# Solar payback calculator

- Human page: https://happytails.ai/en/calculators/solar-payback-calculator/
- Markdown: https://happytails.ai/en/calculators/solar-payback-calculator.md
- Structured JSON: https://happytails.ai/agents/en/calculators/solar-payback-calculator/index.json
- Visibility: public

## Tool capabilities

| Property | Value |
| --- | --- |
| Tool ID | `solar-payback-calculator` |
| Category | calculators |
| Implementation | Registered implementation. Registration alone is not a production-quality guarantee. |
| Browser execution | Use the visible action or interactive controls. |
| Browser processing | Browser; see tool notes for network behavior. |
| HTTP API | Not callable through HTTP. |
| Browser-agent interface | run_current_tool |

### Implementation notes

Calculated on your device for 1 to 100 years. Enter your own import/export prices. Cash flows are undiscounted scenarios, with no tax, subsidy, finance or return guarantee.

### Inputs and settings

No free-text input is required. Use the file inputs and/or settings below.

| Setting | Meaning | Control type | Default | Constraints |
| --- | --- | --- | --- | --- |
| `installedCost` | Installed cost | number | 6000 | min=0 max=1000000000000 step=any |
| `generation` | First-year generation (kWh) | number | 4000 | min=0 max=1000000000 step=any |
| `selfConsumption` | Generation used on site (%) | number | 50 | min=0 max=100 step=any |
| `importTariff` | Avoided import price per kWh | number | "" | min=0 max=100000 step=any |
| `exportTariff` | Export payment per kWh | number | "" | min=0 max=100000 step=any |
| `degradation` | Annual generation degradation (%) | number | 0 | min=0 max=99 step=any |
| `escalation` | Annual import and export price change (%) | number | 0 | min=-99 max=100 step=any |
| `years` | Scenario horizon (years) | number | 25 | min=0 max=100 step=1 |

### Browser-agent workflow

1. Open the human page in a browser that supports WebMCP.
2. Discover the interface exposed by that page; use its actual schema.
3. Select files on the page first when the tool requires files.
4. Call `run_current_tool` with valid input and settings.
5. Inspect the returned result or error and the displayed output. Retrieve files from the displayed download links.

Calls do not automatically copy or download results. Browser permissions still apply. Interface availability alone is not proof of successful execution.

### Planning specification

Installed cost 0 to 1 trillion in one currency; first-year generation 0 to 1 billion kWh; self-consumption 0 to 100%; prices explicitly entered from 0 to 100,000 per kWh. Degradation 0 to 99%; annual price change -99 to 100%; horizon 1 to 100 whole years. Extreme combinations outside the shared finite-output limit are rejected. JSON report, results CSV and full year-zero-through-horizon cash-flow CSV.

This describes intended requirements. Use the implementation notes, interface schema and observed output to determine current support.

### Complete machine-readable capability record

```json
{
  "id": "solar-payback-calculator",
  "category": "calculators",
  "built": true,
  "requirements": "Installed cost 0 to 1 trillion in one currency; first-year generation 0 to 1 billion kWh; self-consumption 0 to 100%; prices explicitly entered from 0 to 100,000 per kWh. Degradation 0 to 99%; annual price change -99 to 100%; horizon 1 to 100 whole years. Extreme combinations outside the shared finite-output limit are rejected. JSON report, results CSV and full year-zero-through-horizon cash-flow CSV.",
  "implementation": {
    "fields": [
      {
        "key": "installedCost",
        "label": "Installed cost",
        "value": 6000,
        "type": "number",
        "min": 0,
        "max": 1000000000000,
        "step": "any"
      },
      {
        "key": "generation",
        "label": "First-year generation (kWh)",
        "value": 4000,
        "type": "number",
        "min": 0,
        "max": 1000000000,
        "step": "any"
      },
      {
        "key": "selfConsumption",
        "label": "Generation used on site (%)",
        "value": 50,
        "type": "number",
        "min": 0,
        "max": 100,
        "step": "any"
      },
      {
        "key": "importTariff",
        "label": "Avoided import price per kWh",
        "value": "",
        "type": "number",
        "min": 0,
        "max": 100000,
        "step": "any",
        "help": "Required. Use the marginal energy price avoided, not a standing charge. Enter 0 explicitly if excluded."
      },
      {
        "key": "exportTariff",
        "label": "Export payment per kWh",
        "value": "",
        "type": "number",
        "min": 0,
        "max": 100000,
        "step": "any",
        "help": "Required. Enter your export payment, or 0 explicitly if exports have no value."
      },
      {
        "key": "degradation",
        "label": "Annual generation degradation (%)",
        "value": 0,
        "type": "number",
        "min": 0,
        "max": 99,
        "step": "any"
      },
      {
        "key": "escalation",
        "label": "Annual import and export price change (%)",
        "value": 0,
        "type": "number",
        "min": -99,
        "max": 100,
        "step": "any"
      },
      {
        "key": "years",
        "label": "Scenario horizon (years)",
        "value": 25,
        "type": "number",
        "min": 0,
        "max": 100,
        "step": 1
      }
    ],
    "registrationFamily": "home-energy-planning",
    "input": false,
    "live": false,
    "presentation": "metrics",
    "note": "Calculated on your device for 1 to 100 years. Enter your own import/export prices. Cash flows are undiscounted scenarios, with no tax, subsidy, finance or return guarantee.",
    "experience": {
      "automatic": false,
      "single": true,
      "inputMaxLength": 1000000,
      "inputMode": "text",
      "label": "Solar value settings",
      "placeholder": "Use the fields below",
      "help": "Enter installation cost, generation, prices and scenario assumptions in the settings. No text input is needed. Up to 1,000,000 characters. Review the settings before running.",
      "action": null
    },
    "mode": "explicit",
    "interactive": false
  },
  "execution": "Browser interface",
  "api": null,
  "browser_agent": {
    "supported": true,
    "name": "run_current_tool",
    "discovery": "WebMCP on the human page in a supporting browser",
    "verification": "See audit/API-AUDIT.md; availability is not verification"
  }
}
```

## Page guide

Explore undiscounted solar electricity value and payback from your generation, self-consumption, import/export prices, degradation and tariff-change assumptions.

### How to use Solar payback calculator

1. Enter installed cost and estimated first-year generation.
2. Enter the self-consumption share and your import and export prices; use an explicit 0 for a price you exclude.
3. Choose annual degradation, a common import/export price-change assumption and the horizon.
4. Review year-zero outlay, annual value, cumulative cash flow and nullable payback, then export JSON and CSV.

How can we improve this tool?

Report a problem or share an idea.

Please leave out private information. Your message and the tool name go to our team via PostHog.

## Useful next steps

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## Value of generated electricity

Self-consumed generation avoids your marginal import energy price. The remainder earns the export payment you enter. Standing charges are not automatically avoided. Prices use one currency, with no tariff, subsidy or tax database.

### A scenario, not a financial promise

Degradation and price changes compound from year two. The self-consumption share remains fixed, and both import and export prices use the same escalation rate. Costs for finance, maintenance, replacements and tax are excluded; cash flows are not discounted.

### Two payback measures

Simple payback divides installation cost by positive first-year electricity value. Cumulative payback finds the first cost crossing in the horizon and interpolates evenly within that year. No crossing is reported as not defined. Zero installation cost has payback zero. The year-zero row records the installation outflow; display rounding occurs after calculations.