Net billing is an arrangement that separately values electricity purchased from the grid and eligible electricity exported to it after applying the specified netting interval and account rules. The arrangement needs more than an export price: the calculation period and remaining bill provisions also matter.
For a homeowner comparing solar financing and savings estimates, ask how the proposal turns your load and production pattern into purchases, eligible exports and a final bill. A percentage labeled “energy offset” cannot establish that result alone.
This glossary explains the mechanism and calculation. The existing South Carolina net-metering guide retains utility comparisons and account-specific buying advice. All unbranded numbers below are original hypothetical examples, not current utility rates, Sunburst measurements or a savings forecast.
Which parts make up a net-billing arrangement?
A complete arrangement connects electricity measurements to prices and settlement. Its name is useful context, but the actual tariff or agreement determines the quantities and rules that belong in the calculation.
The National Laboratory of the Rockies’ compensation-mechanism overview identifies three components: the metering and billing arrangement, sell-rate design and retail-rate design. Its net-billing discussion separates onsite consumption from residual exported energy and its monetary valuation. That framework explains why one export-rate figure cannot describe the whole bill.
For quote reading, identify the following parts before comparing savings:
| Part | Question it answers |
|---|---|
| Measurement boundary | Where are purchases, exports and onsite use counted? |
| Netting interval | Over what period are imports and exports compared? |
| Purchase schedule | How are chargeable grid purchases valued? |
| Export compensation | How are eligible residual exports valued? |
| Other bill provisions | Which fixed, demand, minimum or other charges apply? |
| Settlement | What happens to credits or remaining balances? |
Two arrangements can share a quoted export price while differing in the quantity that receives it. Two proposals can also share annual generation while using different load timing. Keep the mechanism and the modeled household scenario visible together.
The solar export-rate definition owns the per-unit valuation discussion. Net billing owns the process that decides how eligible quantities and their values become account charges or credits.
How do physical electricity flows differ from bill calculations?
Electricity generation, household consumption and meter exchanges describe energy flows. Billing applies account rules to those flows. Do not replace household consumption with imports minus exports: onsite solar use is part of the household energy account too.
For an original simplified period without storage or another generator, assume 20 kWh of solar generation. Household loads use 8 kWh directly, and 12 kWh leaves as export. Household consumption is also 20 kWh, supplied by 8 kWh of direct solar and 12 kWh of imports.
| Hypothetical energy flow | Amount |
|---|---|
| Solar generation | 20 kWh |
| Direct solar use | 8 kWh |
| Export | 12 kWh |
| Household consumption | 20 kWh |
| Import | 12 kWh |
The balances are 8 + 12 = 20 kWh for both generation and household use. The assumed imports and exports have equal totals, but they need not occur at the same time or receive the same financial treatment.
Our grid-tied solar definition explains these directions of flow. Net billing adds the account calculation. A monitoring graph may describe the physical quantities without showing all the charges, adjustments or credit restrictions appearing on a bill.
When a proposal combines those concepts, ask which quantities were measured, modeled or derived. The distinction helps identify what the evidence establishes and which assumptions still affect the estimate.
Worked example: equal generation and consumption, different values
Continue with the hypothetical 20 kWh period above. For this example only, assume the fictional arrangement charges all 12 imported kWh at $0.20/kWh and credits all 12 exported kWh at $0.05/kWh. No additional netting, time-of-use rate variation or other adjustments are included in this teaching calculation.
The import energy charge is 12 × $0.20 = $2.40. The export energy credit is 12 × $0.05 = $0.60. Their difference is $2.40 − $0.60 = $1.80.
| Fictional energy calculation | Amount |
|---|---|
| Imported energy charge | $2.40 |
| Exported energy credit | −$0.60 |
| Remaining energy charge | $1.80 |
Total solar generation equals total household consumption, but the remaining energy charge is positive. Equal kilowatt-hour totals do not establish equal dollar values under the assumed arrangement.
This example also leaves other bill provisions out. It does not produce a final utility bill, determine account eligibility or establish a current purchase/export price. Its purpose is to explain why a production-to-consumption ratio can coexist with electricity charges.
The energy-offset definition owns that ratio. In this case, generation divided by household use is 100%. Reading that as “100% bill savings” would assign a financial meaning the ratio does not contain.
