Illinois Solar Savings Calculator: 2026 Updated

Illinois Solar Savings Calculator

Calculate Illinois solar costs, 2026 federal tax-credit status, Illinois Shines REC payments, ComEd and Ameren net metering, payback period, and 25-year savings.

Illinois 2026 rules: No state income tax credit for solar. The federal Section 25D credit ended for systems placed in service after December 31, 2025. The Illinois Shines program buys renewable energy credits upfront, cutting net system cost. ComEd and Ameren offer retail-rate net metering with annual true-up. Solar value is excluded from property tax under the state special assessment.

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Estimates only. Verify utility rates, net metering true-up terms, Illinois Shines contract value, property tax assessment, and federal tax status with your utility, installer, and tax professional.

What Is the Illinois Solar Savings Calculator?

The Illinois Solar Savings Calculator estimates the installation cost, payback period, and 25-year net savings of a residential solar energy system. It calculates potential savings using system capacity, installed cost per watt, household electricity consumption, solar production, self-consumption, export credit rates, and entered incentives, including Illinois Shines REC payments.

The calculator separates solar electricity into energy used directly in your home and energy exported to the electric grid. Self-used electricity is valued at your entered retail electricity rate, while exported electricity receives the export credit rate you provide.

It also accounts for assumed annual electricity rate increases, declining solar production, recurring utility solar fees, and entered property tax savings.

The main results include gross system cost, net cost after entered incentives, payback period, 25-year net savings, and estimated solar production. These figures are financial projections based on a fixed calculation model rather than guaranteed savings or actual utility billing results.

How the Illinois Solar Savings Calculation Works

The calculator estimates your upfront installation cost, calculates solar electricity production, and assigns financial value to the electricity generated. It then models 25 years of savings to determine when the system may recover its calculated net cost.

1. Calculate Gross Solar System Cost

Gross system cost depends on the installed solar capacity in kilowatts (kW) and the installation price per watt.

\text{Gross Cost}=\text{System Size (kW)}\times1000\times\text{Cost per Watt}

For example, an 8 kW solar system installed at $3.00 per watt has a gross installation cost of:

8\times1000\times3.00=\$24{,}000

The calculator then subtracts the entered federal credit, Illinois state credit, and Illinois Shines REC payment or rebate to determine net system cost.

N=\max\left(0,G-\frac{GF}{100}-\frac{GS}{100}-R\right)

Here, N is net system cost, G is gross system cost, F is the entered federal credit percentage, S is the entered Illinois state credit percentage, and R is the entered Illinois Shines REC payment or rebate in dollars.

Both percentage-based credits are calculated against the original gross system cost. The net cost is limited to a minimum of $0.

The calculator defaults both credit percentages and the Illinois Shines REC payment to zero. Entered values reduce the modeled upfront cost, but the calculator does not determine incentive eligibility or automatically calculate REC payment amounts.

2. Estimate Annual Solar Electricity Production

The calculator uses a fixed first-year solar production assumption of 1,300 kilowatt-hours (kWh) per kilowatt of installed system capacity.

\text{Year 1 Production (kWh)}=\text{System Size (kW)}\times1300

For an 8 kW system:

8\times1300=10{,}400\text{ kWh}

The model assumes solar electricity production decreases by 0.5% each year. This reduction is compounded throughout the 25-year calculation.

P_y=P_1\times(1-0.005)^{y-1}

In this formula, P1 represents first-year production, Py represents production in year y, and 0.005 is the annual solar degradation rate.

The calculator also distributes annual solar production across 12 months using fixed percentages. January receives 1% of annual generation, while June and July each receive 19%. These monthly allocations affect how much electricity is counted as household self-consumption or grid exports.

3. Estimate Annual Household Electricity Usage

The calculator estimates annual household electricity consumption from the entered monthly electric bill and electricity rate.

\text{Annual Usage (kWh)}=\frac{\text{Monthly Electric Bill}\times12}{\text{Electricity Rate per kWh}}

For a $140 monthly electricity bill and a $0.165 per kWh electricity rate:

\frac{140\times12}{0.165}\approx10{,}182\text{ kWh}

This calculation assumes the entire entered electricity bill can be converted into energy consumption using one rate. Actual electric bills may also include fixed charges and other costs. Enter a rate greater than zero to obtain a meaningful usage estimate.

