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June 19, 2007

NREL “Wind to Hydrogen” Facility

Category: Hydrogen,Wind power – Dan 6:31 am

NREL (the National Renewable Energy Lab) recently published information on their new experimental “Wind to Hydrogen” facility. This is an idea that has been promoted for some time by the Leighty Foundation, and it’s a clear example of “Smart Green Energy”.

The challenge: Wind power is intermittent. The solution: Use unneeded power to generate hydrogen which is stored on-site. This hydrogen is then converted back to electricity in a fuel cell when the wind isn’t blowing and power is needed.

“By marrying wind turbines to hydrogen production, we create a synergy that systematically reduces the drawbacks of each,” Richard Kelly, Xcel Energy chairman, president and CEO

While mobile hydrogen storage is a problem (see “Mythbusters – Hydrogen will fuel our cars?“), there’s no problem with industrial-scale hydrogen storage, especially where wind power is generated (which by it’s nature is out in the wide open spaces).

NREL’s Wind2H2 project is designed to analyze the tradeoffs using different types of wind generators, different approaches to convert the electricity to hydrogen, and issues related to the integration of these technologies as well as the operation of electrolyzers with different gas output pressures.

The NREL site also has a very cool animation to show the different configurations being tested.NREL “Wind to Hydrogen” Animation

April 3, 2007

Mythbusters – Hydrogen will fuel our cars?

Category: Hydrogen,Mythbusters – Dan 4:02 pm

I guess my blog entry on hydrogen for transmission and storage created a bit of confusion regarding the most common “talk”, that is hydrogen to power cars. To wit:

Hydrogen Can Provide Long-Term Energy Security Through Use Of Diverse Domestic Resources. The President’s Hydrogen Fuel Initiative and the FreedomCAR partnership will reduce America’s need for imported oil and help clean the air by aiding the development of hydrogen fuel cells and affordable hydrogen-powered cars. Together, these two initiatives constitute a commitment of $1.7 billion over five years.[1]

This was directly off the whitehouse.gov website. I suppose the good news here is that, in more recent white house documents[2] the President isn’t talking so much about hydrogen and cars.

So let me go on record as saying that, in terms of an automotive fuel, hydrogen is a dumb idea. This is a myth that needs to be dispelled. There are better alternatives, both for the near and long term.

Hydrogen – The Perfect Fuel?

But wait? Isn’t hydrogen the perfect fuel? Consider:

  • Abundant – Hydrogen is the most abundant element in the universe
  • Clean – Hydrogen burns clean – no carbon dioxide will come out of your tailpipe
  • Easy electricity – Feed hydrogen into a fuel-cell stack and you get clean electricity
  • Powerful – Pound for pound, hydrogen has three times the energy of gasoline

What’s not to like?

Major technical hurdles for automobiles

Technology review just did an article on the BMW “Hydrogen 7”, a prototype hydrogen vehicle. Their conclusion:

In the context of the overall energy economy, a car like the Hydrogen 7 would proba­bly produce far more carbon dioxide emissions than gasoline-powered cars available today. And changing this calculation would take multiple breakthroughs–which study after study has predicted will take decades, if they arrive at all. In fact, the Hydrogen 7 and its hydrogen-fuel-cell cousins are, in many ways, simply flashy distractions produced by automakers who should be taking stronger immediate action to reduce the greenhouse-gas emissions of their cars.[3]

BMW's Hydrogen 7 Sedan
“BMW’s Hydrogen 7 Sedan”

Why such a negative quote? Let’s consider the current technical realities:

The “hydrogen tank”

We take filling up the tank with gas for granted. Don’t smoke, leave your phone in the car, try not to spill any, and don’t top off. Otherwise, you end up with 10 to 20 gallons of fuel that, at normal temperatures, can sit in your tank for months, propel your car for 300 miles or so, and is relatively unlikely to leak or blow up.

What’s the hydrogen tank alternative. The April’07 issue of Scientific American just did a comprehensive article on “Gassing Up with Hydrogen”[4] that looked at five different technologies for on-board hydrogen storage. The problem is that, although hydrogen, pound for pound has three times the energy content than gasoline, at normal temperatures and pressures hydrogen has only 1/3000 the energy density of gas: a 20 gallon tank of hydrogen would only propel your car about 500 feet!

