Chapter 10 – Full Household Scenarios

This chapter walks through four representative household configurations, applying all tools from previous chapters. Each scenario includes consumption breakdown, system sizing, financial results, and commentary on the key trade-offs.

Scenario 1: Mild Climate, No Electric Heating

Household: 3 persons, 90 m² apartment/small house, Lyon, France Heating: Gas boiler. Hot water: HPWH (250L). Annual consumption: 4,200 kWh/year

Consumption Breakdown

Category kWh/yr % of total
Kitchen (fridge, cooking, dishwasher) 950 23%
Laundry (washer + dryer) 380 9%
Hot water (HPWH) 700 17%
Computers + entertainment 550 13%
Lighting 250 6%
Standby + misc 370 9%
Total 4,200 100%
Component Specification Cost (installed)
Solar PV 3.8 kWp (9 × 420 Wp), south roof €5,500–6,500
Hybrid inverter 3.6 kW Included
Battery 7.5 kWh LFP €3,500–4,500
Total   €9,000–11,000

Annual Performance

Metric Value
Solar production 4,370 kWh/yr
Self-consumed directly 2,100 kWh/yr
Battery charge/discharge 1,050 kWh/yr
Grid export 1,220 kWh/yr
Grid import 1,050 kWh/yr
Self-sufficiency ratio 75%
Annual grid savings €704/yr (at €0.22/kWh)
Payback period 13–16 years

Key Insight

The HPWH is programmed to run 11:00–14:00 (solar peak), consuming ~200 kWh/yr of solar that would otherwise be exported. Without this load shifting, solar self-consumption drops ~5 percentage points. The battery handles the evening 18:00–23:00 gap.

Scenario 2: Cold Climate, Heat Pump Heating

Household: 4 persons, 140 m² house, Paris, France Heating: Air-source heat pump (COP 3.0 seasonal average). Hot water: HPWH. Annual consumption: 9,500 kWh/year

Consumption Breakdown

Category kWh/yr % of total
Kitchen 1,100 12%
Laundry 450 5%
Hot water (HPWH) 800 8%
Computers + entertainment 700 7%
Lighting 350 4%
Standby + misc 400 4%
Space heating (heat pump) 5,700 60%
Total 9,500 100%
Component Specification Cost (installed)
Solar PV 6 kWp (14 × 430 Wp), south roof €9,000–11,000
Hybrid inverter 6 kW Included
Battery 10 kWh LFP €4,500–5,500
Total   €13,500–16,500

Annual Performance

Metric Value
Solar production 6,240 kWh/yr
Self-consumed directly 2,800 kWh/yr
Battery charge/discharge 1,500 kWh/yr
Grid export 1,940 kWh/yr
Grid import 5,200 kWh/yr
Self-sufficiency ratio 45%
Annual grid savings €880/yr
Payback period 15–19 years

Monthly Energy Balance

Month Solar (kWh) Load (kWh) Grid import Self-use
Jan 200 1,300 1,180 120
Feb 285 1,100 910 190
Mar 495 950 590 360
Apr 570 650 250 400
May 665 480 50 430
Jun 715 380 0 380
Jul 735 360 0 360
Aug 685 380 0 380
Sep 540 520 70 450
Oct 360 800 530 270
Nov 220 1,050 880 170
Dec 170 1,530 1,390 140
Total 5,640 9,500 5,850 3,650

Key Insight

With a heat pump, solar covers loads well in spring/summer/autumn but cannot compensate for winter heating demand (Jan, Feb, Nov, Dec account for 4,730 kWh or 50% of annual consumption but receive only 875 kWh of solar, 15% of production). The battery adds ~15% SSR; most of the system value is in the non-heating months.

