California's storage mandate solved!

This post won't be the first time I've expressed my annoyance with the California Public Utilities Commission over their storage mandate of 1.325 "gigawatts of storage" (scare quotes because this is already mixing apples and oranges - it's analogous to saying "65 miles per hour of distance") by 2020.

The linked post gives my more detailed thinking, but this one is just a quickie to bring home the inadequacy of only giving the rate of delivery of electrical energy in the mandate with no reference to the period for which this energy could be delivered. It's obviously (as you'll see) an extreme, but I can meet the mandate as stated for a bit under $2M!

How? A photographer's flash unit takes electricity and stores it in a capacitor. When it's triggered, it quickly (quickly is the key here) discharges the capacitor through a flash tube. Here, we see the Elinchrom Pro HD 1000 flash unit. It can discharge 1000 W-s (photographers use "watt-seconds" but a watt-second is just another name for a joule) through the tube in 1/1430 second. This rate is 1000 watt*second/(1/1430 second)=1.43MW (megawatts). To get to 1.325 GW (gigawatts) I need 1,325/1.43=927 such units. I can purchase each for $1,049.88 ($964.88 if I order no later than January 31) for a total of $973,238.76. Of course, that doesn't include shipping and some rewiring, so double it.

Now, these units are set to power flash tubes but there's no requirement for that. They simply store energy and discharge it quickly. So, wired in parallel, they could supply the 1.325 gigawatts for about 2/3 of a millisecond. Problem solved!

Of course, the total energy delivered is a bit lacking. It's the 1000 joules*927 Elenchrom flash units=927,000 joules or a bit over a quarter of a kilowatt hour. Still, it meets the mandate and I bet I can have them delivered this year, beating the deadline by some five years.

It's rather shocking to me that our esteemed CPUC has managed to put this mandate in

place with no reference as to capacity. I will agree that rate is important (as I mentioned in the post linked above) but it's foolish to not also include capacity. However, I'm speculating that they aren't even aware of the problem. They are, after all, political appointees and, among the five of them, only Carla Peterman appears to have any sort of energy related experience or education. Mostly, it's attorneys. This is, after all, California!

If you know anyone from Southern California Edison, Pacific Gas and Electric, or San Diego Gas and Electric, please don't tell them. I want to get a good earnest money deposit on my simple solution to their storage mandate woes.

OK, enough negativity

There's no doubt that I've spent a lot of keystrokes pointing out things that won't work or won't live up to their hype, from solar chargers to harvesting of kinetic energy. And, while I have posted favorably or at least neutrally on a few things, I seem to have had more fun debunking than bunking.

So I'd like to spend a bit of time discussing what appears to me to be a promising technology and one that, if it fulfills its promise and comes to fruition, would be a potential game changer.

It's no secret that I'm of the opinion that, whether for the reason of the finite amount of fossil fuels available to be exploited ("peak oil") at prices that can sustain an economy or for the reason that the extraction and burning of fossil fuels for energy results in the release of massive amounts of CO₂ and other greenhouse gases, we need to reduce and ultimately eliminate our reliance on fossil fuels for other than production of products needing their chemistry (almost everything really, from pharmaceuticals to plastics to fertilizers).

Thus, I want to see the increasing penetration of renewable energy for all purposes (including transportation). For a couple of the leading candidates, wind and solar, intermittency is a big issue (though others will argue that it's not such a big deal). This is the case not only because intermittent sources will, on occasion, generate more energy than can be used and not enough at others, but also because the grid relies on very fine adjustments of both energy and frequency.

So, what is required to solve this issue? Without a doubt, the ability to store solar or wind generated electricity at times when supply exceeds demand would be outstanding. It would also enable renewable energy to be supplied at a steady rate.

There are a variety of technologies for grid scale storage of electrical energy:

• Pumped hydro
• Compressed air
• Batteries (various varieties, a promising type for this use is the "flow battery")
• Molten salt, hot oil, etc. in solar thermal plants
• Power to gas (e.g., electrolyze water to produce hydrogen for fuel)
• Others (see here)

I want to look at compressed air energy storage and a startup called "LightSail Energy." Their concept is to utilize a variant of compressed air energy storage ("CAES"). The idea is that, typically, compressing air heats the air and, when the air is stored, in cooling the air

loses much of its total energy. LightSail adds a fine mist of water during compression. The water (with its very high specific heat) absorbs the heat of compression and the hot water is stored for process heat or whatever. Then, when the air is utilized, heat (either from the original heating or elsewhere), is added so that the escaping air, which cools upon expansion, has increased energy to be utilized in the piston compressor/expander. So the idea is to use the renewable source to compress air, remove the resultant heat with a water mist, store the hot water for use in a heat exchanger, add heat when the air is discharged through a turbine piston expander. A schematic drawing from a LightSail patent application is to the right.

