EDT domain: d01_renewable_energy_storage
Definition
A community-scale backup diesel generator (genset) — the firming backstop that covers the windless / sunless stretches a solar+wind+battery system cannot economically span. It is dispatchable and the standard off-grid resilience option, but its fuel is bought-in (an import), so every backup kWh is expensive and emitting. In the NI engine it is the default D20 backstop technology. CR_030
Role — backstop, not baseload
- Reaching 100% reliability from renewables alone requires uneconomic oversizing, so an off-grid community either carries a genset backstop or designs to <100% reliability. CR_030
- It runs only during deficits, so capex is low but per-kWh cost is high — the opposite profile to PV/wind. OT_063
Cost & performance
- Genset capital cost is low — ~USD 300–800/kW installed — but LCOE is the highest of all off-grid options, ~35–120 ¢/kWh, because fuel dominates. OT_063
- Fuel: NZ diesel ~NZD 3.0–3.5/L (2026). Mature, dispatchable, covers durations from hours to seasonal. CR_030
Fuel store — the D34 seven-day autonomy tank
D34 sizes a 7-day fuel store (autonomy_total_days). The engine costs it at diesel_tank_capex_per_l = 4 NZD/L — a value tagged assumed (dq low), bracketed by but not established by the only verified NZ retail anchors, the Promax list prices captured 2026-07-14. URL_022
| Product | Capacity | Price (incl GST) | $/L | Diesel-rated? |
|---|---|---|---|---|
| Bunded Diesel Tank | 500 L | $3,805 | $7.61 | Yes (“Diesel Grade UV stabilised LDPE”) |
| Bunded Oil Collection Tank | 1,000 L | $2,913 | $2.91 | No — waste-oil collection |
| Bunded Oil Collection Tank | 2,000 L | $4,079 | $2.04 | No — waste-oil collection |
$4/L bridges two unevidenced gaps at once
The only diesel-rated price is **
7.61/L** (500 L). The cheap/L figures come from waste-oil tanks used as a shell proxy — not diesel-rated. So 4 NZD/L assumes both a scale economy (half the small diesel tank’s per-litre) and a spec premium (double the oil-spec shell). No NZ vendor publishes a diesel-rated price in the 1–2 kL band; Sebco and Fuelchief are quote-only. Supply-only — excludes install, base, pipework, and any recurring compliance cost. A written vendor quote for a diesel-rated 1–2 kL self-bunded tank is still an open gap. URL_022
Where the fuel store goes — and what the law actually requires (REG_016)
A building is permitted but NOT required. reg 17.63 is precisely the genset tank (“supplies the internal combustion engine… directly through pipework” with a class 3.1D substance), and 17.63(2) caps a tank inside a building at 25,000 L (non-fire-resistant) / 50,000 L (fire-resistant) — orders of magnitude above a community store. So an above-ground outdoor bunded tank is the simplest compliant form. REG_016
| Siting choice | Consequence |
|---|---|
| Above ground, outdoors ✅ | No compliance certificate below 5,000 L (reg 17.90(2)(a)(iv); diesel = class 3.1D). Separation distances apply above 500 L. |
| Below ground ❌ | Compliance certificate required at ANY size (reg 17.90(2)(a)(i)). Do not bury the tank. |
| Inside a building ✅ | Permitted; the 25,000 / 50,000 L caps are far above a community store. |
🔴 The "recurring compliance certificate" was WRONG
An earlier reading held that “diesel ≥500 L on a stationary engine → WorkSafe stationary-container compliance certificate (recurring, fee unquantified)”, and it was carried as an OpEx risk. It is false. The 500 L figure appears twice and neither is a certificate trigger for diesel: reg 11.4(2)(c)‘s 500 L is a separation-distance threshold, and reg 17.90(2)(a)(ii)‘s 500 L is for gas. A 1–2 kL above-ground diesel tank needs no certificate and carries no recurring fee. REG_016
Three constraints that DO survive:
- Separation distances above 500 L of diesel (reg 11.9 → Schedule 12 Table 5, class 3.1D column). Extracted 2026-07-15: an above-ground diesel tank sits back from a dwelling (protected place) by 1.5 m at 1,000 L / 2 m at 2,500 L / 3 m at 5,000 L, and 0 m from a public place up to 2,500 L. So a 1–2 kL store needs a ~1.5–2 m ring from dwellings — smaller than the Sch 1A 2 m inter-dwelling spacing, so rarely binding, but now a sourced number for the site-layout model. REG_016
- Bunding — HSW does not require it below 10,000 L for class 3.1D (Table 9). ⚠ But a spill reaching water is an RMA s15 discharge (REG_012), regional plans commonly require it, and the URL_022 tanks are self-bunded anyway → model it bunded.
- “In a workplace” — Part 17 applies only to a stationary container system “in a workplace” (reg 17.1(1)). Whether a purely residential community counts as one is unsettled, and it gates whether the regime applies at all.
The renewable-diesel (HVO) and biodiesel fuel options
- HVO renewable diesel is a drop-in (EN15940) — same genset, no engine change — cutting lifecycle CO₂ ~70–90% at a ~10–30% fuel premium. But it is not yet available at NZ pumps (import/fleet only; government removing barriers). CR_030
- B100 biodiesel (FAME) is a fuel variant for the same genset (with cold-flow and storage caveats), but NZ supply is fragile — Z Energy closed its Wiri plant by 2022, and the cost is ~1.5–1.8× fossil diesel — so it is a niche, not a reliable backstop fuel. CR_030
NZ off-grid cases
- Chatham Islands / Point Durham: 3× Vestas V27 + 576 kWh battery + diesel backstop, 62–68% renewable; diesel spend fell from
1.8M to ~600k/yr, avoiding ~1,300 t CO₂/yr against a historic ~129.5 c/kWh cost. URL_012 - Stewart Island/Rakiura optimisation designs a 100%-renewable multi-carrier microgrid to displace diesel entirely — achievable but capital-heavy. LIT_033
- Where a grid exists, grid connection is itself the preferred “backup” — isolated networks are the most vulnerable. Interview II [INT_002]
Relevance to Neobiome (D20)
The model’s default backstop technology. Its fuel is a bought-fuel import that reduces SSI (extends D18) — the same import-flow mechanism as bought biomass wood (biomass_district_heating), so the engine models both with one concept. Sizing is set by the reliability target: design to 100% with a genset (import) or to an accepted LPSP ~1–5% unmet and shrink/remove it. HVO and biodiesel are fuel-variant swaps that keep the genset but lower its carbon. CR_030
Open questions
- Community-scale genset capex (NZD/kW) and standby fuel-burn for a representative remote NZ install — would firm the backstop cost cell.
- NZ HVO retail/bulk price (NZD/L) once the fuel reaches market.
Connections
Links to
Sources (7): CR_030 · LIT_033 · OT_063 · REG_012 · REG_016 · URL_012 · URL_022
EDT domains (1): D01: Renewable Energy & Storage Systems
Technologies (1): Biomass District Heating (Wood Chip)
Referenced by
EDT domains (1): D01: Renewable Energy & Storage Systems
Technologies (1): Hydrogen Storage (community-scale, seasonal)