grid-billing

Deterministic, regulation-aware German grid settlement engine — NNE, KA, MMM, MSB, and GeLi Gas AWH Sperrprozesse (Prüfidentifikatoren 31001, 31002, 31005, 31006, 31009, 31011 — the five-digit BDEW codes that name each billing Anwendungsfall).

Regulatory ceilings and structure

KAV §2 — Konzessionsabgabe

The Höchstbeträge are checked on every settlement, and each position cites the paragraph its group is actually capped under: §2 Abs. 2 for Tarifkunden and Schwachlast, Abs. 3 for Sondervertragskunden, and Abs. 4 (Strom) resp. Abs. 5 (Gas) where the Verordnung forbids a Konzessionsabgabe altogether.

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

Every figure §30 states is brutto jährlich.

§30 Abs. 1 band	Netzbetreiber	Letztverbraucher	Total
> 6 000 – ≤ 10 000 kWh	80 €	40 €	120 €
> 10 000 – ≤ 20 000 kWh · steuerbare VE · > 7 – ≤ 15 kW	80 €	50 €	130 €
> 20 000 – ≤ 50 000 kWh · > 15 – ≤ 25 kW	80 €	110 €	190 €
> 50 000 – ≤ 100 000 kWh · > 25 – ≤ 100 kW	80 €	140 €	220 €
> 100 000 kWh · > 100 kW	80 €	angemessenes Entgelt	—

§30 Abs. 3 (optionaler Einbau) is 30 € each, 60 € total.

Two conversions before the comparison means anything. The monthly charge is annualised — billing a year in instalments does not raise the cap — and it is grossed up at the Umsatzsteuer rate of the delivery period, because the ceiling is gross and the settlement's figures are net. Comparing net against gross would grant the whole tax rate as headroom: at 19 % a charge could sit 18.9 % above the statutory maximum unreported. A gross charge above the ceiling raises MSB_ABOVE_MSBG_POG, and the finding states both figures.

What is measured is the Grundgebühr together with the Messdienstleistung. §30 caps the „Entgelt für den Messstellenbetrieb", and §3 Abs. 2 Nr. 1 MsbG puts the Messung inside it — Messstellenbetrieb umfasst die „Gewährleistung einer mess- und eichrechtskonformen Messung […] einschließlich der Messwertaufbereitung"; §17 Abs. 7 Satz 1 StromNEV states it from the other side („ein Entgelt für den Messstellenbetrieb, zu dem auch die Messung gehört"). Testing the Grundgebühr alone would let a settlement clear any ceiling by moving part of the charge into the second position. The Messdienstleistung is a flat fee for the whole period, so it is spread over billing_months before annualising.

The Steuerungseinrichtung am Netzanschlusspunkt is the exception, and it is steuereinrichtung_eur_per_month's own position. §30 Abs. 2 charges it „zusätzlich zu den nach den Absätzen 1 und 5 zulässigen Preisobergrenzen" and caps it at 50 € brutto a year per party, so it is measured against that figure and left out of the Abs. 1 comparison — folded into the Grundgebühr it would take headroom the Absatz does not grant, and an excess raises MSB_STEUEREINRICHTUNG_ABOVE_MSBG_POG.

§ 2 Abs. 7 is a classification rule, and it is checked too. A Niederspannungslieferung counts as a Tariflieferung unless the gemessene Leistung exceeds 30 kW in mindestens zwei Monaten des Abrechnungsjahres und the Jahresverbrauch exceeds 30 000 kWh. Konzessionsabgabe::niederspannung carries those two facts (with the Satz-4 lower figures where a Gemeinde agreed them), and a stated klasse that contradicts them raises KA_GRUPPE_WIDERSPRICHT_KAV_ABS7 — the two ceilings are 1,32 ct and 0,11 ct apart, so the label is worth checking.

Two rules forbid a Konzessionsabgabe outright, and a ceiling cannot catch either: § 2 Abs. 4 (Strom) resp. Abs. 5 Nr. 2 (Gas) where a Sondervertragskunde's Durchschnittspreis lies under the Grenzpreis (Grenzpreisvergleich → KA_UNTER_GRENZPREIS), and § 2 Abs. 5 Nr. 1 above 5 Millionen kWh Gas je Jahr und Abnahmefall (read off jahresarbeit_kwh → KA_GAS_UEBER_GRENZMENGE).

The band is derived, not named. Each §30 Abs. 1 Nummer is a disjunction over facts about the metering point, so MessstellenKategorie::Pflichteinbau carries PflichtEinstufung { jahresverbrauch_kwh, installierte_leistung_kw, steuerbare_verbrauchseinrichtung } and PflichtEinstufung::band walks the Nummern top down — a point meeting several takes the highest, and a settlement cannot pick its own ceiling. With no fact at all the tightest applies: a Pflichteinbaufall exists only above 6 000 kWh (§29 Abs. 1), so Nr. 5 is the catalogue's floor.

The schedule is dated. Abs. 1 and Abs. 3 state their figures „für die Zeit ab dem 1. Januar 2025", so preisobergrenze_eur_per_jahr takes the period's end and answers Preisobergrenze::VorSchedule below it — a correction settled today for a 2024 period is governed by rules mako does not carry, and reporting it against these would call a lawful charge an excess (MSB_POG_VOR_SCHEDULE). The three answers are distinct on purpose: Betrag is a ceiling, Angemessen is Abs. 1 Nr. 1's angemessenes jährliches Entgelt above 100 000 kWh, and VorSchedule is "not this schedule's period". Abs. 6 lets a BNetzA Festlegung nach § 33 replace Abs. 1 bis 3 from a date it names; none has issued.

Which Jahresstromverbrauch picks the band is Abs. 4's answer, not the caller's choice: the average of the last three erfasste Jahresverbrauchswerte, the Netzbetreiber's Jahresverbrauchsprognose until three exist, re-checked annually. PflichtEinstufung::jahresverbrauch_kwh is that figure — one year's reading is not.

§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.

Leistungspreis::system names which Leistungspreissystem the price sheet states, and the two are billed differently.

LeistungspreisSystem::Jahr is §17 Abs. 2 Satz 2: „Das Jahresleistungsentgelt ist das Produkt aus dem jeweiligen Jahresleistungspreis und der Jahreshöchstleistung in Kilowatt der jeweiligen Entnahme im Abrechnungsjahr." Two figures multiplied, and §17 states no day-count convention to scale them by — so the rate is billed as published. A settlement period that is not the Abrechnungsjahr raises JAHRESLEISTUNGSPREIS_UNTERJAEHRIG rather than being silently pro-rated into a Zwölftelung no price sheet publishes.

