Methodology: Model 887 derived from peer-reviewed thermal models
The calculator does not invent a new physics model. It composes three published methodologies into a single per-platform output:
- Cabin heat balance — NREL and SAE thermal-load methodology (Rugh et al., NREL/CP-540-37077 and successors) for steady-state cabin temperature under defined solar load.
- Solar load reference — ISO 15469-3 reference solar irradiance (1000 W/m2 perpendicular at AM1.5) for the heat-input boundary condition.
- AC power conversion — ASHRAE 1991 cooling-load to compressor-electrical-power factor, applied to a representative automotive AC system COP of 1.8 to 2.4.
Validation conditions: 35 degrees Celsius ambient, 30 percent relative humidity, full direct solar on horizontal and vertical glazing, target cabin temperature 23 degrees Celsius, occupancy of two adults. SHGC values for clear baseline and ATO-coated laminate are taken from spectrophotometer measurements per NFRC 200 / ISO 9050 across the 300-2500 nm band, integrated against the AM1.5 reference spectrum.
SHGC reduction and indicative optical performance
ATO (antimony-doped tin oxide) is a transparent NIR-absorbing semiconductor. Applied via wet-coating (sol-gel + UV-curable resin formulations) onto a PVB interlayer or directly onto glass, it delivers a narrow optical signature: high visible transmittance, near-zero visible absorption, strong absorption in the 1000-2000 nm range where the bulk of solar heat resides.
| Glazing configuration | Visible Tlum | SHGC | NIR rejection | Haze (post-lam) |
|---|
| Clear laminate baseline | ~85% | 0.60 | ~5% | <0.2% |
| Tinted PVB (privacy) | ~25% | 0.45 | ~30% | <0.3% |
| Milled-particle ATO PVB | ~70% | 0.42 | ~60% | ~1.0% |
| Kriya bottom-up ATO PVB | ~72% | 0.38 | ~75% | <0.3% |
Indicative values from internal characterisation per ISO 9050 / NFRC 200. Haze measured per ASTM D1003 on representative laminate stacks. Compare the synthesis pathways in our bottom-up vs milled ATO comparison.
Range impact for premium vs compact EV segments
The thermal-load benefit scales with glazing area, while the range conversion scales inversely with vehicle-specific energy consumption. Larger premium platforms have more glazing but also higher overall energy use; compact platforms have less glazing but each kilowatt-hour saved buys more kilometres. The net effect for solar heat control glazing on representative EVs:
| Segment | Battery (kWh) | WLTP range (km) | AC saving | Battery saving | Range extension (km) |
|---|
| Compact EV | 39.3 | 227 | ~30% | 4.6% | 7 |
| Mid-size EV | 62.5 | 335 | ~33% | 6.6% | 11 |
| Premium EV | 85.6 | 442 | ~35% | 8.5% | 16 |
Hot-climate driving: 35 degrees Celsius ambient, sustained solar load. Range extension is the kilometre delta versus baseline clear laminate at equivalent comfort setpoint. See EV range extension for application detail.
How ATO solar heat control coatings reduce SHGC
ATO nanoparticles have a localised surface plasmon resonance tuned by carrier concentration. Kriya's bottom-up sol-gel synthesis produces monodisperse particles in the 10-25 nm range, well below the visible-light scattering threshold, with tight control over antimony doping level (typically 8-12 atomic percent). The resulting dispersion delivers strong NIR absorption with negligible haze contribution and full visible transparency.
Two coating pathways are production-validated:
- PVB-laminate interlayer — ATO dispersion incorporated into the PVB film during extrusion or via secondary lamination. Full glazing area is treated; encapsulation in glass laminate protects the coating mechanically.
- UV-curable resin on glass — Kriya-formulated hard coat with embedded ATO, applied by flow coating or slot-die, cured under UV-LED. Suitable for non-laminated glazing or after-laminate treatment.
Both pathways are 100 percent wet-chemistry — no vacuum process, no plasma deposition. This matters at scale: roll-to-roll PVB lines and inline flow-coating lines run at production speeds that vacuum processes cannot match, and they do not require capex on chamber infrastructure.
Eco-innovation credit pathway (EU Regulation 2019/631)
For European OEMs, the cabin energy saving has a regulatory dimension beyond range. Articles 11 and 12 of Regulation (EU) 2019/631 allow manufacturers to claim CO2 credits for technologies whose benefit is not captured by WLTP. Solar heat control glazing qualifies: WLTP runs at controlled lab temperature without solar load, so the AC-saving benefit is invisible to type approval.
