grid-billing

Deterministic, regulation-aware German grid settlement engine — NNE, KA, MMM, MSB, and GeLi Gas AWH Sperrprozesse (PIDs 31001, 31002, 31005, 31006, 31009, 31011).

Regulatory ceilings and structure

KAV §2 — Konzessionsabgabe

The Höchstbeträge are checked on every settlement, and the position now cites the paragraph its group is actually capped under: §2 Abs. 2 for Tarifkunden and Schwachlast, Abs. 3 for Sondervertragskunden, Abs. 7 where the customer is freigestellt. Every position previously cited Abs. 2 regardless.

The rates themselves are undated because the statute has not changed them since the Euro conversion — the annual reductions people remember were the §3 transitional phase-down, which completed long ago.

MsbG §30 — Preisobergrenzen für den Messstellenbetrieb

§30 Abs. 3 (optionaler Einbau) is 30 € each, 60 € total. §30 Abs. 2 adds up to 50 € a year per party for a Steuereinrichtung.

The charge is annualised before comparison — billing a year in monthly instalments does not raise the cap. A charge above the ceiling raises MSB_ABOVE_MSBG_POG. This was previously unchecked: the MSB settlement validated only that the fee was non-negative, while the analogous KAV ceiling was checked.

§17 StromNEV — Netzebene and Benutzungsstundenzahl

Netzebene covers the seven levels, distinguishing network levels from transformation levels. It is recorded, not applied: Netzentgelte are published per level, so the level is what makes a rate checkable against a price sheet, but this crate is given rates rather than resolving them.

The same holds for the Benutzungsstundenzahl (annual energy ÷ annual peak). It does not appear in §17 as a threshold — it is the convention by which a price sheet publishes two rate pairs — so it goes into the trace rather than selecting anything. Zero peak yields None, not zero.

What is enforced is §17 Abs. 6: an Arbeitspreis-only tariff is permitted only in Niederspannung up to 100 000 kWh a year. Billing without a Leistungspreis outside that raises ARBEITSPREIS_ONLY_OUTSIDE_SECT17_ABS6.

§19 Abs. 2 StromNEV — individuelle Netzentgelte

Both forms are settled, with the statutory floors — which are in the ordinance text itself, not only in the BK4-22-089 methodology:

Sect19Vereinbarung carries the agreed fraction; the engine applies it as a reduction over the Arbeits- and Leistungspreis positions only — the Konzessionsabgabe and the levies are untouched, because the Netzbetreiber's lost revenue is recovered through the §19-Umlage billed separately. An agreement below the floor raises SECT19_BELOW_MINDESTENTGELT; a Satz 2 agreement whose utilisation data does not qualify raises SECT19_BANDLAST_CRITERIA_NOT_MET.

§18 StromNEV — Entgelte für dezentrale Erzeugung, under Abschmelzung

settle_dezentrale_einspeisung pays the plant operator the avoided upstream costs, at the factor Festlegung GBK-25-02-1#1 (17.02.2026) leaves standing:

The Tenor cuts in three steps (50 % from 01.07.2026, 50 % from 01.01.2027, 75 % from 01.01.2028) — the annual averages fall by 25 points a year, which is the decision's own cross-check. A period crossing a step is refused, not averaged; an EEG-funded plant is refused outright (§18 Abs. 1 Satz 4 Nr. 1 — the payment would be unlawful).

Gas — Druckstufen and Kapazitätsprodukte (§15 GasNEV)

Druckstufe (Hoch-/Mittel-/Niederdruck) is the gas analogue of the Strom Netzebene; GasKapazitaet bills a booked capacity at the price sheet's annual rate, pro-rated by calendar days, distinguishing feste from unterbrechbarer Kapazität — the latter cites §15 Abs. 5, and its discount stays where the ordinance leaves it: on the price sheet, not in this crate.

Invalid inputs are unrepresentable

NneInput used to be 28 fields with 14 Options. The cross-field rules lived in a validate_nne_input that the engine never called — so a caller who skipped it was billed on the wrong basis with no error. Those rules are now in the types:

The engine now enforces what the types cannot express — negative energy, empty or inverted Modul 3 intervals — and does it inside settle_nne, not in a validator a caller may forget.

validate_nne_input is gone. settle_nne is pure and cheap: run it and read warnings. The other three validators remain for inputs whose engines accept looser shapes.

Modul 3 no longer double-bills

The old cascade emitted the flat Arbeit position and then appended the Modul 3 interval positions, charging the same energy twice. Modul3Spotpreis replaces the flat position rather than adding to it.

