Size to what you use in daylight
South Carolina no longer offers simple one-to-one retail net metering to new solar homes, and under solar choice metering the value of exported power is tied to time-of-use rates. So an exported kilowatt hour and a self-consumed one are no longer interchangeable.
That argues for a system matched more closely to what your household actually uses while the sun is up rather than one built to cover your annual consumption and export the difference.
Ask your installer to model the self-consumed share of production explicitly for your household rather than quoting an annual offset percentage. Two homes with identical arrays and different occupancy patterns get different results, and the model should reflect yours.
Ask for two or three sizes with that share shown for each. Seeing where the return stops improving with size is the clearest way to make this decision rather than accepting a single proposal.
The changes that cost nothing
Raising the self-consumed share is the cheapest improvement available, and unlike equipment it can be adjusted at any time.
Pre-cooling the house in the early afternoon while production is strong is the biggest single opportunity, because air conditioning is where most of the electricity goes in a South Carolina summer. A programmable thermostat makes it automatic.
Running laundry and dishwashing during daylight, and scheduling any vehicle charging for the middle of the day rather than the evening, do the same thing for smaller loads.
Because export value is tied to time-of-use rates, ask your utility when the expensive hours are and map your household against them. Moving a large load out of a peak window is worth something on both sides of the meter.
What the state credit adds, and at what pace
The South Carolina state credit is 25 percent of total system cost, up to a total credit of $35,000, claimed on Form TC-38. It is the largest single incentive available to you now that the federal residential credit has ended.
It is released at $3,500 a year, or 50 percent of your state tax liability, whichever is less, with the excess carried forward for 10 years. A smaller system reaches its credit ceiling sooner, which is worth noting when comparing sizes.
Ask a tax advisor how much you would realistically use given your own liability, and ask any installer to show the credit year by year rather than as a single deduction from the price.
Confirm which utility serves your address before applying any of this, since Santee Cooper does not provide one-to-one net metering and follows its own approach, and South Carolina is also served by electric cooperatives.
The state credit, and how much of it you will actually use
South Carolina offers a state income tax credit of 25 percent of the total system cost, up to a total credit of $35,000, claimed on Form TC-38. That headline is genuinely generous and it is the main reason solar still works here now that the federal residential credit has gone.
The limit that decides what it is worth to you is annual. A taxpayer may use only $3,500 of the credit in a year, or 50 percent of their state tax liability, whichever is less, and the excess for each facility can be carried forward for 10 years.
So a household with modest South Carolina tax liability may not use the whole credit within the carryforward period. That is not a reason to avoid it, but the number in a sales presentation and the number you receive can differ substantially. Ask a tax advisor how much you would realistically realise given your own liability.
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 now receives no federal credit. Section 48E survives at 30 percent for third-party owners under leases and power purchase agreements, so ask any such provider what they claim and what of that value reaches you.