LeistungspreisSystem::Monat is the Monatsleistungspreissystem §17 Abs. 8 presupposes when it offers Tagesleistungspreise for Landstrom „neben einem Jahres- und Monatsleistungspreissystem". StromNEV does not define it; the Netzbetreiber's Preisblatt publishes it as a €/kW·Monat rate against the period's Höchstleistung. It is billed for the months stated, and a month count that does not match the period raises MONATSLEISTUNGSPREIS_MONATE_MISMATCH — a twelvefold over-charge multiplies out perfectly, so only the count can catch it.

§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:

Form	Qualification	Mindestentgelt
Atypische Netznutzung (Satz 1)	peak in the low-load windows (BNetzA-approved)	20 %
Intensive Netznutzung (Satz 2)	≥ 7 000 h and > 10 GWh	20 %
	≥ 7 500 h	15 %
	≥ 8 000 h	10 %

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; one naming neither a Genehmigung (Satz 5) nor an Anzeige (Satz 7) raises SECT19_OHNE_GENEHMIGUNG.

The two Satz 2 thresholds read differently: the Benutzungsstundenzahl must „mindestens 7 000 Stunden im Jahr erreichen", the Stromverbrauch must „zehn Gigawattstunden übersteigen" — so exactly 10 GWh does not qualify. The agreed fraction is a reduction, and outside (0, 1] it is refused as BillingError::InvalidInput.

§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:

Period	Factor
to 30.06.2026	1.00
01.07.2026 – 31.12.2027	0.50
2028	0.25
from 2029	0.00

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's cross-field rules live in the types, not in a validator a caller could forget:

Rule	Enforced by
Exactly one Arbeitspreis form (einheitlich, Modul 1 pauschal, Modul 2 prozentual, Modul 3 zeitvariabel, or spot-linked)	`ArbeitspreisModell` — one variant at a time; each replaces the flat position, so the same energy is never billed twice
`Modul 1 + Modul 3` is the only combination BK8-22/010-A offers	`ArbeitspreisModell` holds one variant at a time, so every pair is unrepresentable — which is right for Modul 1/Modul 2 (alternative base modules) and for Modul 2/Modul 3, and is a limitation for the Modul 1 + Modul 3 pair the Festlegung permits. See `Sect14aModule::combinable_with`
Reduction factors in `(0, 1]`	`Reduktionsfaktor` enforces the range at construction
Leistungspreis needs both peak and rate, and names its Leistungspreissystem	`Leistungspreis` — a pair plus `LeistungspreisSystem`
Grundpreis needs both rate and months	`Grundpreis` — a pair
KAV Höchstbetrag is always checked	`Konzessionsabgabe` pairs the rate with its `KaKundengruppe`
Period ordering	`SettlementPeriod` — constructing it is the check

What the types cannot express — negative energy, empty or inverted Modul 3 intervals — settle_nne enforces itself and returns Err. There is no separate NNE validator: settle_nne is pure and cheap, run it and read warnings. validate_mmm_input / validate_msb_input / validate_gas_awh_input exist for the settlement types whose engines accept looser shapes.

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.

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

No BO4E inside the engine

SpotPriceFormula states the pricing formula behind a §14a Modul 3 rate as a typed value — reference, unit, method, steps — never a serde_json::Value carrying a hand-built BO4E COM. That keeps BO4E schema knowledge out of the engine: the bo4e bridge builds the COM from the value object, and the default build pulls in no serde_json at all — it arrives only with that feature.

SettlementPeriod

A validated pair, not two loose period_from / period_to dates each calculation would have to re-check for ordering. Constructing SettlementPeriod is the check, so an inverted period is unrepresentable rather than rejected at every call site.

Regulatory regime

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

Axis	Turns over	Successor
Netzzugang	31.12.2025	§20 Abs. 3 EnWG via BNetzA Festlegungen (GPKE BK6-24-174, GaBi Gas 2.1)
Entgeltbildung	31.12.2028	BNetzA framework Festlegung AgNeS, replacing StromNEV and ARegV
Umlagen	annually	ÜNB publication each October

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:

Levy	Basis	2026 (nicht privilegiert)
Aufschlag für besondere Netznutzung (§19 StromNEV-Umlage)	§19 Abs. 2 StromNEV	A′ 1.559 · B′ 0.050 · C′ 0.025 ct/kWh
Offshore-Netzumlage	§17f EnWG	0.941 ct/kWh
KWKG-Umlage	§26 KWKG	0.446 ct/kWh

B′ and C′ are published „für Strommengen über 1 000 000 kWh" at one Entnahmestelle, so they are a tranche, not a rate: the year's first Gigawattstunde carries A′ whatever the group. NneInput::enfg_jahresvorverbrauch_kwh places the period against that annual boundary, and one straddling it bills two §19-Aufschlag positions. Omitted, the period is billed as though it opened the year — the over-billing direction — with ENFG_VORVERBRAUCH_MISSING.

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:

Domain	Until 31.12.2025	From 01.01.2026
Mehr-/Mindermengen Strom	StromNZV §13 Abs. 3	GPKE (BK6-24-174) Teil 1 Kap. 8.4
Mehr-/Mindermengen Gas	GasNZV §25	GaBi Gas 2.1 (BK7-24-01-008)
Standardlastprofile Strom	StromNZV §12	GPKE (BK6-24-174), "Profilverfahren"
Standardlastprofile Gas	GasNZV §24	GaBi Gas 2.1 (BK7-24-01-008)
Bilanzkreisabrechnung Strom	StromNZV §4	MaBiS (Anlage 3 zu BK6-24-174)
Konzessionsabgabe	KAV §2 (unchanged)	KAV §2

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 is governed by the KAV plus §48 EnWG — not by StromNZV §17 or GasNZV §7, which concern balancing-group and network-access matters.

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.

Measurement vs profile	Quantity	Money
measured < profiled	ungewollte Mehrmenge	NB vergütet → credit
measured > profiled	ungewollte Mindermenge	NB stellt in Rechnung → charge

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.