4. Calculate Solar Self-Consumption and Export Credits

The calculator divides monthly solar production into electricity used directly by the household and electricity exported to the grid.

Self-used electricity is determined by the entered Daytime Self-Consumption percentage. However, the calculated amount cannot exceed the model’s estimated monthly household electricity consumption.

U_m=\min\left(P_m\times\frac{s}{100},\frac{A}{12}\right)

E_m=\max(0,P_m-U_m)

Um represents monthly self-used solar electricity, Pm is monthly solar production, s is the entered self-consumption percentage, A is estimated annual household electricity usage, and Em is monthly exported electricity.

The calculator values electricity used at home at the retail electricity rate. Electricity exported to the grid is valued at the separately entered export credit rate.

\text{Monthly Solar Value}=(U_m\times r)+(E_m\times e)

Here, r is the applicable retail electricity rate and e is the applicable export credit rate.

Both rates increase annually according to the entered Annual Utility Rate Increase percentage. The calculator adds the monthly energy values, subtracts annual utility solar fees, and adds entered annual property tax savings.

S_y=\sum_{m=1}^{12}(U_{y,m}r_y+E_{y,m}e_y)-F_a+T

Sy represents modeled savings in year y, Fa represents annual utility solar fees, and T represents entered annual property tax savings. Fees and property tax savings remain fixed at their entered dollar amounts throughout the projection.

5. Calculate Solar Payback and 25-Year Net Savings

The calculator adds each year’s savings to a cumulative total. The payback period is the first modeled year when cumulative savings equal or exceed net installation cost.

Its main long-term financial formula is:

\text{25-Year Net Savings}=\sum_{y=1}^{25}S_y-N

This formula adds 25 years of estimated annual savings and subtracts the calculated net installation cost.

If net cost is zero, the calculator displays Immediate as the payback period. If cumulative savings do not recover the net cost within 25 years, it displays 25+ Years. Otherwise, the payback result is reported as a whole number of years.

Worked Example: An 8 kW Solar System in Illinois

Consider a hypothetical Illinois solar installation using the calculator’s default input values.

Input	Example Value
Monthly Electric Bill	$140
Electricity Rate	$0.165/kWh
System Size	8 kW
Installed Cost per Watt	$3.00
Export Credit	$0.165/kWh
Daytime Self-Consumption	30%
Annual Utility Rate Increase	3.5%
Annual Utility Solar Fees	$0
Federal and State Credits	0%
Illinois Shines REC Payment	$0
Annual Property Tax Savings	$0

With these assumptions, gross system cost is $24,000. Since no credits or upfront REC payments are entered, net system cost also equals $24,000.

The system produces an estimated 10,400 kWh during its first modeled year. The model allocates 3,120 kWh to direct household consumption and 7,280 kWh to exports. Because both electricity rates are $0.165/kWh, first-year energy savings equal $1,716.

(3120\times0.165)+(7280\times0.165)=\$1{,}716

The 25-year calculation applies annual electricity rate increases and solar production degradation to produce these results:

Calculated Result	Estimated Value
Gross System Cost	$24,000
Net System Cost	$24,000
Year 1 Solar Production	10,400 kWh
Estimated Annual Household Usage	10,182 kWh
Solar Offset	102%
Calculated First-Year Energy Savings	$1,716
Payback Period	12 Years
25-Year Cumulative Savings Before Installation Cost	$62,421
25-Year Net Savings	$38,421
25-Year CO2 Offset	110.2 tons

Under these assumptions, cumulative savings first exceed the $24,000 system cost during year 12. Over 25 years, the model produces approximately $62,421 in cumulative savings. Subtracting the $24,000 installation cost gives approximately $38,421 in net savings.

The example assumes no Illinois Shines REC payment. Entering an applicable upfront payment would reduce the calculated net system cost and could shorten the estimated payback period.

These figures demonstrate the calculator’s implemented formulas. They are not guaranteed financial outcomes for a particular Illinois property.

