Sentinel-2 L2A + NTBLiang-style, S2 coefficients adapted in-house
ESA satellite (10 m) + narrowband-to-broadband albedo physics.
Feeds: the measured solar reflectance R every roof leads with. Assumes the Liang coefficients for S2 bands.
How we measure every UK roof from free satellites and open data, and turn it into a ranked, costed map of where Emissiv’s coating matters most. The whole chain, in plain English.
We measure how reflective and how hot every roof is, then turn that into where the cooling coating is worth the most.
Emissiv’s product is a radiative-cooling coating. The number that decides where it matters most is a roof’s reflectance. So the tool that measures reflectance nationwide is not a side project. It is the demand-generation engine for the core business.
The output is a drop-in superset of the Google Solar API: the same per-roof geometry schema, plus reflectance, material and thermal, the layers it doesn’t carry.
A radiative-cooling surface does two things: it reflects sunlight and it radiates heat to the sky. The first is governed by albedo (solar reflectance, 0 to 1) and that is exactly what a satellite can read. A dark roof near 0.10 albedo absorbs about 90% of the sun that hits it. That is both the problem (it bakes) and the opportunity (the coating has the most to give there). Find the dark roofs, and you have found the customers.
No imagery bought, nobody waited on. That is the unit economics: national coverage at near-zero variable cost.
| Layer | Source | What it gives | Cost |
|---|---|---|---|
| Imagery | Sentinel-2 (ESA), 10 m (visible/NIR; SWIR bands 20 m, resampled to 10 m), 5-day revisit | the pixels we read albedo from | free |
| Cross-checks | Sentinel-1, Landsat | independent albedo sanity checks | free |
| Footprints + material | OS NGD (Ordnance Survey) | authoritative per-building outline + roof material | free |
| Building record | OS NGD | UPRN, building use, construction year, floors | free |
| Geometry | EA LiDAR, 1 m | roof pitch, orientation, height, form | free |
| Energy + cooling | EPC / SBEM (GOV.UK), joined by UPRN | A-G band, floor area, and per-building cooling demand + efficiency | free |
| Planning + grid | planning.data.gov.uk, PVGIS, National Grid | listed/conservation/flood, irradiance, live carbon | free |
Each step is simple physics or an authoritative lookup. Nothing is a black box.
Sentinel-2 sees in narrow spectral bands. A narrowband-to-broadband (NTB) physics formula converts them to one solar reflectance, averaging only the pixels inside the roof footprint of the least-cloudy recent scene.
Where OS NGD has it (about 92% of roofs) we use its authoritative roof material; elsewhere a model trained on real labels is the fallback, with LiDAR geometry as a sanity constraint (a steep roof is not a flat membrane).
Pure physics for an opaque surface.
Absorbing is only half the story. A roof also radiates heat back to the sky, set by thermal emittance (most roofs ~0.90, bare metal ~0.45). We solve the standard ASTM E1980 energy balance for the surface temperature, which gives a modelled peak temperature and a proper SRI (hot black roof = 0, cool white roof = 100). The payoff: a reflective-looking metal roof can run ~10°C hotter than its albedo suggests, because it cannot radiate.
For a dark roof, a 95%-reflective coating raises albedo by ΔA. The solar heat it stops absorbing is robust physics that applies to every roof; a slice of it converts to money and carbon for cooled buildings. How firmly we ground that cooling demand follows a three-tier ladder, exactly mirroring the material ladder (authoritative → published benchmark → unknown): we use the building’s own EPC cooling figure where it exists, fall back to a published cooling benchmark for its building type where the use implies cooling, and otherwise claim no pounds, only the physics.
Everything down to heat rejected is firm: ΔA and area are measured per roof, and (0.95 − albedo) × G × Area is physics that holds for every roof, cooled or not. G is this roof’s own annual sun, not a flat 1000: the live per-city horizontal irradiation (PVGIS, ~910 Glasgow to ~1140 London) × a sky-view factor from the 1 m LiDAR DSM that accounts for overshadowing by taller neighbours, which also damps the longwave term (a shaded roof sees less cold sky). The cost line is grounded per building, not a borrowed coefficient: the cooling saving is bounded by that building’s own EPC cooling demand (the SBEM-modelled kWh/m² cooling × floor area) and converted at its own EPC cooling efficiency (SSEER), so an uncooled building correctly saves nothing. The cooling cut has two physical terms (the ASTM sol-air balance): a daylight reflectance term (ΔR × G) and a 24/7 emittance term (Δε × L) for the heat the coating radiates to the sky. Emittance is the core lever on low-emittance bare metal (Δε ≈ 0.5, often a fifth to a third of the saving) and a rounding error on already-high-emittance non-metal roofs (Δε ≈ 0.05, a couple of percent). The modelled factors are f = Uroof/ho, the fraction of the surface effect that reaches the conditioned space (~1–3%, because an insulated roof already blocks most of it; using surface heat directly would overstate the indoor effect ~50–100×, Synnefa/Akbari 2007), tiered by construction age; and L ≈ 440 kWh/m²/yr, the UK all-sky annual longwave sky-cooling energy (ASHRAE clear-sky ~63 W/m² derated for cloud), our most uncertain input. We then cap the result at the building’s measured cooling electricity. The £0.26/kWh is a representative UK price (around the Ofgem cap), dated rather than a noisy live spot price. This is a cooling-season figure: high emittance also loses a little heat in winter, and the UK is heating-dominated, so we report the cooling saving and the peak-temperature cut, not a net-annual claim. We lead with the physics; the pounds are the per-building modelled overlay, and zero where there is no cooling signal at all.