The solution will fall into one of three categories:

  • Compressed hydrogen – Simple. If hydrogen has 1/3000 the energy density of gas, then compressing it 3000 times should solve the problem. Except that would require pressuring the tank to over 40,000 psi — 8 to 10 times the pressure of a good scuba tank. While theoretically possible, this requires both new advances in tank technology, special protection so the tank isn’t ruptured in an accident, and a means of providing ultra-high pressure hydrogen at the filling station.
  • Liquified hydrogen – To maximize density, you can liquify hydrogen. In liquid form, hydrogen has about 30% of the energy density of gasoline, so you’d need a tank that was roughly 3 times as big for the same fuel range. Hydrogen liquifies at -253°C (about -420°F). The challenge; you need lots of insulation, it takes lots of energy to cool hydrogen to this temperature, and you’ll constantly loose fuel as it slowly boils off. And there are additional challenges at the filling station. Spill gas on your hands and it smells bad. Spill liquid hydrogen on your hand, and you can snap off your fingers.
  • Chemical compaction – The third means of storing hydrogen is to leverage the fact that hydrogen, when bound to the right materials, packs even closer than with liquid hydrogen. There is intensive research in this area. One promising area, tmetal hydride’s, have attained hydrogen capacity of 2% of the total material weight. Unfortunately this still means that you’d need a 1,000 lb fuel storage system for a 300 mile driving range.

There is another option to have on-board hydrogen — you can generate it on board from natural gas or gasoline. While practical in many ways, this produces just as much CO2 as you would with a traditional natural gas or gasoline powered car.

The bottom line here: this is a big problem, and will remain so without some major technical breakthroughs.

Running your car on hydrogen

Once you’ve stored your fuel, you can consume it and drive around. There are two basic approaches here: burning the hydrogen in something resembling a conventional internal combustion engine, or converting the hydrogen to electricity in a fuel cell to drive electric motors.

The BMW Hydrogen 7 burns hydrogen in a fairly standard engine. Indeed Ford is now producing hydrogen internal combustion engines[5]. This technology is relatively feasible today. This approach can create better potential acceleration and a more thrilling ride, but it’s way less efficient than using fuel cells and electric motors.

The alternative is to create an electric car and include an on-board fuel-cell stack to convert the hydrogen to electricity. While elegant in concept, creating small fuel cells that work at normal temperatures without major compromises is a big challenge[6].

Hydrogen infrastructure

Hydrogen cars need to “fill up” at hydrogen fueling stations, which means we need infrastructure to generate hydrogen and distribute it on a widescale basis. Currently, the most inexpensive way to generate hydrogen on an industrial scale is to strip it from fossil fuels[3]. From the standpoint of global warming and carbon reduction, this of course makes no sense, as what remains from this process is CO2. The alternative is to split hydrogen from water, which requires electricity. At the point where we have extensive renewable wind or CSV generation capacity, this might be cost effective, but it’s certainly not today.

Distribution is another challenge. One proposal to solve this problem is to generate hydrogen from natural gas, which already has a distribution network. This however means that you’re creating CO2; if you’re going to do this, it would make more sense to run cars directly off the natural gas.

As with the challenge of storing hydrogen on board, the hydrogen infrastructure is a big problem.

Smarter alternatives

Are there better alternatives to hydrogen powered vehicles? Absolutely. Let’s look at this from a rational engineering perspective:

First, what makes sense to maximize efficiency? While internal combustion engines have seen major improvements over the decades, they are still an inefficient power suource. The most efficient gasoline powered car ever made was perhaps the 1003 Honda Civic VX, EPA rated at 51 mpg, yielding an efficiency of 0.52km/MJ (MJ = megajoule, a quantity of energy)[6]. Compare this with the estimate for the soon-to-be-released Tesla Roadster (an all-electric car), which has an estimated efficiency of 2.18 km/MJ – over four times as efficient as the Honda. The point is that electric motors are far more efficient for powering vehicles than internal combustion engines.

