Reducing the Cost of Solar Thermal: Integrating a Novel Freeze Tolerance Approach with Flat Plate Solar Thermal Panels

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Solar thermal systems used for domestic hot water applications in the United Kingdom and much of Europe require the inclusion of a frost protection strategy. This is necessary as under these conditions any fluid contained within the solar collector may expand and rupture the fluid channels, permanently damaging the collector. Several strategies are currently employed to prevent this from occurring, with the most common approach to use a glycol anti-freeze fluid within the collector heating loop to indirectly heat the potable water used by the household. The addition of a glycol agent substantially reduces the freezing point temperature and consequently the risk of frost damage from occurring. However, the penalty with this approach is the cost and complexity added to the system due to the material purchase and manufacture of the required heat exchanger. For most customers this means that their existing hot water tank needs to be replaced. Further drawbacks include the additional weight of the heat exchanger within the storage tank which increases both transportation and installation effort, and the possible contamination of the potable water with glycol in the event of heat exchanger material failure. Soltropy Ltd have developed and patented an alternative method of protecting solar thermal collectors from freezing which does not need a separate glycol heating loop and heat exchanger. The method involves the insertion of a compressible silicone tube within the copper manifold of the solar collector. During a frost event, any fluid expansion due to phase change is absorbed by the tube preventing the buildup of pressure which may potentially destroy the collector. This method is significantly cheaper than the glycol heating loop alternative and furthermore has the added advantage that it allows the use of a standard hot water tank, which does not have an internal heat exchanger, to be coupled with a solar thermal collector array. Additionally, by switching from an indirect system to a direct one, there is potential to improve the thermal performance of the system. Presently this solution has, however, only been tested and evaluated with the evacuated tube solar collector type which with respect to its fluid passage design is significantly different to the flat plate collector. As the flat plate collector type makes up approximately 75% of the collector market in Europe, work to integrate this frost protection technology with this collector type has tremendous potential.This project aims to develop a low cost frost protection strategy for flat plate collectors in collaboration with the UK based collector manufacturer, AES Solar. The integration of the Soltropy Ltd patented silicone tube into a flat plate collector for frost protection will involve the design and development of a new flat plate collector design which will be manufactured in the UK. This will include a number of R&D activities including; numerical modelling, prototype fabrication, laboratory and outdoor testing, and marketing/intellectual property related actions. Successful implementation of this frost protection strategy will result in reduced system cost with potential to improve the performance of the system.