Welcome to Charge: the future of energy
A HYDROGEN ECONOMY BASED ENTIRELY ON RENEWABLES
by Daniel C. Sweeney, Ph.D
I am currently involved in preparing a market study on hydrogen—one which focuses primarily on present industrial uses rather than anticipated uses in fuel cell powered cars or fuel cell based distributed electrical generation. There is, however, a segment devoted to energy, and, in preparing that segment, I have been compelled to come to grips with the vision of a hydrogen economy based entirely upon renewable energy and to arrive at some estimate of its feasibility.
Remarkably, no one seems to have performed any detailed analysis in this area. Legions of Greens assume that such a transition is not only a foregone conclusion but that no obstacles stand in the way of its accomplishment other than the greed of large corporations with a stake in the existing energy regime.
But are these assumptions in fact true?
Perhaps the best means of arriving at an answer is to examine the renewable options and to determine what renewable energy resources could be effectively exploited on such a scale as to supplant the current fossil fuel regime.
Renewable energy sources include wind; solar energy; hydroelectric power; ocean power, which in some sense is a subcategory of hydroelectric; geothermal; and biomass. Of this group only wind appears highly promising for truly large scale energy generation in the United States. Solar energy is fine for providing off-grid electrical power to residences and small businesses but is currently far too expensive for utility scale electrical generation, though that may change in the future. The others are either dark horses or not in the running at all. Hydroelectric is limited to certain favorable locales as is geothermal. Ocean power, whether we’re discussing wave or tidal generators or those based on temperature differentials, is largely unproven, while biomass requires such large amounts of land that is unlikely ever to serve as anything more than a supplementary energy source.
So let’s examine wind in further detail while putting the others aside for the moment.
Hydrogen economy prophets like to cite Department of Energy statistics on total wind resources for the U.S. continental land mass, resources that are so plentiful that but a tiny fraction of them would meet our energy needs in full now and for the foreseeable future. They also like to cite various studies that indicate that wind power is now fully cost competitive with fossil fuel generated electricity. Both assertions are essentially true, but they must be considered in the light of certain evidence, that while not directly contradictory, yet calls the case for a easy renewable transition into question.
First the matter of the size and scope of the wind resources.
Wind resources are huge, no doubt about it. Unfortunately they not necessarily easily exploited. Most utility scale turbines require at least an 8 knot breeze in order to operate and thus are limited to areas with strong prevailing winds such as mountain passes, coastal areas or the Great Plains. Lower speed designs exist but they generally trade off efficiency and cost effectiveness. And because the most favorable wind resources are most commonly found in remote areas, expanding the scope of wind generation generally requires a lot of new transmission capacity which is expensive to build and will consequently tend to make wind power uncompetitive with fossil fuel plants. Moreover, wind power, if implemented on a grand scale, would require a fundamentally different kind of electrical grid than we have today.
The key problem here is delivering a steady 110 or 220 volts to residences and businesses with a wildly fluctuating power source. When wind is merely a supplementary source, as it is everywhere today, then the fossil fuel core electrical generation system can provide the steady base line power. But if that’s not the case, then we have a problem.
The solution would be to build significant overcapacity in the wind generation facilities and utilize that overcapacity to create a reserve of stored energy. Most hydrogen advocates see hydrogen functioning as an energy carrier and the hydrogen itself being generated by electrolysis.
The question is how much overcapacity would be required, and that in turn raises the questions of how the hydrogen will be utilized in generating baseline power and how big will the base line generation plant have to be in relation to the renewable plant?
I haven’t been able to arrive at any firm answers to either question as yet, but here are some thoughts. Most renewable advocates favor hydrogen fuel cells for providing base line power. Fuel cells have poor load following characteristics, are extremely expensive, and require DC to AC converters. The last introduce a whole host of problems, and probably the best course would be to use the DC output of the fuel cell to run a large DC motor which would turn an AC generator that would produce pure sine wave AC power. But a better solution would probably be to use hydrogen burning turbines which would emulate the characteristics of the current natural gas generators that produce a large fraction of the electrical power in the U.S. today.
The turbines would have to have a load following capability that would compensate for the fluctuations in output of the wind farms, so one would need data to determine that. An alternative might be to redesign the transmission grid entirely to deliver DC. High voltage DC transmission is already widely used in Russia and would be facilitated by the use of superconducting power cables which are available today, albeit at high price. If power transmission were DC, and AC were only produced locally, the problem of voltage fluctuation would only be visible at the inverter which could be designed to accommodate such fluctuations. In a pure AC system with no conversions voltage fluctuations are propagated through the entire grid as we have seen in regional power outages.
In any event, the cost of wind turbines alone for replacing fossil fuel powered turbines would be in the trillions. In think at least two million turbines would be needed and maybe more. One megawatt turbines go for over a million dollars a piece, and to replace the current 1000 gigawatt output of the existing fossil fuel and nuclear system would appear to cost about 1.6 trillion dollars. But turbines are generally rated at peak power output, not typical power output because that varies with wind speed. Normally, however, average power output is far below peak power, and so large, one megawatt, utility grade wind turbines need to be derated. And then there’s the matter of reserve capacity we talked about. First we’d have to determine just what percentage of total power reserve power should equal and then compute the reserve power requirement, taking into account the fact that we’d only be getting back about a quarter of the energy used in creating the reserve power due to losses in the electrolysis process and the subsequent use of hydrogen to generate electrical power.
If the grid is used to create hydrogen to run the transportation system, then the situation looks much worse. Transportation accounts for almost half the energy usage in the U.S. today, and the well to wheel efficiency of fuel cell powered vehicles is less than 20%. So what are we talking about, more than doubling the total renewable requirement after already increasing it by some multiple to provide reserve capacity?
And that’s leaving aside the cost of creating a new grid.
I believe that building a renewable based hydrogen economy might carry a price tag of over 20 trillion dollars for the United States alone. Such an undertaking would involve a commitment of a major portion of this nation’s total industrial capacity and investment capital. It’s just staggering.
In a purely technical sense it’s probably feasible, but in economic and political terms I just don’t see it happening. I think the U.S. is facing a very dicey energy situation in the first half of this century, a situation for which there are no obvious solutions. I don’t necessarily accept the Doomsday scenarios some have painted, other societies have adapted to shortages in the past, but dependence of the U.S. industrial economy on every increasing supplies of ever less expensive energy is troubling.