Category Fuel of the Future

Carbon Neutral Solar Fuels

The hydrogen economy is a typical ‘‘chicken and egg problem’’ (Figure 3.16). Until a hydrogen infrastructure is built, hydrogen production will not reward investment. Hence, (solar) hydrogen production plants, as well as vehicles, are not yet being manufactured on the large scale required by the urgency of the anthropogenic climate change problem caused by three centuries of burning fossil fuels to power the increasing energy needs of humankind.

Hydrocarbon compounds, however, are very attractive energy car­riers. Reducing our dependence on fossil hydrocarbon fuels as our primary energy source should not therefore prevent us from using (carbon neutral) hydrocarbons as energy carriers...

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Hydrosol: Thermochemical Water Splitting

Very high temperatures are required to dissociate water into hydrogen and oxygen. Given the thermodynamic restrictions, sufficient yields from the direct thermal splitting of water can only be achieved at tem­peratures above 2500 K. Temperatures this high impose extraordinary demands on materials and reactor design. Over the past 30 years numerous thermochemical cycles for hydrogen production through water splitting have been proposed and studied to a varying extent. Several cycles have been demonstrated at the laboratory scale, a couple have reached the pilot scale, but none has yet matured to production.

An interesting concept is that of oxide-based thermochemical cycles, during which a simple oxide (such as iron, zinc or cerium oxide) or a mixed oxide (such as a ferrite) cycles between...

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Thermochemical Water Splitting

3.1 Concentrating Solar Power for Heavy Energy Demand

Solar energy technologies have the flexibility to address global power needs. Earth receives a vast amount of solar energy that is estimated to be approximately 120 000 TW (1 TW = 1012W), which vastly exceeds the current annual worldwide energy consumption rate of B15TW.1 The latter figure includes all available forms of energy from electricity to gasoline combustion and is proportional with the population growth.

For example, energy consumption in 2010 increased by 5.6% com­pared to 2009.2 Most of this power is currently produced by burning fossil fuels, namely coal, oil and natural gas (Table 3...

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Flexible Technology with Large Applicative Potential

Demonstration units such as the Schatz Solar Hydrogen Project stand­alone energy system, which has powered since 1991 the 600 W air compressor that aerates the aquaria at Humboldt State University’s Telonicher Marine Laboratory in Trinidad, California, clearly show that

 

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Figure 2.25 The low cost hydrogen compressor developed by RE Hydrogen in the UK.

(Reproduced from Rehydrogen. com, with kind permission.)

hydrogen can be used efficiently to store solar energy and that the electrolyzer is flexible enough to respond to the fluctuating solar energy yield with respect to both time and capacity.48

The system – the first solar hydrogen energy plant in the USA – consists of a 7...

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Emerging Electrolytic Technologies

For electrolytic hydrogen production, the increase in production effi­ciency reduces the amount (and thus the cost) of electricity consumed, whereas an increase in production rate reduces the size and cost of the electrolyzer stack. Nanochemistry research efforts carried out on a global scale, aimed at manufacturing low-cost electrodes made of metal nanoparticles, featuring an enhanced surface area available for the catalytic reaction that generates hydrogen, thus increasing efficiency and production rates, have lately been successful, at least on the laboratory scale.

In the USA, for example, a number of small hi-tech companies have developed new Ni-based catalysts...

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Reducing the Cost of Electrolytic Hydrogen

In a thoughtful and somehow prophetic analysis33 of photovoltaic – assisted water electrolysis dating back to 1982, Carpetis concluded that:

There are three interconnected subsystems (solar array, electrolysis unit and hydrogen storage unit) which should be optimized for minimum hydrogen costs, according to the local conditions and to the hydrogen utilization schedule…

The cost optimization and the break-even conditions will depend not only on the solar array and electrolyzer performance improvement, but also on the location of the production and the hydrogen utilization schedule.

Observing that, at that time, the electrolysis unit costs contributed ‘‘a relatively low part’’ of the total costs, he continued that, in the near future, the cost reduction for hydrogen produced by solar electro...

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Economics of Water Electrolysis

A detailed cost analysis, performed in 2004,29 of the domestic produc­tion of hydrogen using a photovoltaic-electrolyzer system showed that, for a 1 kWp photovoltaic system with fixed modules, depending on the

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annual solar radiation on a horizontal surface HT, the cost of hydrogen varies from 3.5 to 38 $ kg-1 with a corresponding energy cost from 26 to 268 $GJ-1. Specifically, the hydrogen energy costs CHM (in $kg-1 H2) and CHE (in $ GJ-1 H2) are correlated empirically with the price of the PV plant and of the electrolyzer, expressed in $ per Wp, (Ppv and Pel, respectively) according to the following equations:

 

image077

(2.15)

 

image078

(2.16)

 

In 2004, the price of energy for gasoline engine powered vehicles was about (0.5 $L-1)/(0...

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Photovoltaic-Assisted Water Electrolysis

At first sight, given that the cost of water is negligible, the economics of the process of hydrogen generation by water electrolysis is driven by the cost of electricity and by the cost of the electrolyzer. However, because the cost of photovoltaic (PV) electricity consumed has been more valuable for decades than the hydrogen produced, this method has not been used. Hydrogen generated by water electrolysis, however, is an ideal way to store intermittent solar electricity generated during the day. The advantages of hydrogen as a storage medium are self-evident: i) high specific energy; ii) low or zero self-discharge rate (H2 can be stored for years, unlike other energy storage media); iii) it is clean, because no pollution is produced.

Solar hydrogen can therefore be used to fuel the power...

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