{
  "slug": "solar-array-sizing",
  "title": "Solar Array Sizing Calculator",
  "heading": "Solar Array Sizing Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/solar-array-sizing",
  "summary": "How many panels and kW you need to cover your usage.",
  "description": "Sizing a solar system starts with your actual annual usage, not a rule of thumb. This calculator divides your annual kWh by your location's average sun hours and a system-loss factor to get the DC array size, then converts that into a panel count using the wattage you're quoting. It accounts for inverter and wiring losses (typically 14-18%) and lets you target less than 100% offset if your utility's net-metering rules make overproduction pointless. Real installers use this same math — PVWatts-style production estimate — before ever climbing on a roof. The output includes roof area needed assuming standard 18 sq ft panels, so you can sanity-check against your actual roof before requesting quotes.",
  "formula": "DC size (kW) = annual kWh ÷ (sun hours/day × 365 × (1 − system loss)); panel count = DC size × 1000 ÷ panel watts.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=solar-array-sizing",
  "inputs": [
    {
      "id": "annualKwh",
      "label": "Annual electricity usage",
      "kind": "number",
      "hint": null,
      "default": 11000,
      "unit": "kWh",
      "min": 500,
      "max": null
    },
    {
      "id": "sunHours",
      "label": "Peak sun hours per day",
      "kind": "number",
      "hint": null,
      "default": 5,
      "unit": "hrs",
      "min": 2,
      "max": 7
    },
    {
      "id": "systemLoss",
      "label": "System loss factor",
      "kind": "number",
      "hint": null,
      "default": 16,
      "unit": "%",
      "min": 5,
      "max": 30
    },
    {
      "id": "panelWatts",
      "label": "Panel wattage",
      "kind": "number",
      "hint": null,
      "default": 400,
      "unit": "W",
      "min": 200,
      "max": 600
    },
    {
      "id": "offsetTarget",
      "label": "Target usage offset",
      "kind": "number",
      "hint": null,
      "default": 100,
      "unit": "%",
      "min": 50,
      "max": 150
    }
  ],
  "outputs": [
    {
      "id": "dcKw",
      "label": "Recommended array size",
      "format": "decimal",
      "hint": null,
      "primary": true
    },
    {
      "id": "panels",
      "label": "Panel count",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "roofArea",
      "label": "Roof area needed",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "annualProd",
      "label": "Estimated annual production",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Annual electricity usage: 11000 kWh",
      "Peak sun hours per day: 5 hrs",
      "System loss factor: 16 %",
      "Panel wattage: 400 W",
      "Target usage offset: 100 %"
    ],
    "outputs": [
      "Recommended array size: 7.18",
      "Panel count: 18",
      "Roof area needed: 324",
      "Estimated annual production: 11,000"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter annual electricity usage (kWh).",
      "Enter peak sun hours per day (hrs).",
      "Enter system loss factor (%).",
      "Enter panel wattage (W).",
      "Enter target usage offset (%).",
      "Read your recommended array size 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": {
        "annualKwh": 6600,
        "sunHours": 3,
        "systemLoss": 10,
        "panelWatts": 240,
        "offsetTarget": 60
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "annualKwh": 11000,
        "sunHours": 5,
        "systemLoss": 16,
        "panelWatts": 400,
        "offsetTarget": 100
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "annualKwh": 17600,
        "sunHours": 7,
        "systemLoss": 26,
        "panelWatts": 600,
        "offsetTarget": 150
      }
    }
  ],
  "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": "Why not just size for 100% offset?",
      "a": "Most utilities only credit excess production at wholesale or avoided-cost rates, sometimes near zero. If your net-metering agreement doesn't bank kWh at retail value, oversizing past 100-110% offset wastes capital on panels that pay back slowly. Check your utility's interconnection rules before targeting more than full offset."
    },
    {
      "q": "What sun-hour number should I use?",
      "a": "Look up your city's PVWatts average or NREL solar resource map. Arizona and the Southwest run 6-6.5 hours; the Pacific Northwest and Northeast run 3.5-4.5. Using a national average of 5 will over- or under-size your system by 20-30% depending on where you live."
    },
    {
      "q": "Does panel orientation change this number?",
      "a": "Yes — this calculator assumes a reasonably good south-facing roof. East/west splits or steep tilt mismatches cut production 10-20%, which you should fold into your sun-hours input or check with the roof-orientation derate tool."
    },
    {
      "q": "How much does system loss really vary?",
      "a": "16% is a solid default covering inverter conversion (2-3%), wiring (2%), soiling (2%), shading (varies), and temperature derate (3-8% in hot climates). Microinverters and shade-heavy roofs push this toward 20-25%."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/solar-payback-itc",
    "https://www.revenuelab.fyi/toolbox/roof-orientation-derate",
    "https://www.revenuelab.fyi/toolbox/panel-degradation-25yr"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Solar Array Sizing Calculator (https://www.revenuelab.fyi/toolbox/solar-array-sizing)"
}