Settlement, not invoice

The engine calculates what is owed and why. It does not know what the invoice looks like:

Input → Validation → Settlement Engine → SettlementResult → InvoiceDocument → BO4E → EDIFACT

SettlementResult carries the positions, totals, warnings, the applied RegulatoryRegime and a CalculationTrace per position. InvoiceDocument carries everything that is a property of the document — invoice number, issue and due dates, the Prüfidentifikator that routes it, the reference to what it supersedes — and is built by an adapter around a settlement.

The separation is what makes a settlement recomputable: the same period can be settled twice, for a correction or a dispute or an audit, and the two results compared, without inventing an invoice number each time. Previously the engine could not be run at all without one.

Position numbering follows the same rule. InvoiceDocument::numbered_positions() assigns 1-based numbers at rendering time; the engine no longer threads a counter through the calculation.

No BO4E inside the engine

SpotPriceFormula states the pricing formula behind a §14a Modul 3 rate as a value — reference, unit, method, steps. It used to be a serde_json::Value holding a hand-built BO4E LastvariablePreisposition, which kept the type dependency out while moving BO4E schema knowledge in, untyped and unvalidated. An adapter that needs the COM builds it from the value object. The crate has no serde_json dependency at all.

SettlementPeriod

A validated pair, not two loose dates. Every input struct used to carry period_from and period_to independently and every calculation re-checked their ordering — five copies of one guard, each able to be forgotten. Constructing SettlementPeriod is the check, so an inverted period is unrepresentable rather than rejected five times over.

Regulatory regime

German network-charge law is several timelines, each turning over on its own date:

RegulatoryRegime resolves those dates once, at the edge; every calculation then matches on an enum. Scattering if period_to <= date through the engine is how a rule change becomes a bug — each site has to be found and each has to agree. Adding the AgNeS turnover is a new variant the compiler forces every deciding site to handle.

The regime can also be supplied explicitly, so a historical settlement is reproduced under the rules that applied then rather than under today's calendar. A period crossing a turnover raises REGIME_TURNOVER_IN_PERIOD: different rules govern its start and its end, so it should be split rather than half-billed.

Explainability

Every position carries a CalculationTrace — the inputs used, the paragraphs applied, the tariff source, the reduction factor, the rounding. SettlementResult additionally exposes all_legal_refs(), deduplicated across positions.

These types are Serialize, and the service adapters emit them as BO4E ZusatzAttribute (mako:calculation_trace per position, mako:legal_references and mako:settlement_warnings per settlement). BO4E has no field for a calculation trace and inventing one would break the schema; a ZusatzAttribut is the sanctioned place for what a standard does not model.

This matters because the settlement value itself is dropped once the Rechnung is stored — the attribute is the only surviving record of why an amount is what it is, and it is what a §20 EnWG audit or an LF dispute is answered from.

Netzseitige Umlagen

Three levies ride on the network charge rather than the commodity, and a Strom NNE invoice carries all three:

Rates are set annually by the ÜNB and published by 25 October for the following year. They are held as a year-indexed series in umlagen so a correction reopening an earlier period bills it at the rate that applied then — a single configured scalar cannot express two years at once. NneInput carries a per-levy override for the cases an EnFG decision does not fit the published schedule.

Letztverbrauchergruppen (EnFG §§21 ff.)

The Energiefinanzierungsgesetz replaced the older per-levy privilege rules with one scheme. Letztverbrauchergruppe selects the band: A′ is the full levy and covers the first 1 GWh at an Entnahmestelle; B′ and C′ apply above that, C′ for energy-intensive undertakings; Befreit (§21 EnFG) is zero rather than reduced, and emits no line at all.

Only the §19 StromNEV-Umlage is published as an explicit A′/B′/C′ schedule. The other two publish the non-privileged rate, with privileges granted per Entnahmestelle — supply those through the override.

A year the series does not cover yields no rate rather than a neighbouring year's, and the levy is omitted with an UMLAGE_RATE_MISSING warning. Billing 2027 at the 2026 rate would be wrong by an amount nobody notices until the ÜNB reconciliation.

Regulatory baseline (2026)

StromNZV and GasNZV ceased to apply with the end of 31.12.2025 — Art. 15 Abs. 4 (Strom) and Abs. 6 (Gas) of the Gesetz v. 22.12.2023, BGBl. 2023 I Nr. 405. The successor competence is §20 Abs. 3 EnWG, exercised through BNetzA Festlegungen:

settle_mmm picks its legal references from period_to, so a settlement for a 2025 period still cites the ordinance that governed it and one for 2026 does not. LegalReference::citation appends "(außer Kraft seit 01.01.2026)" to a repealed ordinance, keeping archived invoices self-explanatory.

