eeg-billing

Pure EEG/KWKG feed-in settlement library for German energy markets.

eeg-billing implements all nine settlement models mandated by EEG 2000–2024 (Solarpaket I) and §7 KWKG 2023. It is the calculation core used by einsd — the Einspeiser Registry daemon.

Design constraints

Constraint	Detail
No I/O	All inputs are passed as arguments. No database calls, no HTTP.
No async	Synchronous throughout — wraps cheaply in `tokio::task::spawn_blocking` if needed.
No float money	All monetary amounts use `rust_decimal` with fixed precision.
Deterministic	Same inputs always produce the same output.
EEG-version-aware	Rules and rates dispatch on `EegGesetz` enum (Eeg2000–Eeg2023 + Kwkg).

Settlement models

#	`SettlementModel`	Regulatory basis
1	`Verguetung`	§21 EEG 2023 (§16 EEG 2012, §18 EEG 2017)
2	`Mieterstrom`	§38a EEG 2023
3	`DirektvermarktungGleitend`	§20 EEG 2023 + §20 Abs. 3 Managementprämie
4	`Ausschreibung`	§§22a, 28 EEG 2023
5	`PostEegSpot`	§21b EEG 2023 (expired Förderung)
6	`Eigenverbrauch`	§42 EEG 2023
7	`KwkgZuschlag`	§7 KWKG 2023
8	`Flexibilitaetspraemie`	§50 EEG 2023
9	`Flexibilitaetszuschlag`	§50b EEG 2023

Regulatory features

Feature	Basis
§51 Negativpreisregel — suspend settlement during 6/4/any consecutive negative-price hours	§51 EEG 2023 / §24 EEG 2017 / §6 EEG 2012; version-aware thresholds via `EegGesetz`
§52 Pflichtzahlungen — `SanktionsTyp` (€10/kW or €2/kW per §52 Abs. 3 Nr. 2) + `SanktionAlt` (3-tier old-regime)	§52 EEG 2023
§53 Vergütungsabzug — 0.4 ct solar/wind, 0.2 ct biomasse/gas	§53 EEG 2023
§25 MaStR Bestandsschutz — blocks settlement for unregistered Anlagen after deadline	§25 EEG 2023
§27 Mehr-/Mindererzeugung	§27 EEG 2023
Repowering §22 / Zusammenlegung §24	§§22, 24 EEG 2023
`foerderendedatum_eeg()` = Dec 31 of year+20 (statutory)	§25 Abs. 1 Satz 2 EEG 2023
`foerderendedatum_eeg_ausschreibung()` = exact 20 years (Ausschreibung)	§22 EEG 2023
§12 Abs. 3 UStG (PV Nullsteuersatz) via `mwst_rate_override`	§12 Abs. 3 UStG (seit 01.01.2023)

Usage

use eeg_billing::{
    calculate_settlement, SettlementInput, SettlementModel,
    EegGesetz, ErzeugungsArt,
};
use rust_decimal_macros::dec;
use time::macros::date;

let input = SettlementInput {
    gesetz: EegGesetz::Eeg2023,
    model: SettlementModel::DirektvermarktungGleitend,
    erzeugungsart: ErzeugungsArt::Photovoltaik,
    installed_kw: dec!(100),
    // kWh produced in the settlement period
    kwh_produced: dec!(850),
    // Marktwert Solar from BDEW monthly table
    marktwert_ct_kwh: dec!(8.34),
    // Anzulegender Wert (from Ausschreibungsergebnis or statutory table)
    anzulegender_wert_ct_kwh: dec!(9.20),
    period_start: date!(2026-06-01),
    period_end: date!(2026-06-30),
    managementpraemie_ct_kwh: Some(dec!(0.40)), // §20 Abs. 3
    ..Default::default()
};

let result = calculate_settlement(&input)?;
println!("Marktprämie: {} EUR", result.total_eur());
for pos in &result.positions {
    println!("  {}: {} ct/kWh × {} kWh", pos.name, pos.rate_ct_kwh, pos.kwh);
}

`EegGesetz` variants

Variant	Applies to Anlagen commissioned
`Eeg2000`	before 2012-01-01
`Eeg2012`	2012-01-01 to 2016-12-31
`Eeg2017`	2017-01-01 to 2020-12-31
`Eeg2021`	2021-01-01 to 2022-12-31
`Eeg2023`	2023-01-01+ (including Solarpaket I)
`Kwkg`	BHKW/KWK Anlagen under KWKG

`ErzeugungsArt` variants (20 types)

Photovoltaik, PhotovoltaikFreiflaeche, Wind, WindOffshore, Biomasse, BiomasseFluessig, Biogas, Geothermie, Wasserkraft, Deponie, Klaergas, Grubengas, Klaeranlagengas, SonstigeGase, SonstigeBiomasse, SonstigeErneuerbare, KwkgBhkw, KwkgDampf, KwkgGasmotor, KwkgBrennstoffzelle

Regulatory basis

EEG 2023 (BGBl. I 2023 Nr. 138, in force 29.07.2023) — Solarpaket I amendments
KWKG 2023 (BGBl. I 2023 Nr. 396, in force 29.12.2023)
BNetzA rate tables — published annually at bundesnetzagentur.de
§51 thresholds — version-resolved: EEG 2012 (6h Wind<3MW / other<500kW), EEG 2017 (6h/<500kW), EEG 2021 (4h/<500kW), EEG 2023 (any/<100kW)
§66 EEG 2017 Bestandsschutz boundary — 2016-01-01

Testing

cargo test -p eeg-billing --all-features

190+ unit tests covering all 9 models, all EEG versions, §51 edge cases, §52 Pflichtzahlungen, DST-safe date arithmetic, and §25 MaStR sanctions.

eeg-billing 0.9.0