What is the Efficiency of Solar-Powered Fuel Cell Vehicles?

As a point of clarity from my previous post.

The overall well to wheel of a solar to hydrogen powered car would be:
75% electrolysis efficiency x 90% hydrogen compression efficiency x 35% PEM fuel cell efficiency X 92% electric motor efficiency = 21.7% system efficiency

I would contend these numbers are not 100% accurate.

For example:
A 50% efficient fuel cell is only the theoretical limit of a fuel cell based off its Lower Heating Value (LHV). Fuel cell need additional subsystems to keep them well feed well humidified , and at the right temperature. This requires heat exchangers, fans, compressors, solenoids, coolant loops, water tanks and other balance of plant components that would lower the system efficiency considerably.
Similare subsystems also exist on normal internal combustion engines and therefore one should make sure that both engines (fuel cell or ICE) are being tested on a level playing field.

That leads me to my next point: Lower Heating Value or Higher Heating Value?
Most efficiencies for internal combustion engines are quoted off there Higher Heating Value (HHV) because it takes into consideration the latent heat associated with the steam in the exhaust of the engine. Most fuel cell experts quote efficiencies based on the Lower Heating Value (LHV) because the fuel cells they feel it is the most appropiate given the operation of standard hydrogen fuel cells. I would argue that in order to be compared to an internal combustion enginer one should use the HHV for both systems. This would lower the efficiency of the fuel cell marginally.

If you take my first two points and re-work the numbers such that both the ICE and the FC engines are taking into account real world factors (such as subsystem paracitics) and are both based on the HHV of the fuel the results would be much closer together. An ICE would be still be close to 12-18% based on the type of engine but the fuel cell efficiency would drop significantly to 25-35%.

Now please don't mistake my intentions - I am not saying that we should burn fossil fuels forever. I just wanted to point out some assumptions that might have been overlooked by this simple analysis.

Again, hydrogen is a means for storing energy for longer periods of time and in greater concentrations than is currently available with battery storage. Battery technology has too high of a loss rate for any extended period of time. Batteries and ultra capacitors are great for short term energy storage and their energy density improves almost daily. Let's not forget that hydrogen vehicles are in essence an electric vehicle with a fuel cell/ electrolyzer on board.
Any idiot who thinks that cracking a hydrocarbon to create hydrogen is a "green" idea is about two french fries short of a happy meal. You must still sequester the carbon output or you're just adding to the problem. Electrolysis through clean renewables or even biological means are more in line with a sustainable viewpoint.

On the matter of LHV vs HHV, the choice is in a sense an arbitrary one. The early heat engineers realised that their heat engines could not get useful work out of the exhaust emitted at 150C so they subtracted that heat from their 'idealised' heat content (the 'total' or Higher Heating Value) and resigned themselves to working with what remained, which they called the Lower Heating Value (thermodynamicists please excuse my simple approach here). So, the LHV is the maximum energy extractable by an engine that works between some upper temperature and 150C. Using that figure as the idealised maximum energy, the engine's efficiency is then given by the actual energy extracted as a proportion of the LHV. Fair enough.

How that rationale can be applied to an energy conversion device like a PEM fuel cell that operates more or less entirely below 150C is beyond me. It makes no sense.

I repeat; the choice of LHV by the fuel cell promoters makes their products look better. For hydrogen, using the LHV gives an apparent 18% efficiency boost, or about 7 percentage points in the region of 40% efficiency. That's why they do it.

Even if my cynical views on motivations are not accepted, it seems beyond dispute that efficiency comparisons between different energy conversion devices should all start off with the same energy content figure for a given fuel.

Asogan.
I think we both agree our future energy is with electrons where we differ is how we carry those electrons. You say battery I say hydrogen and I concede it might be a combination of both in our future vehicles.
Another "niche" market for hydrogen is the military whether it be with U.A.V.'s where hydrogen can deliver four times the endurance of todays most advanced batteries or to lighten the load of troops on the ground who are anchored down with heavy batteries.
I think we will see many "niche" markets being developed in the hydrogen industry then ofcourse it will be recognised as mainstream!
Mike H.