Scenario 3: All-Electric House with EV Charging

Household: 4 persons, 160 m² house, Lyon, France Heating: Air-source heat pump. Hot water: HPWH. Transport: 1 EV (15,000 km/year, ~2,500 kWh charging at home). Annual consumption: 12,500 kWh/year

Consumption Breakdown

Category kWh/yr % of total
Kitchen + laundry 1,550 12%
Hot water (HPWH) 900 7%
Computers + entertainment + lighting 900 7%
Standby + misc 450 4%
Space heating (heat pump) 6,200 50%
EV charging 2,500 20%
Total 12,500 100%
Component Specification Cost (installed)
Solar PV 9 kWp (21 × 430 Wp) €13,000–16,000
Hybrid inverter 8 kW Included
Battery 15 kWh LFP €6,500–8,000
Smart EV charger (OCPP) 7.4 kW AC €800–1,200
Total   €20,300–25,200

Annual Performance

Metric Value
Solar production 10,350 kWh/yr
Self-sufficiency ratio 55%
Annual grid savings €1,540/yr
EV charging from solar ~1,100 kWh/yr (44% of EV needs)
Payback period 13–16 years

EV Charging Strategy

The EV charger is configured to:

  1. Prioritize solar excess charging (11:00–16:00, when car is often plugged in at home)
  2. Charge from grid off-peak (22:00–06:00) when solar is insufficient
  3. Never charge at peak prices (17:00–21:00) unless battery SoC is critical

This smart charging strategy reduces EV charging cost by ~35% vs. uncontrolled charging.

Scenario 4: High Self-Sufficiency Target

Household: 2 persons, 110 m², rural location, South of France (Montpellier) Heating: Air-source heat pump. Hot water: Solar thermal + HPWH backup. Goal: >85% self-sufficiency. Grid connection maintained as backup. Annual consumption: 7,200 kWh/year

Consumption Breakdown

Category kWh/yr % of total
Kitchen + laundry 1,100 15%
Hot water (solar thermal + HPWH) 350 5%
Computing + entertainment 500 7%
Lighting + misc + standby 450 6%
Space heating (heat pump, mild climate) 4,800 67%
Total 7,200 100%
Component Specification Cost (installed)
Solar PV 12 kWp (28 × 430 Wp) €18,000–22,000
Hybrid inverter 10 kW Included
Battery 20 kWh LFP (2× 10 kWh) €10,000–13,000
Solar thermal collectors 4 m² flat plate + 250L tank €4,000–5,500
Total   €32,000–40,500

Annual Performance

Metric Value
Solar PV production 17,400 kWh/yr
Self-sufficiency ratio 87%
Annual grid import ~940 kWh/yr (mostly Jan–Feb)
Annual surplus export ~9,900 kWh/yr (mostly May–Aug)
Annual grid bill savings €1,580/yr
Export revenue (€0.08/kWh) €790/yr
Total annual benefit €2,370/yr
Payback period 14–17 years

Key Insight

Achieving >85% SSR requires a very large solar array — one that massively oversizes for summer. The 12 kWp system produces more than twice annual consumption in summer, most of which is exported at low value (€0.08/kWh vs €0.22/kWh self-consumption). The 20 kWh battery helps store daily surplus but cannot bridge multi-day cloudy periods in winter.

The remaining 13% grid dependence (940 kWh) is concentrated in 6–8 weeks in midwinter (late December through early February). Eliminating it would require an even larger PV+battery system or a backup generator — both economically questionable for a grid-connected home.

Practical lesson: Going from 75% to 90% SSR is significantly more expensive per additional percentage point than going from 40% to 75%. The “last 15%” is the most costly.

Cross-Scenario Comparison

Scenario Annual consumption System cost SSR Annual savings Simple payback
1: No heating, Lyon 4,200 kWh €10,000 75% €704 14 yr
2: Heat pump, Paris 9,500 kWh €15,000 45% €880 17 yr
3: All-electric + EV, Lyon 12,500 kWh €22,750 55% €1,540 15 yr
4: High SSR, South France 7,200 kWh €36,250 87% €2,370 15 yr

Payback periods of 13–19 years are within the 20–25 year useful life of the installations, especially as electricity prices continue rising. Every 1% annual electricity price increase reduces the payback period by ~0.5 years.

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