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China Unveils Solar-Powered Heat Pump Boosting Efficiency to COP 4.2

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  Published in Science and Technology on Sunday, December 21st 2025 at 8:49 GMT by Interesting Engineering

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China’s New Sun‑Powered Heat Pump: Turning Sunlight into a Renewable Heat Source

A team of Chinese engineers has announced a breakthrough in domestic heating technology that could reshape how millions of households and industrial facilities use energy. The new device, unveiled in an article on Interesting Engineering, demonstrates how a conventional heat‑pump can be coupled with a solar‑thermal system to capture the sun’s energy and convert it into high‑temperature heat—without the need for electricity or fossil fuels. In this overview we break down the key aspects of the invention, its technical underpinnings, performance figures, and the potential ripple effects across China’s energy landscape and beyond.

1. The Core Idea: A Hybrid Sun‑Heat Pump

Traditional heat pumps rely on electricity to compress a refrigerant, which then transfers heat from a cold reservoir to a hot one. While highly efficient for moderate temperature lift, they require a continuous power draw and can be expensive in regions where electricity is costly or the grid is unreliable. The Chinese team’s approach sidesteps this limitation by using a small, dedicated solar‑thermal collector to pre‑heat the refrigerant before it enters the compressor. In doing so, the system can achieve a higher coefficient of performance (COP) while drawing only a fraction of the power the conventional counterpart would need.

In other words, the solar collector supplies “free” heat, which reduces the compressor’s workload. The design integrates a flat‑plate absorber, a phase‑change material (PCM) for thermal storage, and a compact, low‑pressure heat‑pump loop. The whole assembly is roughly the size of a standard kitchen refrigerator—making it a realistic candidate for retrofit in existing buildings.

2. How the System Works

1. Solar Absorption
   The system’s 2‑square‑meter flat‑plate collector tracks the sun (or, in a simplified version, faces a fixed direction). A high‑efficiency glazing layer lets in a broad spectrum of sunlight, which is absorbed by a copper‑plate heat‑exchanger. The resulting temperature of the working fluid can reach 90 °C during peak summer conditions.

2. Heat Storage with PCM
   The absorbed heat is transferred to a PCM tank (often paraffin or salt‑based). When the PCM melts, it stores thermal energy without a large rise in temperature—a key advantage for maintaining a steady heat supply during cloudy periods or at night.

3. Refrigerant Pre‑Heating
   The stored heat is then released to a low‑pressure refrigerant (often R134a or a more environmentally friendly alternative). The refrigerant is warmed to about 40 °C before it enters the compressor, which only needs to raise it to the desired output temperature (typically 80–120 °C for space heating or industrial processes).

4. Heat Delivery
   The compressed refrigerant discharges into a heat‑exchange coil that supplies warmth to the building or process. Because the starting temperature is higher, the compressor can operate at lower pressure, reducing electrical consumption and wear on components.

3. Performance Metrics and Benchmarks

The researchers report a COP of 4.2 under optimal sunlight, a significant boost over the 3.0–3.5 COP usually seen in off‑grid, conventional electric heat pumps. Moreover, the system’s electricity draw is only about 25 % of that of a comparable electric heat pump. During the test period—roughly 10 hours of peak sunlight—the device achieved 12 kWh of heat output from only 3 kWh of electricity input, yielding an overall efficiency of 400 % relative to electrical energy.

While the device is still in the prototype phase, the authors claim that scaling the collector area and improving the PCM formulation could push the COP above 5, matching or surpassing the best solar‑thermal heat‑pump systems available today. Importantly, the design also retains the ability to operate in reverse mode (air‑conditioning) using a small electric compressor, offering dual functionality.

4. Applications: From Homes to Industry

Residential Use
In China, where heating accounts for roughly 20 % of residential energy consumption, a cost‑effective solar‑heat pump could dramatically lower both carbon footprints and heating bills. The system’s modest footprint and plug‑and‑play nature make it suitable for retrofits in older apartment blocks that lack central HVAC infrastructure.

Commercial and Industrial
Large‑scale commercial buildings (e.g., office towers, shopping malls) and certain industrial processes (like drying, sterilization, or low‑temperature chemical reactions) could benefit from the high‑temperature output. Because the system can be coupled with a thermal storage tank, it can buffer demand peaks, smoothing load on the local grid.

Off‑Grid Communities
Perhaps most compelling is the potential for off‑grid rural communities. In remote villages where electricity is scarce or non‑existent, a solar‑thermal pre‑heated heat pump can deliver affordable, clean heat with minimal reliance on diesel generators.

5. The Wider Context: China’s Energy Policy

China’s 2023–2030 energy strategy places a strong emphasis on renewable integration, decarbonisation of the building sector, and the electrification of heating. The Ministry of Housing and Urban‑Rural Development has already issued guidelines encouraging solar‑thermal and heat‑pump deployment in new construction. The Chinese team’s invention dovetails neatly with these policy goals: it is a domestic innovation that reduces the need for imported advanced HVAC components and lowers greenhouse gas emissions.

Moreover, the research team published a companion paper in Applied Energy (link provided in the original article) that models nationwide deployment scenarios. The model projects a potential reduction of 150 million tonnes of CO₂ per year by 2040 if 15 % of all new buildings adopt the system—a figure that could help China meet its Paris‑Agreement commitments.

6. Links to Further Reading

• The original article on Interesting Engineering (source link) provides a concise overview and includes a short video demonstration of the prototype.
• The research group’s Applied Energy paper offers detailed performance data, thermodynamic analysis, and scalability assessment.
• A related Interesting Engineering feature on “Solar‑thermal heat pumps” (link) explains the broader category of technologies to which this system belongs, placing it in historical context.
• The Ministry’s 2023 policy white paper on “Renewable Energy in Buildings” (link) outlines the regulatory incentives that could accelerate deployment.

7. Bottom Line

China’s new solar‑heated heat pump represents a tangible leap forward in clean heating technology. By harnessing the sun to pre‑heat a conventional heat‑pump loop, the system achieves higher efficiency, lower electricity use, and a reduced environmental footprint—all in a compact, deployable package. As the world grapples with the twin challenges of energy security and climate change, innovations that blend renewables with proven engineering could serve as the next cornerstone of sustainable development.