Geographical variation in unglazed solar performance

An NREL/ASES paper — Jay Burch, Jim Salasovich, and Craig Christensen (National Renewable Energy Laboratory) with Jeff Thornton (Thermal Energy Simulation Specialists) — simulating how an unglazed “triple play” solar system performs across the U.S. for domestic hot water, space heating, and space cooling. The important point is that unglazed collectors are not one-size-fits-all: climate, wind, sky infrared, and building load all change the result.

The acknowledgments credit the archive’s central figure directly: “Steve Baer, CEO of Zomeworks, Albuquerque, NM, is acknowledged for pointing out the advantages of unglazed systems and motivating our work.” The reference list opens with Baer’s 2001 ASES Cool Cell paper.

What the source emphasizes

Factor	Effect
Location	Savings peak in the U.S. southwest — near the CO–NM border, extending through California’s central valley. Cooling savings run about 1/4 of heating savings.
Wind and sky IR	Explicitly included in the collector model, which is based on the ISO 9806-3 test for unglazed collectors.
Load type	DHW, HTG, and CLG behave differently; average unit-area savings (6→24 m²): DHW 0.98→0.34, HTG 0.56→0.40, CLG 0.36→0.20 GJ/m²-yr.
System size	Average heating efficiency falls from ~28% at 6 m² to ~13% at 24 m² (a small unglazed array reaches ~60% of a small glazed SDHW system’s efficiency).
Economics	Annual savings ~$10–23/m² with natural gas backup, ~$23–53/m² all-electric. At a 10-year simple payback, cost goals are $100–230/m² (gas) to ~$230–530/m² (electric) — versus ~$600/m² for then-current solar water heating.

Simulations ran at all 238 TMY2 sites against code-minimum houses whose envelopes vary with local heating degree days — so the maps convolve solar incidence with realistic building load, not collector physics alone.

Why it matters

climate + load + collector size -> system value

The paper argues for an integrated view: unglazed collectors can be attractive because they are lower cost (potentially under $1/ft² FOB versus ~$15/ft² glazed) and can be molded to look like an ordinary roof, but their value depends on the local thermal context. The authors’ sober conclusion — “cost goals for natural gas appear unattainable with today’s system costs” — is the flip side of the southwest-peak result: the systems Baer championed pencil out best exactly where Zomeworks built them. That makes the paper a useful bridge between collector design and site-specific deployment, and independent institutional validation that NREL took the unglazed approach seriously.

See also

• Roof integrated solar absorbers
• Antarctic heat collector
• Consider perihelion
• Index
• Unglazed solar collectors
• The unglazed collector lineage
• Night sky radiant cooling potentials in New Mexico