Battery Arbitrage Sizing Tool

Charge on the cheap night tariff, discharge into the expensive day tariff to offset import (self-consumption, no export). Drag the two price sliders to model tariff renegotiation — every number recomputes live. Compares A: arbitrage-optimal (energy-led, max-NPV sizing) against B: traditional peak×1.1 (power-led spec) for both real load profiles.
Method & assumptions

Capex = nameplate kWh × pack €/kWh × FX + install + EMS (install £20k & EMS £5k are fixed, so they weigh more on small batteries).

Net saving per delivered kWh = day − night/η. Break-even day price = night/η — below it arbitrage loses money (shown red).

A (energy-led): sweep nameplate, pick max 15-yr NPV. Discharge capped at each day's own day-window load (no export); weekend under-load lowers cycles.

B (peak×1.1): inverter = peak demand×1.1; energy = worst-day day-window load×1.1. Robust peak-shaving spec, but oversized for arbitrage → idle capacity.

Day window = 07–23h (17.5p target); night charge window = 00–07h (7h). Pack-level capex — real installed cost is higher; raise “Pack €/kWh” to test. No degradation/O&M.