Developement of a measuring system for efficiency determination

From May to August 2020 the students Steffen Bißwanger, Leon Dungs, Sara Konrad, Nikola Milenkovski and Alexander Zinn  carried out a project as part of their studies at the TU Darmstadt in cooperation with our project SoWaDi. The goal was the development of a self-sufficient measurement system, which allows the determination of SoWaDi units efficiencies in the field. This is to be achieved by automated data collection of solar radiation, water output and environmental conditions.

In the following you can read some recordings from the students’ laboratory book. There they recorded their progress and described how they overcame the challenges they faced during the project.

Phase 1: Selection of components

09.04.2020 09:45

Today we firstly get to know each other, online of course, and get accustomed to the Solar Thermal Water Disinfection Unit we will work with during the project. Two of our team members already know the unit well. The rest of us are just getting to know it. In order to develop a suitable measuring system, it is important to have a good understanding of the function of the unit and the conditions in which it is used.

08.05.2020 15:15

Some time ago, we were able to agree on which quantities we wanted to measure. The important question now is: How? Today we discuss our latest ideas about which low-cost sensors and designs will give us the best results. A special challenge is to measure the amount of water coming out of the unit. In the past, several attempts have been made, which failed due to different reasons. Temperature variations from day to night have led to unreliable results of load cells and a sensor with moving parts blocked when it was used in wind and weather. But we have a new idea: a cut-off glass bottle with a small hole in the lid can be turned upside down to serve as a collecting container and accumulation device for the minutely water flushes from the unit. We then measure the time it takes for the glass bottle to empty again after a flush.

23.05.2020 17:18

We are finally ready: After 5 hours of discussion we have selected suitable components for all sensors, the computing units of the system, the data transmission and the power supply. Now all we can do is wait until the order arrives and hope that everything fits together.

31.05.2020 13:15

We just got the message that the first package has arrived. Now the real work can begin.

Phase 2: Programming and building the measuring system

31.05.2020 14:45

Except for one team member, none of us has worked with the microcontrollers we want to use for the project yet: Arduinos.

After we have set up the programming interface on the computer, we can finally load the first program onto the Arduino.

31.05.2020 14:46

The Arduino starts blinking. Hurray! Let’s see if it will be as easy to connect and read out the sensors as well.

02.06.2020 12:37

We were able to get the SD card reader, the current meters to measure the sun intensity and the simple thermometers working without any problems. The somewhat more complicated thermometers for the higher temperatures, however, only show strange values so far. Where they come from, we cannot explain. One thermometer shows us 65°C and another 9°C, both temperatures are definitely not correct.

02.06.2020 19:36

We just found a way to correct the strange values. One parameter in the calculation formula is a comparative voltage. While measuring this voltage at the sensors we noticed that it is different for each sensor individually. Now that we have incorporated this into the software, all thermometers show plausible values.

13.06.2020 09:42

We are now already in the middle of June, the weather offers optimal conditions to test the new measuring system. It is therefore about time to finally attach the measuring system to the unit. Therefore we are working at maximum effort to complete the circuit board for the measuring system. We solder all connections by hand. Hopefully our plan will work out. Also, the data transfer via the cellular module still doesn’t work. After we have ordered a better module in the meantime, at least we could get a connection to the mobile network, we unfortunately still haven’t managed to send the data automatically. Slowly time is running out. If we don’t manage to solve this, the whole project could fail.

14.06.2020 21:06

After two days of hard work the board is soldered. The measuring system can finally be installed in itscase, where it will be protected from rain when installed on the unit. We also made important progress with the sending of the data. The microcontrollers are now slowly reaching the limits of their computing capacity, further changes are becoming more and more difficult to implement. Fortunately, only a few minor software problems need to be fixed now, and then the measurements can start soon.

Phase 3: Attaching the measurement system to the unit

20.06.2020 09:16

The time has come: Today we can finally install the measuring system. It has been running continuously since yesterday and is ready for use.

20.06.2020 22:03

We have been waiting for the first data to arrive for 3 minutes now. Now comes the moment of truth. If everything goes smoothly today, we are confident that the measurement system will continue to work for the next three months until too little light is available in October.

20.06.2020 22:04

The first data have reached us. We are relived. We have done it and deserve a break for a while. As soon as we have enough data, we can start evaluating it and start to write a full report.


With the measurements over a period of 30 days, the team has succeeded in finding out which sensors are relevant and suitable for the assesment of efficiency. So that in the future it will be possible to build a low-cost measurement system that can perform all important measurements. Almost the entire team will continue to develop the measurement system on a voluntary basis at Engineers Without Borders in Darmstadt. The new measurement system is called MONA (Monitoring Offgrid Node for Assessment of SoWaDi Performance). In the future MONA will help to collect long-term data in Tanzania and to further develop the SoWaDi unit in Darmstadt. In contrast to her mother, MONA is a little smaller and more compact, and also not as transparent, just perfectly equipped for a world tour.