It should be noted that there are other firms out there using other media to capture and reuse the heat of compression of air in energy storage systems, one such is Energy Storage Power Corporation who uses oil for this purpose. A schematic diagram of their process is at left.

LightSail's Chief Scientist and one of its founders is Danielle Fong. Fong is a prodigy who dropped out of junior high school at age 12 to attend college, from which she graduated at 17. She was accepted into a Ph.D. program at Princeton but dropped out (or took leave) to move into something with more immediate applicability in the energy field than plasma physics.

There are a LOT of videos out there with Fong carrying the flag for LightSail (see here, here, here, here, and here for examples). She's photogenic, is "aww shucks" humble, wears interesting clothes, and what media outlet doesn't love an attractive female child prodigy Ph.D. candidate dropout who's founded a startup that can be stated in the blurbs to have the potential to "change the world" (and, as can be seen in the intro photo at the top left, I'm not immune)? One thing I respect about Fong is that, in articles about her firm, she'll address naysayers directly and without obfuscation in the comments.

LightSail claims, I would assume potentially, a round trip thermal efficiency of 90% and shows a working 200 bar, 250 kW prototype (200 bar is about 20 mPa (megapascals) (and, by the way, can one nest parentheses in textual material?)) at a one-way efficiency of 71%. 

LightSail's Technology page (interestingly, the landing page for the site) describes smaller "Power Units" of 250 kW power and "Storage Units" of 750 kWh capacity, clearly highlighting the distinction between rate of energy delivery (250 kW in the "Power Units") and storage capacity (750 kWh "Storage Units"). When I simply assume an ideal gas and evaluate the work that can be done by isothermally expanding [edit: a cubic meter of compressed air] from 300 bar (about 30 mPa) that LightSail is aiming for and ignoring the work against the atmosphere, about 48 kWh is available and so 30kWh certainly seems realistic if a close approximation of isothermal expansion can be achieved. Long term storage, though, will require lots of thought and engineering with respect to the thermal energy carried off by the mist.

According to Fong, LightSail's storage technology is capable of storing and delivering 30 kWh (kilowatt hours) per cubic meter of storage space. Thus, we can infer that the 750 kWh Storage Unit will occupy 25 cubic meters. For reference, a standard shipping container (to the extent that such a thing exists) has a volume of 38.5 cubic meters. Ok, how much is 750 kWh? At my house, my family of four uses electrical energy at the rate of, on average, about 2 kW (embarrassingly enough) or about 1,460 kWh/month. So these 750 kWh would last me a bit over half of a month at my house. My Company's headquarters laboratory facility uses, on average, just short of 750 kWh/day. That facility has about 15 people working there. I don't have (and LightSail probably does not have, though I can't imagine that they haven't made some estimate) any figures on what such a Storage Unit will cost.

The California Public Utilities Commission (CPUC) has mandated that the State bring 1.325 gigawatts of storage on line by 2020. So, at 30 kWh/m^3 storage capacity, how much volume would be needed to meet this mandate? Infuriatingly, there's no way to know! California uses electricity at an average rate of about 34 gigawatts, so 1.325 gigawatts represents the ability to deliver a bit under 4% of the State's electrical energy but there's no way to know for how long. The state has said 1.325 gigawatts but did not (so far as I can find) mandate capacity so there's no telling how long the systems to be implemented could deliver these 1.325 gigawatts. An hour? A day? I've posted on this frustrating situation before.

Such details aside, LightSail has discussed storing the compressed air in underground caverns for utility scale storage and that's a VERY big step up from a 750 kWh Storage Unit. But with funding from Vinod Khosla's VC firm, Bill Gates, Peter Thiel, and Total Energy, there's a fair amount of confidence in LightSail.

A deeper excursion into the thermodynamics of this system will follow and I believe that that will shed light on possible integration of such a system into our generation/transmission/distribution system. My initial feeling is that it's likely to be most useful for such things as frequency regulation rather than solving the intermittency problem thwarting confidence in the wide scale implementation of solar and wind generated energy.

I'll acknowledge that the only connection between this video and LightSail is the word "Sail." But I just wanted to use any excuse to embed this song. It's hard to believe that it's the Beach Boys.

Media Notices America's Grievous Shortage of Laws | Coyote Blog

Media Notices America's Grievous Shortage of Laws | Coyote Blog:

'via Blog this'

Yup. My only addition is that California is doing its best to remedy this travesty of having literally minutes go by without some governmental agency, ANY governmental agency, making a business decision for us.

Supplying energy with footsteps yet again

It just won't go away. On my Galaxy Note 3 (which I mostly really like) I have Flipboard. Generally speaking, I like that as well. When I'm biding my time someplace like a Doctor's office, waiting to meet someone, etc., I'll often flip through it. This evening, lo and behold, I found an article from CNN entitled "Harvesting energy from human footsteps?"(which I've since looked up on the web to refer to here, though it's labelled "CNN" but the site is "Click on Detroit).

