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Energy storage in the form of aluminum.

by esperen 6y ago

Robotbeat 6y ago
Kind of irrelevant if we don’t have carbonfree electrodes for smelting aluminum.
- esperen 6y ago
  If it brings the net carbon footprint down, it could be relevant. Progress is typically iterative
  - Robotbeat 6y ago
    But that hasn’t been established here. The aluminum produces hydrogen (at some level of inefficiency) which then produces electricity in a fuel cell (more inefficiency). Consumable electrodes are actually doing chemical work in the aluminum. It’s not just wear from use. To produce 78 grams of Aluminum directly requires 48 grams of Carbon electrodes (using made by graphitizing some tar or coke) which oxidizes to 176 grams of CO2. Aluminum is 31MJ/kg specific energy. Assuming 70% efficiency conversion from aluminum to hydrogen and 70% from hydrogen to electricity (both fairly optimistic figures), you’re talking about 535 grams of emitted CO2 for each kWh of electricity out. Ignoring the electricity input, inefficiencies and losses in making the aluminum, and assuming perfect conversion of the tar to electrodes. Worse than a good, advanced combined cycle natural gas plant (which can get as good as roughly 350 grams per kWh for record efficiency plants). I just don’t see how this is gonna be a net win without carbonfree electrodes. It seems just about impossible here. Storing hydrogen directly looks to make way more sense.
giantg2 6y ago
"Energy storage in the form of aluminum" And? What's the benefit? We could store energy in concrete if using gravity or use water to produce the hydrogen for the fuel cell.
- esperen 6y ago
  It's mentioned in the 2nd bullet point of the article link: 23.5MWh/m3 The benefit is you can store energy, in aluminum. It has a high energy density, you can safely store it anywhere, it requires no containment at all, etc. Your last statement includes the answer to your own question. They are using the hydrogen, from water reacting with aluminum, to power a fuel cell.
  - giantg2 6y ago
    It can store a lot of energy, but it's not easy nor convenient to release (very slow release rate).

Energy storage in the form of aluminum.

Robotbeat 6y ago

Kind of irrelevant if we don’t have carbonfree electrodes for smelting aluminum.

esperen 6y ago
If it brings the net carbon footprint down, it could be relevant. Progress is typically iterative
- Robotbeat 6y ago
  But that hasn’t been established here. The aluminum produces hydrogen (at some level of inefficiency) which then produces electricity in a fuel cell (more inefficiency). Consumable electrodes are actually doing chemical work in the aluminum. It’s not just wear from use. To produce 78 grams of Aluminum directly requires 48 grams of Carbon electrodes (using made by graphitizing some tar or coke) which oxidizes to 176 grams of CO2. Aluminum is 31MJ/kg specific energy. Assuming 70% efficiency conversion from aluminum to hydrogen and 70% from hydrogen to electricity (both fairly optimistic figures), you’re talking about 535 grams of emitted CO2 for each kWh of electricity out. Ignoring the electricity input, inefficiencies and losses in making the aluminum, and assuming perfect conversion of the tar to electrodes. Worse than a good, advanced combined cycle natural gas plant (which can get as good as roughly 350 grams per kWh for record efficiency plants). I just don’t see how this is gonna be a net win without carbonfree electrodes. It seems just about impossible here. Storing hydrogen directly looks to make way more sense.

giantg2 6y ago

"Energy storage in the form of aluminum" And? What's the benefit? We could store energy in concrete if using gravity or use water to produce the hydrogen for the fuel cell.

esperen 6y ago
It's mentioned in the 2nd bullet point of the article link: 23.5MWh/m3 The benefit is you can store energy, in aluminum. It has a high energy density, you can safely store it anywhere, it requires no containment at all, etc. Your last statement includes the answer to your own question. They are using the hydrogen, from water reacting with aluminum, to power a fuel cell.
- giantg2 6y ago
  It can store a lot of energy, but it's not easy nor convenient to release (very slow release rate).