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Playbook: Is There a Better Option for Solar Thermal Cooling?

The question: is there a better option for solar thermal cooling? Short answer: Usually yes — PV + electric heat pump / vapor-compression now beats solar-thermal sorption cooling for most buildings. Solar-thermal keeps a real but narrow niche. Full analysis: solar-cooling-pv-vs-thermal.

Why PV pulls ahead (one line)

Vapor-compression COP 3-8 on cheap ~20% PV converts more roof sunlight into cold than ~50% collector efficiency × sorption COP ~0.75 — and with one electrical loop instead of hot+chilled loops, big heat rejection, and cooling-tower water.

Decision tree

  1. Is there free or high-grade waste/process heat on site (CHP exhaust, industrial loop, data-center liquid-cooling loop ~40-65 °C)?
    • Yes → solar-thermal / sorption cooling is the better option. Data-center adsorption paid back in ~285 days on free heat.
  2. No waste heat. Is the cooling load large, steady, and ~24/7 (district cooling, hospital, industrial), in a high-irradiance/high-ambient sunbelt?
    • Yes → solar-thermal can compete (sunbelt evacuated-tube absorption: LCOC $0.028/kWh, ~3-yr payback). Use double-effect/Fresnel for hot-climate COP.
  3. No grid export / cheap thermal storage beats batteries, AND you also need year-round low-temp heat (DHW)?
    • Yes → solar-thermal stays competitive (co-supply heat + cold).
  4. Otherwise (bare rooftop, variable demand, monetizable PV export):
    • → PV + heat pump is the better option. Cheaper, simpler, faster payback.

The “third option” — don’t choose, hybridize

  • PV/T collectors co-generate electricity + heat from one aperture (cools the PV cells too): absorption COP 0.615, adsorption effective COP 2.1, PV/T+desiccant+VC overall COP 0.68 — the best system economics (~8-9 yr payback). Strongest frontier bet.
  • Better collectors + higher-effect cycles: evacuated-tube/CPC → single-effect COP ~0.8; concentrating → double-effect COP 1.2-1.4.
  • Passive add-ons: radiative sky cooling, evaporative/desiccant hybrids.

Takeaway for this KB’s waste-heat strategy

Heat-driven cooling here is justified by the free waste heat, not by beating PV on a bare roof. Keep the adsorption strategy where the heat is genuinely free; default to PV+heat-pump where it isn’t.

Sources

See solar-cooling-pv-vs-thermal § Sources (IEA SHC Task 53 & 65, plus 4 peer-reviewed techno-economic / PV-T studies, 2021-2025).