Add h2 fuel cell technology to ReEDS main

[yijinli22]

Summary

Adds h2-fuel-cell (hydrogen-powered fuel cell) as a new technology option in ReEDS, complementing the existing ng-fuel-cell (natural gas fuel cell) already in the model. The H2 fuel cell consumes hydrogen (h2fuel, the same fuel as H2-CT/H2-CC), is gated by a new dedicated switch GSw_H2FuelCell, and offers three cost scenarios (conservative/moderate/advanced) based on Reznicek et al. (2026).

Technical details

Implementation notes

• Separate on/off switches for the two fuel cells. The existing ng-fuel-cell switch GSw_FuelCell was renamed to GSw_GasFuelCell (and the GAMS set fuel_cell(i) → ng_fuel_cell(i); the FUEL_CELL subset column → NG_FUEL_CELL in tech-subset-table.csv and i_subtech.csv) so its scope is unambiguously natural-gas-only. h2-fuel-cell is governed by the new GSw_H2FuelCell. The two fuel cells are fully independent — any on/off combination is valid.
• New H2_GEN subset, decoupled from H2_COMBUSTION. h2-fuel-cell is added to a new H2_FUEL_CELL subset and to a new H2_GEN subset (= {H2-CT, H2-CC, h2-fuel-cell}). H2_COMBUSTION was narrowed to combustion only ({H2-CT, H2-CC}), so GSw_H2Combustion / GSw_H2Combustionupgrade now affect only the turbines. H2_GEN drives the hydrogen fuel/emissions/accounting (H2 supply-demand balance, fuel cost, leakage emissions, retirement eligibility, tg_i('h2') group, first-year, and reporting), so a fuel cell built with the turbines off still consumes and pays for hydrogen. h2-fuel-cell is also flagged GENTECH and RE, matching H2-CT/H2-CC.
• GAMS gating (b_inputs.gms): adds h2_fuel_cell(i), h2_gen(i), and ng_fuel_cell(i) sets. Bans are now per-technology: Sw_GasFuelCell=0 bans ng-fuel-cell, Sw_H2FuelCell=0 bans h2-fuel-cell, Sw_H2Combustion=0 bans H2_COMBUSTION (turbines only).
• Fuel & classification: h2-fuel-cell uses h2fuel (fuel2tech.csv), is added to i.csv and techs_default.csv (region type p).
• Key parameters: unit size 100 MW; lifetime (max age) 40 years; financing/eval period 30 years (same as Gas-CT); construction time 3 years; min load 1%; heat rate 8.461 MMBtu/MWh; VOM 1.7054 $/MWh; FOM ~27 $/kW-yr (moderate, 2030); ramp 100%/min; 6% min CF; 5% forced & scheduled outage; 0 start cost; zero direct CO₂/SO₂. Capital cost and heat rate are from Reznicek et al. (2026); FOM/VOM from Exhibit 5-19 (Case B31A) of NETL Fossil Energy Baseline Rev 4a (Schmitt et al. 2022).
• Per-technology h2-fuel-cell rows were added across the plant-characteristic and financial input files (emitrate, h2_leakage_rate, cost_opres_default/_market, minCF, mttr, outage_forced_static, outage_scheduled_static, ramprate, startcost, unitsize_atb, heat_rate_adj, heat_rate_penalty_spin, degradation_annual_default, years_until_endogenous, construction_times_default, financials_tech_ATB2023/_CRP20/ATB2024, reg_cap_cost_diff_default, nat_gen_tech_frac, ivt_default/_small/_step, futurefiles, runfiles).

