I was again in Washington, DC (actually, National Harbor, Maryland, just down the Potomac) last week for the annual (and perhaps last?) arpa-eEnergy Innovation Summit (about which, more later). But I had learned that one of my targets of opportunity for debunking vacuous green claims, Pavegen, has an installation in Washington, DC. I couldn't feature being so close to an installation and not paying a visit to experience the Pavegen pavers first hand. After Lyfting from the summit site at the Gaylord National Harbor Resort and Convention Center to Dupont Circle in Washington, DC, I had my first chance to observe and experience the Pavegen pavers (or tiles). To the right, you'll see the triangular tiles arranged as hexagons in the Pavegen sytem. Those are my feet and my Cross pen (inscribed with a wonderful message from my beautiful wife, Zandra) for scale. I walked on the pavers, jumped on them, stood on them, and watched the DC pedestrian crowd interact with them. I'll describe my experience "down post" but first I'll describe the reactions from the pedestrians. I'll note that there were no signs or other indicators that the pedestrians and bicyclists were contributing to green energy generation (albeit at a negligibly small scale) with their efforts. No advertising was there and, frankly, the pavers don't look bad.
The video is slow motion of folks walking on the pavers. I didn't survey, or even count, but I'd estimate that somewhere around 5% of the pedestrians noted that there was something different in the small areas where the pavers were installed. And, on three occasions, someone mentioned to their fellow walker that electricity or energy was being generated by the pavers. One said that "I think it runs the lights or something." None seemed troubled either by the extra effort entailed in walking on the tiles, and the company of whomever mentioned the energy typically said "cool" or similar.
My reaction was fairly similar. It wasn't particularly troubling to climb out of the estimated 5mm depression caused by my weight acting on the Pavegen generators. But, as to electricity generation, I'll just say that my opinion is unchanged. To the left is one of several little installations of lit LEDs, again with my pen indicating scale. Based on Pavegen's site, there are also lights for some of the hardscape features. You can barely tell that the three LEDs are lit. In any case, now that I've actually walked on the pavers, seen pedestrian reaction to them, and analyzed them (to death), I think I can finally put my Pavegen focus to rest.
In my day job, I am an executive in a firm that provides consulting services, materials testing, and construction inspection. We don't work in the area of single family housing but, other than that, if it's being built, we want to be involved. And we're located in Southern California. As such, we're very interested in the economics of the State and of its various regions. I was reviewing the 2017 "California Economic Summit Roadmap." On the first content page of that 12 page document, I read the following:
"An additional 6.8 million people are considered “economically fragile,” living in households earning below their area’s median income (which varies by region, from $43,000 a year in the San Joaquin Valley to $64,000 in the Bay Area)."
Indeed. I must point out here that this statement is statistically confusing or, at the least, is poorly phrased. Exactly half of the households in California, or any County, or any State, or the U.S., or any Country earn below their area's median income. And, no matter how hard anyone in government tries, they simply can't fix this problem. Because, well, that's the definition of median! So, clearly, the issue isn't that half the households are below their area's median income but, rather that their area's median income is below the level that would represent not being classified as "economically fragile." The definition of an "economically fragile" household isn't clearly stated, but surely it can't be "any household below its area's median household income" because, by that definition, one half of households everywhere are economically fragile and will be for all eternity or until Armageddon, whichever comes sooner. I'm sure that my sophisticated readers were able to infer the intended meaning of this paragraph but, given the level of innumeracy out there, I'm absolutely sure that there are many readers who think My God, half the households in California are below the median household income! Make the rich pay their fare share, that will fix this!" And, of course, if such persons were asked "what fraction of the households in California would you estimate had below the mean household income?" they'd answer "Why, one half, of course! What a stupid question! " The fact is that, barring an anomaly, significantly more than half are below the mean. For example, in 2014 the median household income in the U.S., per the Census Bureau, was $53,713. The mean household income was $72,641. Clearly, fewer households earned $72,641 and above than earned $53,713 and above. And yet, the mean is what people think of when the word "average" is used. But you knew that, didn't you?
(Note: the zombie image applies both to my blog and to the subject of this post.)
Pavegen, a Company that I've looked at before (see here and here) is still around and, apparently, thriving. Pavegen designs, manufactures, and installs tile systems that generate electricity via footfalls as pedestrians walk over them. Despite my lack of posting, I've not lost interest in all aspects of energy and, in perusing the web, I happened upon their new site. They've developed a new tile design and quite a presentation. The link is to a 49 minute video! I thought I'd keep an open mind and evaluate it, despite my expressed disdain in the previous posts. Getting started, I found a couple of troubling things. At the 19:15 timestamp in the video, CEO and Pavegen inventor Lawrence Kemball-Cook states that the new Pavegen tiles are "200 times as efficient." Later, at the 28:10 timestamp, CTO Craig Webster states that Pavegen is capturing "about 20 times more energy per footstep" than the previous version of the Pavegen tiles.
