NZ solar-thermal hot water + rainwater harvesting — cost & yield (compiled synthesis)
Compiled research — upstream-referenced
A Perplexity Deep Research synthesis. Tank pricing is live NZ supplier data (HIGH confidence); solar-thermal installed cost is HIGH (multiple 2022–25 NZ quotes); solar-thermal per-m² yield is MEDIUM-HIGH (derived from BRANZ SR188 2006-era field data + NIWA physics); community-scale costs and the cost-per-m²-catchment metric are LOW–MEDIUM (derived). Tank prices are excl. GST; add 15%.
Source verification (audit 2026-06-22) — VERIFIED
tank_cost_per_m3130/m³ and solar-thermal `1,750/m²confirmed against live NZ suppliers: Devan 25 kL = $3,200 ex-GST ($128/m³); SunFlow $7,000 installed ÷ 4 m² = $1,750/m². (runoff_coeff` 0.80 → OT_039; solar-thermal yield → OT_084 as a per-m² derivation.)
Summary
NZ cost and performance benchmarks for two MVP technologies: solar-thermal hot water (④ heat) and rainwater harvesting (④ water). Solar thermal installs at ~NZD 1,400–2,250/m² (flat-plate; evacuated-tube +15–25%) and yields ~550–700 kWh-th/m²/yr in central NZ, rising to 600–850 for Nelson/Blenheim — NZ’s highest-irradiance zone, which covers the pilot. NZ field data shows no significant flat-plate vs evacuated-tube difference (install quality dominates). Rainwater HDPE tanks cost ~NZD 110–135/m³ of storage at ≥15,000 L (live supplier pricing); a full household system runs ~3,500–6,000 non-potable to 8,000–15,000 sole-potable; collection efficiency ~80%. Fills RT_183 + RT_184; feeds D01 (solar thermal) and D03 (rainwater). (The rainwater runoff coefficient (0.8), the 35,000 L no-consent tank ceiling and the potable/non-potable treatment standards now have a BRANZ primary — OT_039 — and a supporting technology page rainwater_harvesting.) (The solar-thermal per-m² yield now has its BRANZ primary ingested — OT_084 (SR188): the 434 kWh-th/m²/yr average is SR188’s per-system 1260 kWh/yr ÷ ~2.9 m² mean collector area; the p=0.98 no-difference finding is SR188’s technology-group ANOVA.)
Key claims
- claim: "NZ solar-thermal installed cost is ~NZD 1,400–2,250/m² of collector (flat-plate, household, installed incl. GST; mid ~$1,750/m²); evacuated-tube adds ~15–25% on collector cost; large community arrays (>20 m²) ~$1,100–1,600/m² (low confidence, no NZ benchmark)."
source_location: "§1.4 Installed Cost / §3.1"
- claim: "Solar-thermal annual thermal yield for a well-installed modern system at latitude tilt is ~550–700 kWh-th/m²/yr in central NZ (Auckland–Christchurch), 600–850 for Nelson/Blenheim (NZ's best irradiance), and 430–700 for Dunedin/Southland; BRANZ SR188 measured a 434 kWh-th/m²/yr average across 33 (mostly under-sized, 2006-era) systems."
source_location: "§1.2 Annual Thermal Yield / §3.1"
- claim: "NZ field data shows no statistically significant performance difference between flat-plate and evacuated-tube collectors (BRANZ SR188 ANOVA p=0.98); installation quality dominates. Solar fraction averages 38%, up to 70–95% for well-designed systems, cutting water-heating cost up to 75% in summer / 25–45% in winter."
source_location: "§1.3 / §3.1"
- claim: "NZ rainwater HDPE round-tank pricing (live, excl. GST): ~NZD 110–135/m³ of storage for ≥15,000 L tanks; a 10,000 L tank ~$2,100–2,600; 25,000–30,000 L ~$2,700–3,750. Per-m³ cost falls sharply with tank size."
source_location: "§2.3 Plastic Tank Pricing"
- claim: "A full NZ household rainwater system costs ~NZD 3,500–6,000 (garden/non-potable: tank + diverter + pump + labour) or ~$8,000–15,000 (sole potable supply with UV treatment, 30 kL+ tank); derived cost per m² of catchment ~$50–90/m² (a weak metric — cost is driven by storage volume, not roof area)."