Why is the netting interval so important?
The netting interval is the period over which the arrangement compares the specified energy quantities. A shorter interval and a longer interval can produce different chargeable and creditable quantities from the same underlying exchanges.
For a separate original example, assume two intervals with these prescribed imports and exports. Within each interval, assume the fictional rule subtracts export from import before deciding whether the interval has positive or negative net use.
| Interval | Import | Export | Import minus export |
|---|---|---|---|
| First | 1 kWh | 5 kWh | −4 kWh |
| Second | 5 kWh | 1 kWh | +4 kWh |
| Combined totals | 6 kWh | 6 kWh | 0 kWh |
Under this fictional interval-netted rule, 4 kWh is creditable from the first interval and 4 kWh is chargeable from the second. Applying the same assumed $0.20 purchase and $0.05 export prices gives 4 × $0.20 − 4 × $0.05 = $0.60 of energy charge.
If the fictional comparison instead allowed those quantities to cancel across the entire combined period, the energy difference would be zero before considering any remaining provisions. These are two different calculation rules. They should not be mixed in one forecast.
Notice another distinction: valuing all gross imports and exports separately would use 6 kWh in each direction, producing $0.90 under these assumed prices. That is not the $0.60 interval-netted result. “Separate import and export prices” still needs the eligible quantity definition.
For a real account, follow the actual tariff rather than selecting whichever example gives the lowest bill. Monthly totals cannot establish the interval-netted result when the required interval data is unavailable.
How does net billing differ from net metering?
The broad distinction concerns how energy quantities and credits are treated. Net metering commonly involves kilowatt-hour credits that offset consumption under a defined arrangement; net billing values eligible residual exports financially. Actual programs can contain additional conditions and combinations of rules.
NLR’s compensation overview describes those categories, but a category label should not be treated as a guarantee about every tariff called net metering. Its System Advisor Model rate documentation also notes that terminology varies between descriptions of compensation policies and descriptions of meter-reading or billing processes.
Read the rule rather than arguing from the name. Ask about the netting interval, the value of remaining exports, the treatment of earlier credits and the charges that credits can offset.
| Arrangement or phrase | What to investigate |
|---|---|
| Net metering | Which energy credits offset which purchases, over which period? |
| Net billing | Which residual quantities are charged and credited separately? |
| Buy all, sell all | Are purchases and the system’s generation treated separately without onsite use under that arrangement? |
| Solar Choice or another program name | Which exact schedule, rider and cohort define the calculation? |
Do not classify an entire state’s solar accounts from one program name. Likewise, a rider can contain netting and residual-value rules that need explanation even when its public description uses a familiar category.
The existing utility guides retain that program-by-program work. This entry supplies the mechanism vocabulary needed to read them without assuming a uniform statewide deal.
Does onsite solar use change a net-billing result?
It can change the import and export quantities that enter the calculation. The effect depends on the actual load timing and supported operating arrangement, not just on annual production.
Return to the original 20 kWh no-storage example. Assume 4 kWh of an existing load can move into a period with otherwise exported solar, with no change in total household use or generation. Prescribe the resulting direct use as 12 kWh instead of 8 kWh.
Exports then become 8 kWh and imports become 8 kWh under the stated simplified balance. With the original fictional prices and separate gross valuation, the remaining energy charge becomes 8 × $0.20 − 8 × $0.05 = $1.20.
| Assumed scenario | Direct solar use | Import | Export | Fictional remaining energy charge |
|---|---|---|---|---|
| Original timing | 8 kWh | 12 kWh | 12 kWh | $1.80 |
| Shifted existing load | 12 kWh | 8 kWh | 8 kWh | $1.20 |
The $0.60 difference is an arithmetic result of these prescribed flows and prices. It is not a recommendation to add unnecessary daytime consumption, and it does not establish that a real household can maintain the assumed schedule.
Our solar self-consumption definition explains the physical-use ratio. Ask which loads can realistically move, which time periods matter and what happens when the proposed routine differs from actual use.
How is the full bill different from the energy subtotal?
The energy subtotal includes only the charge and credit quantities specified in the calculation. A complete bill may also include other provisions. Their applicability and interaction must be established from the account’s documents.
