# Possible solar/hydrogen set for the home



## Telco (Jun 28, 2008)

MIT has developed a cheap way to make hydrogen at home for use in a fuel cell, that will let someone use solar 24hrs a day without batteries. They say the same thing can be used to refill a hydrogen powered car. If they can make the theory work in the real world, then things are looking up.


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## NeilBlanchard (Feb 11, 2009)

Hi,

It could also be used to heat a building.


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## Jason Lattimer (Dec 27, 2008)

I saw this before. A man on a show I saw had solar panels that used electrolysis to generate hydrogen with the excess electricity and was stored in large compressed H2 tanks that ran a fuel cell to make electricity for him at night.

I would think batteries would be substantially more efficient though wouldn't it?


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## Technologic (Jul 20, 2008)

Jason Lattimer said:


> I would think batteries would be substantially more efficient though wouldn't it?


Much more efficient.

such a setup with hydrogen would at best be 10% efficient (if you're compressing it)


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## Jason Lattimer (Dec 27, 2008)

The one good thing with the system I saw is that without batteries the rest of the system should be maintenance free shouldn't it?


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## Technologic (Jul 20, 2008)

Jason Lattimer said:


> The one good thing with the system I saw is that without batteries the rest of the system should be maintenance free shouldn't it?


Compressors die fairly quickly actually... especially if poorly lubricated (ie. run by amateurs). I mean you're talking about liquifying a few hundred gallons of hydrogen a month, that will wear a compressor out in about 2-3 years (such a compressor would cost about about $500+ to repair each time depending how large it is)

likewise fuel cells for hydrogen have to be constantly kept at super hot temps (the lowest electrolyte of which is about 200C) many of the electrolytes that are 50%+ efficient (the highest you can get) need to be 600C.

liquid hydrogen at about 5000psi weighs 0.07kg/L and sells currently for about $10 per kg. 
Per unit _mass _hydrogen is 2.6 times or so more energy dense than gasoline. The problem is that volumetrically as you can see above it takes a lot of space to store the same amount of energy.

Likewise if you're talking about fossil fuels being converted to electricity, into hydrogen, compressed, then back into electricity... it would be about 3-4 times more efficient in the realm of both emissions and electricity draw to just stick a gas powered generator there instead.


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## PhantomPholly (Aug 20, 2008)

A compressor not attempting to liquefy the hydrogen but only compress it to, say, 3000psi would not wear as badly. Although bulky, lightweight Kevlar tanks could readily hold enough fuel for most commuters.

Since most ICE vehicles can be configured to run on either gas or hydrogen (at some small expense), this would still allow longer trips using petroleum fuels.

Or, the hydrogen could power a fuel cell for an electric vehicle. Then you'd be out of luck for longer drives (until hydrogen is widely available) unless you tow a genset.


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## Technologic (Jul 20, 2008)

PhantomPholly said:


> Or, the hydrogen could power a fuel cell for an electric vehicle. Then you'd be out of luck for longer drives (until hydrogen is widely available) unless you tow a genset.


The energy density of liquid hydrogen is just too low... that's my point. It must be in a fuel cell period. Burning it in an ICE is a horrible idea for range and performance.

it's PE is only 90,000KWH per kg (or around 6300KWH per liter).

Burning this at 25% efficiency (transmission and ICE losses) means per liter you'd see at most 1500 KWH of power generated (vs. 1kg at 1.25L of gas which yields about 3 times that much)

The best solution is try and get all of that KWH out of it through a 65+% fuel cell (one that requires it to be kept at 600 Celcius). Which could get you 4000KWH... so for 200 miles in most situations you'd need about 12 liters of that (if they kept the horrible high Cd designs america loves).

That's not including the inefficiency of the unit itself though... converting hydrogen out of water via electricity and turning it into liquid hydrogen via a compressor (there are more efficient ways of course) still yields about 15% tops efficiency to get the liquid hydrogen... meaning that you're borderline 3-4% efficient by the time you burn it in a ICE.


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## david85 (Nov 12, 2007)

Technologic and Jason Lattimer are right. Even if the technical, cost and safety aspects could be addressed you are still looking at horrible efficiency of a hydrogen based energy distribution system on a small or large scale. The Fuel cell it self can be anywhere from 20-50% efficient for the lower temp units but the energy involved in making that fuel in the first place is also inefficient.

Its true that liquid hydrogen could in theory give an EV a 2000 mile range rather easily, but I don't think I want a liquid tank of that stuff in my car. Not to mention how easily it could be turned into a bomb.

The fact that the energy comes from solar power is one favorable aspect of the idea, but still the low efficiency makes ICEs look good. I think the absolute best case senario is for 30% net peak efficiency if you use the best of the best tech available right now. I wonder what that would cost, on second thought I don't want to know.


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## PhantomPholly (Aug 20, 2008)

Technologic said:


> The energy density of liquid hydrogen is just too low... that's my point. It must be in a fuel cell period. Burning it in an ICE is a horrible idea for range and performance.
> 
> it's PE is only 90,000KWH per kg (or around 6300KWH per liter).
> 
> ...


Fuel cells are already more efficient than that, and don't require the high temps. I suspect you're referring to outdated info.

But, yes, in any event the fuel cell answer is better long term.


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## Technologic (Jul 20, 2008)

PhantomPholly said:


> Fuel cells are already more efficient than that, and don't require the high temps. I suspect you're referring to outdated info.
> 
> But, yes, in any event the fuel cell answer is better long term.


I know of about 8 different electrolytes for fuel cells and all of them need to be above 200C... the more efficient ones are usually hotter.

"while automotive fuel cells require a 5,000 hour lifespan (the equivalent of 150,000 miles) under extreme temperatures. Current service life is 7,300 hours under cycling conditions"

http://en.wikipedia.org/wiki/Direct_carbon_fuel_cell

Are the only ones with a 70%+ efficiency... and they require 700C temps.

the only 60%+ one that's less than 80C is the alkaline fuel cells


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## NeilBlanchard (Feb 11, 2009)

Hello,

What about the possibility of solid hydrogen storage i.e. in metal powder? Ovonics (Stan Ovshinsky) showed a tank with metal powder in it, that can hold 2X as much hydrogen as a high pressure tank in the same volume; on a Scientific American show a couple of years back.


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## Technologic (Jul 20, 2008)

NeilBlanchard said:


> Hello,
> 
> What about the possibility of solid hydrogen storage i.e. in metal powder? Ovonics (Stan Ovshinsky) showed a tank with metal powder in it, that can hold 2X as much hydrogen as a high pressure tank in the same volume; on a Scientific American show a couple of years back.


Guess it would depend on cost of the powder, how much energy goes into making it, how long it lasts, how much it costs, what the byproducts are (hazardous?)

Batteries are relatively simple, and nearly 100% recyclable.


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