Your numbers
1
Annual totals
Assumed flat across months for this simulation.
Savings and payback
Bill credit rollover calculator
See a month-by-month simulation of how production surpluses and deficits roll forward, ending the year in either a credit balance or an owed amount.
How it works
One step to your rollover simulation
Step 1
Enter your annual production, usage, and rate
The tool applies a typical seasonal production curve and flat monthly usage to simulate how credits and debits roll forward, similar to the pattern shown in the seasonal savings variation calculator and winter vs summer comparison.
Step 2
See your year-end position
Whether you end the year with a credit balance or an owed amount depends on how your total production compares to total usage across the full 12 months.
Understanding how rollover actually works
The basic mechanism
When your system produces more than you use in a month, the surplus becomes a credit that carries forward. When it produces less, the shortfall draws down any existing credit balance first, and only becomes an owed amount once that balance runs out. This is why summer surpluses can help cushion winter shortfalls, though not always completely. To size the array behind this number, the system size by monthly kwh usage turns your usage into a kilowatt target.
When shortfalls outweigh the credits
For a system producing 9,490 kWh against 12,000 kWh of annual usage, monthly shortfalls exceed any credits built up, ending the year with about 2,510 kWh still owed, worth roughly $402 at $0.16 per kWh, matching the remaining bill shown on the 1000 kWh a month calculator and the zero dollar bill calculator. Utility rates drive the whole savings calculation, and the US Energy Information Administration's electricity data track them state by state.
When the year ends in credit instead
For a larger system relative to usage, for example 9,490 kWh of production against 6,000 kWh of usage, the year can end with a positive credit balance around 3,490 kWh. What happens to that leftover credit depends entirely on your utility's specific policy, and doesn't automatically translate to cash in your pocket. The US Energy Information Administration's solar explainer covers how solar generation works and where it fits in the wider grid.
Whether credits actually last
Often not indefinitely. Many utilities reset the credit balance at the end of an annual true-up period, sometimes paying out any remaining credit at a reduced wholesale rate rather than carrying it forward, a mechanism covered in more detail in the annual true-up payment estimator. Output varies by roof and weather, and the real world vs nameplate output gap calculator shows what your site should produce in a typical year.
Questions
Frequently asked
When your system produces more than you use in a month, the surplus becomes a credit that carries forward. When it produces less, the shortfall draws down any existing credit balance first, and only becomes an owed amount once that balance runs out.
It depends on your system size relative to usage. For a system producing 9,490 kWh against 12,000 kWh of annual usage, monthly shortfalls exceed any credits built up, ending the year with about 2,510 kWh still owed, worth roughly $402 at $0.16 per kWh.
For a larger system relative to usage, for example 9,490 kWh of production against 6,000 kWh of usage, the year can end with a positive credit balance around 3,490 kWh. What happens to that leftover credit depends entirely on your utility's specific policy.
Often yes, many utilities reset the credit balance at the end of an annual true-up period, sometimes paying out any remaining credit at a reduced wholesale rate rather than carrying it forward indefinitely. Check your specific utility's net metering terms.