunar Condition Trials: systems who pass the phase 1 trials will be allowed to compete for the lunar condition trials. Here the systems will be tested through 1 lunar cycle (708 hours, or 29.5 days), at low temperatures and pressures simulating the lunar environment.

Awards will be provided for the teams performing the best above our baseline requirements in both phase 1 and phase 2 trials. Award winners will receive a piece of the $1.5 Million prize purse provided by NASA. For specific guidance on the restrictions of what the storage systems must achieve, how they will be tested, and details on the awards, please see the Rules and Regulations.

http://www.nightrover.org/rules-regulations

Or check the PDF below for the rules and specs

[HLA-27b]

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 earlier
ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080012733_2008011106.pdf

So what do you think?

[HLA-27b]

Here is what it might look like:

[HLA-27b]

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/kg
10% 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.

[RCMR]

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 :-(

[HackedFridgeMagnet]

Interesting challenge. thanks for the contribution Hal

Another 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.

[HLA-27b]

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 :-(

I 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?

Interesting challenge. thanks for the contribution Hal

Another 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.

In 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.

[HLA-27b]

It seems like an Aussie company is halfway there already 





http://en.wikipedia.org/wiki/Zinc-bromine_flow_battery

http://www.redflow.com.au/docs/assessment__zinc_bromine_battery.pdf

[HackedFridgeMagnet]

Not all sweet in the land of Redflow.

RedFlow puts expansion on hold, cuts Brisbane workforce


http://reneweconomy.com.au/2012/redflow-puts-expansion-on-hold-cuts-brisbane-workforce-44649

[HLA-27b]

Not all sweet in the land of Redflow.

RedFlow puts expansion on hold, cuts Brisbane workforce
http://reneweconomy.com.au/2012/redflow-puts-expansion-on-hold-cuts-brisbane-workforce-44649

Ugh! 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.

[sacherjj]

I wonder if NASA currently provides heat to their Li power pack or just use charge/discharge thermal inefficiency and insulation?