It features Pavegen, a Company I've looked at before. The concept is the installation of tiles that, when stepped on, deflect and thereby produce electricity via the piezoelectric effect. Does such an effect exist and can electricity be produced in this fashion? Yes and yes. Can the electricity generated thereby be useful in some circumstances? Again, yes. Is this an efficient and effective way to "Transform Tomorrow?" That would be a "no."

Amazingly, Pavegen's CEO, Laurence Kemball-Cook, actually says (and the article duly repeats) that the Pavegen tiles can "produce up to 7 watts of energy with each step." Of course, watts are not units of energy, they are a rate of doing work or converting energy. Kimball-Cook repeats that and, in this TEDx talk, even says "eventually, our vision is that this technology power our cities." This is, frankly, ridiculous and I intend to ridicule it.

The claim is that a single step generates up to "7 watts of energy" (despite the unit confusion, we can infer what they are really claiming if we make some estimates). I went to Vernier's site where  student laboratory measurement, data gathering, and analysis equipment is sold and interesting experiments are described. One of the "Innovative Uses" experiments described was called "Walking Biomechanics Using a Force Plate." There, sufficient data is provided (I'll leave out the calculation details unless requested to add them) to determine that the claim of "up to 7 watts" is not ridiculous, though I'd estimate that a bit under 5 watts is more likely a good average. But we don't care about watts, we care about energy so, based on the data at the Vernier site, the approximately 700 Nt. applied through 0.005 meters over a period of about 0.74 seconds results in kinetic energy delivered to the tile of about 3.5 joules/footfall. This is somewhat confirmed by Pavegen in their graph (at left) of their own office where we can infer that a bit under 250,000 steps produced a bit under 500 watt hours. This translates to about 7.2 joules/footfall. Close enough.

Since there are 3.6 million joules per kilowatt hour, we can say that it would take right at a million steps to generate a kilowatt hour of energy, and that assumes that the piezoelectric system is 100% efficient at converting kinetic energy to electrical energy. Actual data on this efficiency is sparse at best, particularly for those, such as I, who are unwilling to spend $30 to retrieve an article from behind a paywall that may or may not have the information that I want in order to complete a blog post. Nevertheless, I was able to find this document, where it appears that a conversion efficiency of maybe 2.4% can be achieved (yes, you read that correctly).

Thus, our 3.5 joules/footfall is reduced to 0.088 joules/footfall, requiring something on the order of 41,000,000 footfalls to generate a kilowatt hour. I have to say that it seems likely that I'm missing something here. Possibly, 2.4% conversion efficiency is much lower than what these tiles achieve, though I can't find any data that indicates that significantly higher efficiencies have been demonstrated in a laboratory environment. And, in the Wikipedia article on Pavegen, it's stated that "the exact technology is a secret, but PaveGen officials have said it involves the piezoelectric effect and induction by copper coils and magnets."

So it's possible that Pavegen is using something more efficient, so I'll use an upper bound of 3.5 joules/footfall as described above. Here, in an article from Urban Times with a healthy degree of skepticism and yet also open-mindedness, figures from the City of Westminster regarding Oxford Street are cited. Looking there, it's stated that there's an estimated 4.3 million people per week using the street. Urban Times discusses 10 tiles on Oxford Street. So 4.3 million/7 is 614,000 people per day. If they each hit all 10 tiles, the upper bound would be 614,000*10*3.5=21,500,000 joules or just shy of 6 kilowatt hours.

Quoting from the Urban Times article, Pavegen states that

"the pressure of a single footstep creates 4 to 8 watts. It was also calculated that assuming 8 watts is created per step, “during peak hours, one tile produces 12kWh ideally [and] during the off hours, it produces 5kWh ideally” and that “floor tiles, during peak hours will be stepped on 926-1889 times per hour… and 0-719 times during off hours… which works out to about 56 kWh per weekday”.

I can't find that quote from Pavegen, but if it's an accurate quotation, it would imply about 57 million footfalls per weekday. Hmm, I doubt it.

Then, there's the fact that any energy harvested by the Pavegen system is parasitic in nature, in that it's generated by a human converting food energy to kinetic energy. Whatever energy is harvested and wasted by a Pavegen tile is energy above and beyond what the people walking on the tile would otherwise have to exert. It doesn't come from nowhere and it isn't free.

There is likely a place for human generated electricity. As Kemball-Cook points out, there's no need to have the users of gyms merely generate heat on their treadmills, stair climbers, elliptical exercisers, etc. Such folk are going there for the express purpose of burning food energy without a destination or other goal. Such energy might just as well be harvested and, in many cases, it is.

These distractions that allow politicians to have green photo ops and people to get a warm fuzzy feeling about saving the Earth from some oversold "green energy" scheme do much more harm than good. The drastic changes in how we need to live in order to achieve equilibrium with what our planet and our sun can sustainably provide are only put off when people buy into such schemes.

Let Steve Earle describe Pavegen.