In 1993, while at Solec International (a PV module manufacturer now owned by Sanyo) we supplied the solar cells to PVI Corporation (formerly SEA Corp) that went into the concentrator collectors for the Xerox hydrogen vehicle project. See http://www.hygen.com/solar_hydrogen_vehicle_project.htm A few years ago, Xerox ended the project and the solar array was removed to Palm Desert, California. In 2004, while at Solar Integrated Technologies, we hooked up a Stuart Energy hydrogen generator to an SIT array to provide sun-to-wheels power for the Toyota fuel cell vehicle. Recommendation: don't wait for the "hydrogen highway." Go sun-to-wheels now with a net-metered PV system and an EV or plug-in hybrid.

Imagine: A daily commute without using a drop of gas.

The extended-range electric vehicle is no longer just a rumor. We have put tremendous design and engineering resources in place to make this vehicle a reality.

The Concept Chevy Volt, with its revolutionary E-Flex Propulsion System will be different than any previous electric vehicle because it will use a lithium-ion battery with a variety of range-extending onboard power sources, including gas and, in some vehicles, E85 ethanol(1) or biodiesel to recharge the battery while driving.

When it comes to plugging in, the Volt will be designed to use a common 110–volt household plug. For someone who drives less than 40 miles a day, Chevy Volt will use zero gasoline and produce zero emissions.(2) For longer trips, Chevy Volt's range-extending power source kicks in to recharge the lithium-ion battery pack as required. We expect a driving range of an estimated 640 miles.(3)

http://www.chevrolet.com/electriccar/


The best emissions strategy is a zero-emissions strategy.

Chevy has launched a test fleet of hydrogen-powered fuel cell Equinox SUVs.

The Equinox Fuel Cell will go nearly 150 miles per fill-up,(2) and reach a top speed of 100 mph. Green Car Journal has given the Chevy Equinox Fuel Cell its Green Car Vision Award®.(3) The Equinox Fuel Cell won the award over several nominees, including the Honda FCX Clarity and Toyota Prius Plug-In.

The reason for the low efficiency of the automobile engine of today is that it wastes so much of its energy in heat and exhaust pressure. But that situation doesn't have to prevail - it's just easier that way. Well, it was easier when gas was a buck a gallon. Now it's of interest to use that wasted energy. The Scudari engine is one such attempt, and others are underway.
Gasoline engine design may well achieve higher efficiencies soon, and I can see combined-cycle jet engines in cars pretty soon. All this would be simpler that trying to set up a hydrogen economy.

The best electric vehicle is one that takes its power from a cantinary line. Rail electrification uniquely puts transportation on the electrical grid, where wind, solar, "you name the source"...etc. will directly turn the wheels.

A 21st century transportation system should be high speed trains, traveling at 150 mph, powered by a wind farm in North Dakota.

Please excuse my ignorance, but if LHV takes into account the energy of water vapor that goes out in the exhaust, why is that not the appropriate heating value on which to base efficiency - PEM or Otto-cycle? Of course, the Otto-cycle also loses lots of heat through the cooling system radiator, and all heat losses lower efficiency. Said backwards, if we had a way to capture energy from the exhaust and use it to, say, run the headlights or the heater, would that not increase velhicle efficiency? (assuming for the purpose of question that energy capture could be done without increasing weight or otherwise adversely affecting vehicle performance)

There are several points in the previous postings that call for comment.

Fuel cell efficiency: The much-quoted high 'theoretical efficiency' or 'theoretical efficiency limit' of a fuel cell (which by the way is a lot higher than the 50% quoted by Todd Ryan) is a selective figure that ignores a host of causes of efficiency loss, all of which have a perfectly sound theoretical basis in electrochemistry. Anyway, just like a Carnot-limited heat engine, it's not the theoretical limit but the efficiency obtained in practice that counts and that number is generally 40% at most for a hydrogen-powered fuel cell. Efficiencies of that order can be found for example in the specification sheets for various Ballard fuel cell products. Independent verifications (as distinct from vendor claims) of fuel cell efficiencies are surprisingly rare.