Group	Strom	Gas
Tarifkunde, Gemeinde ≤ 25 000 Einw.	1.32	0.51 (Kochen/Warmwasser) · 0.22 (übrige)
≤ 100 000	1.59	0.61 · 0.27
≤ 500 000	1.99	0.77 · 0.33
> 500 000	2.39	0.93 · 0.40
Schwachlast (Strom only)	0.61	—
Sondervertragskunde	0.11	0.03

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 31002, NN-Rechnung) — flat-rate Arbeit, Leistung (RLM), Konzessionsabgabe
NNE Gas (PID 31002, NN-Rechnung) — GasNEV §14 legal basis, auto-set when Sparte::Gas
§14a modules — Modul 1 (pauschale Reduzierung), Modul 2 (prozentuale Reduzierung des Arbeitspreises), Modul 3 (zeitvariable Netzentgelte HT/ST/NT, opt-in since 01.04.2025) — BNetzA BK8-22/010-A / BK8-22/010-A
MMM Strom (PID 31005) — Mehr-/Mindermengensaldo, GPKE (BK6-24-174) Teil 1 Kap. 8.4
MMM Gas (PID 31005) — Gas imbalance, GaBi Gas 2.1 (BK7-24-01-008)
NNE Gas (PID 31002) — GasNEV §14 Arbeits-/Grundpreis and §15 Kapazitätsentgelt
Abschlagsrechnung (PID 31001) — a payment on account: one Positionszeile, no quantity, no Arbeitspreis (INVOIC AHB 1.0b Änd-ID 26817). The invoice that settles the period deducts it from what is owed via InvoiceDocument::abschlaege, never from the net or the tax, because §14 Abs. 5 UStG taxed the Anzahlung when it was received
MMM Mehrmenge selbst ausgestellt (PID 31006) — Mehr-/Mindermenge als Lieferung, self-issued (INVOIC AHB Selbstausstellung)
MSB-Rechnung (PID 31009) — Grundgebühr Messstellenbetrieb + optional Messdienstleistung
GeLi Gas AWH Sperrprozesse (PID 31011) — abrechnungswürdige Handlungen (BK7-24-01-009 §5.4)
§13a EnWG Redispatch-Vergütung — redispatch_verguetung() computes the angemessene Vergütung per activation (entgangene Einnahmen + zusätzliche − ersparte Aufwendungen; eeg_entgangene_einnahmen() for the Nr. 5 EEG basis)
Reversal (Stornorechnung) — reverse() negates any prior settlement immutably; the sign goes on the unit price, so each position still multiplies out
Umsatzsteuer — every settlement states its tax (§14 Abs. 4 Nr. 8 UStG). Network services are 19 % and never reverse-charged (UStAE 13b.3a excludes them by name); a Mehr-/Mindermenge is a Lieferung and takes the §13b Abs. 2 Nr. 5 Buchst. b reverse charge on the asymmetric condition the statute sets — electricity needs both parties to hold §3g status, gas needs the recipient alone. A delivery period straddling a rate change is refused rather than billed at one of the two.

All calculations are pure functions — zero I/O, zero async, no side effects. All monetary arithmetic uses rust_decimal::Decimal via 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, sender_mp_id, recipient_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 }
        │
        ▼   (feature `bo4e` — off by default)
grid_billing::bo4e::into_rechnung(&document) → rubo4e::current::Rechnung {
                              rechnungspositionen[].positionsnummer ← assigned here
                              rechnungspositionen[].artikelnummer   ← via kind.artikelnummer()
                              rechnungstyp                          ← Netznutzungsrechnung (NNE + MMM only)
                              netznutzungrechnungsart               ← Handels-/Selbstausgestellt
                              netznutzungrechnungstyp               ← Mehrmindermengenrechnung (MMM only)
                            }
        │
        ▼
InvoicCheckEngine::check(pid, &sender_mp_id, &rechnung, …)
        │
        ▼
invoice_drafts (PostgreSQL) → AS4 dispatch

Netznutzungsrechnung typing

into_rechnung marks the document so a consumer can recognise it without inspecting positions:

Field	Set for	Value
`rechnungstyp`	Abschlag, NNE Strom/Gas, MMM Strom/Gas, MMM selbst ausgestellt	`Netznutzungsrechnung`
`netznutzungrechnungsart`	the same six	`Selbstausgestellt` for PID 31006, else `Handelsrechnung`
`netznutzungrechnungstyp`	MMM · Abschlag · anything with a stated cadence	`Mehrmindermengenrechnung` · `Abschlagsrechnung` · the cadence

The other four settlement types this engine produces — MSB-Rechnung (31009), Gas-AWH Sperrung (31011), Redispatch Kostenblatt, dezentrale Einspeisung (§18 StromNEV) — are left untyped on purpose. They are not network-use invoices, and typing them as one would assert something the AHB does not.

netznutzungrechnungstyp is the one field two different things decide. The Mehr-/Mindermengen codes follow from the settlement, and so does Abschlagsrechnung, because PID 31001 is that document. The rest — Turnus-, Monats-, Abschluss-, Zwischenrechnung — describe the billing cadence, which the same NNE computation does not carry: it is billed monthly or annually depending on contract. So it rides on InvoiceDocument::cadence, and with neither present the field stays unset rather than guessing a rhythm nothing supports.

BDEW Artikelnummern architecture

Which article number applies to which position in which settlement is domain logic, so it lives here — BillingPositionKind::artikelnummer(settlement_type) returns the BDEW codelist name as a &'static str, a plain string that costs the core engine no BO4E type. The bo4e bridge parses it into the enum (bo4e::kind_to_artikelnummer); a consumer rendering something else parses it its own way.

flowchart LR
    calc["grid_billing<br/>settle_*()"]
    pos["SettlementPosition<br/>.kind: BillingPositionKind<br/>.trace: CalculationTrace"]
    bridge["feature bo4e<br/>kind_to_artikelnummer()"]
    bo4e["Rechnungsposition<br/>.artikelnummer  ← Gas/MMM/KA<br/>.artikel_id     ← NNE Strom/AWH Gas"]

    calc --> pos --> bridge --> bo4e

    note1["BK6-20-160:<br/>NNE Strom replaced<br/>artikelnummer → artikel_id<br/>from PreisblattNetznutzung"]
    note2["BDEW Codeliste v5.6:<br/>Gas NNE/MMM/KA use<br/>classic 9990001… codes<br/>AWH: 2-01-7-001/002"]

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

artikelnummer answers None where the position carries an Artikel-ID instead — every Strom NNE position since BK6-20-160, the AWH Gas 2-01-7-xxx positions, and the Abschlag, which prices nothing. The renderer resolves those from the price sheet or the input.

Responsibility split

Responsibility	Where
Settlement math + legal refs	`grid-billing`
BO4E `Rechnung` conversion	`grid_billing::bo4e` — feature `bo4e`, off by default
INVOIC plausibility checks	`invoic-checker`
EDIFACT serialization + AS4 dispatch	`makod`

The feature is off by default so the settlement engine stays publishable and rubo4e-free for a consumer that renders something else; netzbilanzd and invoicd both enable it.

