What a twelve month carry-forward does
Under PSO monthly netting, generation offsets consumption within each billing period at the retail rate. Where generation exceeds consumption in a month, the resulting excess credits carry forward for up to twelve months.
That matters because a solar array and a household do not line up month to month. Spring and autumn often produce a surplus while summer air conditioning consumes everything the roof makes.
A carry-forward lets an April surplus offset an August deficit, which is exactly the pattern an Oklahoma household is likely to have.
What the carry-forward does not do is turn genuine annual surplus into retail value. Excess sent to the grid is ultimately credited at avoided cost, in the region of 3 to 4 cents per kWh.
The questions that pin the mechanism down
Ask how excess credits are applied: whether they offset kilowatt hours in a later month at the retail rate, or are converted to a monetary credit at avoided cost when they are created.
That distinction is the whole difference between a useful carry-forward and a cosmetic one, and it is not always obvious from a tariff summary.
Ask what happens at the end of the twelve month period to credits that have not been used, and whether anything is paid for them.
Ask what the current avoided cost rate is and how often it is reset. Confirm the answers with PSO rather than accepting them from a sales conversation.
How that shapes the design
A carry-forward makes annual sizing more forgiving than it would be under a strict monthly settlement, because a shoulder-season surplus can be absorbed later in the year.
It does not make oversizing free. A system producing more across a full year than the household uses generates surplus that no carry-forward can convert into retail value.
So build from your last twelve months of bills, ask what percentage of your annual usage the design covers, and require a specific reason for anything above it.
Ask for the monthly profile with the credit balance tracked across a full year. A balance that rises in spring and returns toward zero through summer describes a well-sized system; one that only climbs describes an oversized one.
Building the number without the federal credit
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 Tulsa receives no federal tax credit, and Oklahoma 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 is retail-rate offsetting within the billing period, a twelve month carry-forward of excess credits, avoided cost for what remains, and the electricity you stop buying.
Ask for the monthly profile with the credit balance tracked, and confirm with PSO how excess credits are applied and what the current avoided cost rate is.