Un colector solar para uso en climas fríos, de bajo costo y enfoque autogestivo

This Thesis presents the design, construction, installation, operation and measurement of the performance of a low-cost solar collector for domestic hot water heating. The equipment was installed in the city of Bariloche, Argentina and its performance recorded between April 11, 2016 and September 8, 2017.

The heating of water for sanitary use requires enormous amounts of energy. About 10% of the energy consumed in buildings in Argentina goes to this use, worldwide it is around similar percentages. Most of it comes from burning fossil fuels, which makes domestic hot water heating (DHW) a significant contributor to the emission of Greenhouse Gases (GHG).

Solar collectors are probably the most practical, efficient and least geographically constrained technological alternative for heating water without using hydrocarbons. It is a simple and mature technology that works remarkably well even in cold places or places that receive relatively little sunshine throughout the year. But because of the high initial investment cost, they still compete at a disadvantage against conventional fossil fuel-based technologies (a gas-fired water heater, for example). This problem has limited their use so far.

The replacement of polluting ACS heating systems with other more environmentally friendly ones is fundamental to mitigate climate change. Mass adoption of solar collectors is perhaps the quickest and simplest way to achieve significant progress.

Moreover, if the technology is developed in an open manner, allowing users or the communities where they live to build their own equipment, the benefits exceed the environmental. These additional benefits are explained through Human Scale Development (HSD), a theory that postulates that human development goes beyond the mere economic development promoted by the productivist theories that make up the current paradigm. Using the concepts of HED as a guide, we sought to develop a low-cost solar collector, without technological or commercial barriers and that could be built by its end user in a self-managed or community way.

In order to lower the cost of the equipment and overcome the aforementioned barrier of the initial investment, we opted for the development of a collector made entirely of plastic. To improve performance compared to other existing plastic models, an old idea, tested in the 1970s in the United States, was taken up again: "direct absorption" of radiation using transparent plastics and a dark liquid (black water) as heat transfer fluid.

To install it in the city of Bariloche, where it is common to have several days of frost per year, it was necessary to incorporate in the design a mechanism to protect the equipment from freezing. A simple and reliable system known as drainback, commonly used in the northern hemisphere but with no documented experience in Argentina, was chosen. As any freeze protection system requires an automatic control system, in order to be consistent with the DEH framework we chose to develop a very low cost and open technology (Arduino) system.
The tested system provided 51% of the energy required for a demand of 250 liters per day at 41° south latitude, with 3.15 m2 of collecting surface.  The non-conventional technologies tested (black water, polycarbonate collector, drainback system and Arduino controller) gave good results and have potential to be included in future developments.

The main problem was the weakness of the union between the pieces of different plastics, which caused the repeated breakage of the equipment and makes it unfeasible in its current state. A possible solution to the problem is proposed by means of a single-piece design, which has not been tested to date, but remains as an immediate line of work.