Second, what’s the best way store energy on the vehicle? Note that “Best” is a subjective term, and it’s tied to infrastructure issues (it’s easy to buy a gallon of gas down the street; the same cannot be said for H2), the design question of consider how far you want to go before refuelling, and the engineering question of what form do you want the energy in? (Gas may be a great fuel, but you can’t run an efficient electric motor on gas). Gasoline and diesel are best in terms of energy density (12.2 KWh/kg and 13.7 KWh/kg)[7]. Ethanol is an acceptable liquid alternative at 7.8 KWh/kg. Batteries have much lower energy density, at best a bit over 0.1 KWh/kg.

Third, what’s the best source of the energy? This also has the subjective “best” issue. I’ll argue that best in this case includes flexible, and for that reason, electricity is the best energy source, because we can create it in a variety of ways, and there’s an infrastructure already in place to deliver it.

OK, too many words. What does this mean in terms of the best approach for automobiles. Given these three points, and wearing my engineering hat. I’ll argue that the best approach is:

  • Electric motors – They are the most efficient
  • A plug-in hybrid architecture – It’s allows the use of electricity for modest trips without the range and fast fueling limitations of an electric-only car
  • Ethanol as the on-board liquid fuel – Ethanol (especially over time) can be generated from non-fossil sources, it has a reasonably high fuel density, and the current fuel delivery infrastructure can evolve fairly smoothly to support this

Conclusions?

This was a mythbuster. This post has lots of data, and it may have some controversial points, but my bottom line is that hydrogen as an automotive fuel is a non-starter. Does anyone disagree?

March 28, 2007

What about Hydrogen?

Category: Hydrogen – Dan 10:00 am

Hydrogen is often quoted as a new alternative energy source, particularly with respect to what we’ll put in our gas tank. I will argue that hydrogen is a likely part of the energy future. But it is not a new energy source, and using it as an automotive fuel is not a smart use for hydrogen.

Hydrogen compared with Natural Gas

The closest equivalent to hydrogen today is natural gas, with respect to it’s potential uses and behavior. The obvious difference is that natural gas is a fossil fuel that can be extracted from the earth, whereas elemental hydrogen does not naturally exist in commercially available quantities and so has to be generated. Here’s a simple chart to show the similarities and differences:

Natural Gas Hydrogen
Normal state Gas Gas
Highly compressable Yes Yes
Energy Content 1040 BTU/cubic foot 320 BTU/cubic foot
Practical to transport in pipes Yes Yes
Practical to store underground Yes Yes
Sources Underground extraction Electrolize water or reform natural gas

We all think of natural gas as an energy source. But beyond being a source, natural gas is also an energy carrier, allowing practical energy distribution from source to consumer, and it serves as an energy storage mechanism. Indeed, to balance seasonal demand, natural gas suppliers regularly store natural gas in salt caverns during slack periods to have energy in reserve during peak times. It’s no wonder natural gas is in favor.

Hydrogen can serve as a natural gas alternative for two of these three crucial characteristics: transmission and storage.

Pairing hydrogen with alternative energy sources

Alternative energy sources like wind, concentrating solar power (CSP), or geothermal energy, all share the same good-news/bad-news characteristics:

  • The good news – There’s a huge power potential. We could supply the entire US energy needs by wind power from the midwest or CSP in the desert southwest.
  • The bad news – These sources are intermittent, and they are hundreds or thousands of miles from the demand. In the industry, these are known as “stranded” sources.

Here’s where hydrogen can, and perhaps should, play a staring role. Given a source of energy and a supply of water, it’s fairly straightforward to generate hydrogen. If it’s practical to pipe hydrogen long distances, and store it until needed, one could almost redefine a large wind farm as a hydrogen generation facility.

This topic has considerable depth. I first came to understand some of these ideas after a conversaton over dinner at the PowerGen conference with Bill Leighty of the Leighty Foundation, which has been funding research into this area for some time. I’ll provide more on these ideas, with more information sources in future posts!