What is the general opinion of Carbon Capacitance in Concrete?
I’m an ICF builder in the Northeast, and I’ve been researching the development of carbon capacitance energy storage in concrete structures as outlined by an ongoing study by MIT. As far as I can figure, the potential to offset the carbon emissions of concrete production in the upfront building process makes this concept highly rewarding in the end use. If roughly 50 cubic yards of concrete (roughly the foundation volume of an average family home’s foundation that supports a wood framed structure) has the potential capacitance to power an average traditional home for at least one day, an ICF home, when properly applied and of the same size, could theoretically be able to store a weeks worth of electrical power while avoiding typical storage limitations of battery packs. (In the form of lithium, lead acid, etc., which regularly require strict code qualifications and adherence, not to mention limitations). Thoughts? I am certainly willing to elaborate on the concept, as well as explain what I know of its capabilities and workings within the proper discussion. Thanks.
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Here's the MIT press release:
https://news.mit.edu/2023/mit-engineers-create-supercapacitor-ancient-materials-0731
I'd say it's early days.
I think of how much houses have changed in the past 20 years, let alone the past 100. Who knows what they'll look like in another 20, let alone another 100.
Thanks for the reply, and I obviously read the release from MIT in depth. My question pertained to the hypothetical efficacy, and opinions as such, as to how a modern builder perceives the concept as applicable to contemporary construction reform and the adaptation of new techniques, should they comprehend it in concept.
The concept is pretty easy to comprehend: use concrete as a capacitor. Many builders understand capacitors, as they are present in some electrical fixtures and drivers, and in many tools. If they don't, it could be described as equivalent to a short-term battery, which anyone would understand.
Most builders are very cautious about implementing new ideas, since so many of them have gone wrong in the past, and the market and banks are generally risk-averse. The exception is usually a specific subset of upper-middle-class clients who want custom homes with innovative, climate-friendly materials and techniques. Once the ideas are proven, if reasonably cost-effective and if they have other advantages, they sometimes slowly make their way into commodity construction.
I see a huge benefit of having a day's worth of energy stored in an otherwise inert medium like concrete. I am curious whether there would be any "side effects", such as the surface of the concrete becoming electrically charged and attracting dust, like plastics often do, or if it would have any effect on grounding of the electrical system.
If the electrical system used to charge/discharge the capacitor was electrically isolated from ground (this is easy to do, and you'd need a charger/inverter anyway since capacitors can only store DC, not AC), then it shouldn't affect grounding of the electrical system, although I think using a Ufer ground -- a piece of rerod embedded in a footing -- is not going to be an option with a "capacitor wall". My concern as an EE here would be more along the lines of charge leakage within the concrete (I didn't see anything about that when I skimmed that article), and charge leakage due to moisture effects from the ground against the "capacitor wall". Charge leakage is a sort of self-discharge where the stored charge bleeds off over time, and is basically lost energy. Too much leakage and you limit the usefulness of a system like this.
A capacitor is different from a battery in that a capacitor stores charge in electrostatic form (think of the electrical charge on the plates of the capacitor like condensation on the side of a window pane), batteries store it in chemical form. Capacitors can usually discharge that stored energy MUCH faster than a battery, which has a lot more "whammo blammo" effect -- basically shorting a capacitor can be much more exciting than shorting a battery. That's a potential hazard with a system like this, and I visions of someone drilling into the wall come to mind as a potential way to blow things up... Not sure if that would be an issue here (drilling into the wall as a way to blow it up), but it might require some safety precautions.
It will be interesting to see how this develops though. The big weakness of most systems intended to change energy usage patterns is that storing electrical energy in large quantities is a problem. EV's, for example, are mostly limited by battery technology -- everything else is pretty well developed. If this concrete capacitor can be made to work safely, and is cheap as they say, then it could be a useful innovation. Usually it's either very high costs or very high risks that make these things unworkable.
Bill
Storing electricity in a battery is like storing heat in a phase change material, it goes in at a constant voltage/temperature and comes out at a constant voltage/temperature. Storing energy in a capacitor is like storing heat in a non-phase changing material -- the more you have stored, the higher the voltage/temperature has to be, and when you're taking it out the more depleted it is the lower the voltage/temperature is.
The problem you often run into trying to store heat is that getting the last 20% or whatever out of the storage medium is quite difficult because the temperature delta is so low. And putting the last 20% in is difficult because the delta is so high. You're going to run into the exact same problem trying to store electricity in a capacitor. It's not insurmountable, but it's a real challenge.
I was a little disappointed that the article said, "the team demonstrated the process by making small supercapacitors, about the size of some button-cell batteries, about 1 centimeter across and 1 millimeter thick, that could each be charged to 1 volt, comparable to a 1-volt battery. They then connected three of these to demonstrate their ability to light up a 3-volt light-emitting diode (LED). "
Those capacitors will only be charged to 1V for an instant, as soon as you start drawing power the voltage drops instantly.
