| The right question is what the efficiency of this process is. End to end, not just the charging/discharging. Both charging and discharging seems to require a lot of heat. Waste heat is essentially lost energy that is released in the form of heat. I assume the discharge reaction is exothermic. That would be the energy stored in the summer months. Heating up a lot of tons of iron during charging is also not going to be free. It doesn't matter whether you do it slowly or quickly. Creating the hydrogen is also not a loss free process. Nor is doing something useful with it like using it in a fuel cell (0.85), burning it (0.45), etc. These inefficiencies multiply. All that lost energy comes out of the original budget of energy that came out of the solar panels. Even if you use some wildly optimistic numbers, they multiply to something well below 0.5 pretty quickly even before you consider charging & discharging. But lets do something silly and unrealistic and just do the math for an average step efficiency at 0.7, 0.8, and 0.9. We're talking four conversions here so that's 0.7^4 =0.24 vs. 0.41 and 0.66. And forget about getting anywhere near average 0.9 efficiencies with all of those steps. I'm assuming 0.7 would already be on the high side. Add more steps to the process and it only gets worse. Pipes aren't perfect. If you need to pressurize the hydrogen before you use it (like in a car), that isn't free either. Basically, this takes a system that was already quite inefficient end to end and adds two more steps that sound like they involve some pretty significant energy losses to it (i.e. probably well below 0.5 when combined), thus making the system as a whole a lot more inefficient. Hydrogen as a battery already sucked with normal storage. This doesn't improve things. There's a good reason that most hydrogen produced is used at or close to its site of production: it minimizes the energy losses and producing hydrogen is really expensive so it's not really desirable to lose 80-90% of the energy unless you really need to. |
I see:
1) generation 2) storage efficiency (energy while storing divided by energy upon release)
what are the other 2 you had in mind?