Cost & payback
Your EV as the battery, or a static home battery?
Two ways to store cheap energy and spend it through the expensive hours: use the EV you already own as the battery — what V2L lets you do — or buy a dedicated home battery, what you would install. They answer the same question with very different money, effort and certainty. This page frames the decision; the calculator runs the numbers for your own tariff and vehicle.
Your EV as the battery (V2L)
You spend little — a changeover kit and an essential board, not a battery — because the expensive part, the battery, is the car you already own. The trade-off is availability and scope: the car must be home and charged through the peak hours, it powers a small essential board rather than the whole house, and every kWh you draw imposes wear on a traction battery that is costly to replace. It pays back fast when it pays back at all, but it cannot save on a day the car is away.
A static home battery
You spend a great deal upfront — typically several thousand pounds installed — for a unit that is always home, fully automatic, and sized to cover more than a handful of essential circuits. Because it is not tied to your driving, it captures the cheap-rate saving every day, and its warranty throughput is designed for daily cycling. It pays back slowly, but over a long horizon it can net more than a cheap V2L kit precisely because it never misses a day.
Payback is the wrong test — net cost over the horizon is the right one
A £40 V2L kit that pays back in months can still net less over ten years than a £4,000 battery that pays back in years, because the battery saves on far more days and far more load. The calculator therefore ranks the options on net £ over your chosen horizon (optionally discounted), not on which pays back first — and it shows the payback too, so you see both.
Where each one wins
V2L tends to win when the car is reliably home through the peak hours, the kit cost is low, and you only need to cover essentials. A static battery tends to win when the car is often away, when you want whole-of-evening cover without manual transfer, or when your horizon is long enough for daily saving to overtake the higher upfront cost. Many households sit between the two — which is what the comparison table on the tool is for.
Both routes are notifiable electrical work
Both routes involve fixed electrical work that is notifiable and must be designed, installed and tested by a competent person to the current edition of BS 7671 — a V2L changeover arrangement and a battery installation alike. This page compares the economics and the trade-offs; it is not an instruction to carry out either installation.
Run both options on your own numbers →
New to this? See how V2L load-shifting works →
References & sources (5)
- Octopus Energy — Intelligent Octopus Go — The cheap whole-home window structure (e.g. 23:30–05:30, whole-home; smart slots car-only). Rates are volatile — verify the current p/kWh.
- Octopus Energy — REST API (products & unit rates) — Public, unauthenticated tariff and half-hourly (Agile) unit rates — the source behind this page's optional “Connect Octopus for live rates” button. Octopus is the only supplier currently verified and integrated here; every other supplier stays manual or preset.
- Ofgem — energy price cap — Regional unit rates and standing charges that bound a standard-rate baseline.
- GOV.UK — Electric vehicle smart charge point regulations — Default-off charging schedules and the randomised start delay that can disrupt a fixed-window plan.
- myenergi — Zappi ECO/ECO+ charge rates — An example of a charger's minimum controllable charge current — confirm your own model against its manufacturer help page, never a forum.
- Last reviewed
- 18 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.