I know it’s only been a couple of weeks since I wrote about cement, but now I need to write about concrete, or potential version of concrete that is able to function as a battery. If we can get the technology to work this could an extremely useful item for a future of green energy.

The idea is one example of a more general idea – making structural material that can double as energy storage, either as a battery or supercapacitor. Imagine, for example, if the frame of your car was its battery. Similarly, imagine if the foundation of your house was a massive supercapacitor. That is the idea behind an MIT research project, which right now is in the proof-of-concept laboratory phase.

The researchers added carbon black to cement and the usual other ingredients to make concrete that can function as a supercapacitor. The carbon black is highly conductive, and it can form many branching tendrils in the concrete. These conductive bits are separated by insulating bits – and that is the basic structure of a capacitor. Charge can build up in the conductive carbon black and be maintained by the insulating layers.

At this point their test material can store 300 watt hours per cubic meter. A typical US home uses about 30 kwh per day, so would need 100 cubic meters to have one day’s worth of energy storage. That is in the order of magnitude of the volume of concrete in a, say, 1,500 sq foot home’s foundation (about 50 cubic meters). Larger homes would have larger foundations, and of course the foundations can be made deliberately thick to increase the storage. In other words, this is a useful amount of energy, theoretically. Any incremental advances in energy density would also be very useful, and the researchers are working on that.

The state of the research is still preliminary – proof of concept. One of the authors, Damian Stefaniuk, said the magic words in the BBC interview – “If it can be scaled up, the technology can help solve an important issue – the storing of renewable energy, ” – those fateful words that have killed many a promising new technology – if it can be scaled up. There are some issues that need to be worked out. One is, the more carbon black in the mixture the greater the energy density of the resulting capacitor, but the lower the strength of the resulting concrete. So there is a sweet spot where these tradeoffs are balanced. Of course, we may be able to combine this technology with one of the cement technologies I wrote about earlier that increase the strength of concrete.

Supercapacitors vs batteries also have some interesting tradeoffs. Supercapacitors can store energy very quickly, and don’t degrade over time like batteries do. But they also tend to release their energy quickly, rather than at a slow steady pace over a long period of time. Being able to control the rate of energy release will have to be built into the overall device somehow. Again this is something the researchers are working on by playing with the recipe.

But the big thing is – we simply don’t know what will happen when you start building foundation-sized slabs of this capacitor concrete. How will it function? And what happens when you fill it up with energy? Will the entire foundation need to be insulated in some way? What will this do to the cost of construction? Will this be economically feasible? What is the longevity of the resulting concrete and its energy storage? There are lots of potential deal-killers here. But none are absolute any they may all be solvable with continued development of this technology.

Now let’s play what if. What if this technology ultimately works, is reasonably cost effective (costing no more than adding any other battery storage to a home, let’s say), with reasonable capacity (1-2 days of backup power for a typical home), and there are no deal-killers? What are the likely applications? Obviously, the one I have been discussing – making the foundation of any building into a giant energy-storing supercapacitor. This won’t be viable as a retrofit so only will apply to new buildings going forward. But eventually it would be nice if, say, all new homes came with solar panel roofs and energy storage foundations.

I could also see this being used for grid storage. You know what else needs foundations – wind turbines. Land-based wind turbines need large foundations, with about 700-800 cubic meters of concrete. Let’s say we build a generous foundation with 1000 cubic meters of energy storing concrete. That’s 300 kwh of energy storage, enough to power 10 homes for a day. Perhaps we make deliberately huge concrete foundations for them, making them more stable but also adding energy storage, say 10,000 cubic meters (3 mwh). Multiply that by the more than 70,000 wind turbines in the US and we have 210 gigawatt hours (GWh) of grid storage. The US uses about 11 TWh per day. So that would be about 30 minutes of energy storage for the entire country (I think I did all those calculations correctly but feel free to double check me). This level of storage is useful for short term energy shifting and balancing the grid.

We could also build foundations for fields of solar panels. I wonder if a version of this material could be strong enough for a dam that is part of a hydroelectric plant. What about the containment vessel for a nuclear power plant, or part of a geothermal plant? Any giant construction is likely to use a lot of concrete, and could theoretically double as energy storage.

We could also theoretically make roads out of a version of this material. Could this lead to the infamous “solar roads”? In this more plausible version the roads themselves will not be photovoltaics but just energy storage, while solar panels, or some other energy source, will be placed more optimally. But powered roads could be interesting, allowing for recharging of electric vehicles while driving, or led road signs. I doubt this will happen, and I have questions about what a charged road would be like. What happens if you walk on it? Is the surface entirely insulated, and if so, how does it charge cars? Would we need to also incorporate wireless charging technology into the roads?

As I wrote in the previous article, the world produces 4.4 billion tons of concrete each year. If some of that is energy storage concrete that could go a long way to fill our energy storage needs. It’s also better than using lithium or other limited resources that we need for high specific energy batteries for cars. But for now we are in the “if it can be scaled up” phase.