source_location: "§2.4 Full System Cost / §2.5"
- claim: "Roof collection efficiency is ~75–90% of rainfall (use 0.80); ~65% of a standard household's water needs can be met from rainfall; the largest tank not requiring building consent is 35,000 L (ground-supported). First-flush diversion 20–50 L per 100 m² roof."
source_location: "§2.1 Regulatory / §2.2 Catchment Yield"Solar-thermal yield by region — model data (@solar_thermal_yield)
Well-installed modern system, latitude tilt, kWh-th/m²/yr, from CR_016:
| Zone | Yield (kWh-th/m²/yr) |
|---|---|
| Northland / Bay of Plenty | 440–900 |
| Auckland / Wellington / Hawke’s Bay | 400–860 |
| Nelson / Blenheim (pilot — NZ best) | 600–850 (use ~700) |
| Christchurch | 415–870 |
| Dunedin / Southland | 365–790 |
Rainwater tank cost — model data (NZD/m³ storage, excl. GST)
From CR_016: 10,000 L ~210–300/m³; 15,000 L ~167–174/m³; 25,000–30,000 L ~107–135/m³. Full installed system per m² catchment ~50–90/m² (derived).
Neobiome Intelligence relevance
Fills RT_183 (solar thermal) and RT_184 (rainwater). Recommended model values:
| Cell | Value | Tag |
|---|---|---|
solar_thermal cost | ~1,750/m² household (flat-plate); ~1,400/m² community | sourced (household); low-conf (community) |
@solar_thermal_yield (pilot Nelson/Tasman) | ~700 kWh-th/m²/yr (range 600–850) | sourced (medium-high) |
rainwater cost | ~$60–75/m² catchment (full non-potable system) | sourced (medium) — but see caveat |
| rainwater collection efficiency | 0.80 | sourced — confirms the spec’s runoff 0.8 |
Pilot is NZ’s best solar-thermal site. Nelson/Tasman has the highest irradiance in NZ, so solar thermal performs better at the pilot than the national average — a point in its favour for the water-heat domain. Use flat-plate for costing (NZ field data shows no evacuated-tube yield advantage).
Rainwater cost caveat (don’t mis-model). The model’s cost cell is NZD/m²-catchment, but the report flags this as a weak derived metric — rainwater cost is driven by storage volume, not roof area. The firm number is NZD 110–135/m³ of storage (≥15,000 L). If the model sizes rainwater by catchment area alone, the ~$60–75/m² figure assumes a reference storage:catchment ratio (~10 kL per 120 m²); a community sizing more storage per m² will cost more. Consider sizing rainwater capex on storage volume, not catchment area.
Out of MVP scope but noted: council rebates (Auckland up to 5,000; Far North 500) and potable UV treatment ($500–2,000) — relevant to a real costing, not the MVP cell.
Research targets
Documents to retrieve
- BRANZ SR188 (2008) — The Performance of Solar Water Heaters in New Zealand — the NZ field-study primary behind the yield figures (33 monitored systems; 434 avg, 710 high-performer kWh-th/m²/yr; flat-plate vs evacuated-tube ANOVA). New target RT_204; firms
@solar_thermal_yield. - level.org.nz solar-water-heating + rainwater-harvesting pages — corroborating BRANZ guidance (sizing, collector types, first-flush). Cross-ref; no separate RT.
- PCE — Comparison of solar and heat-pump water heaters in NZ — the solar-vs-heat-pump trade-off (relevant to choosing solar thermal vs heat-pump hot water). Cross-ref.
Research gaps
- No NZ community-scale solar-thermal cost benchmark — the >20 m² figure (~$1,100–1,600/m²) is international-scaling, low confidence. A real community tender would firm it.
- Rainwater cost metric — NZD/m²-catchment is non-standard; NZD/m³-storage is the defensible primary. A model-design choice, not a retrieval target.
Connections
Links to
Technologies (1): Rainwater Harvesting (Roof Collection & Dual R…
Referenced by
Sources (8): LIT_051 · OT_036 · OT_038 · OT_039 · OT_041 · OT_078 · OT_084 · OT_105
EDT domains (2): D01: Renewable Energy & Storage Systems · D03: Water, Waste & Circular Systems
Technologies (1): Rainwater Harvesting (Roof Collection & Dual R…