Approved credits typically fall in the 0.5 to 1.0 g CO2/km per vehicle range for glazing-based AC-load reductions. The combined eco-innovation ceiling is 7 g CO2/km per manufacturer per year. At 95 EUR per g/km per vehicle in fleet penalty terms, a 1 g/km credit applied across 800,000 EU registrations is worth 76 million EUR of avoided penalty exposure annually.
For the full credit pathway — methodology submission, independent verifier validation, Commission Implementing Decision, and per-platform application — see the EU CO2 fleet penalty and glazing eco-credit brief. For the fleet exposure model, see EU CO2 penalty impact.
Model limitations — what this calculator does not do
Calculation Model 887 is thermal-only. Honest scope: it does not simulate aerodynamic drag, rolling resistance, regenerative braking recovery, battery thermal management at low state-of-charge, HVAC blower fan power, or driver-behaviour variability. It assumes a clean steady-state cabin-balance condition under defined solar load and a fixed AC system coefficient of performance.
For end-to-end energy-balance simulation under real-world driving cycles, the calculator output is an input — the AC energy saving in kWh per 100 km or watts continuous — to a full vehicle dynamics model (GT-SUITE, AVL Cruise, Simulink Powertrain). For homologation-grade methodology under Implementing Regulation (EU) 2014/725, Kriya produces a platform-specific dossier with verifier sign-off.
Frequently asked questions
What does this automotive solar heat gain calculator actually compute?
For a chosen EV segment (compact, mid-size, premium), the calculator estimates the cabin temperature reduction under reference solar load, the AC compressor power saving at equivalent comfort setpoint, the resulting range extension in kilometres, and the energy cost saving in five currencies. The thermal model is based on standard solar heat gain coefficient (SHGC) methodology applied across the full glazing area of representative production vehicles.
How is solar heat gain coefficient (SHGC) defined for automotive glazing?
SHGC is the fraction of incident solar radiation that becomes heat inside the cabin — both directly transmitted and absorbed-then-reradiated inward. A clear automotive laminate sits around 0.55-0.65 SHGC; ATO-coated solar heat control laminates can reduce this to 0.35-0.45 by absorbing near-infrared (NIR) wavelengths between 780-2500 nm while preserving visible light transmittance above 70%. The calculator uses the delta between baseline and treated SHGC as its primary input.
Why does AC load matter so much for EV range?
Air conditioning is the single largest non-traction load on a BEV. Under hot-climate driving (35 degrees Celsius ambient, full solar load), AC can draw 2-4 kW continuously, which on a 200-Wh/km vehicle equates to 10-20 percent of total energy use. Reducing AC duty cycle by 30-40 percent — the range observed with ATO solar heat control glazing — translates directly to measurable range extension under the same conditions.
What thermal model underlies Calculation Model 887?
The model derives from peer-reviewed vehicle thermal analyses (NREL/SAE methodology for cabin heat balance, ISO 15469 solar load reference, ASHRAE 1991 air-conditioning power conversion). Inputs include glazing area per platform, reference solar irradiance (1000 W/m2 perpendicular), ambient and target cabin temperature delta, SHGC reduction from coating, and battery-specific energy. Outputs are deterministic — no Monte Carlo simulation — and rounded for engineering use.
Does this calculator account for aerodynamic and rolling-resistance losses?
No. Calculation Model 887 is a thermal-only model. It quantifies the AC-load reduction and converts that to range extension at constant powertrain efficiency. It does not model wind drag, rolling resistance, regen recovery, or HVAC blower power. For an end-to-end energy-balance simulation, the calculator output should be paired with a full vehicle dynamics model.
How does this map to the EU eco-innovation credit?
AC-load reduction via solar heat control glazing is an established eco-innovation category under Regulation (EU) 2019/631, Articles 11 and 12. The CO2 saving per vehicle (typically 0.5-1.0 g CO2/km for solar-control glazing) is computed by converting the AC energy delta via grid CO2 intensity for BEVs, or vehicle-specific fuel-to-CO2 factors for ICE. See the regulatory brief linked below for the credit pathway, ceiling, and approval timeline.
Can the numbers be customised for a specific OEM platform?
Yes. The on-page calculator uses three pre-loaded segment archetypes. For a per-platform run with actual glazing surface area, climate-zone solar load assumptions, battery and powertrain efficiency, and the manufacturer-specific WLTP-to-real-world correction factor, Kriya engineering produces a bespoke methodology dossier. Contact engineering to scope a platform-specific calculation.