Konzessionsabgabe was never governed by StromNZV or GasNZV — it is KAV plus §48 EnWG. StromNZV §17 and GasNZV §7 do not say what they were long cited for.

Mehr-/Mindermengen sign convention

Both quantities are named from the network operator's side, which inverts the intuitive reading. GPKE Kap. 8.4 Nr. 3:

Unterschreitet die Summe der in einem Zeitraum ermittelten elektrischen Arbeit die Summe der Arbeit, die den bilanzierten Profilen zu Grunde gelegt wurde (ungewollte Mehrmenge), so vergütet der Netzbetreiber dem Lieferanten oder dem Kunden diese Differenzmenge.

GaBi Gas 2.1 states the same for gas: the Ausspeisenetzbetreiber nimmt Mehrmengen entgegen and liefert Mindermengen. Consuming below the profile leaves surplus energy the network absorbed — that surplus is the Mehrmenge, and it is reimbursed.

Konzessionsabgabe (KAV §2)

KaKundengruppe models the two orthogonal tests KAV actually applies: Tarifkunde vs Sondervertragskunde is a contract-type test, and Tarifkunden rates band on municipality inhabitants, not on annual consumption.

These are Höchstbeträge, so settle_nne emits KA_ABOVE_KAV_MAXIMUM when the agreed rate exceeds the ceiling for the group, and KA_CHARGED_WHILE_EXEMPT when a rate is applied to a §2 Abs. 7 exemption.

What this crate does

grid-billing computes BDEW INVOIC billing positions with full explainability:

• NNE Strom (PID 31001) — flat-rate Arbeit, Leistung (RLM), Konzessionsabgabe
• NNE Gas (PID 31005) — GasNEV §14 legal basis, auto-set when Sparte::Gas
• §14a Modul 2 ToU — mandatory HT/NT Arbeit split for controllable loads (BNetzA BK6-22-300)
• Selbst ausgestellte NNE (PID 31006) — LF runs the identical formula (§20 MessZV)
• MMM Strom (PID 31002) — Mehr-/Mindermengensaldo, GPKE (BK6-24-174) Teil 1 Kap. 8.4
• MMM Gas (PID 31002) — Gas imbalance, GaBi Gas 2.1 (BK7-24-01-008)
• MSB-Rechnung (PID 31009) — Grundgebühr Messstellenbetrieb + optional Messdienstleistung
• GeLi Gas AWH Sperrprozesse (PID 31011) — abrechnungswürdige Handlungen (BK7-24-01-009 §5.4)
• Reversal (Stornorechnung) — calculate_reversal() negates any prior settlement immutably

All calculations are pure functions — zero I/O, zero async, no side effects. All monetary arithmetic uses rust_decimal::Decimal via billing::EuroAmount — no f64 anywhere.

Architecture

Settlement flow

NneInput / MmmInput / MsbInput / GasAwhInput
        │
        ▼
validate_*_input()          ← optional pre-check: ValidationResult
        │
        ▼
settle_*()                  ← pure, deterministic, no I/O
        │
        ▼
SettlementResult {
  settlement_type, status, period, regime, sparte,
  malo_id, nb_mp_id, counterparty_mp_id,
  positions: Vec<SettlementPosition {
    text, kind,                   ← what was charged
    quantity, unit, unit_price_eur, net_eur,
    spot_price_formula,           ← the formula behind the rate, as a value
    trace: CalculationTrace {           ← "why is this amount here?"
      explanation,
      legal_refs: Vec<LegalReference>,  ← StromNEV §17, KAV §2, §14a Modul 2…
      tariff_source: Option<TariffSource>,
      gross_eur, regulatory_reduction_factor, …
    }
  }>,
  total_eur,
  warnings: Vec<SettlementWarning>,
}
        │
        ▼   (adapter — this is where document identity enters)
InvoiceDocument { settlement, pid, rechnungsnummer, invoice_date, due_date }
        │
        ▼   (rubo4e lives in the service; grid-billing has no BO4E dep)
into_rechnung(&document)  → rubo4e::current::Rechnung {
                              rechnungspositionen[].positionsnummer ← assigned here
                              rechnungspositionen[].artikelnummer   ← via kind.artikelnummer()
                            }
        │
        ▼
InvoicCheckEngine::check(pid, &nb_mp_id, &rechnung, …)
        │
        ▼
invoice_drafts (PostgreSQL) → AS4 dispatch

