Watts per Person: Measuring the SWIS Rooftop Path Before Comparing It
A per-person rooftop solar series for Western Australia's main grid, built from records the site already holds, and the conditions another market's figures would have to meet before they could sit on the same axis.
Solar Analytica DataSWIS referencePublished Reviewed 4 sources
Summary
Measured in one matched boundary, the SWIS rooftop solar path runs from 76 watts per resident at the end of 2011 to 1,045 watts at the end of 2025. No other market can be placed on it yet, and the reason is the measurement, not the market.
Rooftop solar in the SWIS screening boundary rose from 76 watts per resident at the end of 2011 to 1,045 watts at the end of 2025.
Installation records peaked in 2011; capacity added peaked in 2021, as the average system grew from 2.2 kW to 8.8 kW.
No other market is placed on the path: the cross-market series the site holds mixes rooftop with utility-scale solar and does not document its population denominator.
Recent years will still rise while solar certificates can be created up to 12 months after installation.
Why per person, and why one boundary
Installed capacity on its own mostly measures size: a large grid has more of everything. Dividing by the people it serves turns it into a measure of how far rooftop solar has gone into a place. The division only means something when the capacity and the population describe the same place, so both figures here are for the same 246 statistical areas, the site's screening boundary for the SWIS.
The capacity is the Clean Energy Regulator's small-scale solar record, allocated from postcodes to those areas. The population is the ABS estimated resident population for the same areas. Nothing new was collected: both already sit in the SWIS atlas behind the site's other WA reporting.
The SWIS path
solar_analytica™
Cumulative CER small-scale solar capacity at 31 December, including the 2001 to 2010 historic stock, divided by ABS estimated resident population at 30 June, both for the same 246 SA2s. Computed by Solar Analytica from the committed SWIS DER snapshot, CER edition 2026-07. Recent years are incomplete while certificates can still be created.
At the end of 2011 the boundary held 169 MW of rooftop solar, 76 watts per resident. By the end of 2025 it held 3,030 MW, 1,045 watts per resident, while the population it serves grew from 2,213,463 to 2,900,474.
solar_analytica™
1,045 W
of rooftop solar per resident of the SWIS screening boundary at the end of 2025
Derived by Solar Analytica: 3,030 MW of cumulative CER small-scale solar capacity allocated to 246 SA2s, divided by their ABS estimated resident population of 2,900,474 at 30 June 2025.
That is one ratio for the whole boundary. Among the 220 areas with at least 1,000 residents, rooftop solar per resident runs from 173 watts in East Perth to 2,148 in Gingin - Dandaragan, and the median area holds 1,080:
solar_analytica™
Each dot is one SA2: cumulative CER small-scale solar capacity at 31 December 2025 divided by ABS estimated resident population at 30 June 2025. 220 of the boundary's 246 areas are drawn; the 26 with fewer than 1,000 residents, 1,371 people in all, are left out because a ratio over so few residents measures the denominator, not the rooftops: the highest of them computes to 636 kilowatts per person. The boundary-wide line is the figure in the band above, every area's capacity over every area's residents. Computed by Solar Analytica from the committed SWIS DER snapshot, CER edition 2026-07.
The shape underneath changed more than the line suggests. The most installation records came in 2011, 50,380 of them, when the average system added was 2.2 kW. The most capacity came in 2021, 341.6 MW. By 2025 the average system added was 8.8 kW, so fewer, larger systems now carry the growth.
SWIS screening boundary, 246 SA2s: rooftop solar added and in place each year, and per resident. Computed from the committed SWIS DER snapshot (CER edition 2026-07; ABS population).
Year
Added, MW
Average system, kW
Stock at year end, MW
Population
W per person
2011
112.3
2.2
169
2,213,463
76
2012
96.0
2.3
265
2,282,113
116
2013
68.2
3.2
333
2,341,038
142
2014
94.2
4.1
428
2,374,174
180
2015
94.9
4.6
522
2,400,207
218
2016
126.0
5.2
648
2,419,214
268
2017
184.9
5.9
833
2,449,948
340
2018
207.9
6.3
1,041
2,482,533
419
2019
240.5
6.7
1,282
2,524,399
508
2020
324.4
6.9
1,606
2,576,882
623
2021
341.6
7.1
1,948
2,612,742
745
2022
279.2
7.3
2,227
2,655,861
839
2023
267.3
7.7
2,494
2,750,594
907
2024
275.5
7.9
2,770
2,835,802
977
2025
260.0
8.8
3,030
2,900,474
1,045
What the path sits beside
A per-person figure describes adoption, not what the grid experiences. The site's SWIS rooftop solar atlas carries the operating side from the same boundary work: over 1,019 operating days from October 2023, rooftop solar averaged 52.4 per cent of an implied underlying-demand proxy at its daily peak and reached 80.8 per cent, and minimum operational demand fell to 504.3 MW. Isolated Grid Lessons for the World sets out which of those questions travel.
AEMO's WEM ESOO forecasts distributed rooftop PV in the SWIS of about 3,100 MW in 2026-27, a claim held open on the Forecast Ledger. That figure is on AEMO's basis and boundary, not this one, so the two are not compared here.
Why no other market is on the axis yet
The obvious source for other countries is the Ember monthly capacity series the site already reads for ten markets, and its own review of that series says why it cannot carry this comparison. Ember's solar capacity "can include utility-scale and rooftop or distributed capacity", so it is not a rooftop measure. It converts between AC and DC "case by case" with a default factor of 1.3. And the review holds cross-market per-person comparison because Ember does not document the population denominator it uses.
A market can be placed on this path when three things are true of its figures:
Rooftop only. Distributed capacity counted separately from utility-scale plant, on a stated AC or DC basis.
A matched population. Residents counted for the same area the capacity is counted in, with the vintage stated.
An operating record. Minimum demand, or rooftop share of demand, for the same system, so adoption can be read against what the grid saw.
Collecting figures like that for another market is a separate step, taken under the site's research method with its own source pins and receipts, and it has not been taken yet.
What these numbers are not
Not premises. CER figures are certificate records. Replacements, upgrades and some off-grid systems are included, so they are not a count of connected homes.
Not final for recent years. Certificates can be created up to 12 months after installation, so 2025 and the years just before it will still rise.
A screening boundary. The 246 areas approximate the SWIS from public extents, and postcodes are allocated to them fractionally. It is the same boundary for both halves of the ratio, which is what the ratio needs, but it is not the network's own customer boundary.
Two dates. Capacity is counted at 31 December and population at 30 June of the same year.