Source
doi:10.21420/5WW0-J087 — original publication (opens in a new tab; the file is not redistributed)
GNS/EECA (2024) — Bay of Plenty RETA Geothermal Energy Assessment
Carey BS, Alcaraz SA, Wells C, Carden Y, Moore G. 2024. Regional Energy Transition Accelerator — Bay of Plenty — Geothermal Energy Assessment. GNS Science Report 2024/02, 74 p. DOI 10.21420/5WW0-J087. Commissioned by EECA; GSHP input from GeoExchange Australia, high-temperature direct-use from Dobbie Engineers.
Cost figures are explicitly indicative
The four site assessments are pre-design, “indicative only… not to be relied upon for progressing conversion,” and the drilling line-items carry a 30% contingency. They are large-scale (0.7–4.8 MW_th) open-loop aquifer (water-source) systems, not small closed-loop community space-heat GSHPs. Hence
data_quality: medium— they corroborate the model’s GSHP cost band but do not lift it to high.
Summary
GNS Science’s geothermal decarbonisation assessment for EECA’s Bay of Plenty RETA —
the NZ primary behind CR_014’s ground-source heat
pump (GSHP) cost and COP figures. Four sites were costed for fossil-heat replacement
(three GSHP using ambient/low-temperature aquifer water, one high-temperature direct
use). For the NI model the load-bearing content is the GSHP capital-cost estimates
(Tables 5.1–5.2) and the COP-vs-source-temperature table (5.3) — these anchor the
④a heat_pump_ground cost cell and the @cop_gshp coupling. The report stresses
GSHP using ambient groundwater “has application widely across New Zealand,” with
open-loop aquifer systems already common in Christchurch and closed-loop ground heat
exchangers suiting rural sites without an aquifer.
Key claims
- claim: "Whakatāne Hospital — open-loop GSHP on ~15°C aquifer water meeting 100% of heating + cooling (peak 2.1 MW_th heat / 1.2 MW_th cool; annual 3.6 GWh heat + 2.2 GWh cool; 3 abstraction + 4 injection wells ~350 m, 60 L/s). Indicative total $5,607,853 (≈$2,670/kW_th of heating capacity, incl. 30% drilling contingency); cuts peak electrical load >35% and annual electrical energy >40% vs an ASHP."
source_location: "§5.3 + Table 5.1 (p44–45)"
- claim: "Whakatāne Growers — 3.2 ha covered-crop horticulture, peak 4.8 MW_th, four 1.2 MW open-loop GSHPs on 15°C aquifer water (60 L/s, ~350 m wells). Indicative total $6,570,415 (≈$1,370/kW_th); excludes a required ~3 MVA electrical-supply upgrade."
source_location: "§5.4 + Table 5.2 (p45–46)"
- claim: "GSHP system COP rises steeply with source-water temperature (Table 5.3): ASHP 2.0; GSHP@15°C 2.77 (28% energy saving vs ASHP); 20°C 3.2 (38%); 25°C 3.6 (44%); 30°C 4.0 (50%, +31% vs a 15°C GSHP). Generic GSHP COP is ~4–6 vs ASHP ~2–3, GSHP being seasonally stable because ground/groundwater is near-constant year-round."
source_location: "Table 5.3 (p46); §2.2 (p18–19)"
- claim: "Dominion Salt — a 720 kW_th high-temperature GSHP drawing 45°C aquifer water (20 L/s, returned at 37°C) generates 900 kg/hr of 120°C steam at COP 2.8 (253 kW electrical input) to replace gas-fired drying steam. Indicative total $5,198,484."
source_location: "§5.5 + Table 5.4 (p46–47)"
- claim: "Geothermal and GSHP solutions achieve operational greenhouse-gas reductions of 80–100% versus natural gas for the same heating duty (excluding grid-electricity emissions), where the geothermal solution can meet the application's temperature requirement."
source_location: "Abstract (p.v); §7 (p50)"
- claim: "Indicative industrial process-heat cost by fuel (Dec 2023, $70/t carbon): geothermal steam $10.25/GJ (lowest), electricity heat-pump (COP 3.5) $12.38/GJ, biomass $16.25, wood pellets $20.00, gas $18.20, coal $20.01, electricity resistance $43.78/GJ."
source_location: "Table 2.1 (p18)"
- claim: "GSHP using ambient groundwater has wide national applicability: open-loop aquifer systems are common in Christchurch post-2010/11 (e.g. Christchurch Arts Centre, 2.4 MW heat-pump capacity on ~13°C aquifer water; Seward & Carey 2021 document four facilities); where no aquifer exists, closed-loop horizontal ground heat exchangers suit rural/residential sites (≥2 m soil depth, high clay/moisture best)."
source_location: "§2.2.2 (p20–21); §2.2.3 (p22); §7 (p50)"Neobiome Intelligence relevance
Primary behind the ④a heat_pump_ground cost cell + @cop_gshp coupling (heat
domain). Firms CR_014’s GSHP figures, which derive
directly from this report’s Tables 5.1–5.3.
- Cost cell — model
heat_pump_ground=2,500/kW_th**. The two community/ industrial GSHP sites bracket this at **1,370–2,670/kW_th (open-loop aquifer, MW-scale, 30% contingency). The model sits at the upper end → conservative. Stays medium (indicative, open-loop-specific, excludes some electrical upgrades). - COP coupling — model
@cop_gshp= 4.2. ⚠ This report shows GSHP COP is source-temperature-driven: 2.77 at 15 °C ambient → 4.0 at 30 °C. The model’s 4.2 matches the generic range (4–6) and a warm/elevated source, but is optimistic for a generic NZ community on ~12–16 °C ambient groundwater at hot delivery (where ~2.8–3.2 is more realistic). Documented; firming raised as RT_284. - National applicability — supports
heat_pump_groundfeasibility_rule: alwaysfor the closed-loop case (rural GHX needs no aquifer), with the open-loop variant resource-gated (reliable high-volume aquifer + reinjection consent). - Internal inconsistency noted: the report’s exec summary (p.vi) reverses the two site totals vs Tables 5.1/5.2; the tables are authoritative.
Research targets
Documents to retrieve
- None — RT_203 resolved by this report.
Research gaps
- RT_284 (new) — firm
@cop_gshpfor a generic NZ community space-heat GSHP on ambient (~12–16 °C) source (closed-loop GHX or ambient aquifer). The model’s 4.2 reflects a warm/elevated source; OT_086 Table 5.3 shows 15 °C ambient gives ~2.77. A measured NZ closed-loop SCOP at moderate delivery temp would resolve the spread.
Connections
Links to
Sources (1): CR_014
Referenced by
EDT domains (1): D01: Renewable Energy & Storage Systems
Sources (1): CR_014