One statute, two tariffs
Iowa Code Section 476.49 applies to both Interstate Power and Light, which operates as Alliant Energy in Iowa, and MidAmerican Energy. Each files its own tariff under it.
Both use the inflow-outflow method, so the mechanism is common, but the rates and the specific credit terms are set per utility and are not identical.
Alliant residential rates in Iowa have run around 12.5 cents per kWh, against roughly 11 cents for MidAmerican customers in the Des Moines area. On a twenty-five year projection that difference compounds.
So check the utility name on a recent bill, then confirm that the projection used your utility rate and your utility tariff rather than a state average.
The tariff questions worth asking
Ask how outflow is credited under your specific tariff, at what rate, and whether that rate is fixed or subject to periodic revision.
Ask how long outflow credits carry forward and whether there is any point at which they are forfeited or cashed out. That determines whether a seasonal surplus is genuinely useful.
Ask what system size limits apply and whether any threshold changes the treatment, as it does in several other states.
Ask what the interconnection application involves, what it costs, and how long approval typically takes with your utility. Practice varies and the gap between installation and permission to operate is where most project frustration lives.
A scheduled change to ask about
Iowa Code Section 476.49(4) requires the Iowa Utilities Commission to develop a value of solar methodology and rate for eligible distributed generation when statewide penetration reaches 5 percent, or if petitioned by a utility after July 1, 2027, whichever is earlier.
That is a scheduled review rather than a rumour, and it means the current arrangement has a horizon even though regulators have meanwhile ordered modest revisions that broadly continue it in the near term.
Ask what your projection assumes about compensation after that transition. A model holding today terms flat for twenty-five years is making an assumption the statute itself anticipates changing.
Ask also whether existing customers would be grandfathered under any new methodology, and get that answer from the utility or the Commission rather than from a sales conversation.
The pieces to separate in a projection
The 30 percent federal Residential Clean Energy Credit under Section 25D expired for property placed in service after December 31, 2025, and the Iowa solar tax credit expired for residential installations completed after December 31, 2021.
Section 48E survives at 30 percent for third-party owners under leases and power purchase agreements, so ask what a provider claims and what reaches you in the rate.
What exists is the sales tax exemption, the five-year property tax exemption, avoided inflow at your Alliant retail rate, and outflow credits under the Alliant tariff.
Ask for the projection built on your utility own rate and tariff, with the value of solar transition acknowledged rather than assumed away.