{
  "slug": "roof-orientation-derate",
  "title": "Roof Orientation & Tilt Solar Derate Calculator",
  "heading": "Solar Roof Orientation Derate Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/roof-orientation-derate",
  "summary": "How much azimuth and tilt cost you versus a perfect south-facing roof.",
  "description": "Not every roof faces true south at the ideal tilt, and that costs real production. This calculator applies standard production-factor derates for azimuth (compass direction the roof faces) and tilt angle relative to your latitude, based on published solar-industry production tables, so you can see the percentage hit before committing to a specific roof plane. East- and west-facing arrays typically lose 15-20% versus true south; a flat or steep-mismatched tilt loses a smaller but real amount. This is the input that should feed directly into the solar array sizing tool if your roof isn't a simple south-facing plane.",
  "formula": "Production factor = azimuth factor × tilt factor (from standard solar production tables), applied to south-facing/optimal-tilt baseline production.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=roof-orientation-derate",
  "inputs": [
    {
      "id": "baselineProduction",
      "label": "Production at ideal south-facing, optimal tilt",
      "kind": "number",
      "hint": null,
      "default": 12000,
      "unit": "kWh/yr",
      "min": 500,
      "max": null
    },
    {
      "id": "azimuth",
      "label": "Roof-facing direction",
      "kind": "select",
      "hint": null,
      "default": "south",
      "options": [
        {
          "value": "south",
          "label": "South"
        },
        {
          "value": "southeast_southwest",
          "label": "Southeast / Southwest"
        },
        {
          "value": "east_west",
          "label": "East / West"
        },
        {
          "value": "northeast_northwest",
          "label": "Northeast / Northwest"
        },
        {
          "value": "north",
          "label": "North"
        }
      ]
    },
    {
      "id": "tiltMismatch",
      "label": "Tilt vs ideal for your latitude",
      "kind": "select",
      "hint": null,
      "default": "close",
      "options": [
        {
          "value": "close",
          "label": "Within 10° of ideal"
        },
        {
          "value": "moderate",
          "label": "10-20° off ideal"
        },
        {
          "value": "flat",
          "label": "Flat roof / low-slope (<10°)"
        },
        {
          "value": "steep",
          "label": "Very steep (>45°) or vertical wall mount"
        }
      ]
    }
  ],
  "outputs": [
    {
      "id": "adjustedProduction",
      "label": "Adjusted annual production",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "productionLoss",
      "label": "Annual production lost vs ideal",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "derateePct",
      "label": "Total derate percentage",
      "format": "percent",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Production at ideal south-facing, optimal tilt: 12000 kWh/yr",
      "Roof-facing direction: South",
      "Tilt vs ideal for your latitude: Within 10° of ideal"
    ],
    "outputs": [
      "Adjusted annual production: 12,000",
      "Annual production lost vs ideal: 0",
      "Total derate percentage: 0.0%"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter production at ideal south-facing, optimal tilt (kWh/yr).",
      "Enter roof-facing direction.",
      "Enter tilt vs ideal for your latitude.",
      "Read your adjusted annual production on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "baselineProduction": 7200,
        "azimuth": "south",
        "tiltMismatch": "close"
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "baselineProduction": 12000,
        "azimuth": "south",
        "tiltMismatch": "close"
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "baselineProduction": 19200,
        "azimuth": "south",
        "tiltMismatch": "close"
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "Is east/west really that much worse than south?",
      "a": "Yes, roughly 15-20% lower annual production in most US latitudes, though the difference matters less than it used to because panel costs have dropped — many installers now happily use a full east/west roof (splitting panels across both slopes) since it's often the only usable roof space, just sized about 15-20% larger to compensate."
    },
    {
      "q": "What's the ideal tilt for my location?",
      "a": "As a rule of thumb, tilt roughly equal to your latitude maximizes annual production; a few degrees flatter favors summer production, a few degrees steeper favors winter. Most roof pitches (4/12 to 8/12, roughly 18-34°) fall close enough to optimal for most of the continental US that this isn't usually the biggest factor — azimuth matters more."
    },
    {
      "q": "Should I avoid a north-facing roof entirely?",
      "a": "In the Northern Hemisphere, yes if you have any other option — a north-facing array can lose 40-45% of potential production, which usually makes the economics much weaker. Ground-mount systems, which let you choose ideal azimuth and tilt regardless of roof shape, become worth strongly considering if your only usable roof plane faces north."
    },
    {
      "q": "Do these derate factors already account for shading?",
      "a": "No — this tool only covers orientation (azimuth) and tilt geometry. Shading from trees, chimneys, or neighboring structures is a separate, often larger loss that needs a site-specific shading analysis (a Solar Pathfinder or installer's shading report), not a generic table."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/solar-array-sizing",
    "https://www.revenuelab.fyi/toolbox/panel-degradation-25yr",
    "https://www.revenuelab.fyi/toolbox/solar-payback-itc"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Roof Orientation & Tilt Solar Derate Calculator (https://www.revenuelab.fyi/toolbox/roof-orientation-derate)"
}