The Technology
The performance gap in solar thermal
Both solar photovoltaic panels and solar thermal collectors lose output as light intensity drops — due to cloud cover, atmospheric haze, low sun angle, fog, or a combination of these. The difference is in how they fail. PV output declines gradually and continues to produce at relatively low light levels. Conventional solar thermal collectors fall more steeply: below a threshold of irradiation, compounded by insufficient ambient temperature, they produce nothing useful. Cold ambient air makes this worse, since a solar thermal collector must heat up significantly above its surroundings before it delivers anything. PV, by contrast, performs better in cold conditions.
This is not a minor inefficiency. In cold climate winter conditions, a conventional solar thermal system may be mostly idle for three to five months of the year — precisely the months when heating demand is highest. In hot, humid climates, the picture is different, but the underlying problem is the same: useful thermal output becomes unreliable due to cloudy skies when it is needed to drive cooling and dehumidification.
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The growing value of winter energy
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The solar industry has traditionally optimized for annual yield — tilting panels toward summer sun, evaluating systems on total kilowatt-hours produced per year. That logic made sense when every unit of renewable energy had clear value.
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The picture is changing. In many regions, renewable generation is now so abundant during summer — particularly on sunny, windy days when industrial demand is low — that grid operators face the opposite problem: too much electricity. Prices go negative. Wind turbines are curtailed. Inverters are switched off. This is already happening, and as renewable capacity continues to grow, it will become more pronounced.
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The real scarcity is shifting to winter energy — the months when heating demand is highest, solar angles are lowest, and the grid is under genuine pressure. A technology that produces reliably in these conditions is not solving a minor technical gap. It is addressing a structural imbalance that the summer-optimized industry is only beginning to recognize.
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DLCT targets this gap directly. Thermal energy produced in winter and low-light conditions covers heating demand without drawing on electricity that is genuinely scarce at that time — freeing it for lighting, appliances, and electric vehicle charging. The summer surplus and the winter thermal deficit are two sides of the same imbalance. DLCT addresses the latter. DLCT complements STES (Seasonal Thermal Energy Storage) very well, each of these principles making up for potential shortcomings in the other. For any particular climate and building, DLCT and STES can be applied in varying proportions to bring the solar fraction all the way up to 100%, if desired, even for buildings where large STES units aren't possible, practical, or economical.
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What DLCT addresses
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DLCT — Diffuse Light Concentration Technology — is being developed by Ciao Carbon Ltd to close this gap. The design approach prioritizes thermal output under adverse conditions, rather than peak output under ideal ones.
The technology is complementary to existing PV-T systems, not a replacement for them. Where flat plate, vacuum tube, or concentrating collectors perform well under direct irradiation, DLCT is designed to remain effective when irradiation is low, diffuse, or intermittent, including when the ambient temperature is below freezing.
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Hot and humid climate implementations
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In Hong Kong, a village house serves as an early-stage demonstrator. Both PV and solar thermal collectors are installed and operating side by side, with the solar thermal system already delivering hot domestic water. The next phase will apply solar thermal energy directly to dehumidification and space cooling — demonstrating the hot, humid climate use case in a real building. Current installations use conventional solar thermal technology; DLCT integration will follow once the prototype stage is reached.
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Current status
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The technology is at the pre-prototype stage. A working proof of concept is the immediate next milestone. Patent filing will follow successful demonstration. No technical specifications are published at this stage. Development progress will be documented when important milestones have been reached.
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If you work in solar thermal, district heating, building energy, or climate technology — and these challenges interest you — we'd like to hear from you.
