- Thermal Audit
The "Hydrogen Economy"
You may have heard that hydrogen is the fuel of the future. A search on Google for the words, hydrogen fuel of the future, turns up 957,000 hits. Hydrogen is not the fuel of the future. At best, it is a very inconvenient energy carrier.
Consider the purpose of kerosene for a lamp, or diesel for a truck. It is a liquid fuel (stored energy) that can be carried in containers, can be stored in for long periods of time, and contains a great deal of energy in a very small volume. A gallon of gasoline can move a car 30 miles or cut an awful lot of grass. A cup of cooking oil can light an oil lamp all night. Liquid fuels are extremely convenient. Fuels contain stored energy and the ones we are familiar are derived crude oil and natural gas.
Hydrogen does not occur naturally as a fuel -- rather, it occurs as an "ash" which we call water. There are no reservoirs of hydrogen gas or liquid on this planet, although there is on Jupiter. Electricity (electrolysis) can be used to strip the hydrogen out of water so that it can be burnt again but this conversion requires another energy source. Another method is steam methane reforming. It is better to think of Hydrogen as an "energy carrier", something temporary that we add energy to, transport and then release.
Perhaps a better analogy is a battery. Batteries aren't fuel. They can be charged and discharged but the energy must come from somewhere else.
Gaseous fuels like methane, ethane, propane, butane, etc. are also useful. They require pressurized tanks to achieve useful densities, but the pressures required are modest and relatively easy to achieve. They are very similar to liquid fuels like gasoline but differ in that they are shorter molecules and they are gaseous at room temperature.
The energy in hydrocarbon fuels is stored in the chemical bonds between carbon and hydrogen atoms and is released when the fuels are oxidized. The oxidation source is the oxygen in the air we breath. In the process of "burning" the hydrocarbon (gasoline for example) fuel we get water, carbon dioxide and heat.
Now let's compare this to hydrogen gas. Unlike gasoline (which is carbon and hydrogen), hydrogen is just, well, hydrogen - a dangerous and difficult to work with element that doesn't occur naturally as hydrogen gas. If you release hydrogen gas into the air, it eventually escapes the Earth's gravitational pull and heads for outer space because the molecules can exceed the earth's escape velocity.Here is a list of problems with hydrogen storage:
- Its energy density by volume is less than gasoline so it requires larger storage tanks. Liquid hydrogen contains 2,600 Wh/l whereas gasoline is around 9,700 Wh/l
- liquid hydrogen, which would pack more into the tank than hydrogen gas, requires temperatures below –252.882 °C or -423.188 °F. This requires special cooling equipment or the fuel tank will boil, and it will need insulation like NASA's Space Shuttle. Compressing the hydrogen also requires a great deal of energy, equal to about 30% of its energy value. See Gaseous and Liquid Hydrogen Storage.
- Liquid hydrogen is still has 3 times less energy than gasoline per volume, so any tank would have to be at least 3 times larger.
- Environmental Hydrogen embrittlement is a problem where hydrogen reacts with metals and reduces their strength. Special manufacturing techniques have to be employed to minimize the risk and this adds to the cost. This is not the embrittlement that is due to hydrogen getting into the metals during the manufacturing process, but something that happens afterwards. Here is a good article called HYDROGEN ENVIRONMENT EMBRITTLEMENT OF LOW ALLOY STEEL AT ROOM TEMPERATURE from Japan that has more good references at the end.
Hydrocarbons are the ideal way to store hydrogen, and it no surprise that life on earth has evolved to use this technique to store hydrogen in the form of oils and sugars.
So, using what we know about how biological organisms store hydrogen, we could solve the hydrogen problem by attaching it to atoms of carbon, and by varying the chain length to give us a choice of gas, liquid or solid at room temperature. This of course is what we do today, expect we don't make it ourselves, we get it from plants new (vegetable oil) and old (crude oil).
So, that brings us to the question of what we are trying to solve with Hydrogen fuel. (these are rhetorical questions of course).
One possibility is that we are running out of crude oil. However, hydrogen doesn't exist by itself. The main source is burnt hydrogen, also known as water. We can use electricity to strip the hydrogen from water, but this requires energy. The same energy we hope to get out of it later -- so we aren't accomplishing much other than to create an awkward medium to transport energy. After all, the electrical power used to break down the hydrogen, could also have been used to charge electric cars and avoided the hydrogen problem all together.
Perhaps hydrogen is supposed to solve the C02 problem. However, in order for this to work, the electricity used to extract the hydrogen from water would need to be solar/wind/hydroelectric and definitely not coal or natural gas or you would defeat the purpose. However, it would be much simpler to just bypass the step and use the electrical power to charge car batteries.
