Cost & payback

V2L affordability calculator

The saving is not the cheap rate minus the day rate — it is the cheap rate after round-trip losses, battery wear and equipment cost, and only if your car and charger can follow the schedule. Model the economics before you spend; a competent person still designs and tests any fixed-wiring V2L work.

New to this? See how V2L load-shifting works — the method and the formulas →
Wondering if a home battery would beat your EV? See the comparison →

What this quick check is — and isn't

This triages whether the detailed economics are worth modelling for your setup — it is the first step, not the saving figure itself. Losses, battery wear and equipment cost still decide the real payback, and a competent person designs and tests any fixed-wiring arrangement to BS 7671. The full calculator, with your tariff, car, charger and losses, follows.

Detailed calculator

Model the economics for your setup

Every figure below is editable and starts from a worked example — replace them with your own. Results recompute live as you type, and nothing you enter leaves your browser.

1. Your tariff

Enter your import rates and the cheap (whole-home) window. The cheap window is fixed by your tariff — charging more slowly does not lengthen it.

These are example figures from the V2L Workshop worked example — replace them with your own tariff’s current rates. They are not a live or quoted price.

Supplier preset

Pick a sourced preset, or enter rates manually below.

Cheap-window rate (p/kWh)

Peak / day rate (p/kWh)

Cheap window starts (hour, 0–24)

e.g. 23.5 = 23:30

Cheap window ends (hour, 0–24)

e.g. 5.5 = 05:30 (may wrap past midnight)

Standing charge (p/day)

Informational in v1 — a single-tariff comparison cancels the standing-charge difference.

Optional — connect Octopus for live public rates

Manual entry above stays the default and is all you need. Octopus is the only supplier currently integrated here — every other supplier stays manual or preset. This reads Octopus’s current published unit rates for your product and region (no account, login or API key) and fills the off-peak rate, peak rate and cheap window above, which you can still edit.

Octopus product

Your electricity grid region

Sets which regional unit rate is fetched. Not sure? It is usually your distribution area, not your supplier.

2. Your car & charger

Example values for a typical ~60 kWh EV — adjust to your car. V2L runs from the end of your cheap window through the expensive hours while the car's home; the calculator works out how much to bank from your essential load and driving reserve. 'Unknown' is a valid answer for the charger; the model flags what it cannot assume.

EV preset

Pick a researched EV, or enter values manually.

Usable battery capacity (kWh)

V2L output power (kW)

2.2–3.6 kW serves a small base load only — not a shower, oven or hob.

On-board AC charger max (kW)

EV's own minimum charge rate (kW)

Some EVs refuse below ~1.4 kW — a hard floor on the slow-charge plan, independent of the charger.

Driving reserve kept in the car (kWh)

Energy ring-fenced for tomorrow's journey — caps how much V2L can bank.

Daily driving energy (kWh/day)

Charger preset

Pick a researched charger, or enter values manually.

Charger max output (kW)

Charger minimum charge rate (kW)

Tick 'I know this' below — otherwise it's treated as unknown and flagged.

I know my charger's minimum charge rate

Leave unticked if you're not sure — the model will say the optimal slow-charge rate depends on it, rather than assuming a figure.

Can the charger spread the charge across the whole cheap window?

YesNoDon't know

How do you hold the car?

OwnedPCP / financeLeased

When is the car home? (optional log)

Log the days and daytime/evening hours the car is home and plugged in. The model uses only the hours it's home on EVERY logged day (the safe overlap), and scales the saving by how many days a week that is. Leave empty to assume it's always home. Stored only in this browser.

No days logged — the model assumes the car is home and dispatchable every day.

3. Your essential loads

A small essential-loads board — fridge, freezer, router, lights. Heating, immersion, kettle, oven, tumble dryer and heat pumps do NOT belong on a V2L board.

What would V2L power?

A small essential-loads boardA single applianceThe whole house

Average essential load (W)

Continuous base load — ~300 W is typical for fridge + freezer + router + lights.

Hours per day (h)

Share of that load in peak hours (fraction 0–1)

The fraction of the day's essential energy that falls in the expensive window — what V2L can displace.

4. Installation cost

Raw equipment prices only — labour, inspection, testing, certification and any DNO/export work are extra and need a competent-person quote.

Decision-support estimate — not a shopping list

Home-battery, second-hand-battery and any V2L install capex is a decision-support estimate, not a DIY shopping list. Notifiable electrical work must be designed, installed and tested by a competent person to the current edition of BS 7671.

V2L kit cost (£)

Interlocked changeover, control/timer, protection, essential-loads board, adapter, cable — raw product.

Standalone home battery cost (£)

Module, hybrid inverter, EPS gateway, isolators — raw product.