For a deliberately fictional illustration, add an unchanged $15 fixed charge to the earlier example. The $1.80 energy subtotal plus that assumed charge gives $16.80 before any further provisions. Nothing about equal generation and household use removes the assumed fixed charge.
A minimum bill is a different concept from a fixed charge. Ask how it is calculated and which items enter its threshold. Do not add a minimum bill as though it were automatically another fixed fee, or assume a credit can offset it without reading the rule.
If the account includes a demand charge, it needs its own measurement and valuation method. A kilowatt-hour energy balance cannot establish a billed kilowatt peak. Keep the energy, power and account rules separated in the estimate.
| Bill component | Information needed |
|---|---|
| Energy charge | Chargeable quantity, period and purchase value |
| Energy credit | Eligible quantity, period and export value |
| Fixed provision | Amount and applicability |
| Minimum provision | Threshold, included items and calculation order |
| Demand provision | Measurement window, applicable peak and rate |
| Other adjustments | Relevant taxes, riders or account-specific conditions |
A proposal should show the final result and the components behind it. A net energy figure followed by “plus fees” is difficult to review when those fees materially affect the decision.
How should before-and-after savings be calculated?
Compare complete, consistently defined scenarios rather than using the post-solar credit as the entire savings figure. Identify the household load, applicable account arrangement and costs included in each case.
For the fictional 20 kWh example, assume the no-solar household buys all 20 kWh at $0.20/kWh. Its energy charge is $4. The solar scenario’s energy subtotal is $1.80, giving an assumed energy reduction of $4 − $1.80 = $2.20.
That $2.20 is not automatically total bill reduction. If the same $15 fixed charge applies in both scenarios, it cancels in their difference. If a fictional new $5 solar-specific charge applies only afterward, the full simplified comparison changes.
| Fictional case | Energy subtotal | Common fixed charge | Additional assumed charge | Total |
|---|---|---|---|---|
| Without solar | $4 | $15 | $0 | $19 |
| With solar | $1.80 | $15 | $5 | $21.80 |
In this deliberately small-period illustration, the added charge exceeds the energy reduction. The comparison is not a claim about a real utility’s fees or solar economics. It demonstrates why omitted provisions can reverse a conclusion drawn from energy credits alone.
Also disclose when the applicable purchase structure changes after installation. NLR’s SAM documentation distinguishes modeling a rate-switching scenario from using the same rate structure for both cases. Keep that issue visible instead of assuming the earlier account prices remain unchanged.
A current South Carolina example: Santee Cooper’s hourly rule
Santee Cooper’s rates index, checked October 3, 2026, lists its DG-25 Distributed Generation Rider. The published DG-25 document states an effective date for bills rendered on and after April 1, 2025. The code does not mean it is a newly issued 2026 tariff.
Section 3 subtracts measured energy delivered by the customer from measured energy supplied to the customer within each hour. Section 4 separately aggregates positive and negative hourly net usage for charges and credits, with other applicable bill provisions.
This illustrates the interval distinction: a monthly sum of imports minus exports does not reproduce the separate hourly valuation by itself. No numeric current purchase or export rate is asserted in this glossary, and the example is not an eligibility determination.
The rider also describes credit settlement and changes to energy-credit values. Use the controlling document and applicable base schedule for an actual calculation. Do not apply this retail-account illustration to a cooperative account merely because the cooperative has a wholesale relationship with Santee Cooper.
The utility information hub helps locate the relevant account discussion. Verify the full utility name, schedule, rider, effective version and customer conditions before choosing inputs for a quote.
What data does an interval calculation require?
It requires energy quantities aligned with the rule’s measurement periods. A modeled estimate needs appropriate production and load inputs; a measured review needs records covering the same boundary and dates.
Where the tariff uses hourly netting, monthly totals do not reveal which hours produced positive and negative balances. A model can estimate that pattern, but its assumptions must remain identifiable rather than being described as measured history.
| Data question | Why it matters |
|---|---|
| Same dates and time convention? | Prevents shifting production against unrelated load periods |
| Required interval available? | Makes the tariff calculation possible at the stated resolution |
| Import and export definitions clear? | Prevents treating generation as outward meter flow |
| Storage and other sources included? | Identifies additional pathways affecting exchange |
| Missing records disclosed? | Prevents interpreting absent data as zero |
| Measured or modeled values labeled? | Shows what evidence supports the forecast |
A coarse estimate may still be useful for screening. Its precision should match its evidence. Ask which assumptions would need refinement before a purchase decision, especially when projected savings depend strongly on daytime overlap or a changed operating schedule.