Hydrogen gas can also be extracted from natural gas by reacting the methane in the natural gas with high temperature steam. Of course this does nothing for the CO2 problem, because the reaction CH4 + H2O -> CO + 3 H2 followed by CO + H2O -> CO2 + H2 means that large amounts of C02 are going to be generated as a waste product. The efficiency of the process is approximately 65% to 75% - in other words, 25% or more of the energy is lost in this step alone. Furthermore, abundant natural gas won't be around forever.
The CO2 could be reacted with something else to tie it up -- but now we are getting into the realm of large inefficiencies because every step requires energy and has significant losses. After all, the methane was already a fuel that could have powered an engine directly without doing a "Rube Goldberg".
Perhaps the whole thing is a marketing and public relations exercise. Hydrogen infrastructure would cost billions (filling stations, storage facilities, production facilities, etc.) and require a lot of government incentives. Some proposals have been made for multi billion dollar nuclear facilities for nuclear-based hydrogen production, however we only have about 100 years of uranium available according to the AEN. You may find the title of the AEN article odd; "Uranium resources sufficient to meet projected nuclear energy requirements long into the future" -- apparently long for them them is a century, which means that many babies being born now will live to see the end of it. Most of this money would end up in the hands of large corporations. Ethanol from corn is a similar fiasco. To divert attention from the senselessness of it all "green house gas", "carbon emissions" and other buzzwords are being used to manipulate a non-scientific public.
Here is a good FAQ from Stanford.
-- So what does make sense? --
Our primary sources of renewable energy are:
- Solar photoelectric (via solar cells, usually silicon)
- Solar heat (flat plate collectors, evacuated tube collectors, mirrored concentrator systems)
- Wind (axial wind turbines, the ones that have propellers like airplanes. If you see ones that stand vertically and look like an eggbeater, you are looking at a scam.)
- Hydroelectric (Hoover Dam, Churchill Falls, etc.)
- Nuclear power plants
- Tidal power stations
- Geothermal (steam heated by volcanic activity is used to drive steam turbines)
We need to transfer energy from these sources to where the work needs to get done (homes, cars, factories) in the most direct possible way because every time energy is transformed, some of it is lost. There is one exception, and that is heat. It is 100% efficient to degrade electricity into heat. The transport of energy is also wasteful -- whether it is the diesel use to power gasoline tankers, or the electrical losses in transmission lines.
Therefore, any long term solution must factor in this reality. Power generated by a wind farm and consumed by a nearby city, or generated by a wind tower in a back yard by a home owner, will have minimal transmission losses due to the electrical resistance of the electrical wiring. Electric cars make sense if wind power can directly charge car batteries. Diesel cars make sense if they can directly use bio-diesel. Anything which requires transformation, e.g. a bio-diesel powers a generator which generates electricity, or using electrolysis to strip hydrogen from water which is then compressed and transported and burnt again later -- is just a waste.
Another issue is the grade of energy. Only certain wavelengths are going to be generating electricity in a solar cell; all you get from the rest of the sunlight is heat. If the intention is to heat a building, you are better off with an evacuated tube collector (say 50% efficient) rather than generating electricity (say 30% efficient) and then using the electricity to generate heat (100% efficient). Electricity should never be wasted on heat.
Large power generators such as massive hydroelectric facilities, or geothermal facilities in volcanic areas can transport energy via means other than transmission lines. Cement production and aluminum smelting require large amounts of energy, and if located near the generation facility, achieve the same goal. Energy is stored in the finished product, and in this case, transmitted by rail and ship.
Nuclear energy is unlikely to be a permanent solution. We have about a 100 years worth according to the Nuclear Energy Agency -- so this is NOT a long term solution when you are looking ahead a few generations. Breeder reactors and thorium reactors will extend the cycle, but these materials will become exceedingly expensive as the resource becomes scarce -- which is the same problem we will have with oil. Nuclear energy accounts for about 15% of worldwide power production, so if was to expand to replace dwindling oil supplies, nuclear material availability would also decline proportionally.
The successful solutions, and things we can do today, revolve around items like:
- use less (conservation)
- design communities to minimize commuting
- change agricultural methods and eliminate petroleum derived chemical fertilizers
- develop housing stock that is passively heated
- develop inexpensive wind generators, solar photovoltaic and heat collector panels for home owners
- make grid inter-ties a standard feature
- build wind farms where it makes sense
- increase the cost of non-renewable resources to get consumer behavior in line with the long term interests of society.
The simplest solutions are always the best.