Unfortunately, solar and wind cannot be used as industrial-scale transportation fuels unless they are used to crack hydrogen from water via electrolysis. The electrolysis process is a simple one, but unfortunately it consumes 1.3 units of energy for every 1 unit of energy it produces. In other words, it results in a net loss of energy. You can't replace oil - which has a positive EROEI of about 30 - with an energy source that actually carries a negative EROEI.
Message 21353633
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Now we come to the production of hydrogen. Hydrogen does not freely occur in nature in useful quantities, therefore hydrogen must be split from molecules, either molecules of methane derived from fossil fuels or from water.
Currently, most hydrogen is produced by the treatment of methane with steam, following the formula: CH4 (g) + H2O + e > 3H2(g) + CO(g). The CO(g) in this equation is carbon monoxide gas, which is a byproduct of the reaction.
Not entered into this formula is the energy required to produce the steam, which usually comes from the burning of fossil fuels.
For this reason, we do not escape the production of carbon dioxide and other greenhouse gases. We simply transfer the generation of this pollution to the hydrogen production plants. This procedure of hydrogen production also results in a severe energy loss. First we have the production of the feedstock methanol from natural gas or coal at a 32 percent to 44 percent net energy loss. Then the steam treatment process to procure the hydrogen will result in a further 35 percent energy loss.
It has often been pointed out that we have an inexhaustible supply of water from which to derive hydrogen. However, this reaction, 2H2O + e = 2H2(g) + O2(g), requires a substantial energy investment per unit of water (286kJ per mole). This energy investment is required by elementary principles of chemistry and can never be reduced.
Several processes are being explored to derive hydrogen from water, most notably electrolysis of water and thermal decomposition of water. But the basic chemistry mentioned above requires major energy investments from all of these processes, rendering them unprofitable in terms of EROEI.
Much thought has been given to harnessing sunlight through photovoltaic cells and using the resulting energy to split water in order to derive hydrogen. The energy required to produce 1 billion kWh (kilowatt hours) of hydrogen is 1.3 billion kWh of electricity. Even with recent advances in photovoltaic technology, the solar cell arrays would be enormous, and would have to be placed in areas with adequate sunlight.
Likewise, the amount of water required to generate this hydrogen would be equivalent to 5 percent of the flow of the Mississippi River. As an example of a solar-to-hydrogen set up, were Europe to consider such a transition, their best hope would lie in erecting massive solar collectors in the Saharan desert of nearby Africa. Using present technology, only 5 percent of the energy collected at the Sahara solar plants would be delivered to Europe. Such a solar plant would probably cost 50 times as much as a coal fired plant, and would deliver an equal amount of energy.
The basic problem of hydrogen fuel cells is that the second law of thermodynamics dictates that we will always have to expend more energy deriving the hydrogen than we will receive from the usage of that hydrogen. The common misconception is that hydrogen fuel cells are an alternative energy source when they are not.
In reality, hydrogen fuel cells are a storage battery for energy derived from other sources. In a fuel cell, hydrogen and oxygen are fed to the anode and cathode, respectively, of each cell. Electrons stripped from the hydrogen produce direct current electricity which can be used in a DC electric motor or converted to alternating current.
culturechange.org
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The Hydrogen Economy - Energy and Economic Black Hole
2.25.05 Alice Friedemann, Freelance Journalist
The energy-literate scoff at perpetual motion, free energy, and cold fusion, but what about the hydrogen economy? Before we invest trillions of dollars, let's take a hydrogen car out for a spin. You will discover that hydrogen is the least likely of all the alternative energies to solve our transportation problems. Hydrogen uses more energy than you get out of it. The only winners in the hydrogen scam are large auto companies receiving billions of dollars via the FreedomCAR Initiative to build hydrogen vehicles. And most importantly, the real problem that needs to be solved is how to build hydrogen trucks, so we can plant, harvest, and deliver food and other goods.
Making it
Hydrogen isn’t an energy source – it’s an energy carrier, like a battery. You have to make it and put energy into it, both of which take energy. Hydrogen has been used commercially for decades, so at least we don't have to figure out how to do this, or what the cheapest, most efficient method is.
