Electricity vs. Alt Fuels - Toward a Renewable Grid?

This past week the State of Minnesota released a study prepared by EnerNex Corporation and WindLogics on the cost and feasibility of integrating up to 25% wind energy into the area served by the Midwest Independent System Operator. The authors of the study found that while there were significant costs involved in integrating such a large proportion of wind energy into the total energy mix, such a high value of wind would not degrade network reliability and was in fact feasible.

I believe that this study has important implications for both the alternative fuels industry specifically and for the energy industry as a whole, and may lead to a reconsideration of the role of renewables generally.

Our Fifty Thousand Foot View

Earlier this year I prepared a lengthy study for Visant Strategies, presently available at their Website, on the global hydrogen industry. While much of the study deals with industrial uses of hydrogen in oil refining and chemical production, considerable space is devoted to the use of hydrogen as a fuel for both fuel cells and internal combustion engines. One section deals specifically with the production of hydrogen fuel from renewable sources.

Many hydrogen advocates embrace a vision of the future where hydrogen will be generated by means of electrolyzers drawing electrical energy entirely from renewable sources. While some such advocates believe that such a regime will be characterized by distributed generation, many if not most see the current pervasive electrical grid being eventually anchored by wind turbines and other renewable power sources rather than fossil fuel plants or nuclear facilities.

At the time I composed the study I felt that this possibility should be explored, and that, in so far as possible, the logistics of such a renewable grid should be examined. Unfortunately, I found that the renewable grid was more a matter of millennial rhapsodizing than serious investigation. No one, it appeared had ever done any kind of rigorous analysis of the technical feasibility or the probable cost of implementation. Rather the assumption was that a renewable grid could be easily enough put in place if only the oil and coal companies could be held at bay. Thus in attempting to characterize an all-renewables based power grid, I was largely on my own, and I was obliged to construct a highly conjectural model based on the generally known characteristics of large scale interconnected electrical systems and the capabilities of renewable energy electrical generators, both as presently constituted and as they might plausibly evolve.

I did, however, find a number of documents relating to the integration of wind generators into a conventional power grid comprised of fossil fuel fired plants, though never at anything close to a parity level. The assumption among the more serious investigators, all of whom, incidentally, hailed from Scandinavian countries, was that a 20% reliance on wind power marked the upper limit for which one could maintain normal levels of reliability, and that even at that modest level a high voltage direct current transmission grid would probably be required, with AC conversion occurring at the distribution level. The further assumption was that the grid in question was self contained and could not draw from resources from elsewhere.

The Minnesota study supports a considerably higher level of wind usage, and says nothing of the necessity of converting the grid to DC—an extremely costly undertaking. What it is saying in effect is that we can be using a great deal more renewables than we’re using today, especially in favorable wind regimes like the Upper Midwest. If that’s true, and we can go to double digit renewable power, we can supply electric or hybrid electric vehicles with electrical energy while greatly abating greenhouse emissions. This might well have negative implications for alternative fuels, especially if plug-in hybrids win rapid market acceptance.

Not that this kind of growth in renewables is necessarily going to happen. Any expansion of wind power would require a lot of new transmission capacity and would be enormously expensive. And transmission capacity is what has not been growing appreciably in recent decades.

The Minnesota study is available at http://www.puc.state.mn.us/docs/windrpt_vol%201.pdf. My own analysis of an all-renewables based grid follows this article, and makes interesting reading (I think) in the light of the later report. I am, as you will see, quite pessimistic as to the feasibility of an all-renewables based power grid within the foreseeable future.

Further Notes on the Wind Report

The Minnesota study makes a clear distinction between the installed capacity and the load carrying capacity of wind generators. This distinction is fundamental, and, unfortunately, tends to be ignored in discussions of renewable energy in the press.

Load carrying capacity represents the actual ability of the resource to serve the needs of the rate payers. Installed capacity, on the other hand, represents some fairly arbitrary number having to do with the collective output of the wind generators in question. Since wind turbines are fairly optimistically rated as rule by their manufacturers, and since their combined outputs are intermittent even when massed over a considerable geographical area, the installed capacity must be rated well below the load carrying capacity. Interestingly, according to the study, the discrepancy between the two goes up as the percentage of wind power in the mix increases. At 15% wind the installed capacity must exceed the load carrying capacity by a factor of 4.7. At 25% wind the installed capacity should be 5.8 times the load carrying capacity.

The study indicates that when wind resources are widely dispersed, hourly fluctuations in output from the wind resource are typically very low but that longer term fluctuations from day to day and from week to week remain. Obviously, such fluctuations in no way track the demand for electricity on the part of those connected to the grid.

The study cites an integration cost for wind power of $2.11 per kilowatt hour at 15% of load carrying capacity and $4.41 for 25% of load carrying capacity. How these figures are derived is not specified, nor are the intricacies of wind integration discussed.

No mention is made of other renewable resources, an understandable omission in view of the fact that, save for hydroelectric power, wind is the only significant renewable resource being tapped by public utilities today. Hydroelectric power, I might add, is not for the most part intermittent, and hydroelectric plants tend to resemble fossil fuel plants in respect to the way that they are utilized by public utilities. New conventional hydroelectric generating plants are not being constructed in the United States, however, and so hydro will account for ever decreasing part of the energy mix over time.

What is known as concentrating solar energy constitutes the most interesting alternative to wind on the renewables horizon, and concentrating solar generating plants possess operating characteristics that are in many respects complementary to those of wind generators. When placed in regions of clear skies and intense sunlight, such as our own Southwest, concentrating solar plants tend to produce quite constant outputs for up to sixteen hours a day. But for at least eight hours a day they produce no output at all.

Such generators do not use solar panels, which are low voltage, low efficiency DC devices, but instead rely on parabolic mirrors to focus sunlight on heating chambers containing working fluids of various types including hydrogen, helium, molten salts, Freon, etc. The expanding gases in the heating chambers are used to power turbines or Stirling cycle engines which themselves are used to drive generators. The resulting electrical outputs are as constant in voltage and frequency as those from a coal fired power plant.

Concentrating solar installations date back to the earliest years of the twentieth century, and, in some sense, represent fairly mature technology. The obstacle has always been cost. The engines are very expensive to manufacture, and do not produce outputs that are remotely comparable to those of giant turbines used in coal, natural gas, or nuclear plants. As is the case with wind, sunlight is a diffuse energy resource, and one that is expensive to harvest.

At present, concentrating solar is not a real industry, and such generator plants that exist are all pilot projects. I believe that true commercial installations will emerge, but because of the lack of major manufacturer involvement, growth is apt to be slow.

Assaying the place that renewable electricity will play in the U.S. over the course of the next two decades is difficult, and is made more difficult by the impassioned advocacy of renewable energy supporters which tends to impede reasoned discussion of the matter. Most hardheaded energy analysts do not see renewables accounting for more than a couple of percent of utility electrical power by the most optimistic estimates by the year 2025, and I tend to concur. This new study is not likely to change the present trajectory of renewables in the American energy market, but it does appear to indicate that renewable energy could assume a position of considerable importance if the political will were in place to promote. But the politics of renewable energy is a matter for another article or a whole series of article, and I will refrain from discussing it here.

Finally, I do not believe that this study will much impact the investment climate for wind power one or the other. Wind generation is a well proven technology, and its growth has been impressive for the past two decades. Such growth is likely to continue indefinitely without ever attaining explosive intensity.