BDEW Artikelnummern architecture

The service layer owns the BDEW Artikelnummer mapping. grid-billing stays free of rubo4e:

flowchart LR
    calc["grid_billing\nsettle_*()"]
    pos["SettlementPosition\n.kind: BillingPositionKind\n.trace: CalculationTrace"]
    svc["Service layer\nkind_to_artikelnummer()"]
    bo4e["Rechnungsposition\n.artikelnummer  ← Gas/MMM/KA\n.artikel_id     ← NNE Strom/AWH Gas"]

    calc --> pos --> svc --> bo4e

    note1["BK6-20-160:\nNNE Strom replaced\nartikelnummer → artikel_id\nfrom PreisblattNetznutzung"]
    note2["BDEW Codeliste v5.6:\nGas NNE/MMM/KA use\nclassic 9990001… codes\nAWH: 2-01-7-001/002"]

    note1 -.->|Strom| bo4e
    note2 -.->|Gas| bo4e

Responsibility split

grid-billing has zero dependency on rubo4e. BO4E conversion lives exclusively in the service layer, keeping this crate publishable to crates.io without pulling in internal workspace crates.

Domain types

SettlementResult — canonical output

pub struct SettlementResult {
    pub settlement_type: SettlementType, // NneStrom | NneGas | MmmStrom | MsbRechnung | …
    pub status: SettlementStatus,        // Initial | Correction | Reversal | Final
    pub period: SettlementPeriod,        // validated pair, both bounds inclusive
    pub regime: RegulatoryRegime,        // the rules this calculation applied
    pub sparte: Sparte,
    pub malo_id: String,
    pub nb_mp_id: String,                // sender (NB, or MSB for a metering settlement)
    pub counterparty_mp_id: String,      // recipient
    pub positions: Vec<SettlementPosition>,
    pub total_eur: Decimal,              // rounded to 2 dp
    pub warnings: Vec<SettlementWarning>,
}

InvoiceDocument — the settlement presented as an invoice

pub struct InvoiceDocument {
    pub settlement: SettlementResult,
    pub pid: u32,                        // BDEW Prüfidentifikator — routes the document
    pub rechnungsnummer: String,
    pub correction_of: Option<String>,   // what this supersedes
    pub invoice_date: time::Date,
    pub due_date: time::Date,
}

Nothing on InvoiceDocument affects what is owed. numbered_positions() assigns the 1-based document numbering at render time.

Helper methods on SettlementResult:

SettlementPosition with CalculationTrace

Every position carries a full audit record so any amount can be explained without re-running the calculation. The kind field drives the BDEW Artikelnummer mapping in the service layer, and artikel_id carries the new-format article code where applicable (e.g. AWH Gas: "2-01-7-001", NNE Strom: populated from PreisblattNetznutzung):

pub struct SettlementPosition {
    pub text: String,                        // e.g. "Netznutzung Arbeit HT (§14a Modul 2)"
    pub kind: BillingPositionKind,           // what was charged
    pub quantity: Decimal,                   // rounded to 3 dp
    pub unit: QuantityUnit,                  // Kwh | Kw | Kvarh | Kvar | Monat
    pub unit_price_eur: Decimal,             // rounded to 6 dp
    pub net_eur: Decimal,                    // quantity × unit_price_eur, rounded to 5 dp
    pub spot_price_formula: Option<SpotPriceFormula>,  // the formula behind the rate
    pub trace: CalculationTrace,
}

// No position number and no Artikel-ID: both are properties of the document that
// presents the settlement, not of the calculation.

pub struct CalculationTrace {
    /// Human-readable explanation, e.g.:
    ///   "1500.000 kWh × 0.035000 EUR/kWh = 52.50000 EUR"
    pub explanation: String,
    pub input_quantity: Decimal,
    pub input_unit_price_eur: Decimal,
    pub gross_eur: Decimal,                       // qty × price before rounding
    pub legal_refs: Vec<LegalReference>,          // at least one, always
    pub tariff_source: Option<TariffSource>,      // where the rate came from
    pub regulatory_reduction_factor: Option<Decimal>, // §14a Modul 1 factor (0–1)
    pub rounding_note: Option<&'static str>,
}

LegalReference

pub enum LegalReference {
    StromNev { paragraph: &'static str },       // "§21" Arbeit, "§17" Leistung
    GasNev   { paragraph: &'static str },       // "§14"
    Kav      { paragraph: &'static str },       // "§2 Abs. 2"
    Sect14aEnwg { module: Sect14aModule },      // Modul1 | Modul2 | Modul3
    BnetzaDecision { reference: &'static str }, // "BK6-22-300"
    BdewAhb  { reference: &'static str },       // "GPKE BK6-22-024"
    MessZv   { paragraph: &'static str },       // "§2"
    MsbG     { paragraph: &'static str },       // "§§6–7"
    StromNzv { paragraph: &'static str },       // "§15" MMM
    GasNzv   { paragraph: &'static str },       // "§14" Gas MMM
    Enwg     { paragraph: &'static str },       // "§14a"
    ARegV    { paragraph: &'static str },       // "§17" incentive regulation
}

.citation() returns a short German-language string (e.g. "StromNEV §17", "§14a EnWG Modul 2 (HT/NT variable)", "ARegV §17").

