Why does a user have negative daily savings
Negative daily savings are possible - but always temporary
In short periods over winter, a solar + battery system can produce negative savings. This happens because inverters consume approximately 1 kWh per day just to operate. If a property generates less than this through solar, the hardware costs more to run than it saves in imported energy, creating net negative daily savings.
Why this is rarely a problem: Optimisation of multi-rate tariffs will offset this loss. Even with minimal PV generation, the system can shift load to cheaper off-peak periods, generating savings that outweigh inverter consumption.
When it becomes visible: This issue only manifests when the user is on a single rate import tariff and the device has to be left in balance mode, preventing optimisation from generating additional savings.