Hemp supercapacitors might be a good solution to the energy grid storage problem. Hemp absorbs carbon, doesn't leave unplowable roots in the fields, returns up to 70% of nutrients to the soil, and grows quickly just about anywhere.
Hemp bast fiber is normally waste. Hemp anodes for supercapacitors are made from the bast fiber that is normally waste.
Graphene is very useful; but industrial production of graphene is dangerous because lungs and blood-brain barrier.
Hemp is an alternative to graphene for modern supercapacitors (which now have much greater power density in wH/kg)
> “Our device’s electrochemical performance is on par with or better than graphene-based devices,” Mitlin says. “The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene.”
> Graphene is, however, expensive to manufacture, costing as much as $2,000 per gram. [...] developed a process for converting fibrous hemp waste into a unique graphene-like nanomaterial that outperforms graphene. What’s more, it can be manufactured for less than $500 per ton.
> Hemp fiber waste was pressure-cooked (hydrothermal synthesis) at 180 °C for 24 hours. The resulting carbonized material was treated with potassium hydroxide and then heated to temperatures as high as 800 °C, resulting in the formation of uniquely structured nanosheets. Testing of this material revealed that it discharged 49 kW of power per kg of material—nearly triple what standard commercial electrodes supply, 17 kW/kg.
If you're going to be mentioning this again in the future please correct your usage of power/energy density. Power density is measured in W/kg, energy density is measured in Wh/kg. Supercapacitors tend to excel in the former but be poor in the latter. You mentioned power density but used units for energy density. This happens so often in media that I feel the need to correct it even in a comment.
> please correct your usage of power/energy density. Power density is measured in W/kg, energy density is measured in Wh/kg. Supercapacitors tend to excel in the former but be poor in the latter.
I'd update the units; good call. You may have that confused? Traditional supercapacitors have had lower power density and faster charging/discharging. Graphene and hemp somewhat change the game, AFAIU.
It makes sense to put supercapacitors in front of the battery banks because they last so many cycles and because they charge and discharge so quickly (a very helpful capability for handling spiky wind and solar loads).
I think you may still be a little confused. Power density is the rate at which energy can be added to or drawn from the the cell per unit mass. So faster charging and discharging means high power density. Energy density is the total amount of energy that can be stored per unit mass. Supercapacitors are typically higher in power density and lower in energy density than batteries[1].
You're right that it makes sense to put supercapacitors in front of the battery banks for the reasons you said.
> Charge and discharge rates are often denoted as C or C-rate, which is a measure of the rate at which a battery is charged or discharged relative to its capacity. As such the C-rate is defined as the charge or discharge current divided by the battery's capacity to store an electrical charge. While rarely stated explicitly, the unit of the C-rate is [h^−1], equivalent to stating the battery's capacity to store an electrical charge in unit hour times current in the same unit as the charge or discharge current.
It does sound amazing and economical, like almost too good to be true, but I very much hope it is true. What are the downsides? Is there a degradation problem or something similar? Other than the stoner connection in people's minds, what kind of resistance is there to this? Why isn't it widely known?
You know, I'm not sure. This article is from a few years ago now and there's not much uptake.
It may be that most people dismiss supercapacitors based on the stats for legacy (pre-graphene/pre-hemp) supercapacitors: large but quick and long-lasting.
It may be that hemp is taxed at up to 90% because it's a controlled substance in the US (but not in Europe, Canada, or China; where we must import shelled hemp seeds from). A historical accident?
Hemp bast fiber is normally waste. Hemp anodes for supercapacitors are made from the bast fiber that is normally waste.
Graphene is very useful; but industrial production of graphene is dangerous because lungs and blood-brain barrier.
Hemp is an alternative to graphene for modern supercapacitors (which now have much greater power density in wH/kg)
"Hemp Carbon Makes Supercapacitors Superfast” https://www.asme.org/engineering-topics/articles/energy/hemp...
> “Our device’s electrochemical performance is on par with or better than graphene-based devices,” Mitlin says. “The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper than graphene.”
> Graphene is, however, expensive to manufacture, costing as much as $2,000 per gram. [...] developed a process for converting fibrous hemp waste into a unique graphene-like nanomaterial that outperforms graphene. What’s more, it can be manufactured for less than $500 per ton.
> Hemp fiber waste was pressure-cooked (hydrothermal synthesis) at 180 °C for 24 hours. The resulting carbonized material was treated with potassium hydroxide and then heated to temperatures as high as 800 °C, resulting in the formation of uniquely structured nanosheets. Testing of this material revealed that it discharged 49 kW of power per kg of material—nearly triple what standard commercial electrodes supply, 17 kW/kg.
https://scholar.google.com/scholar?hl=en&q=hemp+supercapacit...
https://en.wikipedia.org/wiki/Supercapacitor
I feel like a broken record mentioning this again and again.