Additional changes

• postprocessing/tech_aggregation.csv, tech_map.csv, tech_style.csv updated for h2-fuel-cell display: mapped to H2-Fuel-Cell (color #87A21D) and aggregated with H2-CT/H2-CC. The aggregation label was renamed Hydrogen Combustion → Hydrogen Generation (in both tech_aggregation.csv and the matching tech_style.csv color key) so it accurately covers the fuel cell alongside the turbines.
• GSw_MGA_SubObjective gained an h2_gen option (in addition to the existing h2_combustion).
• cases_h2-fuelcell.csv added with 5 test scenarios: USA_defaults_fc_pr (runs without fc switch turning on), USA_defaults_fc_mid (moderate cost/deployment cost case), USA_defaults_fc_low (advanced/high deployment cost case), USA_defaults_fc_high (conservative/low deployment cost case), USA_defaults_fc_mid_w_ng_fc (moderate level + NG fuel cell switch turned on).
• Documentation: new "Hydrogen fuel cells" subsection in docs/source/model_documentation.md, file entries in sources.md, and Reznicek 2026 + Schmitt (NETL) 2022 entries in references.bib.

Switches added/removed/changed

Switch	Values	Default	Description
GSw_GasFuelCell	0, 1	0	Renamed from GSw_FuelCell — enables ng-fuel-cell (natural gas fuel cell) only
GSw_H2FuelCell	0, 1	0	New — enables h2-fuel-cell (independent of GSw_GasFuelCell and GSw_H2Combustion)
plantchar_h2fuelcell	h2fuelcell_conservative, h2fuelcell_moderate, h2fuelcell_advanced	h2fuelcell_moderate	New — H2 fuel cell cost and performance scenario
GSw_H2Combustion	0, 1	1	Scope narrowed — now bans only H2-CT/H2-CC (fuel cell removed from H2_COMBUSTION)
GSw_MGA_SubObjective	…h2_combustion, h2_gen…	gentech	Option added — h2_gen (H2-CT + H2-CC + fuel cell)

Relevant sources or documentation

• Reznicek, E., Berres, A., Li, Y., et al., Cost Analysis of Heavy-Duty Vehicle Proton Exchange Membrane Fuel Cell Stationary Power Plants (2026), https://doi.org/10.2172/3018256 — unit size and performance parameters

Validation, testing, and comparison report(s)

Ran 1/7 cases under the main ReEDS branch and the remaining cases under cases_h2-fuelcell.csv to test the H2 fuel-cell scenarios (pr baseline, fc_low, fc_mid, fc_high) plus three sensitivities (fc_mid_ngfc, fc_mid_no_h2cc, fc_mid_no_h2combust), and compared capacity, location, and dispatch with compare_cases.py. The new h2-fuel-cell technology builds, is selected over H2-CT as costs decline, and dispatches as expected. (This run uses 3-year solve steps: 2029, 2032, 2035, 2038, 2041, 2044, 2047, 2050.)

Location & technology selection (2029, first build year)

The H2 capacity lands in CA_LA (461 MW) in every scenario; only fc_low adds a second, economic build of 127 MW in NM_W. The location is fixed and only the technology filling the CA_LA slot swaps between scenarios as the fuel-cell cost case improves:

Scenario	CA_LA (461 MW)	NM_W (economic add)
pr	H2-CT	—
fc_low	fuel cell	fuel cell (127 MW)
fc_mid	fuel cell	—
fc_mid_ngfc	fuel cell	—
fc_mid_no_h2cc	fuel cell	—
fc_high	H2-CT	—

This CA_LA capacity is a prescribed build from inputs/capacity_exogenous/interconnection_queues.csv. It appears as a step in 2029, holds flat through 2038, then declines. The model fills that prescribed requirement with the cheapest available H2 technology — fuel cell in the cheaper cost cases (low/mid), H2-CT in pr (baseline) and high where the fuel cell is too expensive.

