Rewiring Aotearoa — Solar generation & area-requirements calculator (2025) (OT_154)
The m²→kWh/yr method (and panel density) behind OT_064's 500 m² ≈ 130 MWh/yr benchmark — resolves RT_231
A Rewiring Aotearoa spreadsheet that converts a roof/ground area (m²) into a PV system size (kW), annual + lifetime generation (kWh), upfront cost, and export/self-consumption value, and inverts it to size a system from an annual energy demand. Its parameter sheet supplies the two things OT_064 left implicit: the effective installed density ≈ 0.221 kWp per m² (0.4 kW panel / 1.627 m² × 90% usable space) and the area→yield rule (≈ 260 kWh/m²/yr rooftop, 270 kWh/m²/yr ground, after 30-yr degradation). For NI this is a candidate solar-sizing method (D01); its cost/tariff inputs are RA’s own and are NOT used for the model’s cost cells.
Summary
This is the Rewiring Aotearoa “Solar generation & area requirements calculator” — a public spreadsheet tool (7 sheets, last updated 29 January 2025) that helps a user estimate solar numbers from either a known area (“how much would I generate from this roof/ground space, and what is it worth?”) or a known energy demand (“how big a system, and how much roof/ground area, do I need?”). The engine sheet (⚙️ Calculation inputs) holds the physical and economic parameters: a 1,640 × 992 mm / 0.4 kW panel (1.627 m²), 90% usable space, giving an effective installed density of ≈ 0.221 kWp/m²; a 15% capacity factor on an optimal roof angle or ground (“average across NZ regions”), reduced to a 14.475% effective roof CF for a double-gabled roof (50% of the roof at the optimal angle, 50% at the opposite face which yields ~93% as much — derived on the 📎 Roof angle capacity factor sheet from NIWA SolarView data for four Canterbury/Hawke’s Bay sites); 0.5%/yr degradation (7.15% average over a 30-yr life); and grid/export price extrapolations. From these it computes ≈ 260 kWh/m²/yr (rooftop, degradation-adjusted) and ≈ 270 kWh/m²/yr (ground). These are exactly the numbers behind the OT_064 Machine Count benchmark (500 m² × 260 kWh/m²/yr = 130 MWh/yr), and the density figure resolves the “m²→kW density not stated” caveat OT_064 flagged. It also gives a clean area→kW→kWh sizing method (system kW = demand ÷ 8,760 h ÷ CF; roof m² = generation ÷ 260; ground m² = generation ÷ 270). The tool’s cost inputs are RA’s own simplified assumptions (1,000/kW default panel cost → 221/m²; a scratch comparison sheet uses a 2,000/kW input, from which a **reconstructed** ≈442/m² — 2,000 × the 0.221 kWp/m² density, not a value the sheet itself outputs — reproduces OT_064’s ~$220,000 for 500 m²) and are not used for the NI cost cells, which are separately sourced.
Key claims
- claim: "PANEL & EFFECTIVE DENSITY (resolves the OT_064 m²→kW gap). Reference panel = 1,640 mm × 992 mm = 1.627 m², 0.4 kW output → 0.246 kW/m² gross module density; applying a 90% usable-space (packing) factor gives an EFFECTIVE INSTALLED DENSITY of 0.221 kWp per m² of roof/ground area (≈ 4.5 m² per kWp). This is the density Rewiring's own 500 m² ≈ 130 MWh/yr benchmark (OT_064) does not state."
source_location: "'⚙️ Calculation inputs'!B2 (1640), B3 (992), B4 (=1.627 m²), B6 (0.4 kW), B7 (0.246 kW/m²), B8 (0.9 usable), B9 (0.221 kW/m² effective)"
- claim: "CAPACITY FACTOR. 15% capacity factor on an optimal roof angle or on ground ('taking average across NZ regions'); the opposite gabled-roof face yields 93% as much (13.95% CF); assuming a double-gabled roof with 50% of area at the optimal angle gives an EFFECTIVE ROOFTOP CF of 14.475%. Hours per year = 8,760."
