Why monitor SWHS?

Monitoring means, to continuously control, if the SWHS is working as expected.

If the SWHS is working, is rather easy to find out, by checking the temperature of the collector and of the storage tank during sunshine and checking, if the pump is operating.

If the SWHS is working with high or low efficiency, is, in comparison, not easy to find out. The efficiency is the relation of the output (solar energy delivered to process) to the input (solar irradiation on the collector), but to measure the efficiency and to assess the result correctly, is challenging.

To assess the monitored result is challenging, since the input (solar irradiation) is varying day by day and the external factors influencing the expected efficiency, like ambient temperature, operation of system and profile of process heat demand, are varying as well.

To measure the solar output (solar yield delivered to process) is possible by installing a heat meter in the hydraulic circuit just before the heat or the fluid is supplied to the process. A heat meter is counting the kWh (Kilowatt hour) heat, which is delivered.

To measure the input (solar irradiation) is expensive, if it is done with precision (with a pyranometer). But although the solar irradiation is varying a lot between days, the solar irradiation per year is quite constant. Since for simple monitoring only annual data are compared, average annual irradiation values can be used from the online available resource data instead of measured irradiation data.

If it cannot be recognised directly, if a technical system, like a SWHS, is working as expected, it is important to monitor the system. Because in each technical system, faults can happen.

Energy flow in a SWHS and possible sources of inefficiencies and losses