Image credit: Pavegen
Well! First, an order of magnitude discrepancy in the claims is hardly something to ignore. But let's use Webster's claim of 20 times, since he's the CTO. Kemball-Cook walks across the tiles to demonstrate the data gathering capabilities of the tiles and the screen shows steps and energy generated (see the graphic at right, click to enlarge). It shows that Kemball-Cook has generated 65 Joules in 14 steps, or about 4.6 Joules/step. As an aside, some quick and dirty calculations with appropriate estimates leads me to conclude that he's generating at something like 8 watts. In my second Pavegen post (this current one is my third) I estimated that the previous generation of Pavegen tiles generated somewhere between 3.5 and 7.2 joules per footfall (the lower from my estimates, the higher from data generated by a Pavegen installation). I'm hard pressed to see an increase of 20 (let alone the ridiculous 200) times in efficiency of energy conversion. Kemball-Cook and Webster both tout the efficiency of the new triangular shape and its ability to capture energy over 100% of the area of the tiles vs. the previous square tiles but that is, in no way, sufficient to justify their claim.
Image credit: Pavegen
I assumed from previous information that the mode of energy conversion was piezoelectricity. but it's clear from the Pavegen video that this is not the case, at least in this incarnation. Rather, it appears that a footstep spins a small flywheel that operates as a generator. Each vertex intersection of the triangular tiles rests above such a generator. I will concede that it's a very clever design. Kemball-Cook and his team have big plans for the Pavegen system. Jeff Martin, CEO and founder of Tribal Planet, apparently has formed a partnership with Pavegen and, through the use of smart phones, anticipates that malls, stores, stadiums, etc. could track the energy delivered through the footsteps of a customer and then provide discounts, loyalty awards, etc. to the customer. Or, one could "donate the energy" to some developing world person who needs it. The mechanism for such a transfer isn't described. But, as I stated in the previous post, I take about 5,000 steps on an average day. If each step were captured, I'd generate (if I weigh the same and walk similarly to Kemball-Cook) 4.6*5,000= 23,000 joules, or 0.0064 kilowatt hours. In my city of Anaheim, CA, that would be worth a little under eight hundredths of a penny. And, to reiterate, that's not my trip to Target, that's my walking for an entire day. The cost of a Pavegen tile isn't stated, but Kemball-Cook does state that Pavegen's goal is to bring the price close to that of a standard tile through mass production. There's no doubt that the tiles do generate electricity, probably at the rate of around 8 watts for each walking adult. And there's no doubt that that level of generation can be used for area lighting or similar. But the energy isn't free, it's energy added to that of walking without the tiles. Now, it may be the case that in the generally overweight United States (I can't say about England, the home of Pavegen), having people spend more energy to walk might be desirable. In any event, at the outset of the video, Kemball-Cook mentions that lighting accounts for nearly 20% of all electricity generated world wide and, after saying that he didn't know that, doesn't say anything further about it. He leaves the impression that he'll show that Pavegen tiles can alleviate the need for mains power for that use. Umm... no. In my office, there are about 32 people. Most don't walk around as much as I do but let's assume that they do. Most of my walking is at work, say 4000 steps over nine hours. This rate, at 4.6 joules/step, equates to 0.6 watts or so. If all 32 people in my office did the same, it would be 19.2 watts. That wouldn't light one of the four fluorescent tubes in my office, let alone the entire 12,800 square feet of the floor we occupy. It's true that LEDs would do better but there's no chance that 19 watts would come close. And that generation, in a work day, would be about 0.017 kilowatt hours, worth less than two cents. Pavegen has a fascinating gimmick and a clever design, but it won't put a dent in electricity use. And the electricity comes, ultimately, from the sun. We eat the plants and animals, and fertilize them with products of sunshine from millions of years ago to give us the energy to pump the Pavegen tiles. Update: There's significant discussion at the website of the ability of the tiles to generate data and wirelessly transmit it. This could be used to determine traffic patterns in stores, malls, museums, etc. and to locate "hotspots" for patron activity. I strongly suspect that, after the "gee whiz" factor of the trivial energy output wears off, such data will be the real value (or, as my close friend and associate, Dr. Boris Stein, would say, "the dry residue"). Were I an officer at Pavegen, I'd offer a cheaper option of the tiles without the generators to be sold for the data gathering capability.
