An Insight into the Solar Hydrogen Economy

Although the English term ‘‘hydrogen economy’’, to describe a system of delivering energy using hydrogen, was coined by John Bockris, a former professor of chemistry at Texas A&M University, during a talk he gave in 1970 at General Motors, scientific interest in the solar

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hydrogen economy goes back to 1912, to the famous paper of Giacomo Ciamician entitled ‘‘The Photochemistry of the Future’’34 (Figure 4.30). This paper emphasized the need for an energy transition from fossil to solar fuels and foresaw that ‘‘our black and nervous civilization, based on coal’’, would be followed by ‘‘a quieter civilization based on the utilization of solar energy’’.

One hundred years later this prediction is eventually coming true. Indeed, a solar hydrogen economy finally makes sense, even if there are efficiency losses in storing (or liquefying) and delivering H2,35 because the available solar power is virtually unlimited and, concomitantly, the solar CSP and PV energy technologies, and the fuel cell and electrolyzer technologies, are eventually becoming low-cost and ubiquitous. Given that the sun delivers 5000 times our present global power needs, an area

as small as 500 x500 km2 is needed to supply the world’s energy needs (a tiny fraction of the world’s desert area). Using mirrors, focused sunlight can heat water viably to generate electricity via a conventional steam turbine.

In a recent investigation based on order of magnitude calculations, without referring to environmental arguments but focusing on economic convenience only, Abbott has suggested that sunlight is the scalable source of power on which our future energy needs must rely, using low – tech CSP, where solar thermal collectors are preferred to PV solar cells.36

The point about solar energy is that there is so much of it that you only have to tap 5% of it at an efficiency as tiny as 1% and you already have energy over 5 times the whole world’s present con­sumption… There is so much solar that all you have to do is invest in the non-recurring cost of more dishes to drive a solar-hydrogen economy at whatever efficiency it happens to sit at.

Solar H2 obtained from water is the fuel of the future because it solves the intermittency of supply of free solar energy, meeting one key requirement of modern societies: incessant flows of energy. Human activity and energy usage of course correlate significantly with the delivery of radiation from the sun, and solar hydrogen produced by water electrolysis is an excellent load-following clean technology.

For Abbott, combustion of solar H2 should be preferred to hydrogen fuel cells because the latter are not scalable owing to the use of expensive membrane technology as well as expensive metal catalysts (platinum). By the same logic, CSP systems integrated with nanocatalysts are cap­able of splitting water directly and will have an immense impact on energy economics, because they require no electrolysis to provide affordable, renewable solar hydrogen with virtually zero CO2 emissions. Such plants can offer new opportunities to regions of the world that have a huge solar potential, which can become important local produ­cers of clean hydrogen.

We argue that the intrinsic versatility and the apparently endless falling price trend of PV electricity supports the use of solar PV stations to produce hydrogen locally from water electrolysis as the price of PV modules approaches a historic low of $0.5 W-1. If, for example, the roof of a 250 m2 (ca. 20 kWp) solar station in Austria can produce 823 kg of pure H2 per year, in regions such as Sicily, where PV electricity has already reached grid-parity,37 this figure should be almost doubled (70% more), further lowering the cost of solar hydrogen.

147

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Figure 4.31 This home in New Jersey runs on solar power and stored solar hydrogen using only 56 solar PV panels on the garage roof and a small electrolyzer. In 2007, when the system was installed, the cost of a PV module was $7W-1. Today, the same module sells at about $0.80W-1.

(Reproduced from Ref. 38, with kind permission.)

Smil agrees that transition to new energy sources is unavoidable, but remarks that even if a non-fossil world may be highly desirable, many decades will be needed for solar energy to capture substantial market shares on a global scale, because of the enormity of the requisite tech­nical and infrastructure developments.39

Yet, low cost solar hydrogen will actually enable the shift to a dis­tributed power distribution infrastructure, both in the developing countries of Africa and Asia, where hundreds of millions of people will start to use electricity and in affluent countries (Figure 4.31), where the price of fossil electricity and heat has been endlessly increasing for more than a decade.

Furthermore, new generation fuel cells and electrolyzers will be nanochemistry-based, requiring ever lower amounts of platinum to afford unprecedented performance in terms of power delivered and power density, and using much cheaper and readily available metal nanocatalysts such as nickel or molybdenum. It is perhaps not surprising

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Chapter 4

that new platinum-free polymer electrolyte fuel cells (PEFC), comprised of alkaline polymer electrolytes (APEs, Figure 4.32), have been invented recently in China.40

In these innovative fuel cells the APE is as conductive and stable as its acidic Nafion membrane (a trademark of Du Pont) counterpart, which has been studied and used for decades in acidic fuel cells that use pla­tinum catalysts. In detail, the new APEs are highly resistant to swelling and show excellent ionic conductivity at 80 °C, i. e. at typical tempera­tures for fuel-cell operation, which opens the route to low cost Ni-based fuel cells for a wide variety of commercial applications.41

Fuel cells, after all, are already selling without subsidies in many markets, and more than 700 000 fuel cells were sold cumulatively between 2005 and 2011 (Figure 4.33).42 Portable, stationary and trans­port applications are all exhibiting growth, with the different electrolytes establishing their roles in the various sectors.41 When low cost, Ni-based

Подпись: 149

Shipments by Application 2007-2011

I Portable Stationary

000’s И Transport 300

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2007 2008 2009 2010 2011

Forecast

Figure 4.33 Fuel cell shipments by application, 2007-2011.

