{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "https://askcalculators.com/uk/solar-payback/schema.json",
  "title": "Solar Payback Calculator — United Kingdom inputs",
  "description": "Compare a simple first-year payback with a discounted cash-flow model that explicitly includes replacement and declining generation. GBP planning view; stated limitations apply.",
  "type": "object",
  "properties": {
    "projectCost": {
      "title": "Installed project price",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 18000,
      "minimum": 0,
      "maximum": 1000000000000,
      "x-step": 0.01,
      "x-prefix": "GBP",
      "x-unit": "currency"
    },
    "confirmedIncentive": {
      "title": "Confirmed eligible incentive",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 0,
      "minimum": 0,
      "maximum": 1000000000000,
      "x-step": 0.01,
      "x-prefix": "GBP",
      "x-unit": "currency"
    },
    "annualBenefit": {
      "title": "First-year gross bill and export benefit",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 1800,
      "minimum": 0,
      "maximum": 1000000000000,
      "x-step": 0.01,
      "x-prefix": "GBP",
      "x-unit": "currency"
    },
    "maintenance": {
      "title": "Annual maintenance",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 100,
      "minimum": 0,
      "maximum": 1000000000000,
      "x-step": 0.01,
      "x-prefix": "GBP",
      "x-unit": "currency"
    },
    "years": {
      "title": "Planning horizon, years",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 25,
      "minimum": 1,
      "maximum": 50,
      "x-step": 1,
      "multipleOf": 1
    },
    "discountRate": {
      "title": "Annual discount rate",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 4,
      "minimum": 0,
      "maximum": 50,
      "x-step": 0.1,
      "x-unit": "percent"
    },
    "degradation": {
      "title": "Annual output degradation",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 0.5,
      "minimum": 0,
      "maximum": 20,
      "x-step": 0.1,
      "x-unit": "percent"
    },
    "energyEscalation": {
      "title": "Annual energy-price escalation",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 2,
      "minimum": 0,
      "maximum": 25,
      "x-step": 0.1,
      "x-unit": "percent"
    },
    "replacementYear": {
      "title": "Replacement year (0 means none)",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 0,
      "minimum": 0,
      "maximum": 50,
      "x-step": 1,
      "multipleOf": 1
    },
    "replacementCost": {
      "title": "Replacement cost",
      "type": "number",
      "description": "Illustrative starting value; replace with your own evidence.",
      "default": 0,
      "minimum": 0,
      "maximum": 1000000000000,
      "x-step": 0.01,
      "x-prefix": "GBP",
      "x-unit": "currency"
    }
  },
  "required": [
    "projectCost",
    "confirmedIncentive",
    "annualBenefit",
    "maintenance",
    "years",
    "discountRate",
    "degradation",
    "energyEscalation",
    "replacementYear",
    "replacementCost"
  ],
  "additionalProperties": false,
  "x-askcalculators": {
    "version": "20.16.0",
    "calculatorUrl": "https://askcalculators.com/uk/solar-payback/",
    "queryExample": "https://askcalculators.com/uk/solar-payback/?projectCost=18000&confirmedIncentive=0&annualBenefit=1800&maintenance=100&years=25&discountRate=4&degradation=0.5&energyEscalation=2&replacementYear=0&replacementCost=0",
    "migrationStatus": "new",
    "reviewStatus": "pending",
    "pageStatus": "live",
    "workStatus": "pending",
    "formula": {
      "expression": "simple payback = (project price − confirmed incentive) ÷ (first-year benefit − annual maintenance).",
      "note": "Inputs are converted to canonical units before evaluating this stated formula."
    },
    "quality": {
      "availability": "live",
      "technicalReviewRecord": "/reviews/v20-uk-solar-payback.json",
      "qualifiedReview": "pending",
      "qualifiedReviewer": null,
      "qualifiedReviewDate": null,
      "formulaVersion": "20.16.0",
      "referenceCoverage": "references-listed",
      "releaseTestScope": "Catalog and regression checks are not a professional formula audit; consult release evidence.",
      "historicalMetadataDate": "",
      "historicalMetadataNotice": "The imported date is not evidence of a completed human review."
    },
    "outputs": {
      "capital": {
        "title": "Net capital cost",
        "type": "number",
        "x-format": "currency",
        "x-currency": "GBP",
        "x-digits": 2
      },
      "annualSaving": {
        "title": "First-year net saving",
        "type": "number",
        "x-format": "currency",
        "x-currency": "GBP",
        "x-digits": 2
      },
      "payback": {
        "title": "Simple payback, years",
        "type": "number",
        "x-format": "number",
        "x-digits": 2,
        "x-primary": true
      },
      "npv": {
        "title": "Discounted net value",
        "type": "number",
        "x-format": "currency",
        "x-currency": "GBP",
        "x-digits": 2
      },
      "breakeven": {
        "title": "Cash-flow break-even year",
        "type": "number",
        "x-format": "number",
        "x-digits": 2
      },
      "cumulative": {
        "title": "Undiscounted lifetime net benefit",
        "type": "number",
        "x-format": "currency",
        "x-currency": "GBP",
        "x-digits": 2
      }
    }
  }
}