Passive Solar Greenhouse Designer

Chinese-style + earth-bermed designs. Glazing angle for your latitude, thermal mass volume, expected temperature lag, off-grid heating-free production.

Design parameters

Latitude (°N) Most US: 25-49°N. Phoenix 33; Chicago 42; Seattle 48; Anchorage 61

Style Chinese-style (south-glazed; insulated north wall) Earth-bermed (3 sides bermed) Walipini / pit greenhouse (sunken) Solar pony wall + freestanding

Length (ft)

Width (ft)

Thermal mass type Water (best — 1 BTU/lb·°F × 1000 lb/cu ft) Concrete (decent — 0.22 × 144 lb/cu ft) Rock / gravel bed (good — 0.20 × 165 lb/cu ft) Soil (modest — 0.20 × 100 lb/cu ft) Mixed (water tanks + concrete walls)

Coldest tolerated inside temp (°F) Cool-tolerant crops: 38°F; subtropical: 50°F

Why passive solar works

A passive solar greenhouse uses three principles together:

1. Capture: South-facing glazing at the right angle for winter sun captures maximum solar energy when needed most.
2. Store: Thermal mass (water, concrete, rock) absorbs heat during sunny day; releases at night when air cools.
3. Insulate: Insulated north wall + roof + perimeter prevents stored heat escaping. Often combined with night thermal blanket on glazing.

A well-designed passive solar greenhouse can grow cold-tolerant crops (lettuce, kale, spinach, herbs) year-round in zones 4-7 with no supplemental heat.

Optimal glazing angle

The "best" angle for winter solar capture is approximately your latitude minus 23.5° (winter solstice solar elevation). For most temperate latitudes:

Latitude	Glazing angle from horizontal
30°N (Houston)	~53° from horizontal
35°N (Albuquerque)	~58°
40°N (Denver, NYC)	~63°
45°N (Minneapolis)	~68°
50°N (Vancouver)	~73°

Higher angles favor winter; vertical glazing (90°) is excellent for far-north sites and reduces summer overheating. Many designs use a slope between latitude and latitude+15° as a compromise.

Thermal mass guidelines

Material	Heat capacity (BTU/cu ft per °F)	Best use
Water (in barrels, tanks)	62.4	Top performer; 4× concrete per cu ft; best at moderating
Concrete	~32	Walls + floors; doubles as structure
Rock / gravel bed	~33	Insulated rock storage; air-circulated
Stone / brick	~28	Walls; visible aesthetic
Soil	~20	Earth-bermed walls; ground floor; cheap

Common rule: 3 gallons of water per square foot of south glazing for adequate thermal mass. More for cold climates; less in mild ones.

Real-world performance

Climate	Inside low (clear sunny day, no heat)	Cold-tolerant crops year-round?
USDA Zone 4 (-30°F outside)	~25-35°F nights without backup	Survives but slow growth; supplemental heat helps
USDA Zone 5 (-20°F outside)	~30-40°F nights	Yes, for hardy greens
USDA Zone 6 (-10°F outside)	~35-45°F nights	Yes, with thermal blanket
USDA Zone 7 (0°F)	~40-50°F nights	Absolutely; full production
USDA Zone 8+ (above 10°F)	~45-55°F nights	Most crops year-round

Free under CC BY 4.0. Cite as "OAT Passive Solar Greenhouse Designer (openagriculturetechnology.com)". Design principles from Chinese solar greenhouse research, Lindsey Schiller's "The Year-Round Solar Greenhouse," and rural development literature.