
Carring the Energy Future: Comparing Hydrogen and Electricity for Transmission, Storage and Transportation.
I would highly recommend taking a look at the paper. I'd love to hear other's thoughts on what I think is a pretty convincing job of illustrating the viable alternatives to potential hydrogen applications. Its time to cut through the hype and get down to exploring alternative before we start (or continue) investing in the what may be a costly mistake.
What follows is a discussion on this thread between myself, and University of Oregon Professor of Physics, Greg Bothun. I would welcome and encourage the continuation of this discussion in the comments section below.
Me:
It seems that the only time that hydrogen is better than the alternatives is perhaps when you are trying to tap remote renewables that cannot be linked to the grid in any other manner (e.g. high voltage DC lines). In that case, tapping what would otherwise be an unusable renewable resource by making electorlytic hydrogen on site and piping it to demand centers would be a worthwhile model.
However, it still makes little sense to use that hydrogen as a transport fuel in fuel cell vehicles (FCVs). A better alternative would be to utilize the hydrogen near the demand center in more centralized hydrogen fuel cell power plants that can use more efficient high temperature fuel cells (like solid oxide FCs) rather than the low temp ones (PEM FCs) found in FCVs. The heat from the fuel cells can also be utilized in this model (and is wasted in PEM FVCs), making the process significantly more efficient.
Here's the back of the envelope math, starting with the H2 arriving at the demand center in pipelines and on through the same electric drive train to power the vehicle. This should allow a direct comparison between the two options:
Option A: Hydrogen FCVs utilize the gaseous H2 at fueling stations:Gaseous H2 at filling station... H2 compression for on-board storage: 92.5% (Liquification is much worse at 70% and has a host of problems regarding dealing with boil-off) PEM Fuel Cell: 45% eff (I think that's about average for PEM cells) Useful electric energy for electric drive train...
Total efficiency: 41.6%
Assuming 1 mmBtu of H2 input, we get 416,000 btu to the electric drive train
Option B: Electric vehicles (or plug-ins) utilizing electricity from central Fuel Cell Power Plants running on gaseous H2:Gaseous H2 at fuel cell power station... Solid Oxide Fuel Cell: 55% efficiency (commercially available SOFCs usually operate in the 50-60% range)
Electric transmission (very short distance as SOFC power plants can be situated within the city, near the point of end use): 99%AC-DC inverter and charge controller on EV: 95% Li-ion battery storage: 99% (99%+ culoumbic efficiency for Li-ion. This is only 66% for NiMH batteries) Battery self-discharge: 92% (assumes 8% per month self-discharge rate) useful electric energy for electric drive train...
Total efficiency: 47.1%
Assuming 1 mmBtu of H2 input, we get 471,000 btu to the electric drive train.
So, it looks like nearly a wash here. The SOFC/EV pathway is better but not significantly so. Why make a fuss? Well, I of course didn't figure in the recapture of most of the waste heat from the SOFC plant that goes to waste in the PEMFC pathway.
We can probably recapture 2/3rds of the waste heat from the SOFC power plant for co-gen (supply it as process heat or steam to a nearby industrial facility or maybe situate each plant within a neighborhood to provide electricity and heat for the whole neighborhood or some such ... SOFC power plants are not shabby neighbors to have, considering they produce zero emissions and produce useful heat or steam for export).
That means that if we assume the same 1 mmBtu of H2 input as above, we will get 300,000 btu of useful heat on top of the 471,000 btu to the electric drive train (66.7% waste heat capture * 45% SOFC waste heat = 30% useful heat; 30% * 10^6 btu = 300,000 btu). Now we end up with a total efficiency for the SOFC/cogen/EV pathway of 77.1% (i.e. (300,000 btu + 471,000 btu)/10^6 btu). That IS something to make a fuss about as it is a significantly more efficient use of the H2 than the PEM FCV pathway above which only manages to eke 416,000 btu of useful energy out of the H2.
Finally, as a briefly mentioned above, if HVDC lines can instead be used to reach the remote renewables, this option would probably be even better as the transmission losses from HVDC and gaseous H2 pipelines are just about a wash (with GH2 pipelines having a slight edge). The fuel cell is the bottle neck in both of the above pathways and the HVDC option avoids it completely. The question here, as with most proposed hydrogen uses, is why go through the phase change from electricity to H2 if you are just going to go back to electricity?
To which Prof Bothun replied:
There is a lot to respond to here, but I will stick to the first paragraph for now.
I am already familiar with this paper and I fully agree with it conclusions within the constraints that it imposes upon itself. Any argument involving efficiencies and traditional economies of scale will render Hydrogen as a poor investment strategy and not a wise choice. This is transparent.
What is left out of the discussion is the following critical point:
--> What happens when the extant infrastructure for delivery electricity is fully saturated and expansion of that infrastructure is neither economically or technially feasiable. At that piont we will require another mechanism to move energy. This critical aspect is left out of the discussion, continually.
If such saturation never occurs, then we will be fine, [but] the grid is not scalable forever and we already seeing that. In the same way that when the electiricty goes out on a cold winter night all night, sometime in the future, I will need to use wood as my energy source, so too would I need an alternative like Hydrogen. As long as we can continue to generate and distribute electricity on a grid basis then we should simply invest in mechanism that pump electricity into the grid. This could work.
Its my personal belief, (and others) that grid saturation and ineffectiviness and unrealiability is going to be a very large problem in the long term (30 years) and will start to be come more of a problem in the near term to the point that will be unable to effectively distribute all the electricity that we are generating. AT that point, everyone will want a hydrogen generator in their house, to kick in when the grid is down. If no one ever believes that the "grid will go down nationally" then there is no need for this proactive solution and investments are better made with just direct electric.
So yes, if direct electric is our future then hydrogen is not part of the generation equation, for pretty obvious reasons. But, if we are more limited by electricity delivery, then we will have problems and I don't believe that advanced battery storage packs powered by PV's on roofs is as scalable of a solution to this problem as using hydrogen as the means of energy transport. We can generate more "energy units" of hydrogen from large scale renewable projects in remote locatoins, than we can access sufficient material for building enough batteries.
This obviously plays in the transportation. If you can't recharge your electric vehicle because the grid is down for the day, then your stuck.
To sum up, if you believe that reliable and continuous electricity delivery will continue far into the future, then the direct electric economy is the right way to go. That could turn out to be the case. The advantage of hydrogen, however, is it can be used by the individuall locally for both electricity and for transportation and so it has flexibility. I liken this very much to the Strategic Petroleum Reserve (which is now down to 35 days capacity). We very much need a strategic Hydrogen reserve.
Please, weigh in with your comments and we can continue this discussion here. What do you think?...