Sect14aModule

pub enum Sect14aModule {
    Modul1, // §14a pauschale Reduzierung — flat % reduction (BK6-22-300 Anlage 2, default 85%)
    Modul2, // §14a HT/NT time-variable — Zaehlzeitdefinition from UTILTS
    Modul3, // §14a Spotpreis-Netzentgelt — spot-price linked (iMSys required)
}

Sect14aModule::Modul1.label() = "§14a EnWG Modul 1 (pauschale Reduzierung)"; .bnentza_reference() = "BK6-22-300" for all three modules.

TariffSource

pub enum TariffSource {
    PublishedTariffSheet { sheet_id: String },
    HistoricalTariff     { valid_from: time::Date },
    RegulatoryTariff     { decision_ref: &'static str },
    ContractTariff       { contract_ref: String },
    ManualOverride       { reason: String },
}

Sparte — commodity dispatch

#[derive(Default)]
pub enum Sparte {
    #[default]
    Strom,  // → StromNEV §21, SettlementType::NneStrom, PID 31001
    Gas,    // → GasNEV §14,   SettlementType::NneGas,   PID 31005
}

Sparte is required on NneInput and MmmInput. The calculation automatically selects the correct legal references, SettlementType, and default PID — no manual r.pid = 31005 override needed for standard Gas paths.

SettlementType

pub enum SettlementType {
    NneStrom,          // PID 31001 — NNE Strom (NB → LF)
    NneGas,            // PID 31005 — NNE Gas  (GNB → LFG)
    NneSelbstausstellt,// PID 31006 — NNE selbst ausgestellt (LF)
    MmmStrom,          // PID 31002 — MMM Strom, GPKE (BK6-24-174) Teil 1 Kap. 8.4
    MmmGas,            // PID 31002 — MMM Gas,   GaBi Gas 2.1 (BK7-24-01-008) (separate to ensure correct legal refs)
    MsbRechnung,       // PID 31009 — MSB-Rechnung (NB → MSB)
    GasAwhSperrung,    // PID 31011 — AWH Sperrprozesse Gas (GNB → LFG)
    RedispatchKostenblatt, // no standard PID — Redispatch 2.0
}

SettlementType::default_pid() returns the standard PID for the type. MmmGas and MmmStrom share PID 31002 but carry different legal references.

BillingPositionKind — BDEW Artikelnummern bridge

BillingPositionKind is the rubo4e-free type carried by every SettlementPosition.kind. The service layer maps it to rubo4e::current::BdewArtikelnummer in into_rechnung().

pub enum BillingPositionKind {
    NneArbeit,           // Wirkarbeit       (9990001 00026 9)
    NneArbeitHt,         // Wirkarbeit       (9990001 00026 9)
    NneArbeitNt,         // Wirkarbeit       (9990001 00026 9)
    NneArbeitModul1,     // Wirkarbeit       (9990001 00026 9) — reduced rate
    NneLeistung,         // Leistung         (9990001 00005 3)
    NneGasGrundpreis,    // Grundpreis       (9990001 00008 7)
    Konzessionsabgabe,   // Konzessionsabgabe(9990001 00041 7)
    Mehrmenge,           // Mehrmenge        (9990001 00074 8)
    Mindermenge,         // Mindermenge      (9990001 00075 6)
    MsbGrundgebuehr,     // EntgeltEinbauBetriebWartungMesstechnik (9990001 00061 5)
    Messdienstleistung,  // EntgeltMessungAblesung (9990001 00062 3)
    GasAwhSperrung,      // artikel_id: "2-01-7-001" (BK7-24-01-009 §5.4)
    GasAwhEntsprrung,    // artikel_id: "2-01-7-002"
    GasAwhSonstige,      // artikel_id from AwhPositionInput.artikel_id
    Blindmehrarbeit,     // Blindmehrarbeit  (9990001 00047 5)
}

NNE Strom (PIDs 31001/31006): BK6-20-160 replaced classic artikelnummer codes with artikel_id from the BNetzA Netznutzungspreisblatt. The service layer (netzbilanzd, invoicd) populates Rechnungsposition.artikel_id from the tariff sheet for those positions; kind_to_artikelnummer() returns None for Strom NNE. Gas NNE, MMM, Konzessionsabgabe still use classic articlenummer codes.

