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Comment by jules | Hacker News Reader

A factor of three (which is very optimistic) doesn't change the conclusion: a week's worth of storage is not feasible with current battery technology, let alone a few weeks.

How much storage would actually be required is not clear to me. It depends on a lot of factors. A week doesn't sound totally crazy to me; we certainly want a good safety margin so that society doesn't collapse in a bad winter. If we take super optimistic numbers and have one day of storage and take your factor of 3 reduction in energy use, then the cost of storage alone would still be about twice what we currently pay for the energy. Expensive but certainly a cost that would be possible to pay.

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> A factor of three (which is very optimistic)

For cars, the factor of three is not "optimistic", it's simple comparison of the respective primary energies consumed by typical vehicles in their respective categories. 20 kWh to drive 100 km = 72 MJ of primary energy. 6 liters of gasoline to drive the same distance = ~220 MJ of primary energy -- roughly triple of the former number.

> A week doesn't sound totally crazy to me; we certainly want a good safety margin so that society doesn't collapse in a bad winter.

Yes, but that doesn't imply you need the capacity to run the country 100% on batteries for a week. That's just not something anyone would ever do. For example, a gas turbine with a low duty cycle would definitely be cheaper than a battery after a certain period of time. So why would you use a battery for that?

The specific factor for cars is not relevant. The factor of 3 is wildly optimistic for general energy use. The point is that even taking the factor of 3, it's still extremely expensive.

Regarding the second paragraph: if you point is that it would be cheaper to duplicate a significant portion of our energy generation, one based on renewables and one based on fossil fuels for safety...that is perhaps true, but that only proves the original point, so I'm a bit confused why you phrase your replies in an antagonistic tone of voice when we seem to agree.

It was an example, since obviously different uses of energy will have different improvement factors - but major uses of energy have considerable improvement factors. In case of heating, for example, the factor is theoretically infinite because it's possible to build net-zero-energy buildings. And specifically in case of Germany, a very large portion of natural gas consumption goes into heating, so this is quite relevant here.

> if you point is that it would be cheaper to duplicate a significant portion of our energy generation, one based on renewables and one based on fossil fuels for safety...

I didn't say a word about basing something on fossil fuels.

> that is perhaps true, but that only proves the original point, so I'm a bit confused why you phrase your replies in an antagonistic tone of voice when we seem to agree

I don't see how we "seem to agree". The comment I initially responded to was proposing storing a WEEK's worth of PRIMARY energy in TODAY'S amounts in BATTERIES. Nobody would seriously consider such a contrived scenario; it would be completely pointless. So I can't possibly agree with those numbers.

I find it fascinating that you call me nonsensical for making the very reasonable assumption that energy consumption will stay the same for a back-of-the envelope calculation, and here you are talking about infinite improvement factors.

> I didn't say a word about basing something on fossil fuels.

You said: "Yes, but that doesn't imply you need the capacity to run the country 100% on batteries for a week. That's just not something anyone would ever do. For example, a gas turbine with a low duty cycle would definitely be cheaper than a battery after a certain period of time. So why would you use a battery for that?"

> I don't see how we "seem to agree". The comment I initially responded to

Note that I responded to that comment with a calculation showing that that plan is economically infeasible. The scenario is not all all contrived; what that person proposed we need is reasonable, and it would in fact be quite dangerous and insufficient to have only one week's worth. Years in which there is more than a week without wind and hardly any sun (due to winter) occur approximately every 10 years in Germany. Thus calling a week's worth of storage contrived is just wrong. If anything, it's contrived in the direction of not being enough.

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