source_location: "'⚙️ Calculation inputs'!B16 (0.15), B15 (0.93 relative), B17 (0.1395), B18 (0.5 optimal share), B19 (0.14475 effective roof CF), B13 (8760 hrs)"
- claim: "ROOF-ANGLE FACTOR DERIVATION (NIWA SolarView). The 93% optimal-vs-opposite ratio is the average of four NZ site pairs (Christchurch western suburb, Christchurch New Brighton, Hawke's Bay Taradale, Hawke's Bay Haumoana), each comparing a north-facing 45° tilt against a south-facing flat (0°) panel; average relative difference in annual sunlight between gabled roof faces = 93.48% (rounded to 0.93 in the engine)."
source_location: "'📎 Roof angle capacity factor'!C10 (=0.9348, AVERAGE of C2:C9); A12 'Data from NIWA Solarview'"
- claim: "DEGRADATION. Panel degradation 0.5%/yr compounded over a 30-yr life; the engine applies the AVERAGE loss over years 0–30 = 7.15%, used to convert nameplate to lifetime-average generation. Panel lifetime = 30 years."
source_location: "'⚙️ Panel degradation'!F3 (0.005/yr), F8 (=AVERAGE loss over 30 yrs = 0.0715); '⚙️ Calculation inputs'!B21 (0.0715), B33 (30 yr lifetime)"
- claim: "AREA→YIELD OUTPUT (the OT_064 benchmark method). Degradation-adjusted specific yield = 269.98 kWh/m²/yr on GROUND (full CF) and 260.53 kWh/m²/yr on ROOFTOP (effective roof CF). ⇒ 500 m² rooftop × 260.5 = 130.3 MWh/yr, reproducing OT_064's '500 m² ≈ 130 MWh/yr'. Pre-degradation figures are 290.8 (ground) / 280.6 (rooftop) kWh/m²/yr."
source_location: "'⚙️ Calculation inputs'!B24 (290.77 ground, =B9*B13*B16), B25 (269.98 ground deg-adj), B28 (280.59 roof, =B9*B13*B19), B29 (260.53 roof deg-adj)"
- claim: "AREA→kW→kWh SIZING METHOD. Required system size (kW) = (1 + redundancy) × demand(kWh/yr) ÷ 8,760 h ÷ CF; roof space (m²) = generation ÷ 260.5 kWh/m²/yr; ground space (m²) = generation ÷ 270.0 kWh/m²/yr. Worked example on the sheet: 9,000 kWh/yr demand → 6.85 kW system → 34.5 m² roof or 33.3 m² ground."
source_location: "'⚡️ Solar system size & area req'!B5 (6.85 kW, =(1+B4)*(B2/B13/B16)), B12 (34.55 m² roof, =B7/B29), B13 (33.34 m² ground, =B7/B25)"
- claim: "COST & TARIFF INPUTS (RA's own assumptions — NOT used for NI cost cells). Default panel cost $1,000/kW → $221/m² of installed area (main 'Solar generation' sheet); a separate scratch 'comparison' sheet carries a $2,000/kW cost input (cell B10). The ≈$442/m² that reproduces OT_064's ~$220,000 upfront for 500 m² is NOT a figure the tool outputs — it is a RECONSTRUCTION (2,000 $/kW × the 0.221 kWp/m² effective density ≈ $442/m²); the scratch sheet's own cost/area cell (B11) is a broken $9,024/m² its author flagged 'To do'. Export price: $0.135/kWh (2024) extrapolated at 1.69% real inflation over 30 yr, averaged → $0.1756/kWh. Grid price: $0.262/kWh (2024) → $0.3405/kWh 30-yr average. Value at 50% self-consumption blends the two."