Source: BDEW Codeliste Artikelnummern und Artikel-ID v5.6 (valid 01.09.2025).

KaKlasse — KAV rate tier

pub enum KaKlasse {
    TarifkundeLow,    // ≤25 MWh/a residential — highest rate (KAV §2 Abs. 2)
    TarifkundeMedium, // ≤150 MWh/a commercial
    SonderkundeHigh,  // >150 MWh/a industrial
    Exempt,           // §2 Abs. 7 KAV exemptions
}

When ka_klasse is set, the KA position text and trace include the tier so auditors can verify the rate matches the correct KAV §2 band without looking up the underlying master data.

Who uses this library

Quick start

[dependencies]
grid-billing = { version = "0.10" }
rust_decimal = "1"
time         = "0.3"

NNE flat-rate (SLP, Strom)

use grid_billing::{NneInput, Sparte, settle_nne};
use rust_decimal::Decimal;
use time::macros::date;

fn d(s: &str) -> Decimal { Decimal::from_str_exact(s).unwrap() }

let settlement = settle_nne(&NneInput {
    malo_id: "51238696780".into(),
    nb_mp_id: "9900357000004".into(),
    lf_mp_id: "9900012345678".into(),
    rechnungsnummer: "NNE-2026-01-0001".into(),
    period_from: date!(2026-01-01),
    period_to:   date!(2026-01-31),
    invoice_date: date!(2026-02-15),
    due_date:    date!(2026-03-17),
    arbeitsmenge_kwh: d("1500"),
    arbeitspreis_ct_per_kwh: d("3.5"),
    arbeitsmenge_ht_kwh: None,
    arbeitspreis_ht_ct_per_kwh: None,
    arbeitsmenge_nt_kwh: None,
    arbeitspreis_nt_ct_per_kwh: None,
    spitzenleistung_kw: None,
    leistungspreis_eur_per_kw: None,
    ka_satz_ct_per_kwh: Some(d("0.11")),
    tariff_sheet_id: Some("Preisblatt-NNE-2026-Q1".into()),
    sparte: Sparte::Strom,
    ka_klasse: None,
    sect14a_modul1_reduction_factor: None,  // §14a Modul 1 not active for this MaLo
    nne_grundpreis_eur_per_month: None,     // no Gas Grundpreis (Strom)
    nne_grundpreis_months: None,
}).expect("valid NNE input");

// settlement.total_eur = 52.50 + 1.65 = 54.15 EUR
assert_eq!(settlement.pid, 31001);
// counterparty_mp_id is auto-populated from lf_mp_id:
assert_eq!(settlement.counterparty_mp_id, "9900012345678");

// Every position is self-explanatory:
for pos in &settlement.positions {
    println!("{}: {}", pos.text, pos.trace.explanation);
    for lr in &pos.trace.legal_refs {
        println!("  → {}", lr.citation());
    }
}

NNE Gas (GasNEV §14)

use grid_billing::{NneInput, Sparte, settle_nne};

// Only Sparte changes — GasNEV §14 legal refs and PID 31005 are automatic:
let settlement = settle_nne(&NneInput {
    sparte: Sparte::Gas,  // ← drives GasNEV §14 + PID 31005
    arbeitsmenge_kwh: d("3000"),  // already kWh_Hs from edmd gas conversion
    arbeitspreis_ct_per_kwh: d("1.80"),
    ka_satz_ct_per_kwh: None,  // KA typically not applicable for Gas
    sect14a_modul1_reduction_factor: None,
    nne_grundpreis_eur_per_month: None,
    nne_grundpreis_months: None,
    // … other identity fields …
}).unwrap();

assert_eq!(settlement.pid, 31005);

§14a Modul 2 ToU (HT/NT split, mandatory since 2024-01-01)

use grid_billing::{NneInput, KaKlasse, Sparte, settle_nne};

let settlement = settle_nne(&NneInput {
    arbeitsmenge_kwh: d("1000"),          // total — ignored when HT/NT supplied
    arbeitspreis_ct_per_kwh: d("3.5"),    // fallback — ignored when HT/NT supplied
    arbeitsmenge_ht_kwh: Some(d("600")),
    arbeitspreis_ht_ct_per_kwh: Some(d("4.20")),
    arbeitsmenge_nt_kwh: Some(d("400")),
    arbeitspreis_nt_ct_per_kwh: Some(d("1.50")),
    ka_satz_ct_per_kwh: Some(d("1.32")),
    ka_klasse: Some(KaKlasse::TarifkundeLow),  // ← auditable tier annotation
    sparte: Sparte::Strom,
    tariff_sheet_id: Some("Preisblatt-14a-2026".into()),
    sect14a_modul1_reduction_factor: None,  // Modul 1 and Modul 2 are mutually exclusive
    nne_grundpreis_eur_per_month: None,
    nne_grundpreis_months: None,
    // … identity fields …
}).unwrap();

