This glossary explains the key fields, assumptions, and outputs used across TheSolarMath calculators. Use it to understand what each input means and how each result is estimated.
Solar Cost Calculator Terms
This section explains the main inputs and outputs used in the Solar Cost Calculator so you can understand what each field means and how the estimate is built.
| Term | What it means | Example |
|---|---|---|
| Monthly electricity bill | Your average monthly electricity cost before solar. This helps estimate your annual electricity usage. | $200 per month |
| Electricity rate | The price you pay per kilowatt-hour (kWh) of electricity. This is used to estimate how much electricity your home uses. | $0.16 per kWh |
| Roof shading | A simplified way to estimate how much shade affects your roof. More shading can reduce solar production and increase the effective cost of reaching your energy target. | Low, Medium, or High shading |
| Battery included | Shows whether a battery is added to the solar project. A battery increases the total upfront cost. | Yes |
| Usable roof area | The approximate roof space available for solar panels. This is optional and is mainly used as a fit check. | 45 m² |
| Solar production factor | A planning assumption for how much electricity each kilowatt of solar capacity may produce per year. | 1,200 kWh per kW per year |
| Installed cost per kW | The assumed installed cost for each kilowatt of solar capacity. This is used to estimate the total project cost. | $2,500 per kW |
| Battery cost override | An editable battery cost assumption used when battery storage is included in the project. | $8,000 |
| Estimated system size | The approximate solar system size needed to support your electricity usage under the current assumptions. | 8.4 kW |
| Gross installed cost | The estimated total project cost before any tax credit or incentive is applied. | $29,000 |
| Estimated federal tax credit | A simplified estimate of the federal clean energy tax credit if the option is included in the calculator. | $8,700 |
| Net cost after federal credit | The estimated project cost after subtracting the simplified federal tax credit assumption. | $20,300 |
| Estimated roof area needed | The approximate roof space required for the estimated system size. | 46 m² |
| Likely roof fit | A simple check showing whether the estimated system is likely to fit within the usable roof area entered. | Good |
| Estimated range | A simplified low-to-high planning range around the cost estimate. | $18,000–$23,000 |
Solar Savings Calculator Terms
This section explains the main inputs, assumptions, and outputs used in the Solar Savings Calculator so you can understand how bill reduction and long-term savings are estimated.
| Term | What it means | Example |
|---|---|---|
| Monthly electricity bill | Your average monthly electricity cost before solar. This is used to estimate your current annual electricity spend. | $200 per month |
| Electricity rate | The price you pay per kilowatt-hour (kWh) of electricity. This helps estimate both current electricity use and the dollar value of solar savings. | $0.16 per kWh |
| Estimated system size | The solar system size used in the savings estimate. This can be entered manually or passed from the Cost Calculator. | 8.0 kW |
| Battery included | Shows whether battery storage is part of the setup. In this simplified model, battery storage can improve usable bill savings. | Yes |
| Solar production factor | A planning assumption for how much electricity each kilowatt of solar capacity may produce in a year. | 1,200 kWh per kW per year |
| Usable savings factor without battery | A simplified factor estimating how much solar production becomes real bill reduction when no battery is included. | 0.75 |
| Usable savings factor with battery | A simplified factor estimating how much solar production becomes real bill reduction when battery storage is included. | 0.82 |
| Current annual electricity spend | Your estimated yearly electricity cost before solar, based on your monthly bill. | $2,400 per year |
| Estimated annual solar production | The amount of electricity the solar system could generate in a year under the current assumptions. | 9,600 kWh per year |
| Estimated annual bill offset | The portion of annual electricity use or solar production that is treated as real electricity bill savings in the model. | 7,200 kWh per year |
| Estimated monthly savings | The approximate monthly electricity cost reduction produced by the solar system under the current assumptions. | $96 per month |
| Estimated annual savings | The approximate yearly electricity cost reduction produced by the solar system. | $1,152 per year |
| Estimated bill reduction | The share of your current annual electricity bill that the solar system could offset in the model. | 48% |
| 1-year savings | A simple estimate of total savings over the next 12 months using the current assumptions. | $1,152 |
| 10-year savings | A simple estimate of total savings over 10 years without modeling financing, incentives, or changing utility rules. | $11,520 |
| 20-year savings | A broad long-term estimate of total savings over 20 years using stable assumptions. | $23,040 |
Solar Payback Calculator Terms
This section explains the main inputs, assumptions, and outputs used in the Solar Payback Calculator so you can understand how break-even timing and long-term return are estimated.
| Term | What it means | Example |
|---|---|---|
| Gross installed cost | The estimated total project cost before any tax credit or incentive is applied. | $30,000 |
| Annual savings | The estimated yearly electricity bill savings used to calculate payback. | $2,500 per year |
| Battery included | Shows whether battery storage is part of the solar project. In this version, it is mainly used as a context setting. | Yes |
| Include federal tax credit | Lets you include or exclude a simplified federal clean energy tax credit assumption in the payback estimate. | Yes |
| Federal credit rate | The percentage used to estimate the value of the federal tax credit when the credit option is turned on. | 0.30 |
| Annual savings growth rate | An optional assumption for how much annual savings could increase over time. | 0.02 (2%) |
| Projection years | The number of years used in the long-term return estimate. | 20 years |
| Estimated federal credit | The simplified dollar value of the federal tax credit based on the selected credit rate and gross installed cost. | $9,000 |
| Estimated net cost | The project cost after subtracting the simplified federal tax credit assumption. | $21,000 |
| Estimated payback period | The approximate number of years it could take for annual savings to recover the estimated net cost. | 8.4 years |
| Break-even estimate | A simple year-based estimate showing when cumulative savings may catch up to net project cost. | Year 9 |
| Annual savings used | The annual savings figure the calculator uses for the payback estimate. | $2,500 |
| Battery setting | A simple output confirming whether the payback estimate was run with or without battery selected. | Battery included |
| 10-year net gain | The estimated net financial gain or loss after 10 years, based on net cost and projected savings. | $4,000 |
| Projection-period net gain | The estimated net financial gain or loss across the full selected projection period. | $18,000 |
| Payback outlook | A simple interpretation of the payback result based on the current assumptions. | Strong, Moderate, or Slow |