{
 "site": "https://batterypayback.co.uk",
 "generated": "2026-10-26",
 "status": "live",
 "note": "Synthetic households, not measurements. Expected results were worked out by hand and are checked against the model on every build.",
 "model_version": "2026-10-23 (monthly PVGIS profile, optional grid-charging power limit, optional load shifting without a battery)",
 "cases": [
  {
   "id": "no-solar-cheap-rate",
   "title": "No solar, cheap night rate",
   "inputs": {
    "verbruik_kwh_jaar": 3650,
    "aandeel_overdag": 0.4,
    "aandeel_goedkope_uren": 0,
    "opwek_kwh": 0,
    "accu_bruikbaar_kwh": 13.5,
    "rendement_rondgang": 0.9,
    "prijs_piek_p": 26.32,
    "prijs_goedkoop_p": 8,
    "seg_p": 0,
    "accu_prijs_gbp": 6500
   },
   "expected_saving_gbp": 381.74,
   "expected_payback_years": 17.0,
   "working": "Evening use 6 kWh a day fits in the battery. Each kWh saves 26.32p − 8p ÷ 0.9 = 17.43p. 6 × 365 × 17.43p = £381.74 a year. £6,500 ÷ £381.74 = 17.0 years."
  },
  {
   "id": "no-solar-flat-rate",
   "title": "No solar, one rate all day",
   "inputs": {
    "verbruik_kwh_jaar": 3650,
    "aandeel_overdag": 0.4,
    "aandeel_goedkope_uren": 0,
    "opwek_kwh": 0,
    "accu_bruikbaar_kwh": 13.5,
    "rendement_rondgang": 0.9,
    "prijs_piek_p": 26.32,
    "prijs_goedkoop_p": 26.32,
    "seg_p": 0,
    "accu_prijs_gbp": 6500
   },
   "expected_saving_gbp": 0,
   "expected_payback_years": null,
   "working": "No price gap and no solar: there is nothing to move, so the saving is £0 and the battery never pays back."
  },
  {
   "id": "solar-flat-rate-low-export",
   "title": "3,650 kWh solar, one rate, 4.5p export",
   "inputs": {
    "verbruik_kwh_jaar": 3650,
    "aandeel_overdag": 0.4,
    "aandeel_goedkope_uren": 0,
    "opwek_kwh": 3650,
    "accu_bruikbaar_kwh": 13.5,
    "rendement_rondgang": 0.9,
    "prijs_piek_p": 26.32,
    "prijs_goedkoop_p": 26.32,
    "seg_p": 4.5,
    "accu_prijs_gbp": 6500
   },
   "expected_saving_gbp": 420.22,
   "expected_payback_years": 15.5,
   "working": "10 kWh solar a day (spread evenly), 4 kWh used in daylight, 6 kWh spare. Stored 6 kWh gives 5.4 kWh in the evening. Saving a day: 5.4 × 26.32p − 6 × 4.5p lost export = £1.15. × 365 = £420.22 a year. £6,500 ÷ £420.22 = 15.5 years."
  },
  {
   "id": "solar-cheap-rate-low-export",
   "title": "3,650 kWh solar, 8p night rate, 4.5p export",
   "inputs": {
    "verbruik_kwh_jaar": 3650,
    "aandeel_overdag": 0.4,
    "aandeel_goedkope_uren": 0,
    "opwek_kwh": 3650,
    "accu_bruikbaar_kwh": 13.5,
    "rendement_rondgang": 0.9,
    "prijs_piek_p": 26.32,
    "prijs_goedkoop_p": 8,
    "seg_p": 4.5,
    "accu_prijs_gbp": 6500
   },
   "expected_saving_gbp": 458.39,
   "expected_payback_years": 14.2,
   "working": "As above, plus the last 0.6 kWh of evening use comes from the battery charged at night: 0.6 ÷ 0.9 × 8p = 5.33p a day. Without battery: 6 kWh × 26.32p − 6 kWh × 4.5p = £1.31 a day. With: £0.05. Saving £1.26 a day = £458.39 a year. £6,500 ÷ £458.39 = 14.2 years."
  }
 ]
}