Feature	Pulls in	Enables
(default)	`billing`, `rust_decimal`, `serde`, `thiserror`, `time`	the settlement engine
`bo4e`	`rubo4e`, `serde_json`	`bo4e::into_rechnung`, `kind_to_artikelnummer`, `rechnungstyp_for`, `netznutzungrechnungsart_for`, `netznutzungrechnungstyp_for`

Domain types

`SettlementResult` — canonical output

pub struct SettlementResult {
    pub settlement_type: SettlementType, // NneStrom | NneGas | MmmStrom | MsbRechnung | …
    pub status: SettlementStatus,        // Initial | Correction | Reversal | Final
    pub korrektur_grund: Option<KorrekturGrund>, // why — None only for Initial
    pub period: SettlementPeriod,        // validated pair, both bounds inclusive
    pub regime: RegulatoryRegime,        // the rules this calculation applied
    pub sparte: Sparte,
    pub malo_id: String,
    pub sender_mp_id: String,            // NB, or MSB for a MSB-Rechnung (31009)
    pub recipient_mp_id: String,         // LF, NB, MSB, MGV or ESA
    pub positions: Vec<SettlementPosition>,
    pub total_eur: Decimal,              // rounded to 2 dp
    pub steuer: Steuerausweis,           // §14 Abs. 4 Nr. 8 UStG — rate, amount, reverse-charge note
    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,
    pub cadence: Option<Rechnungscharakter>,   // IMD+7081 — a document fact
    pub abschlaege: Vec<Abschlagsverrechnung>, // deducted from what is owed, not from the net
}

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

Helper methods on SettlementResult:

Method	Returns	Description
`is_clean()`	`bool`	`true` when no `Warning`/`Error` severity items in `warnings`
`recomputed_total()`	`Decimal`	Re-sums positions — should equal `total_eur` (regression guard)
`all_legal_refs()`	`Vec<String>`	Deduplicated citation strings across all positions
`positions_count()`	`usize`	Number of settlement positions

`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. A position carries no position number and no Artikel-ID: both are properties of the document that presents the settlement, not of the calculation — an adapter numbers the positions it renders and resolves Artikel-IDs (AWH Gas 2-01-7-xxx, NNE Strom from the PreisblattNetznutzung) from the price sheet:

pub struct SettlementPosition {
    pub text: String,                        // e.g. "Netznutzung Arbeit HT (§14a Modul 3)"
    pub kind: BillingPositionKind,           // what was charged
    pub quantity: Decimal,                   // rounded to 3 dp
    pub unit: QuantityUnit,                  // Kwh | Kw | Kvarh | Kvar | Monat | Jahr
    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 2 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"
    Kwkg     { paragraph: &'static str },       // "§26" KWKG-Umlage
    Ustg     { paragraph: &'static str },       // "§14 Abs. 5" Anzahlung, "§13b" reverse charge
    EnFG     { paragraph: &'static str },       // "§§21 ff." Letztverbrauchergruppe
    Sect14aEnwg { module: Sect14aModule },      // Modul1 | Modul2 | Modul3
    MsbG     { paragraph: &'static str },       // "§§6–7"
    BnetzaDecision { reference: &'static str }, // "BK8-22/010-A"
    BdewAhb  { reference: &'static str },       // "GPKE BK6-22-024"
    StromNzv { paragraph: &'static str },       // "§13 Abs. 3" — außer Kraft seit 01.01.2026
    GasNzv   { paragraph: &'static str },       // "§25" — außer Kraft seit 01.01.2026
    Enwg     { paragraph: &'static str },       // "§14a"
    ARegV    { paragraph: &'static str },       // "§17" incentive regulation
}

.citation() returns a short German-language string (e.g. "StromNEV §17", "KAV §2 Abs. 2", "ARegV §17"). Repealed ordinances carry their expiry: StromNzv/GasNzv append "(außer Kraft seit 01.01.2026)".

`Sect14aModule`

pub enum Sect14aModule {
    Modul1, // pauschale Reduzierung des Netzentgelts — flat, needs no extra metering
    Modul2, // prozentuale Reduzierung des Arbeitspreises — needs the device's own metering
    Modul3, // zeitvariable Netzentgelte HT/ST/NT (from 01.04.2025) — Zählzeitdefinition
            // from UTILTS, requires an iMSys; also the Spotpreis-Netzentgelt variant
}

Sect14aModule::Modul1.label() = "§14a EnWG Modul 1 (pauschale Reduzierung)"; .bnentza_reference() = "BK8-22/010-A" 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 31002 (NN-Rechnung)
    Gas,    // → GasNEV §14,   SettlementType::NneGas,   PID 31002 (NN-Rechnung)
}

Sparte is required on NneInput and MmmInput. The calculation automatically selects the correct legal references and SettlementType (from which default_pid() yields the PID) — the caller sets no PID for standard Gas paths.

`SettlementType`

pub enum SettlementType {
    NneAbschlag,       // PID 31001 — Abschlagsrechnung Netznutzung (NB → LF)
    NneStrom,          // PID 31002 — NN-Rechnung Strom (NB → LF)
    NneGas,            // PID 31002 — NN-Rechnung Gas  (GNB → LFG)
    MmmStrom,          // PID 31005 — MMM Strom, GPKE (BK6-24-174) Teil 1 Kap. 8.4
    MmmGas,            // PID 31005 — MMM Gas,   GaBi Gas 2.1 (BK7-24-01-008) (separate to ensure correct legal refs)
    MmmSelbstausstellt,// PID 31006 — MMM Mehrmenge, selbst ausgestellte Rechnung (Lieferung)
    MsbRechnung,       // PID 31009 — MSB-Rechnung (MSB → NB / LF / ESA)
    GasAwhSperrung,    // PID 31011 — AWH Sperrprozesse Gas (GNB → LFG)
    RedispatchKostenblatt, // no standard PID — Redispatch 2.0 Einsatzkosten (NB → ÜNB)
    DezentraleEinspeisung, // no standard PID — §18 StromNEV, NB → Anlagenbetreiber (bilateral)
}

SettlementType::default_pid() returns the standard PID for the type; it is 0 for RedispatchKostenblatt and DezentraleEinspeisung, which are not EDIFACT market processes. MmmGas and MmmStrom share PID 31005, and NneGas and NneStrom share 31002, but each pair carries different legal references.

