Local in both senses
South Dakota has no statewide net metering requirement, so there is no statutory floor beneath any utility arrangement.
A municipal electric utility is also governed locally rather than by a state commission, so there is no regulator setting or reviewing its customer generation terms either.
That means the policy, whatever it is, was decided by the city and can be inspected and questioned through local channels.
It also means nothing about a Black Hills Energy or NorthWestern Energy arrangement tells you what applies to a Brookings address.
What to ask, and of whom
Ask the utility for its customer generation or net metering policy in writing. Ask for the document rather than a description, since a policy you can read is what you can check a quote against.
Ask whether exported electricity is credited at all, at what rate and in what units, and whether generation is netted across a billing period or on a shorter interval.
Ask whether credits carry forward or expire, what interconnection involves and costs, and whether any charge applies specifically to customer generators.
Because the utility is municipal, ask also whether the policy has been reviewed recently and whether any change is under consideration. That is a reasonable question to put to a city utility.
Then design to what you find
If exports are credited near the retail rate, sizing can follow annual consumption as it would in a net metering state.
If they are credited poorly or not at all, size to your daytime load and treat self-consumption as the whole of the case, since it is the portion no policy governs.
Ask for the projection built on self-consumption alone first, with any export value added as a separate line, so the dependence is visible.
And ask for a smaller system modelled alongside the proposal, since in the absence of a guarantee a smaller, well-matched system carries less policy risk.
What the arithmetic rests on here
The 30 percent federal Residential Clean Energy Credit under Section 25D expired for property placed in service after December 31, 2025, so a cash or loan purchase in Brookings receives no federal tax credit, and South Dakota has no state solar tax credit.
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 with certainty is the retail value of self-consumed generation. Everything else comes from your municipal utility policy.
Get that policy document, then ask for the projection rebuilt on it with self-consumption and export shown separately.