At a basic level a controller may offer the ability to provide an estimate of the
heat in kWh supplied by the solar collectors to the cylinder by multiplying the
difference in temperature between the collector and return from the cylinder by the
approximate flowrate (taken from the pump speed, set-up at commissioning).
The estimation in flow rates will
result in estimates of heat gains that are probably about +/- 20%. A better estimate
will be achieved if the controller can take an additional digital input from a flow meter
inserted in the solar loop.
Several controllers offer either a self-contained ability to
record the system variables over time or can link to an accessory
datalogger or even to a BMS Building Management System. Although generally deemed an
unnecessary additional expense in a domestic system, it may become essential
if ROC payments for renewable thermal generation become available. On top
of this, it is a valuable check that the system is working with something
approaching its design performance. Since solar systems always operate with
an auxiliary back-up that may be set to automatically compensate for solar
shortcomings, then it can be difficult to determine actual solar performance,
particularly given the variability of solar irradiance.
If heat-metering becomes established for the payment of Thermal ROCs in the
UK, then probably only a meter from a recognised list will be permissible to
verify the number of units generated. This is no doubt make its way to Ireland.