How to Use the Illinois Solar Savings Calculator

Enter your electricity information and solar system assumptions to calculate estimated installation costs and long-term savings.

Enter Monthly Electric Bill ($). Provide your monthly electricity bill. The default value is $140.
Enter Electricity Rate ($/kWh). Add your retail electricity rate. The calculator starts with $0.165 per kWh.
Enter System Size (kW). Provide the solar system capacity you want to evaluate. The default is 8 kW.
Enter Installed Cost per Watt ($). Use your estimated installation price per watt. The starting value is $3.00.
Select your Utility. Choose ComEd, Ameren Illinois, Municipal Utility, or Electric Cooperative. The selection is informational and does not automatically change the numerical calculation.
Enter Export Credit ($/kWh). Provide the credit rate to apply to exported solar electricity. The default is $0.165/kWh.
Set Daytime Self-Consumption (%). Enter the percentage of solar production assumed to be used directly in your home. The default is 30%, with an input range of 0% to 100%.
Enter Annual Utility Rate Increase (%). Set the assumed yearly increase in electricity and export rates. The default is 3.5%, with an input range of 0% to 50%.
Enter Annual Utility Solar Fees ($). Add recurring annual fees to include in your estimate. The default is $0.
Review the battery checkbox. The form includes Battery storage or high daytime self-use. Checking this option does not independently modify the calculation. Adjust the self-consumption percentage to explore a different assumption.
Review Incentives. Enter Direct Federal Credit (%), Illinois State Credit (%), Illinois Shines REC Payment ($), and Property Tax Savings ($/yr), where appropriate. All four fields default to zero.
Click Calculate Savings. Review the cost breakdown, payback period, 25-year net savings, system production, solar offset, and estimated CO2 offset. Use Reset to restore the starting values and hide previous results.

For a more relevant estimate, use figures from your electricity bill, installation quote, and any documented REC payment offer. The calculator applies the financial assumptions you enter rather than verifying available incentives or utility tariffs.

Understanding Illinois Solar Savings Results and Assumptions

Illinois Shines REC Payments

The calculator includes a dedicated Illinois Shines REC Payment field. A renewable energy credit, or REC, represents the environmental attributes associated with renewable electricity generation.

The supplied calculator describes Illinois Shines as a program that purchases renewable energy credits and can reduce a solar installation’s effective upfront cost. It also references the Illinois Solar for All program for income-qualified households.

However, the calculator does not determine REC payment eligibility, applicable program categories, or contract payment amounts. Instead, it subtracts the dollar amount you enter directly from gross installation cost, along with any entered percentage-based credits.

If you have a solar installation proposal that includes a projected Illinois Shines payment, use the documented amount when exploring your cost assumptions. Confirm actual payment terms with your installer or program administrator.

Net Metering and Utility Selection

Net metering is an arrangement that provides billing credit for solar electricity exported to the grid. The calculator’s informational content describes retail-rate net metering, monthly rollover, and annual true-up arrangements for ComEd and Ameren Illinois.

The implemented calculation is simpler. It multiplies exported electricity by the single export credit rate entered in the form. It does not calculate monthly credit balances, annual true-up settlements, or separate utility-specific billing rules.

Selecting ComEd, Ameren Illinois, Municipal Utility, or Electric Cooperative does not automatically update electricity rates, export credits, or annual fees.

Because actual billing arrangements can differ, your entered export credit and utility fee assumptions are important when interpreting savings.

Tax Credits and Property Tax Savings

The calculator’s stated 2026 assumptions use a 0% direct federal credit and a 0% Illinois state credit. Its informational text describes Illinois Shines REC payments rather than a state solar income tax credit and references a special property tax assessment for solar installations.

These statements are part of the calculator’s supplied content, not an individualized tax determination. Incentive availability and eligibility must be verified separately.

When you enter Property Tax Savings ($/yr), the calculator adds that amount to every modeled year’s savings. The default is $0, and the tool does not calculate property tax savings from assessed property values or local tax rates.

Payback Period and Long-Term Savings

The Payback Period measures when cumulative modeled savings first recover net installation cost. The result is displayed as a whole number of years, along with a progress bar comparing payback time with the 25-year model.