For a bill discrepancy, first reconcile dates, quantities, intervals and balances. An app’s production total and the utility’s net chargeable energy are not necessarily competing measurements of the same thing.
Does net billing make a battery necessary?
No automatic equipment recommendation follows from the billing label. A battery proposal needs a separate evaluation of supported energy flows, losses, added costs and the owner’s objective.
Ask which purchases storage is intended to avoid and which exports are forgone. Also establish energy origin and the beginning and ending charge condition in the modeled period. Battery discharge can include energy from another period or source, so it should not automatically be counted as current solar production.
The battery quote comparison guide retains that buying decision. A battery storage installation proposal should make the additional financial contribution and any backup purpose understandable separately from the solar-only case.
Keep outage operation independent of daily billing. Our anti-islanding definition explains why ordinary connected solar operation does not establish supported isolated backup. A forecast showing lower purchases is not proof that chosen appliances work when the utility fails.
A useful comparison therefore includes a solar-only scenario, the proposed solar-plus-storage scenario and the documented assumptions that differ. Do not credit storage with the solar array’s entire savings or count the same energy twice as an avoided purchase and a compensated export.
Which calculation records should accompany the proposal?
Request a short calculation record that identifies the account arrangement and connects each stage to the modeled or measured energy. It should be possible to follow the result without accepting an unexplained label.
The record should name the measurement boundary, netting interval, chargeable imports, eligible exports, purchase schedule, compensation rule and remaining bill provisions. It should also identify any carried balance and the settlement assumptions used.
Compare proposals under the same household scenario before ranking the financial results. A different load schedule, utility cohort or account arrangement can change the task being modeled. Ask the analyst to make those differences explicit.
When an input is uncertain, retain it as an assumption and request an alternative case. This is especially useful for future prices or routine changes. A sensitivity case should be described as a modeled possibility, not a utility commitment.
Bring your bill, applicable solar rider, available interval records and proposed savings calculation to a free solar assessment. The next step is to connect the net-billing method to the property, realistic electricity use and current account arrangement.
Frequently asked questions about net billing
Does net billing mean my solar energy has no value?
No. Onsite solar use can reduce purchases, and eligible residual exports can receive compensation. Their value depends on the applicable prices, calculation interval and other provisions. Evaluate those contributions separately rather than assuming either full retail value or no value.
Why can equal imports and exports leave an energy charge?
The quantities may be valued at different prices or netted in separate intervals. In the original two-interval example, equal overall exchanges still leave 4 kWh chargeable and 4 kWh creditable under the fictional rule, producing a positive energy subtotal.
Is net billing calculated once for the entire month?
Do not assume that. The bill can be issued monthly while the eligible quantities are calculated over shorter intervals. Read the actual tariff’s netting period and valuation method; the statement date does not establish the measurement interval.
Can I calculate household consumption by subtracting exports from imports?
That subtraction describes a net utility exchange over the stated period, not total household consumption. Onsite generation serving household loads belongs in the consumption account too. Storage or other generation can add further pathways requiring explicit accounting.
Do credits automatically remove fixed or minimum charges?
No universal treatment follows from the net-billing label. The account rules determine which items credits offset and how any minimum is calculated. Include those provisions in the complete bill comparison rather than stopping at an energy subtotal.
Should I add a battery because my utility uses net billing?
Evaluate the separate storage scenario first: purchases avoided, export value forgone, losses, added costs and supported operation. The billing category alone does not establish payback, compatibility or backup capability for the proposed equipment.
Sources and methodology
Primary references were checked October 3, 2026. NLR’s compensation overview supports the mechanism framework; its SAM documentation supports the terminology and modeling distinctions. They are not substitutes for the account’s controlling tariff.
Santee Cooper’s current rates index and DG-25 document support the bounded hourly-netting example. No numerical current tariff price or account eligibility is determined here.
All unbranded flows, prices, fees and bill comparisons are original hypothetical teaching examples. Their assumptions are explicit, and their results are not household savings forecasts. No Sunburst project outcome, equipment partnership or named expert review is claimed.