Imported kWh = usage − self-consumed.
Exported kWh = generation − self-consumed.
Export credit = exported kWh × export rate.
Net energy = import cost − export credit.
Apply minimum bill floor if set.
Use carryover credit down to the floor; add new credit.
- Enter your billing period label, usage (kWh), and solar generation (kWh).
- Add your retail import rate and export credit rate from your tariff.
- Include fixed charges, and set a minimum bill only if your utility enforces it.
- If you have an existing credit balance, enter it as carryover credit.
- Use advanced demand inputs only if your bill includes demand charges.
- Click Calculate Offset, then download CSV or PDF if needed.
Offset
Net metering offset shows how much solar reduces a typical bill for the same period. Baseline = (Usage kWh × Retail Rate) + fixed + demand. Offset = Baseline − Bill After Credits. Example: 900 kWh at $0.18/kWh plus $18 fixed gives a $180 baseline. If 650 kWh is self‑consumed, imports fall to 250 kWh and the bill estimates near $63, a $117 (65%) offset. Imported kWh = usage − self‑consumed, and exported kWh = generation − self‑consumed; both values help reconcile your statement’s net usage line clearly each billing cycle.
Rates
Retail and export rates shape the value of each kWh. When export credit is lower than retail, exported energy is discounted. At $0.18 retail and $0.12 export, an exported kWh is worth about 67% of an imported kWh. That makes higher self‑consumption more important than raw production. For time‑of‑use plans, use weighted average rates for the billing period.
Credits
Credit handling changes cash flow. This calculator treats credits in dollars: when export credit exceeds import cost, the energy line becomes negative and converts into “new credit.” Starting carryover credit is applied to this period’s bill, but it won’t reduce the bill below a minimum floor you enter. Outputs show credit used, new credit generated, and ending carryover for simple tracking.
Charges
Fixed and demand charges often cap the achievable offset. Demand charge = Peak kW × Demand Rate, so reducing a 6 kW peak by 1 kW at $12/kW saves $12 for the period. A fixed $18 charge remains even at 100% energy coverage unless your program allows credits to offset it. Enter a minimum bill to see when excess credits accumulate instead of lowering the invoice.
Planning
Use scenario testing to plan upgrades. If exports are high, shifting flexible loads (EV charging, water heating, laundry) can raise self‑consumption and improve offsets. Many solar‑only homes sit near 25–45% self‑consumption, while storage or managed loads can reach 60–85%. Re‑run with different export rates and carryover credits, and keep the billing label dated for month‑to‑month comparisons.
| Month | Usage (kWh) | Solar (kWh) | Retail Rate | Export Rate | Estimated Offset |
|---|---|---|---|---|---|
| January | 980 | 520 | $0.18 | $0.12 | $88.80 |
| March | 860 | 720 | $0.18 | $0.12 | $129.60 |
| May | 780 | 860 | $0.18 | $0.12 | $158.40 |
| July | 1,050 | 900 | $0.20 | $0.13 | $180.00 |
| September | 920 | 760 | $0.19 | $0.12 | $144.40 |
| December | 1,020 | 560 | $0.18 | $0.12 | $94.80 |
What does “offset percent” mean?
It is the share of your baseline bill that solar and credits eliminate. The calculator compares a no‑solar baseline to your bill after credits, then reports the difference as a percentage.
Why is my bill not zero when generation matches usage?
Fixed charges, demand charges, taxes, and minimum bills can remain. Also, if export credit is lower than retail, exporting kWh may not fully compensate for later imports.
Should I enter self‑consumption percent?
Only if you know it from monitoring data. Leaving it blank uses a conservative default where self‑consumed energy equals the smaller of usage and generation for the period.
How do carryover credits work here?
Carryover credit reduces the current bill down to your minimum bill floor. Any unused carryover plus new credit generated from excess exports becomes your ending credit balance.
How can I improve my offset under low export rates?
Increase self‑consumption by shifting loads to sunny hours, using smart controls, or adding storage. Reducing peak demand can also lower demand charges where applicable.
Is this the same as true‑up or annual netting?
Not exactly. This estimates one billing period using dollar credits. Annual true‑up rules can reset credits or pay out at different rates, so use your utility’s true‑up policy for year‑end planning.