Another system for solar cooling is being developed in the Nottingham laboratories. Evacuated tube solar collectors heat water to around 110°C. The resultant high-pressure steam is expelled at around mach 2. The steam passes through an ejector where the Venturi effect causes the pressure to drop. A liquid refrigerant is fed to the ejector where it vaporizes under the vacuum created in the ejector, causing a cooling effect which is transmitted to the internal space. This adiabatic cooling drops the temperature to — 1°C. The low-pressure steam exiting the ejector is condensed and the water recirculated. In the Nottingham project the evacuated heat pipe array collects 13 kW of solar heat and converts it to 6kW of refrigeration. The system is backed up by natural gas when the temperature is high but cloudy conditions cut out the solar gain. This system is patented but not yet licensed.
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The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.