What Warren Meyer (a staunch "small l" libertarian) said. But, to make it easier, I'll paste it here:
"Dear Conservatives: As you wallow around in your election-day schadenfreude, I offer you this note of caution: Except perhaps on immigration and a few miscellaneous issues like climate, Trump is not a Conservative. He has no apparent respect for the Constitution, or free speech, or any number of individual freedoms. He is a serial abuser of eminent domain and has lived off of crony rents for decades. We often compare government unfavorably to private individuals when it comes to budgeting, observing that most of us can only spend as much as we bring in, unlike a profligate Federal government -- but Trump can't control spending in his own private sphere and has run up huge amounts of debt he has had to disavow in various quests for self-aggrandizement. Do you really think he won't do the same thing with public funds?I said this morning I would give up political prognostication, but I am fairly sure in less than 6 months we are going to see prominent Conservatives coming out publicly with buyer's remorse." By Warren Meyer at Coyote Blog
Having spent six days traveling to, attending, and returning from arpa-e 2016, it's time to start chronicling some of my thoughts. At the broadest level, the summit was very well attended, much better than last year. As is typical, the demographic was predominately male, predominately Caucasian with a significant sprinkling of Indian (subcontinent type) as well as Asian attendees. There were extremely few African Americans and other "people of color" and a relatively small population of women.
It was stated by Katie Fehrenbacher, a senior writer at Fortune Magazine who focuses on energy and technology, that, at her first arpa-e summit attendance in 2010, there were many VCs (venture capitalists) whereas, in 2016, "not so much." The decline in funding for clean energy startup ventures that her comment implies has been well documented elsewhere.
I'm not an expert investor but, as I implied in one of my posts on LightSail Energy and stated in my post regarding Bell Laboratories, today's investors' demands for quick returns on their investment are anathema to ventures that develop over periods of many years and require huge capital investments. Further there have been well-publicized failures of some large cleantech startups, e.g., Solyndra, Range Fuels, KiOR, A123, etc. Cleantech is HARD! While at the opening session, I drew a little diagram on my Samsung Galaxy Note 4, a phone on which one can legitimately take handwritten notes and make such sketches. Here's the sketch I made:
I'll concede that it's cryptic and hard to read but the idea is that the U.S. funds entrepreneurial innovations that lead to development in such a way that private equity of one sort or another sees the potential and ponies up sufficient funding to take the innovation to market. To date, arpa-e funded ventures have attracted $1.25B in private funding. To do so, it has provided $1.3B to some 475 projects. I'm unable, however, to find an arpa-e funded venture that has individually gone to market, though at least four have been purchased by large companies as of FY 2014.
I'll provide further input over the next few posts (perhaps interspersed with other topics) but I want to say that that $350M per year funding level for something as important as the goals of arpa-e is a pittance, especially in comparison to the scale of the problem. There are those who say government should stay out of such ventures and ask "what good has government investment ever done?" I'd point out Boulder (now Hoover) dam, Tennessee Valley Authority, Rural Electrification Administration, ARPANET, etc.
I'm rather shocked to find that this is the sixth (!) arpa-e energy innovation summit that I've attended. I intend to blog about my adventures here and, in particular, about some of the energy storage sessions as it's my considered opinion that storage breakthroughs are key to a sustainable energy future.
But for this post, I'm going to discuss getting to Washington, DC. I used three modes of transportation: my (new) Jeep SRT Grand Cherokee (with apologies to commenters who had suggestions for my avoidance of such a joule hog) to KSNA, i.e., John Wayne Airport; two legs of air carrier transport (KORD, O'Hare Airport was a layover); and a SuperShuttle van from DCA, i.e., Reagan National Airport to the Gaylord National Harbor Resort.
The trip to KSNA was about 18 miles, the Jeep is currently displaying an average mileage of about 15.5 m.p.g. (as stated in my previous post, I'm not driving for economy) so I burned about 1.16 gallons of premium fuel, thereby converting something like 137,000,000 joules of chemical energy to thermal energy to turn the wheels, move air out of the way, heat the atmosphere, etc. Therefore, I my rate of energy use in "joules/(passenger*meter) was about 4,730.
The leg from KSNA to KORD was in a United Airlines Boeing 737-724 aircraft featuring two CFM InternationalCFM56 turbofan engines (of the "dash 7B24" variety). These engines are rated at 24,200 pounds thrust each. It's not easy to estimate the fuel burn for airline flights, I wish that I'd remembered to ask the Captain or First Officer, they're very cooperative to sharing such data. But, as best I can estimate, we burned around 18,000 pounds or 8,165 kilograms of fuel (fuel calculations for airplanes are typically done in pounds since aircraft weight enters into literally every aspect of every maneuver and operation) to take 118 passengers 1,818 statute miles. A kilogram of jet A fuel releases 43.5 megajoules of energy upon oxidation, and so we converted 3.55*10^11 joules of thermal energy. The plane carried its full complement of 118 passengers, and so the energy use in "joules/(passenger*meter) was about 1,040. Of the 3.55*10^11 joules converted, I was responsible for about 3 billion of 'em.
