Section 25D expired on 31 December 2025, so a purchased residential system in
2026 receives no federal credit. Most published payback figures still include
the 30%, which makes them roughly three to five years too short. I recalculated
all 50 states without it.
Data: https://energycostmap.com/states.json
DOI: https://doi.org/10.5281/zenodo.22305313
Repo: https://github.com/chameerasampathkorea/us-solar-payback-by-state
Method: https://energycostmap.com/methodology/
Licence: CC BY 4.0
Fields per state: annual generation (NREL PVWatts v8), retail rate (EIA), export
factor and netting period from the serving utility’s tariff, installed cost,
incentives, simple and degradation-adjusted payback, 25-year net return, plus the
source URL and date the export terms were checked against.
Range: Hawaii 4.1 years to Alabama 24.5. Alabama is the outlier because Alabama
Power bills solar customers $5.41/kW/month — about $390 a year on a 6 kW system,
a charge a federal judge upheld in March 2026.
The field I would point at is nettingPeriod. Before a utility compensates
exported power it nets exports against imports — over a whole monthly bill in
some states, over fifteen-minute intervals in others. With monthly netting,
power exported at midday offsets power drawn at 7pm at the full retail rate.
Iowa and Oregon both credit exports at 100% of retail, but Iowa nets in
fifteen-minute intervals and Oregon monthly, and Oregon pays back faster despite
weaker irradiance. Almost no published comparison records this field.
Known limitations, also listed in the method: one utility modelled per state
(normally the largest); the retail rate is an EIA state average rather than a
specific tariff; self-consumption is assumed rather than measured; loan interest,
dealer fees, resale premium, leases, batteries and roof replacement are all
excluded.
Happy to answer questions on any state’s figure.
submitted by /u/Ok-Map-7006
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