Ninety-six percent of hydrogen is made from fossil fuels, mainly to refine oil and hydrogenate vegetable oil--the kind that gives you heart attacks (1). In the United States, ninety percent of hydrogen is made from natural gas, with an efficiency of 72% (2). Efficiency is how much energy you get back compared with how much energy you started out with. So an efficiency of seventy-two percent means you've lost 28% of the energy contained in the natural gas to make hydrogen. And that doesn’t count the energy it took to extract and deliver the natural gas to the hydrogen plant.
Only four percent of hydrogen is made from water. This is done with electricity, in a process called electrolysis. Hydrogen is only made from water when the hydrogen must be extremely pure. Most electricity is generated from fossil fuel driven plants that are, on average, 30% efficient. Where does the other seventy percent of the energy go? Most is lost as heat, and some as it travels through the power grid.
Electrolysis is 70% efficient. To calculate the overall efficiency of making hydrogen from water, the standard equation is to multiply the efficiency of each step. In this case you would multiply the 30% efficient power plant times the 70% efficient electrolysis to get an overall efficiency of 20%. This means you have used four units of energy to create one unit of hydrogen energy (3).
Obtaining hydrogen from fossil fuels as a feedstock or an energy source is a bit perverse, since the whole point is to avoid using fossil fuels. The goal is to use renewable energy to make hydrogen from water via electrolysis.
Current wind turbines can generate electricity at 30-40% efficiency, producing hydrogen at an overall 25% efficiency (.35 wind electricity * .70 electrolysis of water), or 3 units of wind energy to get 1 unit of hydrogen energy. When the wind is blowing, that is.
The best solar cells available on a large scale have an efficiency of ten percent when the sun is shining, or nine units of energy to get 1 hydrogen unit of energy (.10 * .70). But that’s not bad compared to biological hydrogen. If you use algae that make hydrogen as a byproduct, the efficiency is about .1%, or more than 99 units of energy to get one hydrogen unit of energy (4).
No matter how you look at it, producing hydrogen from water is an energy sink. If you don't understand this concept, please mail me ten dollars and I'll send you back a dollar.
Hydrogen can be made from biomass, but then these problems arise (5):
Biomass is very seasonal
Contains a lot of moisture, requiring energy to store and then dry it before gasification
There are limited supplies
The quantities are not large or consistent enough for large-scale hydrogen production.
A huge amount of land would be required, since even cultivated biomass in good soil has a low yield -- 10 tons of biomass per 2.4 acres
The soil will be degraded from erosion and loss of fertility if stripped of biomass
Any energy put into the land to grow the biomass, such as fertilizers, planting, and harvesting will add to the energy costs
Energy and costs to deliver biomass to the central power plant
It’s not suitable for pure hydrogen production
energypulse.net
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Alternatives...combination of solar, wind, small and mini-hydo & wave, biofuel, conservation,increased rail transport of goods with coming-on-the-market efficient locos, mass transit, everybody getting 80 mpg hybrids like my friend Burke, and a 12 gauge. No easy or fast fix for any of this.
Wouldn't be checking the mail every day for my state solar rebate approval if I didn't think it was part of the equation. Takes about 3 years to pay back the EROEI, about that to pay for itself, since the Fed tax credit will be in effect B4 I get it. Enron cost the Cal economy about 70 billion. For that, we could have built some solar plants and retrofitted about 10M houses, which is probably about what there are in the state. For what we are spending in Iraq, we could do the same with solar/wind/hydro here; I've got a seasonal creek I would plug in, if it was subsidized and if I got paid for XS electricity. Lots of empty land in flyover, with lots of sun and wind.
Brazil seems to be doing quite nicely with their vehicle fleet running off of ethanol, made from sugar cane.They want to export it to us. Alcohol from corn is debatable, +/- on EROEI, depending on the study. But hemp and coconut have 10X the output/acre as corn, and algae is 15 times better than them.
Rat@don't takeitpersonallybuthttp://www.pbase.com/image/43000355 |