I'll spare my patient readers the detail of the KORD to KDCA leg on an Embraer 175 regional jet. I estimate that we converted 1.14*10^11 joules traveling 650 miles. This works out to about 1430 (joules/passenger*meter) for the 76 passengers on board. My allocation was about 1.5 billion of those joules.
Finally, I rode a SuperShuttle van for the approximately eight miles to complete the journey. I estimate that it burned about 0.5 gallons and converted 42,800,000 joules of chemical energy to thermal over the eight miles. My rate of energy use was thus about 3,320 joules/(passenger*meter).
My grand total of turning the energy in chemical bonds to thermal energy in the atmosphere
(and a very small amount in ground) was 4.68 billion joules. Of these, 4.5 billion or about 96% were in aircraft (I can't say "in the air" because we did taxi). But note that, of the 2,495 miles traveled, 99% were in the air. Thus, purely in terms of energy conversion, the air travel was quite efficient in comparison to ground transport. Of course, I was the solo passenger in my vehicle as I was (surprisingly) in the van, and having several passengers would change the joules/(passenger*mile) metric significantly. And, as some will no doubt point out, so would staying home.
And, so I understand (not having read enough to know why), hydrocarbons oxidized in the upper troposphere/lower stratosphere are much more damaging than those oxidized on the ground.
I'll be responsible for more joules and a greater rate of conversion when I return to Southern California on Thursday, since we'll be flying against the prevailing winds. For a round number, I'll add 20% to the eastbound total for 10.3 billion joules. It is to be hoped that I'll learn enough here to be able to participate in saving many times that number, at least, that is, from the burning of fossil fuels. Addendum: Perhaps 10.3 billion joules has little meaning for some. This is about 2,860 kilowatt hours. The average US home uses about 2,733 kilowatt hours of electrical energy in three months.
In September of 2005, gas prices rose abruptly enough that I stopped driving as I had as a teenager in my Plymouth Roadrunner Detroit muscle car and started to do my best to squeeze every possible foot out of each gallon of gas. That was in a Jeep Grand Cherokee, which I followed up with a Land Rover and finally my current Lexus CT200h which I acquired in the summer of 2011. I've driven that vehicle in such a way that I've exceeded the EPA combined estimate of 42 m.p.g. by 8.5 m.p.g. I've done so using light touch on the pedals, attempting to maximize the vehicle's use of regenerative braking, maximizing time in traffic jams that the engine is off and motive power provided by the battery and electric motor, and a cruise controlled 55 m.p.h. maximum speed (except when converting potential energy to kinetic on long, steep downhill grades). This blog started out as documentation of my efforts in that direction and has since grown to cover a variety of other energy related topics and even ventured into politics, economics, and philosophy at times. But, notably, I've failed to save the world and I'm finished with this decade plus long experiment. I'll be going out this weekend to test drive and possibly drive away in a vehicle such as the Jeep SRT Grand Cherokee or the Audi SQ5. And I have no intention of driving such a purchase so as to maximize fuel economy. Now, was this change motivated by the steep decline in fuel prices? It was not. It's simply the case that I have had enough, the experiment has gone on long enough. I'm tired of having people run up on my rear bumper, honk, flash their high beams, etc. I'm tired of explaining to passengers why it takes me 27% longer to get anywhere. I'm tired of a car that, though it has a Lexus badge, is a Prius at heart (the passenger side seat has a pull bar to adjust position). So:
There you have it.
Now, does this mean that I'm also finished with blogging on energy and related topics? It most assuredly does not and I intend (though it has been said, in particular by my mother, that the road to hell is paved with good intentions) to post more regularly.
It should come as no surprise that Presidential candidate Marco Rubio is at the forefront of an effort to stymie local municipalities' efforts to prevent complete monopolization of broadband by Charter Cable, AT&T, and their ilk. I'm all for private enterprise but with monopoly comes a necessity for regulation. (edited for clarity) What Rubio, et al, want to prevent is States that are beholden to carriers that currently enjoy, at worst, a near monopoly, being constrained by the FCC from legally shielding those companies from competition from local municipalities who deploy broadband networks. This sentiment is proffered under the guise of "private, competitive broadband marketplace" which, for all intents and purposes, does not exist. And, to the extent that it does, the would-be monopolists are doing all in their power (including the purchase of politicians) to stomp it out. A further contention is the "States' rights" plea. Unpacked, what this means is Rubio, et al's insistence that States have the sovereign right to accept money from broadband monopolists who pay them to squelch local efforts to provide reliable and affordable broadband access. I hardly think that that's what the Federalist Founding Fathers had in mind.
It's been a while (and this isn't my first such apology) since I've posted an article. The long-awaited article (actually, articles) on the cost effectiveness of renewable energy with storage as base load and/or dispatchable electrical energy has taken a lot more time than I thought. And, of course, life intercedes. Nevertheless, lest I lose my faithful audience, I wanted to post.
