Last night I got drawn into a very long Twitter discussion with an acolyte of Dr. Marc Z. Jacobson and his colleagues in the Wind, Water and Sunlight (WWS) series. The discussion revolved around the most recent in Dr. Jacobson (et al.’s) stream of road maps for a 100% Clean and Renewable (WWS) future. The newest is a roadmap for 139 Countries of the World. As regular readers of my blog know, I have banged my head against the 100% WWS drum a couple times, but since Dr. Jacobson continues on his journey, I feel I should probably continue to accompany him. The topic of last night’s discussion revolved around energy storage technologies in the 100% WWS series. As I have mentioned in my previous blogs (discussed below) Dr. Jacobson (et al.) tend to spend a lot of time figuring out exactly what combination of WWS will meet each scenario in each region/state/country but in doing so they gloss over important topics like raw material limitations and energy storage. Having looked at the former previously, today I intend to look at the latter.
For those of you new to the cycle of papers Dr. Jacobson has produced in the series, it all began (in my estimation) with an article titled “Review of solutions to global warming, air pollution, and energy security” (hereafter Jacobson 2009). Jacobson 2009 created the underlying energy framework for his subsequent work. All his subsequent papers rely heavily of the analyses in Jacobson 2009. As I describe in my post Deconstructing the 100% Fossil Fuel Free Wind, Water and Sunlight USA paper – Part I Why no nuclear power? the foundation for this series is definitely not built on bedrock. In Jacobson 2009, Dr. Jacobson creates what can best be described as a “unique” ranking system to establish that wind, water and sunlight are the best energy sources to power our future society. Most people in the renewable field agree that these are definitely critical energy sources for a fossil fuel-free future. Curiously one other energy source, considered critical by other researchers, is discounted by Dr. Jacobson: nuclear energy. As I describe in my post, in Jacobson 2009, Dr. Jacobson eliminates nuclear as a useful option through what can best described as an inventive approach. The approach includes calculating mortality associated with nuclear energy based on a future nuclear exchange scenario and discounting the use nuclear power internationally out of fear of nuclear proliferation. Yes, you read that correctly, he apparently feared that nuclear power plants in the United States, China and a Russia might encourage these three nuclear powers to develop nuclear weapons? As if the only thing keeping Canada, Sweden and Germany from producing nuclear weapons was access to nuclear power plants? Finally, in a coup de gras, he uses what can nicely be described as an outlier from the academic literature, to assign an incredibly high carbon footprint for nuclear power. For details on this discussion, feel free to look at my earlier blog post.
Building on Jacobson 2009, Dr. Jacobson and Dr. Delucchi prepared a pair of papers titled “Providing all global energy with wind, water, and solar power”, Part I and Part II (called 100% WWS World Part I and 100% WWS World Part II hereafter). These built on the intellectual framework of Jacobson 2009 by crunching the numbers on how 100% WWS could be used to power the world in a very general sense. The papers look at the various energy scenarios and argue that if scaled up they would provide adequate power given a lot of interesting assumptions. One of the biggest assumptions, which I discuss in my blog post Deconstructing the 100% Fossil Fuel Free Wind, Water and Sunlight USA paper – Part II What about those pesky rare earth metals? is that the critical raw materials for use in these technologies can be obtained both easily and at a reasonable cost. As I point out in my blog post, the assumptions of the paper are belied by actual planetary material limitations. As I discuss, even supplies of the simplest elements like Lithium are under strain by current usage rates. Expansion for global use would simply bust the market. Certainly we can mine the sea for Lithium, as suggested by Dr. Jacobson, but only at a huge cost in energy and money. As a recent study points out to simply replicate our current lithium mineral production by filtering ocean water we would need 10% of the present world production of energy power! At that energy cost for production Lithium would be more valuable than platinum is today. Somehow I cannot see any scenario where we could make batteries affordable at that price for Lithium. People would be stealing cars just for the batteries. As for the suggestion that we could enhance our supplies through recycling? Well the battery needs of those scenarios would require 100% usage of Lithium, leaving no Lithium to exploit via recycling.
Having addressed the initial shortcomings of the 100% WWS papers, I will now consider another topic not previously covered in my writing: energy storage and loss. Throughout the series of 100% WWS papers the various authors have glossed over the issue of energy storage as a means of buffering for intermittency of the energy supply/power needs equations. In Jacobson 2009, Dr. Jacobson provides a very brief paragraph (124 words in a 23 page paper):
A fourth method of dealing with intermittency is to store excess intermittent energy in batteries (e.g., for use in BEVs), hydrogen gas (e.g., for use in HFCVs), pumped hydroelectric power, compressed air (e.g., in underground caverns or turbine nacelles), flywheels, or a thermal storage medium (as done with CSP). One calculation shows that the storage of electricity in car batteries, not only to power cars but also to provide a source of electricity back to the grid (vehicle-to-grid, or V2G), could stabilize wind power if 50% of US electricity were powered by wind and 3% of vehicles were used to provide storage.113 The only disadvantage of storage for grid use rather than direct use is conversion losses in both directions rather than in one.
I note that he correctly identifies that vehicle-to-grid storage results in conversion losses in both directions but does not quantify those losses.
