Carbon Accounting

[embeagle]

Set up CHEC constraint to sum globally over the entire system such that $\sum CHEC\text{demand} \le \sum CHEC\text{produced}$

for each producer type, $CHEC_{produced}$ is based fractionally compared to the baseline emissions of a standard SMR unit

• electrolysis with dedicated renewables: 1 CHEC (0 carbon emissions)
• electrolysis with grid electricity: 0.7 CHEC (25 g/MJ compared to 80 g/MJ for SMR)
• SMR with 55% capture: 0.55 CHEC
• SMR with 90% capture: 0.9 CHEC
• unabated SMR: 0 CHEC

for each demand type $CHEC_\text{demand}$ is given by carbonSensitiveFraction Do we want to set all new hydrogen demand to be completely carbon sensitive? ie. carbonSensitiveFraction = 1 How much of the existing demand do we want to replace with low carbon hydrogen? iw. carbonSensitiveFraction = what fraction Currently carbonSensitiveFraction is set by demand type (ie. transportationFuel, industrialFuel, or existing and not by hub location, so we can't currently, for example, say that Austin would want a higher fraction of clean hydrogen for transportation than El Paso. Do we want to adjust this? If we decide to set all new hydrogen demand to be only clean hydrogen demand this won't matter

_What is breakevenCarbon_g_MJ?_ NOTE: the breakevenCarbon_g_MJ for existing demand in demand.csv is different from the carbon_g_MJ in production_existing.csv

Carbon accounting in the objective function variables

P_carbon: what producers will play for the carbon emissions from their hydrogen production U_carbon: added utility to the model based on the avoided cost of paying for carbon emissions for each consumer

• I don't think the units of this equation check out - need to review
• Can we treat this as a carbon price paid by each consumer rather than an avoided cost that adds utility to the objective function?
• I also am not sure if the carbon price framework will apply to every demand type we have in the model (mostly meaning not transportation)

U_carbon_capture_credit: the tax credit that producers (specifically SMR with CCS) get for capturing and storing carbon (45Q essentially)

• still think that this should not be (1- CO2 captured) but just CO2 captured since the credit is per ton stored but would love a second eye to confirm that change
• the fractional CHEC valuation from production takes into account the percent of CO2 stored so I suspect that in its current formulation we are double multiplying the capture fraction
• propose rewrite as $U\text{carbon capture credit} = \sum(ccs\text{h2 produced} carbon \textunderscore rate percent \textunderscore CO2 \textunderscore captured * carbon \textunderscore capture \textunderscore credit)$ someone to confirm this change?

Add clean hydrogen production tax credit to model

• a credit to consumers (so added utility to the model) based on the amount and carbon intensity of hydrogen production
• I wonder if the easiest way to implement this would be to add a new column to each production.csv input file with the corresponding tax credit value for that production type based on emissions intensity

[bradenpecora]

U_carbon and breakevenCarbon_g_MJ

breakevenCarbon_g_MJ is the carbon rate of the non-hydrogen producers that currently meet that demand (before using hydrogen). The breakeven carbon is converted from g/MJ to tonCO2/tonH2 (?):

# unit conversion 120,000 MJ/tonH2, 1,000,000 g/tonCO2:
 self.carbon_g_MJ_to_t_tH2 = 120000.0 / 1000000.0
...
m.cons_breakevenCarbon = pe.Param(
        m.consumer_set,
        initialize=lambda m, i: g.nodes[i].get("breakevenCarbon_g_MJ", 0)
        * H.carbon_g_MJ_to_t_tH2,
    )

This is used to calculate the utility of a CHEC: $U\text{carbon} = \left ( \sum\text{nodes} CHEC_\text{demand} \text{(TonH2)} breakevenCarbon ( \frac{\text{TonCO2}}{\text{TonH2}} )\right ) carbon \textunderscore price (\frac{Dollar}{TonCO2})$.

I think this framework is intended to give more value to a CHEC when it is utilized by a sector that emits more CO2.

There is currently a constraint over consumer nodes in the model that is the only other instance of breakevenCarbon:

consumer_co2_rate = m.cons_breakevenCarbon[node]
consumption_not_satisfied_by_h2 = m.cons_size[node] - m.cons_h[node]

constraint = (
    m.co2_nonHydrogenConsumer[node]
    == consumption_not_satisfied_by_h2 * consumer_co2_rate
)

which seems to define the pyomo variable m.co2_nonHydrogenConsumer as the amount of carbon produced by demand that was unable to be met by the model. This is the only place this variable appears in the model. It is not in the objective nor in any other constraints. Removing the constraint has no impact on the model solve.