`BillingPositionKind` — BDEW Artikelnummern bridge

BillingPositionKind is the rubo4e-free type carried by every SettlementPosition.kind. bo4e::kind_to_artikelnummer maps it to rubo4e::current::BdewArtikelnummer under the bo4e feature; the core engine only ever holds the codelist name.

pub enum BillingPositionKind {
    NneAbschlag,         // the single line of an Abschlagsrechnung — no article number
    NneArbeit,           // Wirkarbeit       (9990001 00026 9)
    NneArbeitHt,         // Wirkarbeit       (9990001 00026 9) — §14a Modul 3 Hochtarif
    NneArbeitSt,         // Wirkarbeit       (9990001 00026 9) — §14a Modul 3 Standardtarif
    NneArbeitNt,         // Wirkarbeit       (9990001 00026 9) — §14a Modul 3 Niedertarif
    NneArbeitModul1,     // Wirkarbeit       (9990001 00026 9) — Modul 1 Arbeit + pauschale credit
    NneArbeitModul2,     // Wirkarbeit       (9990001 00026 9) — Modul 2 reduced Arbeitspreis
    NneArbeitModul3,     // Wirkarbeit — §14a Modul 3 spot, one position per dispatch interval
    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,      // Sperrkosten — Artikel-ID "2-01-7-001" (BK7-24-01-009 §5.4)
    GasAwhEntsperrung,    // Entsperrkosten — Artikel-ID "2-01-7-002"
    GasAwhSonstige,      // Artikel-ID from AwhPositionInput.artikel_id
    Blindmehrarbeit,     // Blindmehrarbeit  (9990001 00047 5)
    Sect19StromNevUmlage,// §19 StromNEV-Umlage — artikelnummer PARAGRAF_19_STROM_NEV_UMLAGE
    OffshoreNetzumlage,  // §17f EnWG — artikelnummer OFFSHORE_HAFTUNGSUMLAGE (legacy code name)
    KwkgUmlage,          // §26 KWKG — artikelnummer ABGABE_KWKG
    DezentraleEinspeisung,   // §18 StromNEV payment out (negative rate); no article number
    Sect19IndividuellesEntgelt, // §19 Abs. 2 StromNEV reduction over the Netzentgelt; no article number
    GasKapazitaetsentgelt,   // §15 GasNEV booked capacity — Leistung on Gas
}

NNE Strom (PID 31002): 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; BillingPositionKind::artikelnummer(settlement_type) returns None for Strom NNE. Gas NNE, MMM, Konzessionsabgabe still use classic Artikelnummer codes.

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

`KaKundengruppe` / `GemeindeGroesse` — KAV §2 classifier

KAV applies two orthogonal tests: contract type (Tarifkunde vs Sondervertragskunde), and — for Tarifkunden — municipality size, not annual consumption.

pub enum KaKundengruppe {
    Tarifkunde {                     // KAV §2 Abs. 2 — rate bands on municipality size
        gemeinde: GemeindeGroesse,
        nur_kochen_warmwasser: bool, // Gas only: cooking/hot-water column vs übrige; ignored for Strom
    },
    Schwachlast,          // KAV §2 Abs. 2 — Strom only; gas has no such tier
    Sondervertragskunde,  // KAV §2 Abs. 3 — flat, independent of municipality size
    Exempt,               // KAV §2 Abs. 4 (Strom) / Abs. 5 (Gas) — keine KA zulässig
}

pub enum GemeindeGroesse {
    Bis25k,    // bis 25 000 Einwohner
    Bis100k,   // bis 100 000
    Bis500k,   // bis 500 000
    Ueber500k, // über 500 000
}

KaKundengruppe::hoechstsatz_ct_per_kwh(sparte) returns the statutory KAV §2 Höchstbetrag (or None for Exempt, and for Schwachlast on Gas). .kav_paragraph(sparte) returns the paragraph the group is governed by ("§2 Abs. 2", "§2 Abs. 3", or — where no Konzessionsabgabe may be charged at all — "§2 Abs. 4" for Strom and "§2 Abs. 5" for Gas) and .label(sparte) the position text. The group is carried on Konzessionsabgabe.klasse, so the ceiling check always has what it needs: settle_nne emits KA_ABOVE_KAV_MAXIMUM when the agreed rate exceeds the ceiling, and KA_CHARGED_WHILE_EXEMPT when a rate is applied where the Verordnung forbids one.

The two prohibitions are Abs. 4 and Abs. 5, not Abs. 7. Abs. 4 forbids a Konzessionsabgabe for Strom-Sondervertragskunden below the Grenzpreis, Abs. 5 for Gas above 5 Millionen kWh je Jahr und Abnahmefall or below the Gas-Grenzpreis. Abs. 7 is a classification rule: a Niederspannungslieferung counts as a Tariflieferung unless the gemessene Leistung exceeds 30 kW in at least two months of the Abrechnungsjahr and the Jahresverbrauch exceeds 30 000 kWh. Deciding that is the caller's, which is why the group arrives with the rate.

Who uses this library

Consumer	Role	Use case
`netzbilanzd`	NB (and MSB for 31009)	Generate INVOIC 31001/31002/31005/31011 to LF/LFG, and 31009 from the MSB to NB/LF/ESA
`invoicd`	LF	INVOIC PID 31006, selbst ausgestellt — same formula, LF-initiated

Quick start

cargo add grid-billing
cargo add rust_decimal time

NNE flat-rate (SLP, Strom)

use grid_billing::{NneInput, Sparte, SettlementType, settle_nne};
use grid_billing::types::{
    ArbeitspreisModell, MengePreis, Konzessionsabgabe, KaKundengruppe, SettlementPeriod,
};
use grid_billing::umlagen::Letztverbrauchergruppe;
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: "51238696012".into(),
    nb_mp_id: "9900357000004".into(),
    lf_mp_id: "9900012345678".into(),
    // The delivery period is a validated pair — inverted bounds are unrepresentable.
    period: SettlementPeriod::new(date!(2026-01-01), date!(2026-01-31)).unwrap(),
    // Letztverbrauchergruppe drives the network-levy rates (EnFG §§21 ff.).
    letztverbrauchergruppe: Letztverbrauchergruppe::A,
    // A′ has no EnFG 1-GWh boundary, so the year to date does not place it.
    enfg_jahresvorverbrauch_kwh: None,
    // Exactly one Arbeitspreis form — here a single flat rate.
    arbeitspreis: ArbeitspreisModell::Einheitlich(MengePreis {
        menge_kwh: d("1500"),
        preis_ct_per_kwh: d("3.5"),
    }),
    leistungspreis: None,   // SLP — no RLM demand charge
    grundpreis: None,       // Strom has no separate Grundpreis
    konzessionsabgabe: Some(Konzessionsabgabe {
        satz_ct_per_kwh: d("0.11"),
        klasse: KaKundengruppe::Sondervertragskunde,
    }),
    sparte: Sparte::Strom,
    tariff_sheet_id: Some("Preisblatt-NNE-2026-Q1".into()),
    netzebene: None,
    jahreshoechstleistung_kw: None,
    jahresarbeit_kwh: None,
    sect19: None,            // no §19 Abs. 2 individual charge
    blindarbeit: None,       // no reactive-energy charge
    gas_kapazitaet: None,
    sect19_umlage_ct_per_kwh: None,   // use the tabled rate for the delivery year/group
    offshore_umlage_ct_per_kwh: None,
    kwkg_umlage_ct_per_kwh: None,
}).expect("valid NNE input");

