Add a curve variant that isolates the PEM Faraday term

[erikfilias]

Additive. Nothing already run changes.

The problem

The baseline ulleberg PEM column was generated before the PEM half was rebuilt, and it carries no Faraday term at all. It assumes every electron makes hydrogen at every load.

That is not physical, and it is not what the paper says. Yodwong et al. 2020 measured the crossover directly on a PEM cell at three pressures, and analysis/electrolyser_curve.py now models it. Reproducing the baseline row requires deleting the Faraday term from the derivation entirely — confirmed to 2e-4.

What the baseline understates:

load	baseline	with crossover	understated by
0.05	134.9	166.9 kWh/kg	24%
0.08	99.4	112.0	13%
0.14	78.5	83.9	7%
0.22	66.8	69.2	4%
1.00	60.5	60.5	0%

That is exactly the deep turn-down range PEM is valued for, and PEM is the technology under test — so the baseline flatters it where it matters most.

Figure 1(a) of the paper already draws the corrected curve. So the figure, the manuscript text and the model currently disagree, and the model is the one that is wrong.

Why a new variant rather than fixing the baseline

ulleberg_conservative already has the corrected PEM column, but it also swaps alkaline's Faraday parameters from Ulleberg to Sánchez. It moves both technologies at once, so it cannot say which one did the work.

ulleberg_pemfaraday is baseline alkaline plus corrected PEM. One change. It answers whether the baseline needs replacing, and at the cost of a single solve rather than a full campaign.

If the answer is that it matters, the baseline row gets replaced in a follow-up and the campaign runs again. If it does not, the completed campaign stands and the corrected curve is reported as a sensitivity.

Verification

Both columns of the new entry reproduce analysis/electrolyser_curve.py to better than 5e-4. The baseline, the two balance-of-plant variants and the conservative set are untouched.

[codacy-production]

Up to standards ✅

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