Through a variety of feeds, I was led to a series of innovations by Manoj Bhargava, the founder of 5-Hour Energy (quite a few little bottles of which I've slugged down). He's committed to give away 99% (or 90%) of his (as of this writing) $4 billion dollar fortune. One venue for his philanthropy is his engineering and invention facility, called Stage 2 Innovations. Bhargava and his people have created a series of videos highlighting some of their innovations and concepts. The site is called "Billions in Change" and you can watch a 43 minute video on three of the concepts here or watch the shorter video that involves the subject of this post here.
Image credit: video screen capture from "Billions in Change,"
Capture by Treehugger.com
He's encouraged his engineers to do big things, and one cited example is the "Free Electric hybrid bike." The idea is that a human peddles a mechanism (similarly to operating a recumbent bicycle) that turns a large flywheel. In turn the flywheel operates a generator which charges a battery bank. If you think that such a concept is unheard of, I invite you to look here or here or here or... well, Google is your friend. So what is special about this unit? It certainly appears to be very well made and the large flywheel should ensure very smooth running. On the other hand, in comparison to the more standard versions linked above, it's sure to be dramatically more expensive to produce. But, if Bhargava is going to give them away, as they might say in Australia, good on him. I do think that the claims are quite misleading though. Multiple times in multiple places, it's stated that a user can "pedal for an hour and have electricity for 24 hours." While this is, no doubt, true, it certainly won't be a lot of electricity. It's also true that much of the developing world is either completely without electricity or suffers extremely intermittent availability. But let's think. A world class (as in, the very best in the world) cyclist can deliver about 400 watts for an hour. I strongly suspect that someone in a village in an underdeveloped country would be fortunate to deliver 150 watts for an hour. It's certainly the case that the cyclist to flywheel to generator to battery to load efficiency will be significantly less than 100%, I'll be optimistic and use 80%. So we'll have 120 watt hours available to do work. And we're going to use this energy over a 24 hour period and so our average load can be 6.25 watts. A single LED bulb with approximately the luminous intensity of a 60 watt incandescent bulb will use around 7 watts. Now, we won't need the single bulb during the daytime or when sleeping, let's say we use it for five hours. That will use about 34 of our 120 watt hours, leaving us with 86 watt hours. We'll use some of them to charge a smart phone. A typical battery might have a capacity of 8 watt hours or so and let's assume a couple of people in the family have phones. We now have 70 watt hours remaining. Of course, it could be that we don't use our phone enough to need to charge it every day but, if we have kids and there's internet, we will. We certainly can't use the energy for heat. While such a use is very efficient (approaching 100%) it's extremely power hungry. Let's figure that our family wants to use a Chromebook or some such to have internet access. The Samsung Chromebook battery features a 30 watt hour battery that lasts 7 hours. If we only use it for 3.5 hours per day we'll use 15 watt hours, leaving us 55 watt hours. We'll assume that the smart phone provides a wifi hotspot so that we don't need a router and some sort of IP service provider. So, we have a single light on for five hours, two smart phones and a Chromebook and we've used over half of our stored power. We certainly won't be able to pump water, provide heat, charge a vehicle battery, etc. So, while there's no argument that 24 hours of electricity can be provided by pedaling for an hour, it's not the sort of electricity use that a denizen of a developed country thinks of. My family uses electricity at an average rate of about 2,000 watts (we're hogs though), a ratio of about 300:1.
Further, contrary to another Bhargava claim, this is not free. If we figure the human body
Image credit: unknown
to operate at 20% efficiency in turning food chemical energy to mechanical energy (I think that this is high, others think that it's low) then these 150 watt hours or about 129 kilocalories (that is, food calories) will require ingesting about 650 kilocalories of food. My suspicion is that a family whose life will be changed by the ability to light a bulb for five hours, charge two phones, and use a Chromebook for 3.5 hours isn't sedentary and thus in need of exercise.
Might there be a use for the pedal powered generator/battery combination? I think that there could well be. But the idea is not original (though this application may be). Bhargava's heart would seem to be in the right place, I don't think he's charlatan. He also has innovations in health care, water purification, and to use graphene cables to draw heat from the Earth's mantle. He also funds and houses other innovators in an incubator fashion. You can't accuse him of not thinking big. In due time, I hope to look at some of his other innovations.
Update: Bhargava is interviewed about some of his innovations at CNBC. He says that the Free Electric hybrid bike can power "24 lightbulbs, a fan, a phone charger, and a tablet." He goes on to say that you can either use it all at once or store it in a battery. On the video linked in the second paragraph, someone working for him states that it can power "1050 equivalent watts of lighting." None of my physics books discusses the unit "equivalent watt" but the video shows 24 lit bulbs. A closeup reveals the labeling on the bulbs. Looking them up, they're 4 watt, 12 volt LED bulbs so we're talking about 96 watts. I'm sure that the "equivalent watt" is the conversion to the luminous intensity of incandescent bulbs. Also shown is a blowing small fan, a tablet with the display appearing to be on, and a smart phone in a charger. I'd estimate the total load of all that at something like 110 or 120 watts and so I'm confident that my discussion above does apply. They show a closeup of a digital meter that is displaying 274 but don't mention 274 of what. I assume that it's watts, and that the peddler was pushing himself at that moment.
