The H?O Question
By David Behn
Plug-In America is at it again: getting overzealous to the point of ridiculousness. In their latest PIA Report, a Congressman is pictured sitting in the Calcars PHEV, holding the plug, while the caption proclaims that he is "holding up the infrastructure".
Now, wait a minute, guys. If I understand the concept of a PHEV (and I can assure you that I do), there is no advantage to a PHEV over a regular HEV, UNLESS you actually intend to plug into something, sometimes. And there is a near 100% chance that that is going to be the electric grid, one of the largest and most expensive infrastructures in North America.
I think I can also assume that you are going to actually use the gasoline engine once in a while (if you aren't, why did you purchase a PHEV? You would be better off with a full electric). This means you will also be tapping into another monstrous infrastructure (and possibly the most inefficient)-the gasoline infrastructure-as well as (did you guess it?) our hydrogen infrastructure.
Yes, Virginia, we do have a hydrogen infrastructure. And a good portion of its output (as much as a third, by some estimates) is used to refine gasoline.
To be useful in a modern ICE engine, even regular grade gasoline needs to have an octane booster. This used to be lead, but because of environmental issues, we tried switching to other substances, each of which was found wanting, until we got to ethanol, which is fast becoming the preferred octane booster. This brings us to infrastructure number four, the booming ethanol production industry.
So we have so far identified four major infrastructures on which the PHEV depends. We could go on-the coal industry (three quarters of North America's electricity is still produced from coal), the gas industry, the nuclear industry, etc.-but you get the idea, I hope. It has often been referred to as The Interconnectedness of All Things.
Infrastructures are not forever, so it's no good using the excuse that we already have these things. Our infrastructures age, wear out, evolve, and need constant maintenance, repair, and upgrading, for as long as we continue to depend on them. Our grid has been under constant change of this sort since Westinghouse installed the first AC generating station near Buffalo, New York, in 1895.
The PIA also keeps flailing away at the fuel cell EV, claiming that "the use of renewable electricity to generate the hydrogen for fuel cell vehicles is four times less efficient than using the same electricity to power a battery EV". They base this on a 2002 paper by Alec Brooks. They are now challenging CARB to refute those claims, and claim that CARB has "ignored" the report
My college statistics professor (whose name, unfortunately, has been lost to memory, (that was oh, so long ago) had a number of favourite sayings, including that "figures don't lie, but liars figure". I personally don't like the term "liar", as it conveys intent, and I suspect that these people actually believe what they are repeating; but this doesn't change the fact that they are wrong.
CARB has good reason to "ignore" the Brooks study; it was flawed. It is not CARB's mandate to use their time to refute every armchair analysis that comes along; their time is too valuable. But I've got some time, and the inclination.
I have already responded in detail to the Brooks study in a previous issue, and I refer everyone back to it, to avoid covering exactly the same ground again. Therefore I will introduce you to another study, this one published in Home Power magazine, issue #114, August/September 2006, which makes a similar claim (these people are persistent, if nothing else).
The modus operandi of these studies is simple: make hydrogen from the electric grid, do everything it is possible to do with hydrogen (whether it needs it or not) to turn it back into AC electricity, and ignore as many losses as possible in the alternative system (or ignore the alternative system altogether, hoping we will assume we don't need one).
In this study (titled "the myth of the hydrogen future") the author starts with grid AC electricity, and takes it through eight steps to get back to AC electricity, using two different storage methods (liquid hydrogen and gaseous hydrogen) to come up with an efficiency (for gaseous hydrogen) of 26% (which is incidentally, about the typical efficiency of a coal-fired generating plant) and (for liquid hydrogen) 16% (about the efficiency of an average silicon solar cell, and about twice that of a thinfilm solar cell).
But take a look at what we have done. We have taken AC electricity, converted it to hydrogen, and then back to AC electricity. Along the way we have compressed it or liquefied it. For what purpose?