LHV vs HHV: There is no good reason for fuel cell folk to prefer the LHV over the HHV except that the efficiency they can quote becomes greater. The politest way to put it is that the LHV convention for fuel cells is a straight marketing ploy.

Fuel cells in fork lifts: If fuel cells are becoming more popular in electric fork lifts, despite the price, it's because they allow longer operating times, something that is greatly valued in that business. Efficiency is of less interest to those customers.

Well-to-wheel efficiency: The solar PV vs gasoline exercise is an apples vs oranges comparison. One could also start off with the 20% efficiency of a PV cell in converting solar energy, in which case Sandy Thomas's number would go down to one-fifth of her calculated figure, say, 6%. But that approach would be equally wrong. It's just not a fair comparison.

1. Our civilization will have to live off insolation eventually whether we wreck the planet first or not.
2. Whichever route gives us the best results for a fixed amount of solar will win
3. The fewer conversions you do the more efficient the overall process tends to be as shown in the above calculations.
4. PV/battery/wheel is less stages than PV/electrolysis/compression/fuel cell/wheel so will win if battery or capacitor technology comes up to scratch. There seems to be no law of physics that says it wont.
5. Hydrogen leakage may well wreck the ozone layer ( see SciAmer ) so is a bad technology to invest in since you may have to write off your investment suddenly.
6. So focus on the battery/capacitor vehicle for mid term investment and forget hydrogen.

Michael,

The fork lift industry is a niche industry compared to the automobile industry.

That aside, my point is that the electron is a lot more versatile as a fuel compared to hydrogen and is a better enabler of renewables.

With the exception of biomass (which can also generate electrons via biomass boilers), all the other renewable options have to generate electrons first before making hydrogen.

Solar photocatalysis of water MIGHT make direct generation of hydrogen feasible, as MIGHT algae-but conversion efficiencies are too low and it's not economical as far as I know. Whereas wind generated electrons already compete with fossil fuels.

The extra step of electrons to H2 will make renewables even more uncompetitive with fossil liquid fuels due to the longer value chain.

Electrons level the playing field and the infrastructure is already in place.

Asogan.
Are you living beyond the black stump? Take for example the fork lift industry. The powers to be are replacing batteries in their machines with H.F.C.'s quicker than you can say the word HYDROGEN.

Mike H.

The whole fuel cell concept will remain just that - a concept except for niche applications. Solar PV with battery electric vehicles just makes a lot more sense.

There's an excellent WWF report that highlights this. http://assets.panda.org/downloads/plugged_in_full_report___final.pdf

The H2 economy was a useful way for the oil companies to 'stay in the game' as they're best suited to produce H2 from the reforming of natural gas or gasification and reforming of coal.

I should know; i worked as a mechanical engineer and business analyst for 6 years at an 'oil' company (Sasol - mentioned in the report with CTL technology).

Thank god that the costs of fuel cells and H2 storage remains prohibitive. Meanwhile the battery breakthroughs are coming in thick and fast, and will continue to do so, driven in part by the cash of the electronics industry, particularly laptop and cellphone manufacturers.

The fuel of the future is the electron.

If one pays attention to Sandy Thomas' words at the top, does a little research, and a little arithmetic an interesting scenario emerges. Here are some data to begin with:

The average daily commute is 32 miles round trip, 8,000 miles per year. An easy range for any H2 ICE powered car like the H2 converted Priuses currently being delivered by Proton Technologies.

BMW is testing dual fuel H2/gasoliine cars.

The average car is driven 15,000 miles per year. Probably at least 2/3 of those miles are commutes and other short trips.

One square ft. of solar panel can conservatively produce 23KWh e in a year which with conversion and compression efficiencies can produce .4Kg of H2 compressed to 7,000PSI.

At 50 miles/Kg (current city tests show 58 to 60) 500 sq. ft of solar panels can make enough H2 to power a Prius for 8,000 miles in a year. A 500 sq. ft. solar installation could easily be installed at most suburban homes. City dwellers,well----.

A duel fueled Prius type car carrying 1.6Kg of H2 and 6 gallons of gasoline or ethanol would have a range of 300 to 400 miles and then could be refueled with gasoline or ethanol. No new fueling infrastructure required.