This will be a short one. LightSail Energy, a startup with innovations in compressed air energy storage, has already appeared in my writing twice, the most recent being after co-founder Danielle Fong was generous enough with her time to take me on a tour of their facility in Berkeley. In the first article I mentioned that I'd delve deeper into the thermodynamics of their process. After the second Ms. Fong mentioned that, in general, she felt that I'd been fair and accurate but that my skepticism regarding LightSail's ability to manufacture systems in the facility I visited was unfounded. Hmm... "uncalled for" is the actual quote. I'd like to take a look at both, but first the manufacturing capacity.
Image courtesy of LightSail Energy
As it happened, it turned out that I hadn't seen the whole facility. Further conversation with Ms. Fong revealed that LightSail's existing Berkeley facility does have some manufacturing capabilities and, in fact, has production runs of tanks in particular. It should be noted (and I've seen Fong tout this publicly in some of the amazingly large number of video presentations in which she's featured) that LightSail states that they have designed, prototyped, tested, and produced tanks with unprecedentedly high merit indices. These tanks can be sold for uses other than compressed air energy storage. Further, LightSail is able to assemble, commission, and sell their compressor expanders out of their R&D facility. Thus, while LightSail is unlikely to be able to meet full scale production of their storage units at the Berkeley facility in the event that their compressed air energy storage technology takes off at the scale that the Company envisions, it's clear that they do, in fact, have significant manufacturing capabilities there. I stand corrected.
My previous post in this series related some of the drawbacks of my simplistic analysis, the objectives I want to achieve, and a sketch of the methodology I've employed. Briefly, I've used a Monte Carlo simulation (yes, I linked to something other than Wikipedia, you're welcome Doctor Steve) to determine a likely outcome for generation of energy by a single hypothetical wind turbine in Dalhart, TX.
I ran 1000 simulations of 8760 data points of wind speed from what turned out to be a mixture distribution combining a normal and a Gamma distribution. This generated a total of 8,760,000 wind speeds. Each was delivered to an interpolating function generated from a digitized power curve of a 3MW nameplate capacity wind turbine. This resulted in 8,760,000 data points, each representing the average power delivered by the turbine for a hypothetical hour.
From there, finding the average power delivered was a simple process, and the result of this simulation was a mean power of 788 kW. This equates to a capacity factor of ~788*100/3000=26.3\%~. This is a surprisingly low number for the location and turbine chosen, given published figures at sites such as this that yield an implied capacity factor of 33.1%. Further, the model estimate has no allowance for planned and unplanned maintenance outages. And, of course, the 33.1% number is ostensibly from measured data, so, as Dr. Steve might say, "who ya gonna believe, me or your lyin' eyes?" All that said, perhaps Dalhart isn't the ideal location, perhaps the wind gradient is steeper than the model I used, perhaps they've used more highly optimized equipment, perhaps the measured year had, for some reason, particularly strong (but not too strong) winds. I'm going to proceed with my analysis based on the model data. So, the next step is to determine the storage required for the ability to deliver a given power at, say, 99.99% reliability. That is, the system should be able to supply the specified power for all but ~8760/10000=0.876~ hours/year. This is actually less than the SAIDI*SAIFI (system average interruption duration index, measured as the average duration of outages*system average interruption frequency index, measured as the average number of outages per customer per year) and so sounds quite reasonable if not overly conservative. One assumption will be that, when the turbine is delivering more than the power under consideration and the storage facility is "topped off," we can send the power to the grid. Another will be that, for the level of power being considered, the storage system is capable of delivering power at that level. As I've discussed in previous posts, there are two primary characteristics of an energy storage installation: the quantity of energy that the system can store; and the rate at which it can deliver that energy. Of note, approximately 4.0% of the time, the wind is below the cut in speed of the turbine and thus all energy delivered by the system must come from storage. The modeled wind exceeded the cut out speed of the turbine a negligibly small 0.0004% of the time. But there are no black swan events in the distribution (think tornadoes). It took me a little time to decide on an effective way to proceed, but ultimately I decided to start with a guess of storage and loop through each increment (i.e., each hour's worth) of power (since the power is in kilowatts and the increments are hours, no conversion is necessary). If the storage plus the increment minus the steady use exceeded the maximum available storage, the excess was discarded and the maximum was kept for the next iteration. If the sum was less, that was kept for the next iteration. Upon completion, determine the number of iterations at which storage was zero or less, adjust maximum storage if and as necessary and try again. Using the mean power from all of the trials, no amount of storage sufficed, but reducing it to 725kW gave me what I wanted. And finally, the result: If our 3MW turbine plus storage system is committed to delivering 725 kilowatts and we can provide 40MWh* of storage, there's effectively zero chance of not having the committed power available. Of course, the system can deliver greater power than that when the wind blows and/or when plenty of energy is stored but committing to greater power than 725kW or installing less storage than 40MWh means that there will be times when the system cannot deliver. Obviously, installing it in an integrated grid system can offset this, but the goal here was to determine what storage will enable what level of reliable base load power for a single turbine so the result is likely to be conservative. This is a virtue in the world of engineering. Below is a chart showing the first 100,000 increments with increment number on the x-axis and energy stored on the y-axis.