In 100% WWS Part II, Jacobson and Delucchi repeat the mantra of storage in “batteries, hydrogen gas, pumped hydroelectric, compressed air (e.g in underground caverns or turbine nacelles), flywheels, or thermal storage units”. As with the previous work, an examination of the 100% WWS papers finds a dearth of information about energy loss in the conversion and storage of energy. This is interesting because one of the big points in the 100% WWS premise is that by electrifying everything we can generate major savings in energy use. As described in the papers, Dr Jacobson sees savings of up to 30% in energy requirements by converting from fossil fuels to electric vehicles. Yet with the exception of transmission losses and battery decay, the papers don’t address the losses associated with any of the alternative technologies suggested. So let’s look at some of these.
Author’s Note: Coincidental to the production of this blog post a new paper by Dr. Jacobson and his team was published in PNAS titled: Low-cost solution to the grid reliability problem with 100% penetration of intermittent wind, water, and solar for all purposes. It addresses a number of the storage issues identified in this post. Dr. Jacobson was kind enough to supply a pre-print with all the supplementary information included. Specifically it addresses some of the questions I raise about storage technologies and also points out that the paper only addresses the 48 contiguous states. As such some of the text below has been struck-through and some additional comments added in italics.
One of the solutions suggested in the 100% WWS series to address both the lack of raw materials (like Lithium) and the need for dispersed storage is the idea of “vehicle-to-grid” (V2G) storage. Realistically V2G will form an important way of managing energy supply in a fossil fuel-free future,
but Jacobson (et al.) fail to include energy losses associated with this storage medium in their calculations. Looking at the literature, the generally accepted figure appears to be that that the charging of electric vehicles through the use of an on-board inverter has about a 5% -10 % energy loss per cycle. A study of V2G storage in Poland showed a charge/discharge efficiency loss of 22%. This number matches the rest of the literature pretty effectively. In my reading of the 100% WWS series I cannot see anywhere where this loss is reflected in the necessity to add additional generating capacity. The series includes a consideration of transmission losses but says nothing of charging/discharging efficiency? One would think if you are counting on energy demand to go down by around 30% from conversion efficiency and around 7% from end-use efficiency you should also consider how the 22% loss via charge/discharge efficiency will affect your calculations? An examination of the follow-up paper indicates that they have left V2G storage out of their follow-up analyses.
Another suggested energy storage solution in the 100% WWS series is the use of underground thermal energy storage (UTES), borehole thermal energy storage (BTES) or aquifer thermal energy storage where excess heat is stored underground in summer to produce heat in winter and cold is stored underground in winter to provide cooling in summer. This was the topic of the Twitter discussion that served as the impetus for this blog post. A great example of a BTES system is Drake Landing Solar Community in Okotoks, Alberta. Currently Drake Landing is providing over 90% of its residential space heating needs through use of solar thermal energy. This is an excellent thing and worth pursuing; but there are drawbacks. The most obvious is the loss of energy in the system. In the best BTES systems you can still expect to lose 33% of the solar energy collected via heat loss to the surroundings. Incorporating a heat pump will improve this number at a loss of some additional energy to the heat pump.
Looking at Dr Jacobson’s numbers the results don’t look nearly as good when you realize that up to one third of the energy collected by the 100% WWS system could be lost in the storage phase of the cycle. In an extreme locale like Fairbanks Alaska, in winter, there is not a lot of WWS to work with so losing one third of the minimal energy you generated during the “day” might leave you suffering through a very long and cold “night”. In the follow-up paper Dr. Jacobson uses a UTES efficiency of 56% which seems a reasonable number for this analysis.
Storage losses aren’t the only drawback to these underground storage systems. The creation and operation of the systems can have serious environmental consequences as well. From an environmental perspective we have to consider the thermal, chemical and biological impacts of these systems. Dr Jacobson and his team are primarily engineers and do not appear to have taken into account the fact that aquifers are not simply closed boxes where you can store energy. Aquifers flow; are in chemical balance with their surrounding rock; and can represent biological communities in their own right. Depending who you believe the injection of all that heat/cold into aquifers can have either few serious effects or serious deleterious effects with the serious effects ranging from the growth of undesirable biological communities to the release of metals like arsenic into the groundwater. In communities dependent on groundwater as a potable water supply, these systems may not even be possible/advisable. Moreover, in many locations geological formations are not naturally conducive to such systems and fracking may be necessary to make the groundwater accessible. I’d like to see anyone trying to sell fracking for underground thermal storage to the folks in New York State anytime soon.
As this post is getting long (which seems to happen in these posts) I will stop here. Before I leave though, I want to make something perfectly clear. I am not against the ideas put forth by Dr. Jacobson and his team. I believe that we, as a society, need to move beyond fossil fuels. Like many others I see WWS as part of the solution. Where I differ with Dr. Jacobson is that my research makes it clear that WWS can only be part of the solution. Without baseline power from sources like nuclear energy I cannot foresee us achieving a fossil fuel-free future. What I find annoying (and the reason for these posts) is that many activists lack a sufficient grounding in science to recognize the flaws in this proposed system. These activists continue to fight against both fossil fuels and nuclear power. By demonstrating the real, and likely insurmountable, issues associated with the 100% WWS scenarios I hope to help work towards a future where renewable and nuclear energy can work together to power a growing and prosperous society.