// HT: 600×4.20ct=25.20; NT: 400×1.50ct=6.00; KA: 1000×1.32ct=13.20 → total 44.40 EUR
assert_eq!(settlement.positions.len(), 3);  // HT + NT + KA
assert!(settlement.all_legal_refs().iter().any(|r| r.contains("§14a EnWG Modul 2")));

§14a Modul 1 (flat percentage reduction, mandatory offer since 2024-01-01)

use grid_billing::{NneInput, Sparte, settle_nne};
use rust_decimal::dec;

// BK6-22-300 Anlage 2: default reduction factor = 0.85 (customer pays 85% of full rate).
// The NB may publish a different approved value in their PreisblattNetznutzung.
let settlement = settle_nne(&NneInput {
    arbeitsmenge_kwh: d("1500"),
    arbeitspreis_ct_per_kwh: d("3.5"),
    sect14a_modul1_reduction_factor: Some(dec!(0.85)),  // ← 15% reduction
    sparte: Sparte::Strom,
    // All HT/NT fields must be None — Modul 1 and Modul 2 are mutually exclusive
    arbeitsmenge_ht_kwh: None, arbeitspreis_ht_ct_per_kwh: None,
    arbeitsmenge_nt_kwh: None, arbeitspreis_nt_ct_per_kwh: None,
    // … other fields …
}).unwrap();

// 1500 × 0.035 × 0.85 = 44.625 → 44.62 EUR (MidpointNearestEven)
assert!(settlement.all_legal_refs().iter().any(|r| r.contains("Modul 1")));
assert!(settlement.positions[0].trace.regulatory_reduction_factor == Some(dec!(0.85)));

Gas NNE with Grundpreis (GasNEV monthly standing charge)

let settlement = settle_nne(&NneInput {
    sparte: Sparte::Gas,
    arbeitsmenge_kwh: d("3000"),
    arbeitspreis_ct_per_kwh: d("1.80"),
    nne_grundpreis_eur_per_month: Some(d("15.00")),  // monthly base fee from PreisblattNetznutzung
    nne_grundpreis_months: Some(1),
    sect14a_modul1_reduction_factor: None,
    // … other fields …
}).unwrap();

// Positions: Grundpreis (15.00) + Arbeit (54.00) = 69.00 EUR
assert_eq!(settlement.positions.len(), 2);
assert!(settlement.positions[0].text.contains("Grundpreis"));

GeLi Gas AWH Sperrprozesse (PID 31011)

use grid_billing::{GasAwhInput, AwhPositionInput, settle_gas_awh};

let settlement = settle_gas_awh(&GasAwhInput {
    malo_id: "51238696780".into(),
    nb_mp_id: "9900357000004".into(),
    lf_mp_id: "9900012345678".into(),
    rechnungsnummer: "AWH-2026-01-0001".into(),
    period_from: date!(2026-01-01),
    period_to:   date!(2026-01-31),
    invoice_date: date!(2026-02-15),
    due_date:    date!(2026-03-17),
    tariff_sheet_id: Some("Preisblatt-AWH-2026".into()),
    awh_positionen: vec![
        AwhPositionInput {
            beschreibung: "Sperrung Gaszähler".into(),
            anzahl: 1,
            preis_eur: d("45.00"),
            artikel_id: Some("2-01-7-001".to_owned()),  // BDEW Codeliste v5.6 §3.2
        },
        AwhPositionInput {
            beschreibung: "Entsperrung Gaszähler".into(),
            anzahl: 1,
            preis_eur: d("45.00"),
            artikel_id: Some("2-01-7-002".to_owned()),
        },
    ],
}).unwrap();

assert_eq!(settlement.pid, 31011);
assert_eq!(settlement.total_eur, d("90.00"));
// Both positions cite BK7-24-01-009 §5.4
assert!(settlement.all_legal_refs().iter().any(|r| r.contains("BK7-24-01-009")));

