Firstly, it should be noted that the OWL Intuition-pv is designed to provide useful indicative information showing both live and historic data; and usage / generation patterns. It is most useful for relative reading comparisons and it is not meant to be or to replace a metering product.
Due to limitations of current clamp sensor technology, all products of this type will have a level of inaccuracy. These sensors only measure the current flowing, they cannot measure the voltage or the power factor and assumptions therefore have to be made (OWLs defaults are 230v and PF 1.0) in the calculations. Equipment capable of such measurements would be relatively costly and have to be wired into the circuit by an electrician.
Additionally, the current clamps are least accurate with low readings. During the Winter months in the UK this can be applied to a large proportion of the day due to a lack of sunlight. This can have the effect of making the cumulative generation reading somewhat out-of-step when compared to your actual Generation meter.
Whilst this may not be desirable, this is normal for the sensing technology used; during the Summer months the figures will be much closer.
It is possible to fine tune the OWL Intuition configuration to minimise differences between the OWL Intuition readings and the meter readings. Through the web dashboard System menu, click on "Property Voltage" here you can change the default Voltage and Power Factor setting. It is suggested for ease of calculation that you adjust the Power Factor setting. So for example if your system over the course of a day is under reading by say 10%, adjust the Power Factor to 1.1 and click Save. Please remember that the true voltage and true power factor are actually variable, so your improvements will also be variable. The longer the period you compare the more accurate you should be able to get this fine tuning.