One widely discussed concept in energy generation is "capacity value," a very different concept (and number) than capacity factor. Basically, this number represents how much other generating capacity can be avoided with the installation of a generator and, for wind in particular, it is typically much lower than the capacity factor. Since there are times when no wind is blowing and demand does not abate, for an unaided turbine, sufficient generating capacity must be available to meet the demand, even though it may only be used sporadically. The goal of adding storage in this analysis is to bring the capacity value of the wind turbine close to the capacity factor. As I noted in my previous post (on another topic), most utilities are not looking for days of storage (my analysis above determined that 48 hours of storage at 24.2% of the turbine's nameplate capacity would provide that power continuously and reliably), they're looking for a few hours. And, of course, the myriad complexities of transmission constraints, demand side variability, planned and unplanned generator outages, etc. have not been considered. Others have taken some of these into account using a similar methodology (i.e., Monte Carlo simulation). None that I've found, however, incorporate storage into the analysis. If I were a professor at a research institution or an NREL researcher or, perhaps, if I worked for a turbine manufacturer or a storage technology firm, I'd implement a much more sophisticated model incorporating the above factors as well as a wind farm as opposed to a single turbine. Next in this series (which, as readers may have noted, may be interrupted by posts on other topics) will be an analysis of the economics of such a system, or at least the beginning of such an analysis. I anticipate that the cost will be prohibitive without pricing the externalities of fossil fuel generation (i.e., without implementing a carbon tax).
*In several trials, 35MW would have sufficed with no increments less than 0, but this run had a particularly calm stretch and, even with 40MW, had 0.0088% of the increments less than 0. However, this met the criteria of 99.99% reliability at 99.9912%.
Image credit: Advanced Rail Energy Storage North America
In an earlier post I covered a concept of utilizing a massive rock piston over pressurized water to store energy. Another firm uses a concept analogous to pumped hydro storage but, rather than massive amounts of water and pumps and turbines, they use large solid masses and motor/generators. That firm is ARES, an acronym for Advanced Rail Energy Storage. First, the headline numbers: ARES claims that their technology allows storage facilities of from 200 MWh of energy that can be delivered at a rate of 100 MW (i.e., it can run at full power for two hours) to 16-24 GWh that can be delivered at a rate of 2-3 GW (i.e., it can run at full power for eight hours). It's claimed to have a round trip efficiency of 80% (or 85%, depending on which interviewee you're listening to). The claimed ramp-up time is on the order of 8 seconds, dramatically better than any fossil fuel plant or pumped or stored hyrdro system, the only storage system to better that number is electrochemical (battery) storage. Finally, ARES says that the cost of an Advanced Rail Energy Storage facility is about 60% of that of an equivalent pumped hydro installation. All this sounds pretty good. OK, what actually happens? During times of plentiful generation by intermittent generators or of low electrical prices if arbitrage is the name of the game, rail cars full of rocks are transported by rail up inclines via axle mounted motor generators on the cars. Unfortunately, their technical page has scant information regarding the specifics of the system, that information must be gleaned from other articles. Nevertheless, we can see that ARES envisions three classes of system:
Ancillary services: The system is used as a Limited Energy Storage Resource (LESR) for frequency stabilization, spinning reserves, VAR (volt ampere reactive) support, etc.
Intermediate scale: The system is used for ancillary services as above, as well as for short duration storage to facilitate intermittent generation integration. Such a system is envisioned as capable of delivering 50 to 200 MW and having a two hour capacity.
Grid scale storage as described above, with 200 MW to 3GW delivery for up to 16 hours.
While the system cannot compete with pumped hydro for systems requiring days of storage, it is far less complex to construct and appropriate siting is dramatically easier to locate, and should be far easier to shepherd through the myriad review and permitting processes. And many systems don't require several days of storage. William Peitzke, ARES Founder and Director of Technology Development is quoted as saying "Generally, the market for storage tends to be an 8 hour requirement and in fact a lot of the utilities we talk with really only require five to six hours of discharge.”
