Source
https://www.branz.co.nz/pubs/research-reports/sr188/ — original source (opens in a new tab; the file is not redistributed)
BRANZ SR188 (2008) — The Performance of Solar Water Heaters in New Zealand
Pollard AR & Zhao J. 2008. The Performance of Solar Water Heaters in New Zealand. BRANZ Study Report SR188, BRANZ Ltd, Judgeford. ISSN 1178-4938. Funded by the Building Research Levy + EECA. (Companion to SR184 on installation practices.)
NZ field-study primary — pre-improvement baseline
The 35 solar + 4 heat-pump water-heating systems were monitored over one year (HPWH over summer only), installed June 2004 – October 2006 — i.e. before NZ’s G12/AS2 solar acceptable solution (Dec 2007) and EECA’s mandatory performance-testing requirement (May 2007). BRANZ frames it explicitly as the benchmark prior to the rapid 2007–08 industry improvement, so its yields are a conservative real-world floor, not a modern well-installed expectation.
Summary
BRANZ/EECA-commissioned monitoring of 39 water-heating systems in Auckland,
Wellington, Christchurch and Dunedin across four technologies (pumped evacuated
tube, pumped flat plate, thermosiphon flat plate, air-to-water heat pump). The
headline finding is that individual system design and installation quality
mattered more than technology type or region for how much renewable energy a
system delivered. Solar systems supplied on average 38% (1260 kWh/yr) of household
water-heating needs, with a wide spread driven by install quality, standing losses
and supplementary-heating control. The report is the NZ empirical primary behind
the @solar_thermal_yield model cell (via CR_016).
Key claims
- claim: "Across the monitored solar-only SWH systems, the average annual solar contribution was 1260 kWh/yr, supplying on average 38% of household water-heating needs."
source_location: "Exec summary; §5.2.3 Fig 14/15 (p36)"
- claim: "Performance clustered three ways (cluster analysis, Table 6): High cluster — 8 systems, mean 2060 kWh/yr renewable contribution, 43% solar fraction (range 1600–2540 kWh, 20–62%); Medium — 17 systems, mean 1140 kWh/yr, 43%; Low — 6 systems, mean 550 kWh/yr, 26% (range 320–760 kWh, 8–49%)."
source_location: "§5.2.4 Table 6 (p38)"
- claim: "Between-system variation dominated region and technology: one-way ANOVA gave p=0.31 for region and p=0.98 for technology group — 'the amount of renewable energy contributed... is more dependent on having a system capable of delivering a high renewable contribution than where it is located or what type of system it is.'"
source_location: "§5.2.4 Table 5 (p38)"
- claim: "The average Coefficient of Performance (COP, = draw-off energy ÷ non-environmental input) for the solar-only systems was 1.2 — about a 74% improvement over an average NZ electric storage cylinder (COP ≈ 0.67, whose standing losses run ~33% of water-heating energy per HEEP)."
source_location: "§5.2.3.1 Fig 16 (p37)"
- claim: "Collector areas ranged 1.0–5.7 m² (evacuated-tube 1.0–2.4 m²; flat-plate/thermosiphon 1.8–5.7 m²; sample mean ≈2.8 m²). Mean daily hot-water use was 140 L (SD 70; range 35–290 L/day)."
source_location: "Table 10 (p49); §5.2 (p29)"
- claim: "The heat-pump water heaters delivered approximately 1190 kWh/yr of environmental (renewable) heat over summer, ≈52% of these (smaller-user) households' water-heating needs; winter and year-round HPWH performance will be lower as it depends on ambient temperature."
source_location: "Exec summary; §5.2.4 (p36)"
- claim: "Study-period global horizontal solar radiation totals: Auckland 1341, Wellington 1358, Christchurch 1369, Dunedin 1236 kWh/m²/yr — Auckland/Wellington/Christchurch within 2% of each other, Dunedin ~8% lower (NIWA CliFlo data)."
source_location: "§4 Table 2 (p25)"
- claim: "System standing losses were high (many systems >1000 kWh/yr; thermosiphon systems with large outdoor cylinders worst); 6 of the 35 solar systems were retrofitted onto B-grade cylinders — BRANZ recommends against allowing this."
source_location: "§5.2.2 Fig 13 (p33–34); §1.3.2 (p10)"Neobiome Intelligence relevance
Primary behind @solar_thermal_yield (model ④a solar_thermal, ② resource cell).
SR188 is the NZ field source CR_016 cites
for the solar-thermal yield figure. Critical audit nuance:
- SR188 reports per-system contributions (1260 kWh/yr avg; 2060 high; 550 low), not per-m². The model’s cell is per-m² (collector sized in m²). CR_016’s 434 kWh-th/m²/yr (avg) and 710 (high-performer) are a derivation: 1260 ÷ ~2.9 m² ≈ 434; 2060 ÷ ~2.9 m² ≈ 710 (sample mean collector area ≈2.8 m² from Table 10). The per-m² figure is sound but rests on that area normalisation — recorded here so the audit trail is explicit, not implied.
- Conservative floor, not a clean rating. These are delivered contributions net of high standing losses, on 2004–06 systems installed below latitude tilt, pre-G12/AS2. That is the right quantity for displaced electric heating, but it sits at the low end — CR_016’s 550–700 kWh-th/m²/yr “modern well-installed” band is the upgrade, and Nelson/Tasman’s higher irradiance lifts it further.
- Technology choice is second-order (ANOVA p=0.98): the model is justified in costing flat-plate generically and not splitting yield by collector type.
- Heat-pump DHW corroboration: SR188’s HPWH summer COP/contribution complements OT_038 (CO₂ HPWH year-round) and CR_026 (space-heat SCOP) — same direction, independent dataset.
Research targets
Documents to retrieve
- RT_282 (new) — a post-G12/AS2 (≥2008) NZ SWH field-performance dataset to pair against SR188’s pre-improvement baseline, so the model can use a modern well-installed yield with a current primary rather than CR_016’s extrapolation.
Research gaps
- None new — SR188 resolves RT_204 (the yield primary). The per-m² normalisation caveat above is documented, not a gap.
Connections
Links to
Referenced by
Sources (4): CR_016 · OT_095 · OT_105 · OT_162
EDT domains (1): D01: Renewable Energy & Storage Systems