In our attempt to wean ourselves off fossil fuels, there have been many suggestions as to the best ways of replacing our current primary sources of energy; coal, oil and gas. While many forms of renewable energy are gaining a foothold, we still don’t seem to be able to keep up with demand and are still searching for that elusive eureka! moment when we can all relax, knowing that our energy problems are solved. Of course this clean energy utopia will not be achieved over night, but there are a couple of energy sources that come up time and again in relation to this issue; one of them is nuclear fusion, the other is hydrogen. In this article I want to look at what hydrogen is, how it may be used and then talk about the hydrogen economy; a vision where we may solve our energy woes and live clean, peaceful lives. It is by no means universally accepted that this vision will actually work, but there is defiantly something in it and it should not be ignored.
What is hydrogen?
Hydrogen is the lightest and most abundant gas in the universe, it has an atomic number of 1 and is represented by the symbol H. You are no doubt aware of the chemical equation for water, H2O – two hydrogen atoms and one oxygen atom. As a naturally occurring gas on Earth, hydrogen is quite rare, but it can be artificially produced. At present, hydrogen is mainly produced from the steam reforming of natural gas, but this uses a fossil fuel and produces carbon dioxide (not what we’re aiming for). The methods that we’re interested in for manufacturing hydrogen are:
- Electrolysis – This is a process where electricity – from a renewable source, ideally – is passed between two electrodes immersed in water. Hydrogen and oxygen are then collected at the electrodes.
- Biomass gasification – Although this method requires high levels of energy, it is seen as a green(er) technology because its primary fuel source is biomass. Agricultural wastes, such as animal manure, rice husks, forestry residues, etc. could all be turned into hydrogen by reacting them with hot steam and oxygen.
- Thermal dissociation – This process is similar to electrolysis, in so much that it converts water into hydrogen and electricity, but the process would use concentrated solar collectors operating at very high temperature. While it may represent a valuable use for the Earth’s barren deserts, this is still a relatively new technology.
How would we use this hydrogen?
First of all let me clarify that there are two possible uses for hydrogen in the context of this article: the first is burning it, just as you would gas or petrol. The second use is in a fuel cell, which I’ll explain later. Hydrogen has been used before as a fuel source in the form of ‘town gas’ many years ago and is currently used heavily in the manufacture of fertilisers. In the future however, hydrogen could be used in the following ways:
- To create electricity – Power stations would use fuel cells to generate electricity. In basic terms, a fuel cell is a devise where hydrogen and oxygen are pumped in via two electrodes, and through a process that is essentially the reverse of electrolysis, the hydrogen and oxygen are combined. The result is the generation of an electric current, with water and a small amount heat being the only by-products.
- To cook our food and heat our homes – In a well-established hydrogen economy we could see hydrogen replacing – or being mixed with – natural gas as the fuel of choice for domestic users. If this happened, I would like to see the horrible smell additive they put in gas changed for a sweeter aroma – something like vanilla, Old Spice or freshly cut grass, perhaps.
- To fly us on holiday – Boeing have already tested a single seat propeller aircraft running on fuel cells [1]. But in the future we could see much bigger passenger aeroplanes using combustible hydrogen for fuel. Again at the forefront, Boeing have developed the Phantom Eye spy plane, which flew for 4 days (swapping jet fuel for hydrogen), with water as its only emission [2].
- To power our cars – There are two types of cars that could use hydrogen as fuel. The first uses a fuel cell supplied by a tank of hydrogen and the flow of air coming into the car to power an electric motor. The first fuel cell vehicle to go into mass production is Honda’s Clarity; a nice bit of kit, but it only represents the very beginnings of what’s acheiveable. The second method would be to use the combustion of hydrogen to run the engine, in much the same way as we use the combustion of petrol or diesel, this is known as the hydrogen internal combustion engine (HICEV). BMW have made such a car but it is not commercially available. Both of these vehicle types emit only water, but do however, require hydrogen filling stations.