// The settlement carries what was settled, not a PID — invoice number, dates and
// the Prüfidentifikator are properties of InvoiceDocument. SettlementType maps to
// the standard PID:
assert_eq!(settlement.settlement_type, SettlementType::NneStrom);
assert_eq!(settlement.settlement_type.default_pid(), 31002);
// recipient_mp_id is auto-populated from lf_mp_id:
assert_eq!(settlement.recipient_mp_id, "9900012345678");

// A Strom NNE settlement also carries the three netzseitige Umlagen (§19 StromNEV,
// Offshore, KWKG) alongside the Arbeit and Konzessionsabgabe positions.
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, SettlementType, settle_nne};
use grid_billing::types::{ArbeitspreisModell, MengePreis};

// Only Sparte changes — GasNEV §14 legal refs and SettlementType::NneGas are automatic:
let settlement = settle_nne(&NneInput {
    sparte: Sparte::Gas,  // ← drives GasNEV §14 + NneGas (PID 31002)
    arbeitspreis: ArbeitspreisModell::Einheitlich(MengePreis {
        menge_kwh: d("3000"),        // already kWh_Hs from edmd gas conversion
        preis_ct_per_kwh: d("1.80"),
    }),
    konzessionsabgabe: None,  // KA typically not applicable for Gas
    grundpreis: None,
    leistungspreis: None,
    // … other identity + levy-override fields, all None …
}).unwrap();

assert_eq!(settlement.settlement_type, SettlementType::NneGas);
assert_eq!(settlement.settlement_type.default_pid(), 31002);

§14a Modul 3 — zeitvariable Netzentgelte (HT/ST/NT, opt-in since 2025-04-01)

use grid_billing::{NneInput, Sparte, settle_nne};
use grid_billing::types::{
    ArbeitspreisModell, MengePreis, Konzessionsabgabe, KaKundengruppe, GemeindeGroesse,
};

let settlement = settle_nne(&NneInput {
    // Modul 3 requires all three bands; the enum makes the flat/ToU states exclusive.
    arbeitspreis: ArbeitspreisModell::Modul3ZeitVariabel {
        ht: MengePreis { menge_kwh: d("600"), preis_ct_per_kwh: d("4.20") },
        st: MengePreis { menge_kwh: d("250"), preis_ct_per_kwh: d("2.80") },
        nt: MengePreis { menge_kwh: d("400"), preis_ct_per_kwh: d("1.50") },
    },
    konzessionsabgabe: Some(Konzessionsabgabe {
        satz_ct_per_kwh: d("1.32"),
        // The group fixes the KAV §2 ceiling and annotates the position for audit.
        klasse: KaKundengruppe::Tarifkunde {
            gemeinde: GemeindeGroesse::Bis25k,
            nur_kochen_warmwasser: false,
        },
    }),
    sparte: Sparte::Strom,
    tariff_sheet_id: Some("Preisblatt-14a-2026".into()),
    leistungspreis: None,
    grundpreis: None,
    // … identity + levy-override fields …
}).unwrap();

// Positions: HT + ST + NT Arbeit, the three netzseitige Umlagen, and Konzessionsabgabe.
assert!(settlement.all_legal_refs().iter().any(|r| r.contains("§14a EnWG Modul 3")));

§14a Modul 1 — pauschale Reduzierung (offered since 2024-01-01)

Modul 1 is a flat annual amount, credited pro rata for the settlement period. It does not scale with consumption — that is what makes it pauschal, and what separates it from Modul 2, which reduces the Arbeitspreis by a percentage. The energy is billed at the full Arbeitspreis and the credit sits beside it as its own position, so the invoice shows both.

use grid_billing::{Jahresanteil, NneInput, Sparte, settle_nne};
use grid_billing::types::{ArbeitspreisModell, MengePreis};
use rust_decimal::{Decimal, dec};

let settlement = settle_nne(&NneInput {
    // Modul 1 is a variant of ArbeitspreisModell, so it cannot coexist with a
    // flat rate or the Modul 3 bands — the conflict is unrepresentable.
    arbeitspreis: ArbeitspreisModell::Modul1Pauschal {
        basis: MengePreis { menge_kwh: d("1500"), preis_ct_per_kwh: d("3.5") },
        // The NB's published annual amount, and the share of a year this
        // period covers.
        pauschale_eur_pro_jahr: dec!(120.00),
        jahresanteil: Jahresanteil::MONAT,
    },
    sparte: Sparte::Strom,
    leistungspreis: None,
    grundpreis: None,
    konzessionsabgabe: None,
    // … other fields …
}).unwrap();

// Two positions: 1500 kWh × 0.035 = 52.50 EUR Arbeit, billed in full, and the
// credit beside it — 0.083333 of a year × −120.00 EUR/Jahr = −9.99996 EUR.
assert!(settlement.all_legal_refs().iter().any(|r| r.contains("Modul 1")));
assert_eq!(settlement.positions[1].unit_price_eur, dec!(-120.000000));

Gas NNE with Grundpreis (GasNEV monthly standing charge)

use grid_billing::{NneInput, Sparte, settle_nne};
use grid_billing::types::{ArbeitspreisModell, MengePreis, Grundpreis};

let settlement = settle_nne(&NneInput {
    sparte: Sparte::Gas,
    arbeitspreis: ArbeitspreisModell::Einheitlich(MengePreis {
        menge_kwh: d("3000"),
        preis_ct_per_kwh: d("1.80"),
    }),
    // Grundpreis pairs the monthly rate with the months billed — one without the
    // other is meaningless, so they travel together.
    grundpreis: Some(Grundpreis {
        eur_per_month: d("15.00"),  // monthly base fee from PreisblattNetznutzung
        months: d("1"),
    }),
    leistungspreis: None,
    konzessionsabgabe: None,
    // … other fields …
}).unwrap();

// Gas carries no netzseitige Umlagen: 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, SettlementType, settle_gas_awh};
use grid_billing::types::SettlementPeriod;
use time::macros::date;

let settlement = settle_gas_awh(&GasAwhInput {
    malo_id: "51238696012".into(),
    nb_mp_id: "9900357000004".into(),
    lf_mp_id: "9900012345678".into(),
    period: SettlementPeriod::new(date!(2026-01-01), date!(2026-01-31)).unwrap(),
    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();