The three-tier cooling ladder. Only about 38% of roofs carry an EPC, so a measured cooling figure is the exception, not the rule. To avoid a blank for every other commercial roof, the cooling demand walks the same ladder as material does. Tier A · measured: the building’s own EPC/SBEM cooling electricity (best, used wherever present). Tier B · estimated: no EPC cooling, but OS NGD building use implies cooling (office, retail, commercial, health and the like), we apply a published UK cooling-intensity benchmark for that use class (BEES 2014-15, the BEIS Building Energy Efficiency Survey: e.g. offices ≈ 18, health ≈ 10, retail ≈ 8 kWh/m²/yr of cooling electricity) through the identical sol-air formula and cap, and the card badges it “estimated”, a distinct, lower-confidence tier, never shown as a certificate-backed figure. Tier C · physics only: no cooling signal, so we report the heat rejected and the peak-temperature cut and claim no pounds. A non-domestic EPC that was assessed and found to have no air-conditioning is a measured “no cooling” signal and stays in Tier C rather than being overwritten by a benchmark.
OS NGD gives each building its UPRN, which we use to join the EPC energy band, the use and the age. So a hot dark roof becomes “a retail building, built 1985, rated D”, which tells you whether it actually carries a cooling load. A physics target becomes a qualified commercial target.
The ideal customer is a large, dark, hot, commercial roof. The engine ranks every one of them across a city or the country, for free, with no site visits. Cold outreach becomes a targeted map.
Total dark-roof area is the addressable market; per building you get the energy, £ and CO₂, costed against the live grid, with listed and conservation buildings flagged so the targetable market is the real one.
The same satellites revisit every few days, so reflectance change can be measured over time and impact verified remotely, the evidence funders and carbon markets need.
Free data in, a scalable pipeline, so one estate or the whole country costs roughly the same to survey.
Google owns geometry-for-solar in the UK with its Solar API. Nobody holds material, reflectance and thermal at national scale. We match Google’s geometry fields and add the layers that decide a cooling sale. The barrier is not the data, which is open. It is the physics pipeline and the honest, validated joins that turn it into a decision.
Every number is labelled measured or modelled, and regenerable from a script. That discipline is what makes it credible to the people writing cheques.
What each source is, and exactly how it enters the calculation. The point of leading with measured physics is that each step can be checked against its reference. Grouped below; tap a heading to open it, swipe each row sideways.
ESA satellite (10 m) + narrowband-to-broadband albedo physics.
Feeds: the measured solar reflectance R every roof leads with. Assumes the Liang coefficients for S2 bands.
Ordnance Survey authoritative building data (~97% of GB).
Feeds: roof material, flat/pitched shape, height, UPRN, building use/age/floors. Shown without a hedge.
Environment Agency surface-elevation model.
Feeds: roof pitch / aspect / form / roughness, and the surrounding building heights used for shading.
Sky-view-factor algorithm from a DSM.
Feeds: the per-roof sky-view factor (16 rays to 100 m) that damps both sun-in and heat-radiated-out. Base height = footprint median.
EU solar-radiation database (live API).
Feeds: the per-city annual horizontal sun (GHI), 914 (Glasgow) to 1158 (Cardiff) kWh/m²/yr, replacing a flat national average.
Free live weather API.
Feeds: the “now” surface temperature: live irradiance, air temperature and wind (wind drives convective cooling).
Solar Reflectance Index standard.
Feeds: the SRI and the modelled surface temperature, combining reflectance and emittance (not reflectance alone).
Building heat-transfer reference.
Feeds: the cooling-load split: a daylight reflectance term (ΔR·G) + a 24/7 emittance term (Δε·L). Constants: longwave ≈63 W/m², hₒ≈17.
Peer-reviewed cool-roof study.
Feeds: the insulation factor f ≈ U/hₒ (~1–3%): only a small share of surface heat reaches the room below. Tiered by building age.
Spectra of Emissiv’s coating.
Feeds: the 95% reflectance + 95% emittance the coated-roof maths uses, modelled opaque. Measured 300–1400 nm; full spectrum to come.
GOV.UK Energy Performance certificates.
Feeds: energy band, floor area, and the per-building cooling demand (kWh/m²) + cooling efficiency (SSEER). England & Wales only.
UK building-energy benchmarks (BEIS BEES 2014-15, Tables A.1 + B.3).
Feeds: the use-class cooling estimate (tier B) where a building has no EPC cooling figure, badged “estimated from type”.
Live UK grid-carbon API.
Feeds: converts cooling-electricity saved into CO₂ avoided at the current grid mix.
Open planning register.
Feeds: listed / conservation / flood flags → coating eligibility.