It's hard to imagine a technology like this being pioneered in residential construction.
Bill,
I think you are being waaay too generous with the idea of "super capacitor concrete". When I first encountered the article I laughed. As you rightly noted the "ufer" grounding rod would short the "capacitor wall". I also wondered what effect all the other rebar would have on charge capacity and how one would be able to isolate the concrete from any soil and water contact permanently. Adding the potassium chloride bathing the whole matrix of concrete and rebar also gave me pause. How long would the now charged rebar last in such a soup? Would the concrete weaken over time? How could anyone expect to find a contractor capable of creating all this affordably. What if the foundation shifts?
The proposed 10kWh capacity seems quite marginal compared to Lithium Iron batteries. I believe that Tesla packs could provide the same energy in less than 2 cubic yds easily and be far more recycle-able. It could be a carbon wash to compare the damage caused by cement production versus lithium mining, so I won't go down that rabbit hole. In any case, 10kWh a day seems very short of actual usage for most people unless they have natural gas for heat, hot water and cooking. Which kinda makes the carbon saving from solar not so good.
My limited understanding of capacitor design suggests charging can occur slowly or quickly depending on voltage and amperage, so feeding a capacitor from a variable DC output source maybe pretty straightforward. Hopefully, the same goes for discharge as 120vac. However, I am really not understanding where the separation of charge states is occuring in this matrix of concrete and self assembling carbon hairs. I thought that surface area more than bulk was a major factor in capacitor design. Can you explain how they are creating capacitance in a bulk matrix full of conductors?
Regarding the main electrical feature of capacitors, I spent a couple of decades lugging around large (heavy) capacitor banks that drove studio flash tubes. Definitely makes for a whammo bammo discharge event. And those were tightly controlled at that. I can only imagine a future DIYer not versed in electrical engineering merrily jabbing a hammer drill into the wall for shelf anchors. Instant hotdog cooker?
You can't get AC out of a capacitor, only DC. Even so-called "AC" capacitors are not going to give you DC -- they can just handle charging and discharging repetitively in opposite directions as they track the sinewave voltage.
Typical home energy consumption is around 24-36kWh per day, more if you're using electricity to heat or cool in many cases. I agree energy density is key here, which I mentioned. What interested me is that they think it can be made very cheaply. There are two ways to make a green gizmo viable: make it really efficient, so the expensive gizmo can get a LOT done, or make it really cheap, so the large quanity of gizmos needed to be useful doesn't break the bank. If the "concrete capacitor" could be made super cheap, which is what they imply, then it might be practical, even if it has poor energy density, because you would be able to afford to make a LOT of it.
DC: conventional supercapacitors are usually rated for 3-5v or less. When I first heard about those, I thought "not very useful". The first ones out were 0.47F 3V capacitors, about the size of a stack of several of the larger coin cells. They could only handle relatively small discharge currents of maybe 10mA or so. They were mostly used to replace lithium batteries to backup clocks in computers. Newer "ultracaps" are still low(ish) voltage, but can be 40-50+ farads. That's a good amount of energy stored up, and you can easily connect them in series/parallel strings to get more useful voltages and capacities.
Varying voltage is an issue with batteries AND capacitors in this kind of application, but that's easily dealt with with charge controllers and inverters that would be part of the system anyway. With a typical PWM inverter, if you want higher output voltage, you use a wider pulse width. This can compensate for lower input voltage too. It's not difficult to deal with energy sources with varying voltages. Batteries have the same issue, they have a discharge CURVE, and it's not linear. Different cell chemistries have different discharge curves. Lithium tends to be flatter than some, but it's still not like you get constant voltage out until there is no power left.
It's a bit different for me to be supporting a potential technology on here instead of explaining why it's not likely to work, but in this case there MIGHT be SOME promise. I kinda laughed when I first saw this too. A CAPACITOR made from CONCRETE? Hahaha. Good one. But I read the article (well, skimmed it), and what did I see? They are describing an internal microstructure that is very similar to what is inside of tantalum capacitors, which have been around for a long time, and have good longevity. That made me think there might be something to this.
I've also been known to show people pictures of the first transistor, which looks very much like a high school science project, as an example of a technology that everyone knows was hugely impactful, but started out very simply. The first transistor looked kinda silly, but it demostrated that the physics worked, and that justified further research. We all know where that ultimately led. Note also that the guy primarily responsible for inventing the liquid crystal display -- the LCD -- that is ubiquitous these days, almost got fired from his job for wasting his time. It can be difficult to predict where a new technology might go in the future. Maybe we'll get lucky with this one, maybe not, but I'd say it's too early to know for sure either way.
Bill
It's an open question whether the future of electricity is in decentralized or centralized facilities. For example, it may well turn out that large ground-based solar facilities make more sense than trying to put panels on every rooftop, I've heard cost estimates that the solar farms end up costing half as much in the long run.
Capacitance storage may or may not make sense. Even if it makes sense, doing it on the individual household level may or may not make sense too.