// Invoice number and dates live on InvoiceDocument, not on the settlement:
assert_eq!(settlement.settlement_type, SettlementType::GasAwhSperrung);
assert_eq!(settlement.settlement_type.default_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)

Two different facts are recorded in two different places, and the split is deliberate:

What was replaced — invoice numbers — lives on the InvoiceDocument. The same pair of settlements can be presented under different invoice numbers, so the chain is a property of the documents exchanged.
Why the recalculation happened — KorrekturGrund — lives on the SettlementResult. That is a fact about the settlement, and the invoice numbers never answer it: they cannot say whether the meter was wrong, the tariff was wrong, or the law changed underneath. Those have different consequences, so reverse() and correct() require the reason.

use grid_billing::{settle_nne, correct, KorrekturGrund, SettlementStatus};

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

let (reversal, replacement) =
    correct(&original, corrected, KorrekturGrund::Tarifkorrektur);

assert_eq!(reversal.status, SettlementStatus::Reversal);
assert_eq!(reversal.total_eur, -original.total_eur);
assert_eq!(replacement.status, SettlementStatus::Correction);
assert_eq!(replacement.korrektur_grund, Some(KorrekturGrund::Tarifkorrektur));
assert!(replacement.lineage_is_consistent());

`KorrekturGrund`	Meaning	Defect?
`Messwertkorrektur`	replaced or re-read metering (§ 60 Abs. 1 MsbG — the Aufbereitungs- und Übermittlungspflicht the corrected value discharges)	no
`Tarifkorrektur`	wrong tariff or price-sheet version applied	no
`Stammdatenkorrektur`	wrong Netzebene, KA-Klasse or Konzessionsgemeinde	yes
`RegulatorischeAenderung`	a regulatory change applies retroactively	no
`Rechenfehler`	arithmetic or logic error in the original	yes
`Clearing`	a clearing result between the parties (MMM, MaBiS)	no
`Sonstiges`	anything else — detail rides in the warnings	no

indicates_defect() separates the two: a rising Rechenfehler count is an engineering signal, a rising RegulatorischeAenderung count is not. lineage_is_consistent() catches the state this exists to prevent — a Correction with no reason, which looks like a complete settlement and answers none of the questions an audit asks of one.

use grid_billing::{settle_nne, reverse, KorrekturGrund, SettlementStatus};

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

// reverse() mirrors every position with the sign flipped. It takes the reason
// too — the storno invoice number and dates belong to the InvoiceDocument, but
// *why* the settlement was withdrawn is a fact about the settlement.
let storno = reverse(&original, KorrekturGrund::Messwertkorrektur);

assert_eq!(storno.status, SettlementStatus::Reversal);
assert_eq!(storno.total_eur, -original.total_eur);

Pre-calculation validation

use grid_billing::{MmmInput, validate_mmm_input};

let input = MmmInput { /* … */ };
let v = validate_mmm_input(&input);

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

(settle_nne validates inline — malformed NNE input returns Err directly; validate_mmm_input / validate_msb_input / validate_gas_awh_input exist for the settlement types where a pre-flight warning list is useful.)

Running them is not optional. ValidationResult::is_valid goes false on any Error-severity finding, and for a long time nothing read it: the engine computed the finding, attached it to the result, and the service billed the settlement anyway. An MSB input with billing_months = 0 produced a Grundgebühr of nothing; a Gas-AWH input with no positions produced an empty invoice — both sent to a counterparty who then had to dispute them back. netzbilanzd and invoicd now refuse an invalid input before settling, naming the finding.

Conversion to a BO4E `Rechnung` (feature `bo4e`)

use grid_billing::{InvoiceDocument, bo4e};

let rechnung: rubo4e::current::Rechnung = bo4e::into_rechnung(&document);

into_rechnung takes the document, not the settlement: rechnungsnummer, rechnungsdatum and faelligkeitsdatum are document facts, and the 1-based positionsnummer is assigned here rather than carried through the calculation. Each position's artikelnummer comes from kind_to_artikelnummer, which is None where an Artikel-ID applies instead; einzelpreis is rounded to 6 dp and gesamtpreis to 5, the same figures the settlement states.

The trace travels with the position it explains, as a mako:calculation_trace ZusatzAttribut, alongside settlement-level mako:legal_references and mako:settlement_warnings. Once the Rechnung is stored the SettlementResult is dropped, so those attributes are the only surviving record of why an amount is what it is — and what a §20 EnWG audit or an LF dispute is answered from.

Generated invoice types

PID	Description	Direction	Sparte
31001	Abschlagsrechnung Netznutzung	NB → LF	both
31002	NN-Rechnung Strom (Netznutzung)	NB → LF	Strom
31002	NN-Rechnung Gas (Netznutzung)	GNB → LFG	Gas (auto via `Sparte::Gas`)
31005	MMM-Rechnung (Mehr-/Mindermengensaldo)	NB → LF	both
31006	MMM Mehrmenge, selbst ausgestellt	LF	both
31009	MSB-Rechnung	MSB → NB / LF / ESA	Strom
31011	AWH Sperrprozesse Gas	GNB → LFG	Gas

Billing position reference

NNE

#	Position text	Unit	`kind`	Condition	Legal basis	Artikelnummer
1	`Netznutzung Arbeit`	kWh	`NneArbeit`	`arbeitspreis: ArbeitspreisModell::Einheitlich`	StromNEV §21 (Strom) · GasNEV §14 (Gas)	`Wirkarbeit` (Gas); `artikel_id` (Strom)
1–2	`Netznutzung Arbeit (§14a Modul 1)` + `§14a Modul 1 pauschale Reduzierung`	kWh · Jahr	`NneArbeitModul1`	`arbeitspreis: ArbeitspreisModell::Modul1Pauschal`	§14a EnWG Modul 1 · BK8-22/010-A	same as NneArbeit
1–3	`Netznutzung Arbeit HT/ST/NT (§14a Modul 3)`	kWh	`NneArbeitHt` / `NneArbeitSt` / `NneArbeitNt`	`arbeitspreis: ArbeitspreisModell::Modul3ZeitVariabel`	§14a EnWG Modul 3 · BK8-22/010-A	same as NneArbeit
opt	`Netzentgelt Grundpreis Gas`	Monat	`NneGasGrundpreis`	`grundpreis` set	GasNEV §14	`Grundpreis`
next	`Netznutzung Leistung`	kW	`NneLeistung`	`leistungspreis` set (RLM) — the Jahresleistungspreis pro-rated by calendar days	StromNEV §17 Abs. 2	`Leistung` (Gas); `artikel_id` (Strom)
next	`Blindmehrarbeit`	kvarh	`Blindmehrarbeit`	`blindarbeit` set and the draw exceeds the free share	StromNEV §17 (Preisblatt)	`Blindmehrarbeit`
last	`Konzessionsabgabe[tier]`	kWh	`Konzessionsabgabe`	`konzessionsabgabe` set	KAV §2 Abs. 2	`Konzessionsabgabe`

Blindmehrarbeit

A Netzbetreiber supplies a free share of reactive energy alongside the active energy and charges only what exceeds it. The customary boundary is a power factor of cos φ 0,9 — reactive energy up to tan φ ≈ 0,4843 of the active energy — but many Preisblätter round that to a flat 50 %, and some set separate shares for inductive and capacitive draw.