Home battery usable capacity (kWh)

Home battery inverter power (kW)

Tick 'I know this' below — otherwise the model uses a ~0.33C assumption and says so.

Second-hand battery cost (£)

Budget/repurposed bank — safety & warranty risk; competent-person install only.

Second-hand battery usable capacity (kWh)

I know my home battery's inverter power

Home battery has 0% UK VAT (domestic storage)

0% VAT on domestic battery storage has applied since 1 February 2024 — verify it is still current.

5. Losses & wear

These are editable assumptions, not hidden constants. Round-trip losses and battery wear are what turn an attractive spread into a modest real saving.

Derived EV battery wear ≈ 8.9p/kWhdelivered — often a third or more of a typical peak-to-cheap spread. This is the figure rosy “V2L saves £X” claims leave out.

V2L round-trip efficiency (0–1)

~0.80: what you put into the car is not what you get back out.

Home-battery round-trip efficiency (0–1)

~0.90.

Second-hand battery round-trip efficiency (0–1)

~0.85.

Charge-side efficiency (0–1)

~0.92 — used to size the cheap-window charge target.

EV battery replacement cost (£)

EV battery lifetime throughput (kWh)

e.g. ~1,500 cycles × 60 kWh ≈ 90,000 kWh.

Home-battery lifetime throughput (kWh)

Second-hand battery lifetime throughput (kWh)

Shorter, no-warranty life — so a used pack is not flattered by a new battery's figure.

Battery standby / parasitic draw (W)

Continuous inverter/keep-alive draw, valued at the day's average rate.

Winter capacity/output factor (0–1)

1.0 = no derating. Cold cuts both EV capacity and V2L output — the season you most want backup.

EV minimum-SOC cutoff (%)

0 = no cutoff. The SOC at which the car stops V2L — caps the usable bank.

Horizon (years)

Discount rate (%/yr)

HMT Green Book ≈ 3.5% — the time value of money for the multi-year net.

Electricity price inflation (%/yr)

Your home & solar

Whole-home use sets the bill the comparison works against. Solar is optional — leave at 0 if you have none.

Whole-home daily use (kWh/day)

Rough daily electricity use for the whole house — not just the essential board.

Share of home use in peak hours (0–1)

Solar freed to export on V2L (kWh/day)

PV you would export while the house runs on V2L. 0 if you have no solar.

Export (SEG) rate (p/kWh)

Only credited where it beats the all-in V2L cost (charge loss + wear).

6. Results

Best net result over the horizon: Smart cheap-rate charging only (no discharge). Confidence: Medium

Strategy	Status	Annual saving	Payback	Net over horizon
Do nothing (pay standard rate)	Computed	£0	—	£0
V2L load-shifting (EV → essential board)	Computed	£102	≈ 5 months	£812
Standalone home battery	Computed	£197	20.3 years	-£2,360
Smart cheap-rate charging only (no discharge) Best net	Computed	£584	No upfront cost	£4,857
Second-hand / budget battery bank	Computed	£175	8.6 years	-£42

What would change the answer: below a peak-to-cheap spread of about 12.5p per kWh, V2L load-shifting cannot pay back here — after round-trip losses, wear and kit cost.

Net is over a 10-year horizon, after capex, discounted to today. The winner is chosen on net £, not on payback — a cheap kit that pays back fast can still net less than a battery that pays back slowly.

What the model is telling you

V2L load-shifting (EV → essential board)

Charger minimum charge rate unknown — the optimal slow-charge rate and finish time depend on it.
Whether this charger can spread the charge across the whole window is unknown — the slow-charge benefit and the optimal rate depend on it.

Standalone home battery

Inverter power is an assumed ~0.33C default (no sourced figure) — edit it if your battery's inverter kW differs.

Second-hand / budget battery bank

Inverter power is an assumed ~0.33C default (no sourced figure) — edit it if your battery's inverter kW differs.

What change pays? — total annual cost

Each option on your current tariff, compared on whole-home annual cost (import + driving − export − saving + amortised kit). Lower is better; the cheapest is starred.

Setup	What's on	Total annual cost	vs do nothing
Run your essentials off the EV (V2L) Cheapest	V2L, cheap-rate tariff	£851	saves £98
Do nothing (your current tariff)	cheap-rate tariff	£949	—
Install a home battery	home battery, cheap-rate tariff	£1,152	costs £203 more

Martin — Qualified UK electrician; BEng Mechanical Engineering; qualified vehicle mechanic.

Last reviewed: 16 June 2026
Written against: BS 7671:2018 + A4:2026

General information, not project-specific design advice. Standards are cited by reference only and never reproduced. How we source this.

V2L affordability calculator

Could V2L load-shifting pay back here?

Model the economics for your setup

6. Results

What the model is telling you

What change pays? — total annual cost