Much has been made of the fact that hydrogen is an energy carrier, not an energy source. But exactly the same thing can be said of electricity. It is an energy carrier, not an energy source. But hydrogen is storable, while grid AC is not. To store its energy requires rectification and storage in another form, either as a charge on a plate (capacitors), or as chemical energy (battery), or as hydrogen.
Since it would be insane to convert
AC to hydrogen and back to AC just to have a "hydrogen economy", we can safely
assume that we are doing it because we need to store it. The most likely
competitive system would be a battery system, as supercapacitors are still too
bulky and expensive. So I propose we compare two storage systems. In the left
column I will list the nine stages listed by the author for gaseous hydrogen,
and his figures for efficiencies (the figures for accumulated efficiency will be
listed in parenthesis beside the figures for stage efficiency). In the middle
column I will list the equivalent battery stages and assign some reasonable
efficiencies. Comments will appear on the right.)
|AC electricity||AC||electricity grid or renewable, see note 1|
|Rectification 95%||Rectification 95%||authors' inclusion, see note 2|
|Electrolyzation 75% (71%)||Charger eff 85% (81%)||see remarks, note 3|
|Compression 90% (64%)||Batt eff on charge 88% (71%)||see remarks, note 4|
|Transportation 90% (58%)||Tran (who knows, lead's heavy)||see remarks, note 5|
|Transferred 95% (55%)||Transf (not app)||see remarks, note 6|
|Stored 100% (55%)||Stored 100% (71%)||author's figure, see note 7|
|Fuel Cell to DC 50% (27%)||Battery to DC 88% (62%)||author's fig. for cell, note 8|
|Inverted to AC 95% (26%)||Inverted to AC 95% (59%)||author's figure, see note 9|
Now my comments:
- I suppose there is a rationale for backup storage of grid electricity, given the blackout of a few years ago, but it is obvious from the figures for both battery and hydrogen storage that if you are on the grid you would want to capture most of it directly and store just enough for emergencies. This is how most backup systems work, anyway
- I don't know why the author included this as a separate item, as it is usually covered in the appliance's efficiency rating, but as it has no significant effect I have left it in.
- The author's figure for electrolyzation is consistent with figures I have seen for high-pressure electrolyzers. I know some people assume 90% efficiency for chargers, but I believe this to be unrealistic, especially if we are working from the variable output of a solar cell or wind generator I have not seen a manufacturer claim more than 85% efficiency.
- High pressure electrolyzers can store hydrogen at up to 10,000 psi without external compression There certainly is no need for more than that. You can strike item 4 off the list for hydrogen efficiency. Battery efficiency of lithium batteries can run as high as 93% but they are much too costly and problematic for large capacity storage, so lead-acid deep cycle batteries reign here. I have no actual figures for their efficiency but my guess is probably pretty close. So the efficiency of hydrogen and batteries at this stage are virtually matched at 71%.
The study is dated 2002, about the same time as the data in the Brooks study. High pressure equalizers are relatively new, and it is possible that the author was unaware of them. Such are the dangers of relying on 4-year-old studies for relevant data.
- What is this doing here? Grid electricity, which is an energy carrier, and perfectly capable of delivering electricity to the point of use, or onsite renewable energy, is already at the point of use. Is it our purpose to use this energy, or to transport it endlessly about? Strike this one!
- One would think that any self-respecting high-pressure electrolyzer would be perfectly capable of stuffing the hydrogen into the tanks by itself. The hydrogen will be used on site, so there is no need of a transfer. Strike this one, too!
- I fear the author is just a tad optimistic on this one, since both hydrogen storage and battery storage losses do occur, but since they are small, we'll let it pass.
- 50% is pessimistic for a PEM cell on hydrogen. A state-of-the-art hydrogen-fueled PEM cell today should be able to do at least 65%. Another case of obsolete data.
- A tad optimistic, I think, but since it affects both sides equally we'll let it pass.