Image credit: ARES
The cars carry a mass consisting of concrete and rock, and utilize electric traction motors to lift the masses up inclines. The same motors then act as generators when descending. Complex, automated control systems enable quick adjustments to suit system requirements, and the system can have some cars ascending while others descend. Scale can be increased simply by adding more mass. Energy is received and delivered via electrified rails. The cars themselves are modified ore cars. ARES holds patents on the system, but the individual components and systems are mature technologies with no technological breakthroughs needed. ARES has constructed a pilot system in Tehachapi at about 1:3.75 scale (see photo at right) but, according to various reports, in Pahrump, Nevada, the Valley Electric Association has agreed to work with ARES to implement a 50 MW system. The projected cost is $40M. The objective is actually to accomplish frequency stabilization for the California ISO (Independent System Operator, known as "Cal-ISO"). The planned system would use 34 cars on a 9.2 km track with approximately a 7% incline. The difference in elevation between the top and bottom will be approximately 640 meters. Each shuttle will transport a mass of 230 tons (209 tonnes). A quick calculation [(34 cars)*(209 tonnes)*(1000 kg/ton)*(9.8 m/s)*(640 meters)*(80%)/(3.6*10^9 joules/MWh)] shows that this system may be able to store and deliver a maximum of just under 10 MWh. However, this is an "Ancillary Services" installation and thus not designed for primary purpose of storage per se, but rather for the regulation goals mentioned above. Unfortunately, I'm not able to find recent information on progress to date. The Valley Electric Association web site is silent on ARES with the exception of a pdf magazine from October of 2014.
I'd not go so far as to say that rail energy storage is the silver bullet for solving the integration of intermittent renewables into the grid, but it certainly seems to have significant benefits and few drawbacks, assuming that it hasn't jumped the track.
Update: A great set of photos of the pilot project in Tehachapi can be found at gizmag.
Previously, I imported the daily mean wind speed recorded at Dalhart, TX (at the airport, I assume) for the period beginning January 1, 2000 through the most recent day recorded in Wolfram's curated weather data. I adjusted the wind speeds using a relatively standard model to estimate the wind speed at a turbine hub height of 120 meters from the (presumably) data at 10 meters. I also have digitized the data for a 3 MW nameplate capacity wind turbine. Further, I've used Mathematica'sInterpolation capability to provide a "plug and play" function whose input is a wind speed and whose output is power from the turbine. The plan from here is to do a Monte Carlo simulation from the smooth kernel distribution that's the best fit to the wind data. I'll use 8,760 points per simulation (the number of hours in a non-leap year) and use the speeds and the turbine data to determine power available over that hour. Now, there are quite a few "yeahbutz" here, among them:
I've not done an analysis of any periodicity in the wind data, at some point that will need to be done via a Fast Fourier Transform from the time domain into the frequency domain to determine whether adjustments are necessary.
Wind speed is a continuous variable, assuming a constant speed for each hour will lead to inaccuracies.
There will never be 120 meter hub height towers with 108 meter diameter rotors at an airport. As a pilot, I certainly support this! Thus, any real wind turbine will be at some other location.
Nevertheless, this calculation should provide a baseline estimate for the order of magnitude of storage necessary for a single turbine to deliver some amount of base load power.
From Czisch & Ernst 2001
And it's likely that the estimate will be conservative, given that the most likely scenario is a wind farm rather than a single turbine and that several wind farms with reasonably wide geographic separation are most likely to be feeding energy to the grid. And many studies have shown that the correlation of power produced by groups of wind farms decreases with increasing geographic separation at all time scales (see chart at right, h/t to Dr. Steve Carson). To be clear, low correlation is a good thing when considering base load power because we desire that, when turbine/wind farm A suffers a low wind speed, turbine/wind farm B takes up some of the slack and vice versa.
Next, it's time to state the specific goals of the simulation:
Determine the average power (and thus the capacity factor) of the turbine.
For a series of specified base load capacities, determine the storage necessary to provide this power through the periods when the turbine is not providing that power.
Determine minimum reliability (i.e., how many hours can be tolerated per year during which the turbine/storage cannot deliver the base load capacity. This will either need to be tolerated or supplemented with some other, typically natural gas fired, power plant).
OK, enough preamble, next will come the actual results of the simulation and conclusions, with suggestions for where to go from here, both with respect to the model and with respect to some speculation on what it means for the combination of renewables and storage as they penetrate the grid at greater levels.
After Lyfting from the summit site at the Gaylord National Harbor Resort and Convention Center to Dupont Circle in Washington, DC, I had my first chance to observe and experience the Pavegen pavers (or tiles). To the right, you'll see the triangular tiles arranged as hexagons in the Pavegen sytem. Those are my feet and my Cross pen (inscribed with a wonderful message from my beautiful wife, Zandra) for scale.