source_location: "'⚙️ Calculation inputs'!B11 ($1,000/kW), B12 ($221.28/m²), B31 ($0.1756 export, note cell C31), B32 ($0.3405 grid, note cell C32); 'Solar generation area compariso'!B10 ($2,000/kW input), B11 ($9,024/m² broken scratch output — the $442/m² is a reconstruction, not this cell)"Neobiome Intelligence relevance
Resolves RT_231 — the m²↔kW density and area→yield method behind the OT_064 benchmark (D01). OT_064’s Machine Count solar benchmark (“500 m² rooftop OR ground ≈ 130 MWh/yr for ~$220,000”) was recorded with the explicit caveat “m²→kW density not stated — order-of-magnitude.” This calculator is the Supporting-Documents artifact behind that benchmark and supplies the missing method:
- Effective installed density ≈ 0.221 kWp/m² (≈ 4.5 m²/kWp) — the clean answer to the m²↔kW gap. This is a standard-panel spec (0.4 kW / 1.627 m² module × 90% usable space), so it is reproducible and appropriate for a community rooftop/ground packing estimate. (Contrast utility-scale OT_056 ~35 Wp-ac/m² ≈ 0.035 kWp/m², which is far lower because it includes inter-row spacing and tracker land — the two densities answer different questions: panel-packed roof area vs. ground-array footprint.)
- Area→yield rule ≈ 260 kWh/m²/yr rooftop / 270 kWh/m²/yr ground (degradation-adjusted), built from CF 15% × 8,760 h × density × (1 − 7.15% avg degradation). The 15% CF independently agrees with the model’s
pv_yield(~15%, RD_013) and EECA’s ~16% (URL_013). - A ready area↔kW↔demand sizing method for a “how much roof do I need?” NI feature: system kW = demand ÷ 8,760 ÷ CF; area = generation ÷ specific-yield.
What NOT to take from it. The cost side is RA’s own simplified assumption — the 1,000/kW default (and the 2,000/kW scratch-sheet input whose reconstruction against the 0.221 kWp/m² density — ≈442/m² — reproduces OT_064's 220,000) are round advocacy-tool inputs, not market benchmarks; the NI community-PV capex is already anchored to OT_077 (~1,800/kWp) and [[cr_024_nz-community-pv-battery-cost-2026|CR_024]] (~1,600/kWp). The export/grid 30-yr price extrapolations (0.1756/0.3405) are RA modelling choices; NI’s tariff inputs come from CR_022/URL_014/REG_005. Feeds D01 as a method/density source, not a cost source.
Research targets
Documents to retrieve
- None. This resolves RT_231 (RA “Solar generation & area-requirements calculator” — the m²→kWh/yr method behind the 500 m² = 130 MWh/yr benchmark), the doc raised by OT_064.
Research gaps
- No new RT. The density (0.221 kWp/m²) and CF (15%) are already independently corroborated (RD_013, URL_013, OT_056, OT_064); the cost/tariff inputs are deliberately not adopted (NI uses OT_077/CR_024/CR_022). A NZ per-region specific-yield refinement is already covered by the national solar layer (RD_013 + CR_025 validation) — no additional target warranted.
Notes
Primary artifact (Rewiring Aotearoa public spreadsheet, “Last updated 29 January 2025”), read via openpyxl at both formula and cached-value level — every figure in key_claims traces to a named cell (sheet!cell recorded in source_location). data_quality: high, not verified: the core density/CF/yield figures trace to the raw AND are independently corroborated (RD_013/URL_013/OT_064/OT_056), but Rewiring is an advocacy organisation and the tool’s economic inputs (the 1,000/kW default cost, the 30-yr export/grid price extrapolations) are RA's own assumptions and are **not** used for any NI calculation cell. Interpretation caveats: (1) the `Solar generation area compariso` sheet is a broken scratch sheet (its author left a "To do: reference Calculations sheet rather than values" note and it hard-codes a 10 kW "panel" at 2,000/kW, producing an absurd 9,024/m² in its own cost/area cell); do not use its output table — but its 2,000/kW cost input IS the origin of the reconstructed ≈442/m² that reproduces OT_064's 220,000. (2) The 15% CF is a national average; NI already carries per-region yield (RD_013). context:ni — feeds D01 as the density/area-sizing method behind OT_064. Resolves RT_231; cross-references OT_064.
Connections
Links to
Referenced by
EDT domains (1): D01: Renewable Energy & Storage Systems