The 25-Year Net Savings result represents cumulative savings after subtracting net system cost. A positive figure means modeled savings exceed net installation expense. A negative result means the calculated savings fall short over the modeled period.

The model does not separately calculate solar financing interest, maintenance expenses, equipment replacement costs, or the present value of future savings. These factors can change the financial return of an actual installation.

Solar Offset and Environmental Impact

Solar Offset compares estimated first-year solar production with estimated annual household electricity consumption.

\text{Solar Offset (\%)}=\frac{\text{Year 1 Production (kWh)}}{\text{Annual Usage (kWh)}}\times100

The calculator rounds the solar offset to a whole percentage. A result above 100% means modeled annual solar production exceeds estimated annual consumption. It does not mean the household’s electricity bill will necessarily reach zero.

The calculator also estimates a 25-Year CO2 Offset using cumulative solar electricity production and a fixed factor of 0.45 tons per 1,000 kWh.

\text{CO2 Offset (tons)}=\frac{\text{25-Year Production (kWh)}}{1000}\times0.45

This output is shown to one decimal place. It is a simplified environmental estimate, not a measurement of actual avoided emissions from the local electric grid.

Important Result Display Details

Some result labels in the current calculator do not match the underlying values. The rows labeled Year 1 Self-Use kWh and Year 1 Export kWh actually display the final modeled year’s quantities, from year 25, rather than year 1.

The row labeled Net Year 1 Savings also does not represent actual first-year savings. It displays the calculated 25-year net savings when positive, or $0 when the 25-year result is zero or negative.

The separately labeled Payback Period and 25-Year Net Savings outputs display their stated calculations. Currency values are formatted as whole U.S. dollars, production and usage are displayed as whole kWh, and the CO2 estimate is shown to one decimal place.

These formatting choices affect how results appear, not the underlying calculations.

Frequently Asked Questions

How much can solar panels save in Illinois?

Potential solar savings depend on system installation costs, electricity prices, solar generation, self-consumption, export credits, and available incentives. The Illinois Solar Savings Calculator estimates 25-year net savings using these assumptions. Entering your own electricity bill, installation quote, and documented incentive amounts creates a more relevant estimate than relying only on the default values.

How does the Illinois Shines REC payment affect solar payback?

An entered Illinois Shines REC payment reduces the calculated upfront net system cost. Since payback occurs when cumulative savings recover that net cost, a larger payment may shorten the estimated payback period. The calculator does not calculate REC eligibility or payment amounts automatically. Use a documented contract value rather than assuming a payment is available.

How long does it take for solar panels to pay for themselves in Illinois?

The payback period depends on the net installation cost and accumulated financial savings. This calculator evaluates savings over 25 years and reports the first whole year when cumulative savings reach net system cost. If recovery does not occur within the modeled period, it displays 25+ Years. Actual payback can differ from this estimate.

Does the calculator automatically apply ComEd or Ameren net metering rules?

No. The calculator includes ComEd and Ameren Illinois in its utility selector, but the selection does not alter the calculation. Exported electricity is valued at the rate entered in the Export Credit field. The calculator does not independently model monthly net metering credit rollover or annual true-up settlements.

Does the calculator include solar panel degradation?

Yes. The calculator assumes solar electricity production decreases by 0.5% annually throughout the 25-year projection. Each year’s production is calculated from the preceding year’s reduced production. This is a fixed assumption and does not change based on panel manufacturer, equipment specifications, or actual operating conditions.

Does battery storage change the solar savings calculation?

No. The calculator includes a Battery storage or high daytime self-use checkbox, but checking it does not modify the mathematical calculation. You can manually increase the Daytime Self-Consumption percentage to explore a different energy-use assumption. The model does not separately calculate battery installation costs, storage efficiency, or replacement expenses.

Can the Illinois solar calculator show negative 25-year savings?

Yes. The 25-Year Net Savings result becomes negative when cumulative modeled savings are lower than net installation cost. Higher installation costs, lower electricity values, or larger recurring fees can contribute to this outcome. A negative estimate means the entered scenario does not recover its modeled cost over 25 years, not that an actual financial loss is guaranteed.

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Illinois Solar Savings Calculator