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Solar-Led Winter Heating for 3,500 Rural Households in Yongdeng County (–15 °C Climate)
Solar-Led Winter Heating for 3,500 Rural Households in Yongdeng County (–15 °C Climate)
Replacing scattered coal with SOLETKS manifold vacuum tube collectors cut household running costs by over 70% and removed 7,000 tonnes of coal a year.
Location
Yongdeng County, Lanzhou, China
Application
Rural residential winter heating
System Type
Solar thermal + electric auxiliary
Scale
3,500 households · 100 tubes + 400 L tank each
Commissioning
2022
Client Type
County-level livelihood program
Background: Coal Heating in a Sub-Zero Climate
Yongdeng County sits in a temperate continental climate where winter temperatures regularly fall below –15 °C. For years, rural households here heated with scattered coal combustion — energy-intensive, expensive, and a direct source of indoor and outdoor air pollution.
Most homes in the survey area were self-built at 50–60 m² with minimal thermal insulation. Scattered coal could not hold a stable indoor temperature and carried real safety risks. The pattern villagers described was "burning coal during the day and enduring cold at night."
In 2022, under China's dual-carbon and rural revitalization agenda, the county launched a clean-heating conversion program and selected SOLETKS manifold vacuum tube collectors as the core equipment after demonstration and testing.
The Challenges
The project had to solve a combination of climate, cost, and usability problems at the same time — and do it across thousands of dispersed homes.
High recurring fuel cost
Each household burned about 2 tonnes of coal per year, costing close to ¥2,000 — a heavy load on rural budgets.
Severe cold and freeze risk
Winter lows below –15 °C cause poorly built collectors to freeze and crack, ending equipment life in a single hard night.
Unstable indoor comfort
Scattered coal could not maintain a steady temperature, leaving homes cold overnight and on cloudy days.
Usability for elderly residents
Many homes are run by elderly villagers who cannot manage complex controls, so the system had to operate unattended.
Solution Overview
SOLETKS designed a standardized "solar-led, electric-assisted" configuration that could be repeated per household while still matching local building stock and climate. Solar covers the bulk of the heating load; electric resistance fills the gap during the coldest, darkest stretches — the realistic model for cold-climate rural heating.
Cold-rated collector choice
Manifold vacuum tubes were selected over flat plate because the vacuum gap suppresses convective heat loss, holding useful temperature in freezing air.
Standardized per-household kit
One repeatable configuration for 50–60 m² homes simplified procurement, installation, and maintenance across 3,500 units.
Built-in auxiliary heating
A 2 kW water-electric dual-purpose fan switches to electric backup automatically and distributes heat evenly to avoid cold spots.
Unattended smart control
A customized control system monitors and adjusts the equipment in real time, so residents get stable heat without manual operation.
System Configuration (Per Household)
Manifold Vacuum Tube Collector
100 tubes · borosilicate 3.3 glass with low-temperature strengthening · selective absorption coating for high absorption, low emission
Hot Water Storage Tank
400 L · double-layer stainless steel inner tank · polyurethane foam insulation holding heat for 24h+
Auxiliary Heat Source
2 kW water-electric dual-purpose fan · automatic electric backup · even heat distribution
Control System
Customized smart controller · real-time monitoring and adjustment · unattended operation
Manifold Flow Channel
Food-grade 304 stainless steel · improved heat transfer efficiency vs industry average
Collector Housing
Thickened galvanized steel with electrostatic spraying · corrosion- and sand-resistant · 15+ year design life
Before vs After
The change is clearest at the household level, where recurring fuel cost and emissions fall sharply while indoor comfort becomes stable.
| Indicator | Before (Coal) | After (Solar-Led) | Improvement |
|---|---|---|---|
| Energy source | Scattered coal | Solar + electric backup | Clean conversion |
| Annual running cost / household | ~¥2,000 | ~¥300–500 | Over 70% lower |
| Annual coal use / household | ~2 tonnes | 0 | Eliminated |
| Indoor temperature | Unstable, cold at night | Stable 18 ± 2 °C | Meets heating standard |
| Operation | Manual, labor-intensive | Automatic, unattended | Hands-off comfort |
70%+
Lower household running cost
7,000 t
Coal removed per year (project)
18,000 t
CO₂ cut per year (project)
56 t
SO₂ cut per year (project)
"Burning coal used to be tiring and left the house cold. Now with SOLETKS solar heating, the house stays warm, and it's so hassle-free."
Planning a cold-climate heating project? Get a configuration matched to your climate data.
Request a Similar QuoteKey Takeaways for Cold-Climate Projects
For EPC contractors and developers planning similar work, the engineering lessons matter more than the headline numbers.
Select against the coldest condition
Collector type should be chosen for the lowest expected temperature, not the annual average. Below –15 °C, vacuum tubes outperform flat plate.
Plan for solar-led, not solar-only
Pure solar rarely carries 100% of winter load. Built-in auxiliary heating is what keeps comfort stable on the worst days.
Standardize for rollout
A repeatable per-household kit cuts procurement, installation, and service cost across thousands of dispersed sites.
Automation reduces service calls
Where end users can't operate controls, unattended smart control is the difference between delivered comfort and field complaints.
Frequently Asked Questions
Do vacuum tube collectors work below –15 °C?
Yes. The vacuum gap limits heat loss to cold air, so collectors keep absorbing well below freezing. Survival depends on the glass and freeze design — these used borosilicate 3.3 glass with low-temperature strengthening rated for harsh winter conditions.
What happens at night or on cloudy days?
The 400 L insulated tank holds heat for over 24 hours, and the 2 kW electric backup engages automatically when solar input is insufficient, keeping indoor temperature at a stable 18 ± 2 °C.
How much can a coal-to-solar switch save?
In this project, annual household running cost fell from close to ¥2,000 in coal to roughly ¥300–500 in electricity — over 70%. Actual savings depend on local fuel prices, electricity tariffs, irradiance, and building insulation.
How is maintenance handled in remote areas?
The standardized kit and corrosion- and sand-resistant housing with a 15+ year design life reduce maintenance demand, and the smart control system runs the system unattended for elderly residents.
Can this model be replicated in other cold regions?
Yes. The same solar-led, electric-assisted configuration applies to cold rural areas in Central Asia, Eastern Europe, and high-altitude regions, with sizing recalculated against local climate and load profiles.
