Researchers from the University of the Republic in Uruguay, together with colleagues from Argentina’s Institute for Non‑Conventional Energy Research, have developed a pilot solar installation in which heat for industrial enterprises is proposed to be stored in a concrete thermal accumulator. The system is designed to produce heat at temperatures of 100 – 150 °C with a nominal thermal power of about 10 kW. The storage unit, with a volume of 2.73 m³, is intended to store energy received from the sun and release it during periods when solar radiation is insufficient.
Industrial enterprises require not only electricity but also large amounts of heat, for example, for heating raw materials, water, and producing steam. In the food, chemical, and other industries, many processes operate at temperatures of 100 – 200 °C, and the heat required for them is still often obtained by burning fossil fuels. Solar thermal installations can partially replace this, but the same problem arises as in solar power generation: energy production depends on weather and time of day.
To generate heat, the developers chose compound parabolic concentrators (CPCs). They consist of vacuum tubes and curved metal reflectors that direct additional solar radiation onto the tubes. Unlike more complex solar concentrators, CPCs do not require a system for continuous tracking of the sun’s movement. Inside the installation, a mixture of water and 30% propylene glycol circulates: when passing through the collectors, it is expected to heat from approximately 135 to 160 °C. The full field will consist of six modules with a total area of about 24 m².
The heat obtained can be sent directly to the consumer or stored in the concrete accumulator. This consists of a massive concrete block with steel pipes laid inside it. During charging, a hot heat‑transfer fluid passes through them and heats the surrounding concrete. When solar energy is insufficient, a cooler fluid is passed through the pipes again, picks up the heat stored in the concrete, and transfers it to the consumer. In this way, the concrete acts as a thermal battery, allowing the time of solar energy collection to be separated from its use.
Inside the 2.73 m³ of concrete used in the design, two parallel steel pipes, each measuring 107.6 meters in length, are incorporated. The storage unit is divided into five sections, with a 50‑mm layer of thermal insulation between them. This arrangement helps maintain thermal stratification: one part of the storage unit can remain hot while another is still being heated. On the outside, 300 mm of thermal insulation is provided. According to the researchers’ calculations, a fully heated storage unit will be able to maintain a temperature above 135 °C for approximately one week, even under winter conditions.
Modelling showed that after three hours of charging, the storage unit reaches 66.6% of its maximum capacity. At the beginning of the process, the concrete accepts heat at a power of about 10 kW, but as it heats up, the rate of energy transfer decreases, reaching about 6 kW after three hours. The average charging power over this period was 8.37 kW. This happens because, as the concrete warms up, the temperature difference between it and the fluid circulating through the pipes decreases.
In a separate study, the scientists selected a concrete composition capable of better conducting heat. The maximum measured thermal conductivity reached 2.65 W/(m·K). At the same time, the addition of metal fibers, which was initially expected to improve heat transfer, did not produce the desired effect and presumably increased the porosity of the material. The authors emphasize that these measurements are still preliminary and require additional verification.
The first solar collector with an area of 3.9 m² has already been manufactured and tested. Its peak efficiency was 33.5%, compared to the expected 48–50%. Thermal losses were close to the calculated values, so the researchers attribute most of the discrepancy to the reflectors, the accuracy of their installation, and the assembly features of the collector. The team is now building a second prototype in which these shortcomings are planned to be eliminated.
In the future, the researchers intend to assemble the full installation with a solar field of about 24 m² and the concrete storage unit, and test it under real conditions. After that, it will be necessary to estimate the cost of the heat produced and the economic viability of the technology. If the tests confirm the calculations, such systems will allow enterprises to use solar heat more reliably for industrial processes and reduce their consumption of fossil fuels.