Now the hydrogen figures look like
- AC electricity
- Rectification 95%
- Electrolyzation 75% (71%)
- Stored 100% (71%)
- Fuel cell to DC 65% (46%)
- Inverted to AC 95% (44%)
This compares to 59% for batteries. That is a ratio of 1.3:1, not 4:1 (note that even if we used the author's fuel cell efficiency figures we would still be only at a 1.7:1 ratio). Even if we stop there, this is not bad And at large storage capacities (more than about 40 kWh or so) it becomes more cost-effective than batteries, since batteries are more costly and require more maintenance than hydrogen tanks.
But we don't have to stop there. If we plan wisely, we can take advantage of cogeneration. The operating temperature of a fuel cell is high enough to provide hot water and space heat for a dwelling I have seen claims of achieving an effective efficiency of 95% using such methods. That is probably a stretch. But if we can achieve even 85% we would be at par with batteries for overall storage efficiency.
Notice that these figures would also apply, with only minor changes, to the case of running a fuel cell vehicle, as opposed to a battery electric, from grid electricity. We would have to charge the transfer item (95% efficiency), stage 6 in the author's analysis to the fcv (since we will transfer hydrogen from storage to the vehicle), while crediting it with providing space heat by cogeneration.
It should also be noted that if we are on grid electricity, we can "opportunity charge" the tanks at low-usage times, just as we can do with battery electrics.
We should also keep in mind that
it is not really our intention to displace battery EVs with FCVs2,
but to replace the ICE, which has a much lower efficiency than either battery or
fuel cell vehicles. Neither is it our intention to generate hydrogen from the
grid to run FCV's on grid electricity, except in limited special circumstances.
There are too many other good ways to get hydrogen. Any renewable process that
can yield ethanol, methanol, biodiesel, or methane can also yield hydrogen. And
hydrogen is a byproduct of waste processing, water purification, and many
industrial processes3 Fuel cells can convert these sources into grid
electricity more efficiently and more cleanly than any current method. It is on
this side of the grid-the production side-that hydrogen can have the greatest
So there is my analysis. I even used most of the author's figures for the hydrogen side. I just chucked out the dead wood. Makes a dramatic difference, doesn't it?
I also ignored the liquid hydrogen
option. It should be used only where long-distance transport of hydrogen is
absolutely unavoidable, or when the desired end product is liquid
CARB did not pull the plug on EV's, as PIA has suggested; certain car manufacturers did. They did it because they had a perception (justified or not) that they could not sell enough of them to make money, and they lobbied hard to pressure CARB to soften its mandate. Other manufacturers who do not need the encouragement of a CARB mandate will take their place, if we let them know we want EV's.
PIA should take another look at the
fuel cell issue. They ought to realize that research on fuel cells and fuel cell
vehicles will benefit EV's and PHEV's as well. Let's get
2 In some cases, however, we are doing that. Many warehouses these days are removing the battery packs from forklifts and other goods movers that operate indoors and replacing them with fuel cells and hydrogen tanks, and installing refueling appliances. The reason is that they want to keep these vehicles, which represent a considerable investment, working 24 hours per day. They can't afford the downtime it takes to recharge their batteries.
For similar reasons, vehicles that spend a lot of time making long trips won't be battery electrics. Travelers don't want to sit around and wait hours to recharge their vehicles. Transport trucks can not afford the down time. Fuel cell vehicles can do the job, and much more efficiently than ICE vehicles.
3 An example of the latter is chlorine production, which yields large amounts of hydrogen. The plant also consumes large amounts of electricity.
Dow Chemical has now added fuel cells to their chlorine production facilities. The hydrogen is fed onsite to the fuel cell, which converts it to electricity and feeds it to the grid. Every kWh returned to the grid this way means 1 less kWh that has to come from a power plant somewhere else on the grid.
4 Incidently, quite a number of our EVCO members have PHEV's. One of these was pictured in the March/April EV circuit. They run on either electric power or meat and potatoes, and are called Human-Powered PHEV's (HPPHEV's?) or electric-assisted bicycles.
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