Vehicle-to-Home (V2H) – What does your EV bring to your home?
Calculate in seconds: Backup duration, effective kWh costs, annual savings, payback period, and CO₂ impact.
⚙️ Advanced Values (CO₂, Safety)
What is V2H? Vehicle-to-Home means that your electric car can supply power back to the house via a suitable bidirectional inverter. In practice, this is often used in two scenarios: (1) Emergency Power/Backup during a power failure and (2) Self-consumption & Load Shifting, where you store cheap (or PV) electricity and replace expensive household electricity later. This calculator provides a clear, quick orientation – without technical jargon.
How is it calculated? The usable energy is crucial: Battery capacity × usable percentage range minus reserve buffer. This results in the energy you could theoretically withdraw. Because losses occur during charging and discharging, the Round-Trip Efficiency is also considered. For the backup duration, this available energy is divided by the critical house load (kW). Important: The house load must also be below the inverter power – otherwise the system may limit or shut down.
Added Value Note: The biggest "Aha moment" with V2H is usually not the maximum capacity, but the question: How many kWh per day do I really use? Many households shift around 3–10 kWh/day (dishwasher, hot water, cooking, IT, base load). This is exactly what the "Planned V2H Energy per Day" field is for: it turns a technical idea into a practical everyday calculation.
FAQ 1: Do I need a specific EV for V2H?
Yes. V2H requires a vehicle that supports bidirectional charging, plus suitable equipment (e.g., a bidirectional DC charger or compatible solution). Some cars only do V2L (socket on the car), others V2H/V2G. This calculator is deliberately manufacturer-neutral and helps you classify the benefit roughly – regardless of the model.
FAQ 2: Why is there a "Usable Range" and "Reserve"?
In practice, one does not use 0–100% of the battery for the house. Many leave a buffer so the car remains mobile and the battery is protected. The percentage value is your planned working window, and the reserve is an additional fixed "please do not touch" block. This gives you a more realistic backup estimation.
FAQ 3: What does Round-Trip Efficiency mean?
When charging, energy is converted into chemical energy, and when discharging, it is converted back – losses occur in the process. 85% means: of 10 kWh of charging, approximately 8.5 kWh end up in the house. This affects both the effective kWh costs and the CO₂ balance.
FAQ 4: PV Surplus or Grid Power – what is "cheaper"?
In PV mode, the calculator uses the lost feed-in tariff as "costs": if you do not feed in 1 kWh, you waive this amount. In grid mode, you use the specified charging electricity price. This results in the effective delivered kWh cost calculation including losses.
FAQ 5: How realistic are savings & payback?
Good as an orientation – but not as a guarantee. Whether V2H is worth it depends heavily on how many kWh you really shift, how large the price difference is, what hardware you need, and how often you use the system. The calculator shows you: In your daily life and at these prices, it could "work out" after X years.
FAQ 6: Can V2H supply my whole house?
Technically often only partially. Many systems are intended more for "critical consumers": refrigerator, light, router, heating pump, a few sockets. High loads (stove, instantaneous water heater, large heat pumps) can overwhelm the inverter. That's why the calculator asks for inverter power and "critical household load".
FAQ 7: Why is CO₂ sometimes negative or near zero?
If you charge with grid power and replace grid power later, the CO₂ effect is low or even negative depending on the factors (due to losses). In PV mode, V2H can save CO₂ because you use more solar power yourself and need to draw less grid power. Adjust the CO₂ factors to your situation.
Important: This calculator does not replace electrical planning, network operator approvals, or standard testing. It is a marketing-focused, understandable utility calculator for visitors – which is exactly what it was made for.
V2H Calculation: 6 Results Explained
V2H (Vehicle-to-Home) uses your EV battery as a home energy source. The calculator computes six output metrics live from your inputs:
Available Energy (kWh)
Battery Capacity × Usable % − Reserve Buffer. This is the real energy available for your home before efficiency losses.
Backup Duration
Available Energy (kWh) ÷ Critical Household Load (kW). How many hours/days the battery powers your essential appliances (fridge, lights, router).
Effective Cost/kWh
In PV mode: opportunity cost = lost feed-in tariff. In Grid mode: charging price ÷ round-trip efficiency. Shows true cost of V2H energy vs. buying from grid.
