On Energy: The Hydrogen Economy

I have been meaning to write on this topic for a while – Energy. In the interest of full disclosure, my experience in this field is from working on hydrogen production (from natural gas) and fuel cell design and development (both PEM or low temperature, and SOFC or high temperature flavors) for four years. In the first part of this series, I will review hydrogen.

1. Is the Hydrogen Economy really feasible?

I once attended a talk on evaluating the economic aspects of using hydrogen as our primary fuel. The talk referred to the 1970’s oil crisis, and how natural gas emerged as a potential replacement for gasoline. Natural gas burns cleaner than, is just as widely available (cheap at that time, though presently expensive), just as safe as gasoline. Besides there is tremendous potential to produce natural gas from farm waste. Most importantly, the existing gasoline engines can burn natural gas with very little modifications. Yet it did not “stick”. For anything to stick, Americans have to buy into it – and they simply couldn’t give up the comfortable feeling of a liquid gushing into their fuel tanks. A simple google search landed me at this article from last summer:

http://www.usatoday.com/money/autos/2007-05-08-natural-gas-usat_N.htm

Excuses include safety concerns or the lack of refueling stations. If we can not replace the entire refueling network of the country with natural gas to service an existing engine (the same ICE that you have today), what makes us think that we will replace the entire refueling network with hydrogen filling stations, and develop a new type of engine to burn it (fuel cells)?

2. Where does the hydrogen come from?

Let’s say we actually do accept hydrogen as a fuel. Where does the hydrogen come from?

The best known way to make hydrogen today is from natural gas!! The best and largest natural gas reformers today work at about 75% efficiency, meaning that the total amount of hydrogen produced from 100 megajoules worth of natural gas is worth about 75 megajoules of energy only. We lose upwards of 25% of the energy content just to split the hydrogen out of the methane, propane, or what have you. That fuel cell based cars have higher net efficiency (> 45%) when compared with an internal combustion engine (~ 30%), doesn’t make the economics much better. (Natural gas à Hydrogen à Fuel cell = 70% * 45% = 31.5%, is not much better compared with Natural gas à IC Engine @ 30%). By the way, making hydrogen from natural gas makes sense for industries that require hydrogen as an input.

For those others who want to produce hydrogen from coal gasification, or diesel reforming, or from other carbon-based fuels, I will not continue the discussion. It does not make sense at the very high level.

Now – the more relevant hydrogen production methods are: (1) electrolysis from wind power and (2) electrolysis from power generated by solar panels, or (3) direct solar electrolysis – using sunlight and catalysts to directly split water. In each of these cases, we are essentially using hydrogen as a means to store and carry energy from the place where it is available (i.e. where the wind blows or where the sun shines), to where it is used (your car). These techniques make sense to me. Barriers to these methods include cost and storage technology.

The cost of hydrogen produced by electrolysis is rather high. Let’s start with gasoline, which costs $0.36/kWh at $3/gal used at 25% efficiency. You need as much energy to split water to hydrogen as you get from burning it. So if wind energy costs $0.10/kWh, the hydrogen produced, used at 40% efficiency (including cost of transporting the fuel), will cost $0.25/kWh. Add to that the cost of (1) hydrogen compression (2) transportation and (3) fixed capital – which all may double this number to $0.50/kWh. (Consistent with DOE’s findings of current costs of $10/kg H2, or $0.35/kWh.) Cost reduction in electrolyzers and other equipment could see the cost of hydrogen produced from wind electrolysis drop to at or below gasoline equivalent prices.

Solar photovoltaic energy is still not cheap enough to beat these numbers ($0.10/kWh is not here yet).

3. Summary

The biggest challenge in realizing a hydrogen economy may be people’s acceptance of the system, and the costs and inertia against transitioning to such a system. Wind based electrolysis is perhaps the most economical and sensible method of producing hydrogen, but electrolyzer cost and technology is still catching up.