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Solar Air Collector Drying Case: 445 m³ Facility in Shanxi | Soletks
Double-Pass Evacuated Tube Solar Air Collectors Power a 445 m³ Agricultural Drying Facility in Shanxi
A hybrid solar-air-collector and air-source heat pump system delivering 50–70 °C process heat for crop drying — featured in a global solar air collector market survey commissioned by CanmetENERGY, Natural Resources Canada.
Referenced by Solar Thermal World — Product overview showcases the global evolution of solar air collectors
Output Temperature50–70 °C
Project Background
Northern China's agricultural belt — grains, herbs, chili, dates, edible fungi — has historically relied on open-air sun drying and coal-fired hot-air furnaces. Open-air drying is weather-dependent and vulnerable to contamination; coal boilers face increasingly tight emissions limits under the national Clean Heating and Blue Sky programs, and diesel or LPG backups carry volatile fuel costs.
The site in Shanxi needed a stable 50–70 °C hot-air supply for a 445 m³ drying chamber, with year-round operability and a fuel bill that made sense against the crop margin. Standalone solar air collectors could not guarantee schedule reliability under cloudy days; a standalone heat pump would run at high electricity cost during peak drying loads. A hybrid design was the practical answer.
Why solar air, not solar water, for drying: Drying loads consume warm air directly. A solar air collector removes the intermediate water loop and heat exchanger losses, avoids freeze protection glycol, and matches the daytime load curve of the dryer. For 50–70 °C process heat, this is the shortest energy path.
Client Challenges
The operator's brief listed four hard constraints. Every one had to be solved on the same site, on the same budget cycle.
Volatile Fuel and Coal Restrictions
The existing coal-fired hot-air furnace faced regional restrictions under Shanxi's clean-heating enforcement, and diesel backup priced drying margins into negative territory during winter batches.
Temperature Window: 50–70 °C
Too high for a flat-plate air collector to hold reliably in winter, too low to justify a full boiler system. The technology gap needed a purpose-built collector.
Schedule Reliability
Post-harvest drying batches cannot wait for good weather. The system had to hit setpoint on cloudy days and continue through evening finish cycles.
Payback Under 4 Years
Agricultural operators do not accept 8–10 year paybacks. The CAPEX-to-fuel-saving ratio had to close within a realistic financing horizon.
Solution Overview
Soletks specified a hybrid architecture built around its double-pass evacuated tube solar air collector, launched in 2020 as an upgrade to the flat-plate air collector line the company has supplied to clean-heating projects since 2015. The design routes intake air through the evacuated tube twice, lengthening absorber contact time and pushing outlet temperatures into the 50–70 °C process-heat range.
Double-Pass Evacuated Tube Air Collector
Selected over flat-plate air collectors for its ability to hold target outlet temperature under northern China's winter irradiance and ambient conditions.
Air-Source Heat Pump Backup
Two 30P ASHP units act as the stabiliser: solar carries the base load during daylight, the heat pump fills gaps at start-up, cloud cover, and evening completion.
Direct Air Delivery, No Water Loop
Warm air is ducted directly to the drying chamber. No intermediate heat exchanger, no glycol, no freeze-protection valves — fewer failure points, lower maintenance.
Zonal Control by Collector Field
Four collector fields are controlled independently, allowing the system to modulate output against real-time drying-chamber demand rather than running the full array at all times.
System Configuration
Soletks double-pass evacuated tube solar air collector, deployed in 4 independent fields. [Total aperture area: to be confirmed on datasheet release]
2 × 30P (approx. 84 kW nameplate each) air-source heat pump units, configured as backup and stabiliser.
445 m³ agricultural drying chamber, hot-air supply at 50–70 °C, day-and-night operation during peak drying season.
Solar-priority control. Heat pump activates only when collector output falls below setpoint, minimising electricity draw.