Annual Savings
Daily V2H Energy (kWh) × 365 × (Household Price − Effective Cost). How much you save per year by using V2H instead of buying from the grid.
Payback Period
Setup Investment Cost ÷ Annual Savings. How many years until the V2H hardware pays for itself through energy savings.
CO₂ Effect
Daily kWh × 365 × (CO₂ Grid Factor − CO₂ Charge Factor). Negative = CO₂ saved vs. grid (especially when charging from PV).
PV Surplus Mode vs. Grid Mode
The charging mode toggle fundamentally changes how the calculator values the energy you use from your EV:
| Aspect | ☀️ PV Surplus Mode | 🔌 Grid Power Mode |
|---|---|---|
| Charging source | Excess solar energy that would otherwise be fed to grid | Electricity bought from the grid (ideally at night tariff) |
| Effective cost used | Lost feed-in tariff ($/kWh) ÷ efficiency | Charging price ($/kWh) ÷ efficiency |
| Typical effective cost (DE) | 0.09–0.13 €/kWh | 0.20–0.35 €/kWh |
| CO₂ factor for charging | 0 g/kWh (set manually) | Grid mix (default 350 g/kWh) |
| Savings potential | High (low charge cost vs. 0.30–0.40 €/kWh grid price) | Moderate (depends on tariff spread) |
| Best for | Households with PV system and EV parked at home during day | Night-tariff users, shift workers, no PV |
PV Surplus mode almost always shows higher savings and better CO₂ impact. Set CO₂ factor for charging to 0 in Advanced Values when using PV-charged V2H for accurate emission calculations.
How to Plan Your Backup Setup
The backup duration result is only useful if your household load estimate is realistic. Here is a guide to typical critical load figures:
| What runs in "critical mode" | Approx. Load | Duration from 40 kWh |
|---|---|---|
| Fridge + router + LED lighting | 0.3–0.5 kW | 80–133 hours |
| + Freezer + laptop + TV | 0.7–1.0 kW | 40–57 hours |
| + Small heating appliance | 1.2–2.0 kW | 20–33 hours |
| Normal household (no heat pump) | 2.0–3.5 kW | 11–20 hours |
| With heat pump or EV charging | 5–11 kW | 4–8 hours |
For realistic blackout backup, enter only the "critical mode" load — the minimum appliances you need running. Enter the V2H inverter power to see the inverter limit bar; if household load exceeds inverter kW, some appliances will not run simultaneously.
Frequently Asked Questions
What is the "Reserve Buffer" in advanced settings?
The reserve buffer (default 3 kWh) is the amount of battery charge the calculator sets aside and does not count as available V2H energy. This represents the minimum charge you want to keep in the battery for driving — similar to how you would not drain a tank completely. Increase it if you need guaranteed driving range after a V2H session. The available energy for your home = (Capacity × Usable%) − Reserve.
What is Round-Trip Efficiency and why does it matter?
Round-trip efficiency (RTE) is the ratio of energy out vs. energy in across the full charge-discharge cycle. If RTE is 85%, you need to charge 1/0.85 = 1.18 kWh to deliver 1 kWh to your home. This loss increases the effective cost per kWh. Typical V2H systems achieve 80–92% RTE. Lower values (60–75%) indicate older hardware or very slow/fast charge rates. The default of 85% is a reasonable middle estimate.
Does V2H work during a power outage?
It depends on your setup. Standard grid-tied V2H systems switch off automatically during a grid outage for safety (anti-islanding protection). To power your home during a blackout, you need an "island-capable" inverter and a transfer switch (Notstromfähigkeit). This requires a more specialized installation. If blackout resilience is your primary goal, confirm with your installer that the system supports island mode operation.
Will V2H significantly degrade my EV battery?
Regular V2H usage does add battery cycles beyond driving. The impact depends on depth of discharge, temperature, and frequency. Studies from Nissan Leaf CHAdeMO V2H users in Japan suggest moderate degradation acceleration, though it remains manageable with sensible operating windows (40–80% SoC for daily V2H use). The calculator does not model degradation directly — use the reserve buffer and limit usable % to reduce cycle depth.
Embed this Calculator on Your Website
You can integrate this calculator for free into your own website. Get the embed code on our overview page.