Illinois Solar Buyback Rates Explained

“Buyback rate” describes what the utility pays a solar homeowner for electricity the system exports to the grid rather than consumes on-site. It is one of the largest single inputs to a residential payback calculation, and it is the input most often misrepresented in sales pitches. The headline number is rarely the all-in delivered rate the household pays for grid electricity, the comparison most buyers are running in their head. The page below explains what the compensation actually is under ComEd Smart Solar Billing, how Ameren Illinois compensates differently, and what changed for new installs after January 1, 2025.

ComEd transitioned residential customers to Smart Solar Billing effective January 1, 2025, under ICC-approved Rider POGNM . The structure replaced the prior 1:1 retail-rate net metering arrangement for new installations. Systems with permission to operate dated before January 1, 2025 remain grandfathered to the prior retail-rate structure for the original term of their interconnection agreement.

Under Smart Solar Billing, the homeowner is credited at two different rates depending on whether the production is consumed instantaneously or exported to the grid.

• Instantaneous offset. Production consumed by the home as it is generated offsets the all-in delivered rate, which currently sits near 16¢/kWh. This is the full value of each kWh, and it is the same value as not buying the kWh from ComEd in the first place. Self-consumption is the most valuable kWh a residential system produces.
• Net export credit. Production exported back to the grid (when the home is not consuming it, for example during the midday peak in a quiet house) is credited at the supply rate, not the delivered rate. The supply rate is currently 9.66¢/kWh through May 2026, per ComEd’s current ICC-filed schedule. After the May 2026 supply auction, the rate resets; CUB monitors and publishes the post-auction figure.

The economic gap matters for sizing. A system sized so that most production is consumed on-site (typical for a household with always-on loads: heat pumps, EVs, electric water heating) earns the full retail rate for the majority of its output. A system sized well above the home’s daytime consumption sends a larger share to export and earns the supply rate, roughly half the per-kWh value, on that share. The Citizens Utility Board lays out the supply-versus-delivered math in detail in its 2026 ComEd rate report .

Ameren Illinois operates a separate net-metering structure from ComEd. The current residential rider compensates net exports against on-peak consumption with monthly reconciliation and a carry-forward for any excess generation in a given billing month. The Smart Solar Billing transition that reshaped ComEd’s structure on January 1, 2025 did not apply on the same timeline to Ameren; the Illinois Commerce Commission is the authoritative source for the current Ameren tariff and any pending changes.

Because Ameren’s territory covers central and southern Illinois (a different residential rate base than ComEd, with different supply rates), the buyback math comes out differently per kWh. The general framework, full retail offset for self-consumption, a lower export credit for grid-bound generation, applies in concept; the specific rate figures and the program name should be verified against Ameren’s current ICC tariff filing before treating any number as fixed.

• Rates change with each ICC filing. Both ComEd and Ameren file rate cases periodically. The supply rate component (which controls Smart Solar Billing net export credit for ComEd) resets after each supply auction. The figure printed on a proposal in February is not necessarily the figure in effect in October. Quote dates and effective rate dates should match.
• Time-of-use plans interact differently. A residential customer on ComEd’s Hourly Pricing program (or Ameren’s Power Smart Pricing) pays variable rates that change hourly. Solar export economics on a TOU plan are not the same as on a flat-rate residential plan. The instantaneous offset value depends on what the household would have paid for grid power at that specific hour, not on the monthly average rate.
• Legacy NEM is real but ending eventually. Systems with PTO before January 1, 2025 are grandfathered to retail-rate net metering for the original term of their interconnection agreement. The grandfathering is not permanent; verifying the specific end date in the interconnection agreement matters for any homeowner buying a home with an older system or planning a panel replacement that might trigger a new interconnection.

For the reference 7 kW south-facing system in ComEd territory that Summit uses as a baseline (9,274 kWh/year per PVWatts at the Lake Zurich coordinates), the split between self-consumption and export matters significantly. A representative 50/50 split values half the production at the all-in delivered rate (about 16¢) and half at the supply rate (9.66¢ through May 2026), for a blended effective value near 12.8¢/kWh. The exact split depends on the household’s daytime load profile.

The same system on a pre-2025 PTO grandfathered to retail-rate net metering would value every exported kWh at roughly the full retail rate, for a blended effective value closer to 16¢/kWh on the same production. Across a 25-year system life, the difference is meaningful: thousands of dollars of lifetime value depending on the regulatory regime the system sits under.

A ±20% change in either the supply rate or the delivered rate moves the cash payback by roughly a year in either direction at typical Illinois residential rate levels. Quotes that ignore rate sensitivity (or that use a single static buyback figure for a 25-year horizon) are modeling something simpler than reality. Summit’s Lake Zurich worth-it page shows the cash and financed payback ranges using current Smart Solar Billing rates.