Scientific monitoring of SWHS

Why scientific monitoring?

The lack of reliable data of the energy output of Solar Water Heating Systems (SWHS) is one barrier for their deployment. Investors want to know, how much fossil fuel and money they can save with a SWHS. Scientific monitoring shall provide reliable data on energy yield and savings for typical SWHS.

It is no doubt, that there is room for further improvements in the performance of SWHS, by using more efficient components, by better hydraulic designs and by improvements in control and operation. Improving the performance will increase the cost-competitiveness and attractivess of SWHS and therefore support their deployment as well. Detailed scientific monitoring shall identify the reasons for inefficiencies and enable improvements of the technical concept of SWHS.

Definition and objectives

Scientific monitoring is characterized by

High precision (sensors are used, which provide data with low uncertainty)

High resolution (data are measured and stored with high temporal resolution, e.g. one data set per 5 seconds, to record the dynamic of the system)

Detailed measurement (measurement of all steps of the energy supply chain to evaluate the reason for the results measured)

Detailed analysis (data are processed, evaluated, and interpreted and results presented in graphs)

The objectives of scientific monitoring are

to provide reliable and precise data of a few exemplary SWHS operating in the field

to evaluate and assess the performance of the SWHS monitored

to discover the reasons for inefficiencies in the SWHS monitored

to derive general recommendations for SWHS from the monitoring results

Scientific monitoring concept

Within SoPro India highly sophisticated monitoring systems, which are typically used by Fraunhofer ISE to do monitoring on a scientific level in the field, are implemented to two SWHS at Himachal Dairy in Thesil-Rampur Bushar, Himachal Pradesh, and at Synthokem Labs in Hyderabad, Telangana. In the following the monitoring systems are described.

The scientific monitoring system consists of a Monitoring box (MB), which consists of the following units.

Sensor control unit

Fieldbus coupler with M-Bus, nearly every kind of analog signal can be processed (0-10V, 0-20mA, and frequencies up to 500Hz), number of analog channels is flexible. Up to 20 digital M-Bus slaves can be operated.

Control and data storage unit

Composed of a Linux embedded PC, USB-Stick and Ethernet switch. The Sensor control unit and Communication unit is controlled as well as data stored. The C-language software on the embedded system is customised for the monitoring system.

Communication unit

Enables remote access and fully automated data transfer via mobile communication like GSM-Routers. Measured data are stored on an USB stick at the Control and data storage unit and can be picked up, if the remote access is not working.

Power supply unit

All MB-components are supplied by a 24V power system, protected against blackout by an uninterruptable power supply (UPS). The UPS also avoids voltage peaks etc. caused by an instable grid.

Structure of the scientific monitoring systems

Look in the open monitoring box, the box is connected by a LAN cable (green) with a Laptop for maintenance

Following sensors are used:


To measure the global solar irradiation, a pyranometer is installed in the collector surface layer to measure the irradiation falling on the collector surface. This value is higher than the horizontal solar irradiation, which is usually published.


Heat meter

To measure the heat, two temperature sensors, a flow rate sensor and a calculator is needed.

A pair of calibrated PT 100 temperature sensors are used and installed in the circuit, one close to the flow rate sensor and one in the return flow pipe. An ultrasonic flow rate sensor is measuring the flow rate of the fluid.

Display of the heat meter calculator

The sensors are connected with the calculator, which multiplies the temperature difference with the flow rate and correction parameters. A lithium battery is integrated in the calculator box to store data if electricity supply is disrupted. The measured values are displayed and sent to the monitoring box via M-Bus (see photos).

Temperature and flow rate sensor, look into the heat meter calculator box during installation (from left to right)

Within the SoPro India project, the experiences with scientific monitoring provided a good understanding on the typical designs of SHIP systems and possible reasons for inefficiencies were identified. The performance for two SHIP system was evaluated in detail utilising the reliable and precise data gathered. Based on these findings the basic monitoring recommendations are derived, taking into account crucial points for monitoring.