69% of the petroleum used in the United States goes for transportation.

66% of our oil is imported, mostly from Canada and Mexico, not Saudi Arabia.

If 2/3 of the transport fuel was H2 and ethanol, oil imports and usage would be reduced dramatically. This would seem to be a reasonable near term/mid term solution to fueling the nations vehicles.

A few weeks ago, the Sietch Blog posted an article about how carbon emissions can impact our health: http://www.blog.thesietch.org/2008/03/18/your-car-is-trying-to-kill-you-or-at-the-very-least-make-you-sick/.

Although evaluating and understanding fuel efficiency is important, hydrogen carries the promise to guide us away from using oil and coal, while simultaneously improving our environment by reducing greenhouse gases. The Hydrogen Education Foundation is helping people understand these benefits.

Yes, there is room for improvement, but that is true for any technology. The fact remains that combining the production of hydrogen from solar energy via electrolysis creates a completely clean system - the only emission in the process is water. Only hydrogen provides the ability to be produced from any renewable resource via electrolysis of water, or a few other options such as anaerobic digestion, and then be stored in large quantities for later use.

To learn more about the benefits of hydrogen, we invite everyone to
please visit www.h2andyou.org.

Being trained in thermodynamics, I feel it necessary to clarify the understanding of the Higher Heating Value (HHV) and Lower Heating Value (LHV) as these have been grossly misused by many professionals in many fields.

HHV by definition considers the products of combustion of the fuel to be
1) Carbon dioxide vapor, and
2) Liquid water
This is because the prodcuts of combustion are considered to be in their normal state at 25C which for water is as a liquid.

LHV by contast defines the products of combustion as;
1) Carbon dioxide vapor, and
2) Water vapor
The difference is the latent heat of the water in the hot exhaust.

Having defined these terms, an internal combusiton engine (ICE) is correct in using the LHV in its efficiency calculations as the exhaust is hot and the water is in the vap[or form. On the other hand, a Fuel Can operate at much lower termepratures and can produce a liquid water stream (NASA does this to produce water for astronauts). Therefore, it is more reasonalble and technically correct for the fuel cell to use the HHV in its efficiency determination.

Good question, Mike. 66% is imported total. Canada is the largest supplier, then Mexico, then Saudi Arabia, then a string of smaller sources according to to official government data.

A correction: Quantum Technologies, Not "Protpn" is converting Prius Hybrids to H2. Sorry for the error.

Ray.
You have come up with some interesting figures if 66% of oil imported into the United States comes from Canada and Mexico why are they fighting a multi trillion dollar oil war in the middle east.
Surely that money would be better spent on a home grown hydrogen economy?
MIke H.

To back up some of the commenters here.
http://greyfalcon.net/hydrogen2.png
http://greyfalcon.net/hydrogen4.png
http://greyfalcon.net/hydrogen3.png
http://greyfalcon.net/hydrogen2
http://greyfalcon.net/hydrogen3
http://www.efcf.com/reports/E11.pdf
http://www.spiegel.de/international/spiegel/0,1518,448648,00.html

==The powers to be are replacing batteries in their machines with H.F.C.'s quicker than you can say the word HYDROGEN.==
I call BS.
http://www.posicharge.com/ford.html
http://www.posicharge.com/5-0.html
(Tower Automotive is a posicharge customer, and creates parts for nearly every significant car manufacturer you can think of)
http://www.towerautomotive.com/customers

I strongly suspect you gain some efficiency if you put the electricity into batteries rather than into generating hydrogen. A couple of your percentages then do not apply. Also, using excess energy when it is available is definitely the way to go. For this demand balancing (as opposed to supply balancing) to be effective, we must have enough renewable energy mixed into the grid so that fairly often excess power is being produced. As far as hydrogen generation is concerned, one musn't forget that in a commercial set up, a by product is the very salable very pure oxygen which is used in medicine, steel manufacture, welding, cutting and so forth. Has anyond factored this into the financial equation.

http://mtkass.blogspot.com/2007/07/excess-energy-what-to-do.html