H2 fuel cell capacity build (MW)

Scenario	2029	2032	2035	2038	2041	2044	2047	2050
pr	0	0	0	0	0	0	0	0
low	588	588	588	588	279	233	233	63
mid	461	461	461	461	254	211	211	34
high	0	0	0	0	0	0	0	0

H2-CT capacity build (MW)

Scenario	2029	2032	2035	2038	2041	2044	2047	2050
pr	461	461	461	461	209	182	168	0
high	461	461	461	461	209	182	168	0
low / mid	0	0	0	0	0	0	0	0

Sensitivities: NG fuel cell and H2-CC

• NG fuel cell does not build. fc_mid_ngfc is identical to fc_mid (fuel-cell capacity and generation match exactly across all years; only second-order solver noise elsewhere). Enabling NG fuel cells added zero capacity.
• H2-CC does not build. fc_mid_no_h2cc is identical to fc_mid, so removing the H2-CC option changes nothing. There is no distinct h2-cc technology in the output (H2-CC would be gas-cc on hydrogen fuel), so a verified zero requires the fuel-consumption output.
• fc_mid_no_h2combust (H2-CT and H2-CC both prohibited): H2-CT generation is 0 and the fuel-cell build is unchanged from fc_mid. Prohibiting all H2 combustion has no effect on the mid case because the fuel cell was already the selected H2 technology — H2 combustion only builds when the fuel cell is prohibited or too expensive (pr, high).

Dispatch / capacity factor

Annual CF is a flat 6.0% across every scenario and year. The 6% is the annual minimum CF requirement imposed in inputs/plant_characteristics/minCF.csv; peak hourly utilization reaches ~16% max in the gen_h.csv output. H2-CT and fuel cell dispatch identically (same CF, same hourly shape).

comparison reports

comparison with main

Checklist for author

Details to double-check

• References for all H2 fuel cell operational data (Reznicek et al. 2026, DOI 10.2172/3018256)
• Charge code provided to reviewers
• Included comparison reports for appropriate test cases
• Documentation updated if necessary
• If input data added/modified:
  • Dollar year recorded and converted to 2004$ for GAMS (dollaryear.csv updated for h2fuelcell_* scenarios, 2022$)
  • Units specified (MW capacity, $/kW capex, $/kW-yr FOM, $/MWh VOM, MMBtu/MWh heat rate)
  • No large data files — all inputs are small CSVs
• No change to process flow (runreeds.py, solve.py)
• No change to spatial/temporal resolution

General information to guide review

• Zero impact on results of default case (GSw_H2FuelCell=0 by default — no change when switch is off)
• No large data file(s) added/modified
• No substantive impact on runtime
• No change to process flow
• No change to package requirements

Did you use LLM tools (chatbot or copilot) in the preparation of this PR? If so, describe how

Yes — Claude Code (Anthropic) assisted with documentation modification and writing this PR language.

Tag points of contact

@yijinli22

[patrickbrown4]

Small comment: I'm not sure if I'm a representative sample, but at first glance I would expect GSw_FuelCell to control H2 fuel cells rather than methane fuel cells. The comment on GSw_FuelCell also doesn't reflect its operation; it says it controls both H2 and methane, but only controls methane.

To try to avoid confusion, my suggestion would be to rename GSw_FuelCell to GSw_GasFuelCell, in keeping with the other non-default gas techs (GSw_GasCC_H_1x1, GSw_GasCC_H_2x1, GSw_GasCT_Aero). Its functionality can stay the same, but the switch comment should be modified to remove the reference to H2.

[patrickbrown4]

Because fuel cells don't involve combustion, including H2 fuel cells in H2_COMBUSTION seems confusing to me. I would suggest keeping these separate. If you need a new category to refer to H2-CT, H2-CC, and H2-FuelCells together, I'd suggest adding a column to tech-subset-table.csv and calling it something like H2_GEN.

Relatedly, I think it'd be best to allow the user to turn on H2 fuel cells and turn off H2-CT/H2-CC if they want to. So if H2 fuel cells are removed from H2_COMBUSTION, you can remove this compatibility check.

[louisaserpe]

Can you update the PR text to mention the changes to the NG fuel cell switch?

[patrickbrown4]

Can you add a comparison report against the main branch for the USA_defaults case?

[louisaserpe]

Let's add a link to the comparison report in the body of the PR: comparison with main