Correction lifecycle (reversal + replacement pair)

use grid_billing::{settle_nne, calculate_correction, SettlementStatus};

let original = settle_nne(&nne_input).unwrap();
let corrected = settle_nne(&corrected_input).unwrap();

let (reversal, replacement) = calculate_correction(
    &original,
    corrected,
    "STORNO-NNE-2026-01-0001".to_owned(),
    date!(2026-03-01),
    date!(2026-03-31),
);

assert_eq!(reversal.status, SettlementStatus::Reversal);
assert_eq!(reversal.total_eur, -original.total_eur);
assert_eq!(replacement.status, SettlementStatus::Correction);
assert_eq!(replacement.correction_of.as_deref(), Some("NNE-2026-01-0001"));

use grid_billing::{settle_nne, calculate_reversal};
use time::macros::date;

let original = settle_nne(&/* … NneInput … */).unwrap();

let storno = calculate_reversal(
    &original,
    "STORNO-NNE-2026-01-0001".to_owned(),
    date!(2026-03-01),
    date!(2026-03-31),
);

assert_eq!(storno.total_eur, -original.total_eur);
assert_eq!(storno.correction_of.as_deref(), Some("NNE-2026-01-0001"));

Pre-calculation validation

use grid_billing::{NneInput, Sparte, validate_nne_input, WarningSeverity};

let input = NneInput { /* … */ };
let v = validate_nne_input(&input);

if !v.is_valid {
    for w in &v.warnings {
        eprintln!("[{}] {}", w.code, w.message);
    }
    return;
}
let settlement = settle_nne(&input).unwrap();

Service-layer conversion to BO4E Rechnung

// In netzbilanzd/src/billing.rs — grid-billing itself has no rubo4e dep:
use grid_billing::{InvoiceDocument, QuantityUnit};
use rubo4e::current::{Betrag, Menge, Mengeneinheit, Preis, Rechnungsposition, Rechnung, Zeitraum};

fn into_rechnung(d: &InvoiceDocument) -> Rechnung {
    let lz = Zeitraum {
        startdatum: Some(s.period_from),
        enddatum: Some(s.period_to),
        ..Default::default()
    };
    let positions = s.positions.iter().map(|p| {
        let einheit = match p.unit {
            QuantityUnit::Kwh   => Some(Mengeneinheit::Kwh),
            QuantityUnit::Kw    => Some(Mengeneinheit::Kw),
            QuantityUnit::Kvarh => Some(Mengeneinheit::Kwh),   // map kVARh → kWh bucket
            QuantityUnit::Kvar  => Some(Mengeneinheit::Kw),    // map kVAR  → kW  bucket
            QuantityUnit::Monat => Some(Mengeneinheit::Monat),
        };
        Rechnungsposition {
            positionsnummer:    Some(p.number as i64),
            positionstext:      Some(p.text.clone()),
            // BDEW Artikelnummer from BillingPositionKind (Gas/MMM/KA positions)
            artikelnummer:      kind_to_artikelnummer(p.kind, s.settlement_type),
            // BDEW Artikel-ID (NNE Strom from tariff sheet; AWH Gas 2-01-7-xxx)
            artikel_id:         p.artikel_id.clone(),
            lieferungszeitraum: Some(lz.clone()),
            positions_menge: Some(Menge { wert: Some(p.quantity), einheit, ..Default::default() }),
            einzelpreis:  Some(Preis  { wert: Some(p.unit_price_eur.round_dp(6)), ..Default::default() }),
            gesamtpreis:  Some(Betrag { wert: Some(p.net_eur.round_dp(5)), ..Default::default() }),
            ..Default::default()
        }
    }).collect();
    Rechnung {
        rechnungsnummer:   Some(s.rechnungsnummer.clone()),
        rechnungsdatum:    Some(s.invoice_date),
        faelligkeitsdatum: Some(s.due_date),
        rechnungsperiode:  Some(lz),
        gesamtnetto: Some(Betrag { wert: Some(s.total_eur), ..Default::default() }),
        rechnungspositionen: Some(positions),
        ..Default::default()
    }
}

Generated invoice types

Billing position reference

NNE

MMM

MSB

AWH Gas Sperrprozesse (PID 31011)

Source: BDEW Codeliste Artikelnummern und Artikel-ID v5.6, Section 3.2 (valid 01.09.2025).

Design invariants

See also

• invoic-checker — validates the generated Rechnung in the service layer
• netzbilanzd — NB billing service that calls grid-billing
• invoicd — LF service using grid-billing for selbstausstellen
• Operator guide → netzbilanzd

grid-billing computes BDEW INVOIC billing positions for:

• NNE (Netznutzungsentgelt) — flat-rate or §14a Modul 2 ToU (HT/NT split)
• KA (Konzessionsabgabe) — KAV §2, included as separate position
• MMM (Mehr-/Mindermengensaldo) — actual vs. SLP profile deviation, credit when Mindermengen dominate
• MSB-Rechnung — metering service fee (NB → MSB, PID 31009)

All calculations are pure functions — zero I/O, zero async, no side effects. All monetary arithmetic uses EuroAmount = i64 × 10⁻⁵ EUR — no f64 anywhere in the billing path.