2020: Development of the measuring system MONA
The measuring system, which we affectionately call MONA, measures not only the water flow of the unit, several temperatures at different points of the system and the available solar energy, but also all relevant environmental parameters, such as wind, pressure and ambient temperature, which affect the efficiency of the unit. The measuring system performs the measurements automatically and sends the data to the project group via mobile phone and e-mail every night. Thanks to a small solar cell and a battery, the system is completely autonomous. Thus, the measuring system makes it possible to collect and evaluate the data of many plants simultaneously and in high resolution. This will allow a more precise investigation of system failures of individual units in the future and also increase the efficiency of the SoWaDi unit in general.
A prototype of the measuring system MONA was added to the SoWaDi test unit DE01 in Darmstadt in June 2020 as part of a student project. After measuring the system activities over a month, the measuring system was checked thoroughly. By evaluating the measurements, the measuring system and the partly self-developed sensors could be further optimized, so that future MONA measuring systems can be built more cost-efficiently by the group.
2020: Construction and repair of test plants in Tanzania
The team first repaired the two plants from the previous trip in 2017 in Mwanga where high temperatures inside the plants had caused breaks in the glass panes insulating the absorber. In addition, the plants TZ04, TZ05, TZ06 were built in Kidia: TZ03 and TZ05 at the Primary School and the other two at the homes of private individuals – Mr Maruchu and Mr Njau. Both were part of the construction team. Each plant now has a responsible person who takes care of the maintenance and regularly provides the team in Darmstadt with data.
Indeed, another goal of the trip was to obtain long-term data from these new plants to have as much data as possible for evaluation. This extensive data collection and evaluation is very important because it provides fundamental information about the service life and performance of the plant. Based on this, the next step is to work out a dissemination strategy. Therefore, it was important for the SoWaDi team to find people who feel responsible for the plants and are willing to maintain a constant communication channel with the group in Darmstadt to enable a stable exchange of data. This is essential because there is no data yet on how the plant will perform in the long run. So, we want to find out whether the performance decreases over the course of the service life and how much it varies with the location, what effects certain weather conditions have and how durable the individual components are.
2019: Test device DE01
The DE01 test device was used in 2019 to further develop and test the glass construction of the facility. In the past, the high temperatures inside the plant (up to 160°C) had caused damage to the test facilities in Tanzania. In order to avoid expensive damage to the plants, a glass breakage caused by overheating of the plant was traced and analysed in Darmstadt. As a result, the design could be adjusted and the risk of expensive plant damage was reduced.
2018: Prototype of a heat exchanger
The aim of the heat exchanger is to increase the amount of water disinfected by the SoWaDi plant. This is realized by warming the cold water from the input container with the already boiled water without mixing them. Thus the input temperature of the water to be boiled is increased, so that less solar energy is needed to reach the boiling temperature.
After designing several models through theoretical considerations and numerical simulations, the most promising concept was built and then tested in the laboratory. The results suggest a mean increase in output of about 6 liters. The design of the heat exchanger, like the system itself, can be manufactured from simple materials from the sanitary sector and is cost-effective. The heat exchanger’s test on the SoWaDi system is still pending.
2017: Construction of two SoWaDi test plants in Tanzania
First, the project team met with some NGOs to discuss the SoWaDi plant with them, in the best case to convince them of its advantages and to win new partners. These meetings offered the opportunity to get valuable feedback from people who deal with the water supply situation in Tanzania on an almost daily basis.
Another goal of the trip was to check the instruction manual for its comprehensibility. This was done during the installation of the system by the vocational students. After a short introduction to the functioning of the plant by the project team during a workshop, the students built our first test devices in Tanzania TZ01 and TZ02 in two groups. It was important for us to observe whether there were any difficulties in understanding and to identify these as precisely as possible in order to be able to adapt the instructions in the further course of the project and make them as comprehensible as possible. In the long run, the system should be able to be set up by anyone and everyone without the assistance of the SoWaDi team.
2014: Microbiological tests
We developed a test plan to examine the performance of the system. Using time switched pumps and valves the system was run totally automated. We chose different dilutions, up to very dirty water as input for the system, in order to test even higher contaminations than what is expected for a normal day to day usage of the system. Over a period of multiple months data about different parameters was collected multiple times a day, among others the amount of water, concentration of germs, turbidity and pH-value.
The results of these tests are summarized at technical data (6.2 and 6.3).
2013: Thermal examination
The prototype was run with a closed water cycle, where the output water was collected and used to refill the input tank. The throughput was measured with a pressure sensor.
We also collected data about the solar radiation, as well as temperatures at different points of the water cycle and the absorber. Over the following weeks and months we used this data to validate our thermodynamic model and the associated calculations and improve the construction. Parts of the data can be found in the scientific publication. The focus of the operation of the prototype was laid on potential weaknesses of the system and insights on the aging of the used materials and necessary maintenance.
In the following summer we used the prototype to test alternative construction techniques and materials. We were able to test alternatives for the building process of the absorber and the cover and were able to evaluate the experience of the prototype construction regarding the manufacturing techniques.