The share is therefore an input, not a constant: it is a term of the price sheet, and hard-coding one would bill some networks wrongly. Blindarbeit::COS_PHI_0_9 is the documented default.

use grid_billing::{Blindarbeit, NneInput};
use rust_decimal::dec;

let blindarbeit = Some(Blindarbeit {
    blindarbeit_kvarh: dec!(600),
    freigrenze_anteil: Blindarbeit::COS_PHI_0_9,
    preis_ct_per_kvarh: dec!(2.0),
});
// 1 000 kWh active → 484,3 kvarh free → 115,7 kvarh charged.

An unused allowance is never a credit — the excess floors at zero. The charge rests on the Netzbetreiber's published Preisblatt, formed under StromNEV §17; it is not §18 (Entgelt für dezentrale Erzeugung) and not §19 (Sonderformen der Netznutzung).

MMM

Both positions are always emitted; the one that does not apply carries a zero quantity. The sign convention is GPKE's, from the network operator's side: measured below profile is an ungewollte Mehrmenge the NB reimburses, and measured above it is an ungewollte Mindermenge the NB invoices.

#	Position text	`kind`	Artikelnummer	Condition
1	`Mehrmengen (Gutschrift)`	`Mehrmenge`	`Mehrmenge`	`actual < profil` — the Mehrmengenpreis is negated, so the position multiplies out
2	`Mindermengen`	`Mindermenge`	`Mindermenge`	`actual > profil`

MSB

#	Position text	`kind`	Artikelnummer	Condition
1	`Grundgebühr Messstellenbetrieb`	`MsbGrundgebuehr`	`EntgeltEinbauBetriebWartungMesstechnik`	Always
2	`Messdienstleistung`	`Messdienstleistung`	`EntgeltMessungAblesung`	`messdienstleistung_eur` set

AWH Gas Sperrprozesse (PID 31011)

#	Position text	`artikel_id`	Condition
any	`Sperrung Gaszähler`	`2-01-7-001`	Unterbrechung reguläre AZ
any	`Entsperrung Gaszähler`	`2-01-7-002`	Wiederherstellung reguläre AZ
any	`Erfolglose Unterbrechung`	`2-01-7-003`	Sperrung failed
any	`Stornierung Sperrauftrag (Vortag)`	`2-01-7-004`	Cancelled day before
any	`Stornierung Sperrauftrag (Sperrtag)`	`2-01-7-005`	Cancelled same day
any	`Entsperrung außerhalb AZ`	`2-01-7-006`	Out of hours

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

Design invariants

Invariant	Detail
No floating-point money	`rust_decimal::Decimal` throughout; `EuroAmount` for overflow guard. No `f64`.
rubo4e is opt-in	The engine returns `SettlementResult` and depends on no BO4E type; `bo4e::into_rechnung()` ships behind the off-by-default `bo4e` feature.
`recipient_mp_id` auto-populated	`lf_mp_id` (NNE/MMM) or `empfaenger.mp_id` (PID 31009) copied automatically; `sender_mp_id` is the NB, or the MSB for 31009.
`Sparte` drives settlement type	`Sparte::Gas` → `SettlementType::NneGas`, `GasNEV §14`. NN-Rechnung is PID 31002 for both Sparten — the Sparte rides on `Rechnung.sparte`, not on the Prüfidentifikator.
Every position cites regulation	`trace.legal_refs` is non-empty for every position. Enables BNetzA audit without re-calculation.
Artikelnummer decided in this crate	`BillingPositionKind::artikelnummer(settlement_type)` returns the codelist name, or `None` where the position carries an Artikel-ID instead (Strom NNE, AWH Gas, Abschlag). The decision is never left to the renderer.
`MmmGas` ≠ `MmmStrom`	Separate `SettlementType` variants ensure correct legal refs (`GaBi Gas 2.1 (BK7-24-01-008)` vs `GPKE (BK6-24-174) Teil 1 Kap. 8.4`) per position.
Immutable correction chain	`reverse()` mirrors positions, sets `status = Reversal`, links via `correction_of`. Original never mutated.
`correct()` pair	Returns `(reversal, replacement)` — both get status set atomically; caller dispatches both.
Abschläge reduce `zuZahlen` only	`gesamtnetto` and `gesamtsteuer` stand; §14 Abs. 5 UStG taxes an Anzahlung on receipt, so the settling invoice does not tax it again.
Cadence is a document fact	`IMD+7081` rides on `InvoiceDocument::cadence`, not on `SettlementType`: the same NNE settlement is the same arithmetic at any billing rhythm. The two exceptions are decided by the settlement — MMM and the Abschlag, whose PID is its cadence.
Pure functions	All settlement functions are sync with no side effects.
`recomputed_total` guard	`debug_assert_eq!(result.total_eur, result.recomputed_total())` inside `settle_nne` and `settle_gas_awh` — catches rounding bugs in debug builds. `settle_mmm` is asserted in the test suite; `settle_abschlag`, `settle_msb` and `settle_dezentrale_einspeisung` are not yet covered either way.

Related crates

Crate	Role
`grid-billing` ← this crate	Grid-side settlement arithmetic — NNE, KA, MMM, MSB, Sperrprozesse Gas
`mako-markt`	Marktstammdaten — Marktlokation, Messlokation, Marktpartner, Rollenzuordnung — the model the settlement inputs are keyed on
`invoic-checker`	Validates the resulting `Rechnung` in the service layer
`energy-billing`	The retail (LF) counterpart — the customer's invoice
`mako-invoic`	The INVOIC settle/dispute workflow these invoices travel through
`netzbilanzd` · `invoicd`	Production daemons — NB billing, and LF selbstausstellen

Part of mako, an open-source Rust platform for German energy market communication (Marktkommunikation). Full documentation: https://hupe1980.github.io/mako/

grid-billing 0.20.0