Before vs After
The table below compares the previous coal-fired hot-air furnace baseline against the delivered hybrid system. Values marked [est.] are engineering estimates pending on-site metering data; confirmed values will be released in the project's full technical report.
| Indicator | Before (Coal-Fired Furnace) | After (Solar Air + ASHP) | Improvement |
|---|---|---|---|
| Primary Energy Source | Coal (with diesel backup) | Solar + Electricity (heat pump) | Fossil fuel eliminated |
| Delivery Temperature | 60–90 °C (unstable) | 50–70 °C (stable) | Process-matched, controllable |
| Fuel / Energy Cost per Drying Season | Baseline 100% | ~35% [est.] | ~65% reduction [est.] |
| CO₂ Emissions per Season | Baseline 100% | ~30% [est.] | ~70% reduction [est.] |
| Regulatory Compliance | Restricted under regional coal policy | Fully compliant | Long-term operability secured |
| Product Quality Risk | Contamination from flue-gas, uneven drying | Clean warm air, uniform | Higher-grade output |
Performance Results
Field data from the first full operating season delivered the following headline metrics. Estimates are flagged; the project engineering team will release verified figures in the full technical brief.
"We have offered an air-based flat-plate collector since 2015, and it has been successfully deployed in a number of clean heating projects. As market demand increased, we developed a double-pass evacuated tube solar air collector in 2020."
Planning a solar drying facility for grains, herbs, chili, dates, or edible fungi? Get a system sizing based on your crop, chamber volume, and local irradiance.
Request a Similar QuoteKey Takeaways for Similar Projects
Four engineering lessons transfer directly to EPCs and operators evaluating solar drying installations in comparable climate zones.
Match Collector Type to Temperature Window
Flat-plate air collectors are cost-effective up to ~45 °C. For 50–70 °C process heat under variable winter conditions, double-pass evacuated tube designs are the pragmatic choice.
Size the Heat Pump as a Stabiliser, Not a Primary
Oversized ASHP inflates CAPEX and electricity bills. Sized as a gap-filler behind a solar-priority controller, it delivers reliability without eroding payback.
Zone the Collector Field
Independent control of 3–5 collector fields lets the system modulate against real drying-chamber demand, cutting parasitic fan power and improving seasonal yield.
Design Around the Crop Calendar
Drying loads are seasonal and predictable. Aligning collector tilt and orientation to the harvest window — not the annual average — gives measurably higher usable yield.
Frequently Asked Questions
What crops is this system suitable for?
Any crop or product with a drying temperature target between 40 °C and 70 °C: grains, chili, herbs, dates, edible fungi, tea, tobacco leaf, medicinal plants, and pre-dried aquatic products. Higher-temperature applications require a different collector class.
How does the system perform in winter or at high latitude?
Double-pass evacuated tube collectors retain useful output at low ambient temperatures because the vacuum layer suppresses convective loss. Combined with the ASHP backup, the system holds setpoint through the northern China winter drying season.
What is the maintenance burden?
Because the collector delivers warm air directly, there is no water loop, no glycol replacement, and no heat-exchanger scaling. Annual maintenance is limited to tube cleaning, fan inspection, and standard heat-pump servicing.
Can the system be scaled up or down for smaller facilities?
Yes. Collector fields are modular. Soletks has supplied systems from small cooperative-scale dryers to industrial-scale drying halls; the Shanxi 445 m³ configuration sits in the mid-range.
Is the technology suitable for markets outside China?
Yes — solar drying is a strong fit for high-irradiance agricultural regions including Southeast Asia, South Asia, the Middle East, North Africa, and Latin America. System configuration is adjusted for local irradiance, ambient temperature, and grid tariff structure.
Build Your Solar Drying Facility with a Manufacturer, Not a Trader
Soletks Solar was included in the CanmetENERGY global market survey on solar air collectors, published via Solar Thermal World. Talk to the engineering team behind the Shanxi installation.
Related reading: Solar Air Heater Guide · Solar Air Drying System for Industrial Applications · How to Choose a Solar Air Collector Manufacturer · Solar Air Collector vs Air PVT
Source: Solar Thermal World — Product overview showcases the global evolution of solar air collectors (CanmetENERGY–Ottawa / Natural Resources Canada market survey, 2026).