(Reproduced from Ref. 38, with kind permission.)

catalysts are made available for alkaline fuel cells in the 10-200 kW power range, namely that of scooters, cars, trucks and boats, expect the transport column in Figure 4.33 to grow exponentially.

However, when are our global energy needs likely to be met using sunlight as energy input and water as raw material? Very shortly, we argue, within the next decade. This time, our argument is based on economic and technological reasoning. Where is, for example, the eco­nomic interest of countries such as China and the USA, the world’s largest economies, to go ahead with dependence on foreign oil and natural gas when both countries own huge desert regions that are exceptionally suited to massive adoption of solar and solar hydrogen energy? Many countries, furthermore, have an urgent need to reduce the large public debt accumulated following public bailout of the financial system, create new jobs and reduce import of foreign oil and natural gas, which, even in a relatively small country like Italy, costs 63 billion Euros

per year.43

Thermochemical water splitting using free and unlimited solar energy as the only energy input, via the highly scalable CSP technology coupled to nanocatalysis (see Chapter 3), will be used to produce massive amounts of carbon-free hydrogen by deploying very inexpensive solar reactors and mirrors on acres of vacant, non-productive land. To

increase the scale of this system, it will be sufficient to add more solar reactors and more mirrors. The very same reactors will also be available to split carbon dioxide and produce carbon neutral solar fuels that can be piped into the existing natural gas or oil infrastructure for everyday use in homes, power plants, factories, and vehicles.

For almost a century, scientists have tried to split water cost effec­tively by electrolysis to produce hydrogen and oxygen. Today, however, using innovative nanochemistry techniques described in Chapter 2, low cost electrolyzers and compressors are now available, along with low cost PV modules, opening the route to economically viable distributed generation using part of the overall roof surface of existing buildings. Their products not only help to reduce CO2 emission but will also help to produce electricity where it is needed, in the home. This also helps to avoid the need for massive new power stations and new transmission lines.

In a thoughtful and realistic analysis,44 dating back to 2007, of the conditions that need to be met for the success of a hydrogen-based economy (Figure 4.34), Marban and Valdes-Solis concluded that, first,

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Figure 4.34 Expectations for the hydrogen society in the distant future. Renewable energies are intensified and hydrogen fuel cells are employed to achieve higher efficiencies.

international organizations should be strong enough to enforce the international agreements on global reductions in CO2 emissions via a global emission market (an estimated cost of $50 per ton of CO2 was estimated to be sufficient to force energy companies to adopt carbon-free energy sources). Second, technological development should bring about a reduction in the costs of H2 production, distribution, storage and utilization.

The latter change is actually taking place, as we assist in the con­tinuous reduction in the cost of solar energy and related solar hydrogen technologies that goes along with the consistently high price of oil, which remains at > US$90 per barrel, despite the prolonged global economic recession that started in 2008.45

Fuel cell prices, for example, are rapidly declining thanks to improving technology and scaling up of production. The year 2011 saw the first profitable fuel cell firms,46 such as Electro Power Systems and Horizon Fuel Cells Technologies, mentioned above. The management of both these companies understood that in terms of the fuel-cell binomial it was the ‘‘fuel’’ and its availability on which they should focus their efforts. Their fuel cell devices integrate a water electrolyzer and a safe hydrogen storage system so that the user, by simply tapping water, becomes the ‘‘hydrogen infrastructure’’.47

As a result of these (and forthcoming) advances, we believe that fuel cells running on hydrogen will soon be found in many households, where solar H2 will be produced locally using solar electricity.

As the number and reach of similar successful projects implemented worldwide grows, the huge potential of solar energy, in both developing countries endowed with ample solar energy, such as China, India and Brazil, and wealthy countries such as the USA and Australia, will become self-evident. We add to this our idea that further progress will increasingly make use of alternative forms of finance whose focus is on funding ethically and environmentally sound projects, and this will naturally have a great impact on the solar energy business. This will accelerate further widespread adoption of solar fuel energy that even­tually will become the most economically and technically convenient fuel option, replacing our dependence on fossil fuels.

[1] Faraday 96.4%

• Electrolyzer 79.2%

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