As it stands, fuel cell vehicles are predicted to reduce total life cycle greenhouse gas emissions by around 55% compared to petrol vehicles [3]. If, however, the hydrogen is produced from a renewable resource, current emissions from this source will drop to practically zero.
The hydrogen economy
The hydrogen economy basically involves a network of hydrogen producing plants, storage/distribution centres and power stations. The hydrogen production plants would produce the hydrogen. Ideally they would be close to the coast, thus having ample water supplies, and utilise offshore wind, wave or tidal power. Alternatively they could be run off hydro-power stations. Once the hydrogen has been produced it would then be shipped via pipeline or hydrogen-powered vehicles to fuel cell power stations where the hydrogen could be transformed into electricity. At the same time as using hydrogen for electricity production, it could also be distributed to filling stations for use in hydrogen and fuel cell vehicles, aircraft would fly on it and households would cook with it. If all of the hydrogen were created using renewable energy, then carbon emissions from this sector would decrease dramatically. The production could also be accomplished using traditional coal and gas fired power stations, but one which utilise the capacity to ‘bury’ their carbon emissions back underground in the empty aquifers where gas and oil have already been removed. This is a process known as carbon sequestration and is currently in use in the North Sea by the Norwegian company, Statoil. Carbon sequestration, however, would have to be only a stopgap; for the hydrogen economy to really make a difference to resource depletion and climate change, it must by powered by renewables.
The Downsides
Hydrogen has not yet achieved the status of ‘our miracle cure’, otherwise we would all be driving hydrogen or fuel cell powered cars and fossil fuelled energy production would be a thing of the past. A few spanners in the hydrogen works are:
- Current alternative energy production techniques can easily fit in with existing energy networks, it’s not so easy with hydrogen.
- The renewable energy used to produce the hydrogen could just as well be used to make electricity for direct use. Although on the flip side, hydrogen can act as an ‘energy store’, meaning that it would be produced when conditions are favourable to wind, solar and wave power and then be on standby for when they’re not.
- One by-product from the creation of hydrogen is nitrogen oxides, which can be harmful to human health and contribute towards ground-level ozone, or smog, as it’s affectionately known.
- The costs of switching to a hydrogen economy are huge. Even without considering the massive investment in infrastructure, as it currently stands we would pay about four times as much for our electricity if it were produced from hydrogen [4]
- Hydrogen requires a lot of storage space. Although hydrogen has a higher energy per unit mass than petrol, being a gas it has a very low energy per unit volume. It would be possible to store hydrogen in pressurised containers or as a liquid form, but both methods entail quite high energy usage.
- Hydrogen, especially when stored at pressure, is highly combustible – just look at the Hindenburg. Lets not forget though, that petrol and natural gas also have a tendency to explode, and oil just loves to pollute oceans and other sensitive ecosystems.
In summary then…
While hydrogen may not be the answer to our eco-prayers, and the hydrogen economy is still only a pipe dream, they do both provide visions of the future where we depend less on fossil fuels and can dramatically reduce our carbon emissions. For this to happen, though, we would need to see a sharp rise in the construction of renewable power solutions and a heavy investment in infrastructure. But, having said that, any vision for a low-carbon society will also require these two things. The UK is exceedingly well placed to implement a hydrogen economy. Being a windswept island with some of the highest abundance of potential wind, wave and tidal power in Europe, we could build hydrogen-producing plants along our coastline, which would then be attached to a distribution network that would take advantage of our country’s relatively small size. The hydrogen economy cannot exist on its own, however. It would need to find its place within a renewable energy mix and also be combined with, an energy efficiency drive. Yes I know it sounds a bit like the stuff of sci-fi, but it is possible we could find our society heading down the hydrogen route – who knows? With that in mind I’m off to purchase myself one of those hydrogen-powered BMWs.
References
[1] http://news.bbc.co.uk/2/hi/7330311.stm
[2] http://www.bbc.co.uk/news/10617075
