Home Battery Dynamic Tariff: Savings and Payback After 2027

The year contains 8,760 hourly energy balances in fixed CET. NOAA solar-position equations give solar direction. Haurwitz clear-sky GHI is modulated by an author-defined weather pattern and normalized to annual horizontal irradiation. Erbs decomposition, isotropic sky and ground reflection give tilted-plane irradiance. PVWatts uses −0.004/K, a 45 °C NOCT cell-temperature approximation, 14% aggregate system losses and AC clipping. Published pvlib examples independently test the PV functions.

For hourly household energy $L$, PV energy $S$, battery AC energy $a$ (positive charging) and usable stored energy $E$:

Both one-way efficiencies equal $\sqrt{\eta_{rt}}$. The Bellman recursion minimizes

Capacity, AC power and charging/export permissions constrain every action. Each daily problem covers 36 hours; execute its first 24 hours and carry SOC forward. Initial usable energy and terminal credit are zero. Reserved energy is untouched.

SOC value functions and executed policies use linear interpolation. Controls include SOC-grid destinations, exact power/energy limits and zero grid exchange. Convex Bellman searches use derivative bisection; nonconvex prices require enumeration. Simultaneous charge/discharge and simultaneous metered import/export are forbidden.

Selection compares complete annual bills plus cycling wear for the daily price dispatch, greedy self-consumption and idle policies. Bills include actual monthly settlement and the annual fee only if exports exceed numerical tolerance. When self-consumption can absorb all surplus, an extra zero-export Bellman policy is evaluated: backward reachable SOC bounds reserve enough space for future surplus, and SOC grids follow those bounds. This family competes against export-enabled dispatch after fees. In floor-active months a second marginal-price candidate treats gross compensation as zero; final billing always applies the complete monthly rule. This candidate comparison is not a year-wide mixed-integer optimum.

Import prices are $(p_{spot}+f_{purchase}+t_{energy})(1+0.21)$. Wholesale prices, the purchase fee and energy tax exclude VAT. Household gross export compensation assumes KOR exemption; entered export charges include VAT. The protected contract uses $\max(p_{spot},0.5(p_{spot}+f_{purchase}))$, floors each monthly gross credit at zero and bills charges separately. Spot and fixed modes omit this protection.

Equivalent cycles are discharged DC energy divided by usable capacity. Year-$y$ cash flow is first-year bill saving times $(1-f)^{y-1}$ less operating cost. NPV discounts these flows and subtracts investment. Wear affects dispatch and economic saving; it is not a second cash expense in NPV.

Defaults represent 4.5 kW PV, 3,500 kWh/year household demand, 10 kWh nominal storage with 10% reserve, 5 kW AC power and 90% round-trip efficiency. Weather, prices and occupancy are editable synthetic scenarios, not observations or a 2027 forecast. They share a short deterministic weather cycle without a calibrated joint probability model.

The protected default uses DELTA's February 2026 terms for 2027–2029; illustrative supplier purchase and export fees are not a quotation. Energy tax is the September 2026 budget baseline of €0.088/kWh excluding VAT. All purchase components receive 21% VAT. Investment, operating and wear costs are household cash amounts including irrecoverable VAT. Gross export compensation receives no added VAT under the assumed KOR exemption.

Self-consumption charges only from PV surplus and discharges into household deficit. Battery export is disabled in the protected PV mode. There is no curtailment, standby load, self-discharge, battery-temperature model, backup scheduling or replacement. Capacity is constant during the operating year; revenue decline affects cash flow only.

The historical saldering row is an illustrative annual flat-rate benchmark with its own import and surplus rates and a fixed assumed €0.02/kWh historical feed-in charge. Common grid/subscription charges and household tax credits are omitted from every case because they cancel in battery savings.

Rules snapshot: 2 November 2026. Net metering ends on 1 January 2027. The protected default implements one documented supplier settlement, not all Dutch contracts; use the actual fees and contract. The minimum-compensation requirement expires in 2030. Payback and NPV extrapolate the selected first-year settlement with an editable revenue decline: they are constant-contract sensitivities, not forecasts of post-2029 law, prices or revenue.

Daily planning assumes perfect hourly forecasts with 12 hours of next-day lookahead. Annual fee activation and monthly compensation are evaluated exactly for each feasible candidate, but finite-grid daily planning and candidate selection do not establish a global annual optimum. Charges may make the net export proceeds negative even when gross compensation is protected. Tiered feed-in fees are represented by an entered marginal fee and one export-activation fee.

The default uses 10 usable-energy intervals and runs near three seconds. Fee-avoidance or floor-active scenarios require extra year-long policies; they use 40% of the requested intervals, rounded up, with a minimum of four, to retain the complete dispatch and settlement physics within a similar runtime. The executed interval count is shown in the calculation. This coarser grid can move close cost rankings: in the fixed-fee regression four intervals raise the bill by about 0.5% relative to ten. Increase the requested grid to resolve close choices, accepting longer runs. Default annual bill saving changes by less than 1% at twice the grid; the convergence check verifies this case only. Extreme negative prices require slower exhaustive transition searches.

EPEX quarter-hour products, DST and intrahour arbitrage are not resolved. There is no live price connection. Power/price staircases apply over their integer-hour intervals; animated SOC varies linearly within each hour. Final stored energy is included in conservation and has no cash credit.

Simple payback uses constant first-year net cash. The assessment-life verdict also allows declining revenue. Unrecovered payback is left blank in the comparison table. NPV excludes financing, replacement, residual value and uncontracted trading income. Installation work belongs to a qualified person.