8
in watts. The production meter (C) measures the
PV power production, the consumption meter (D)
measures the power consumption (energy usage)
in the house.
If the production is higher than the
consumption, the surplus will be stored in the
battery modules (E). The storage system’s inverter
(F) converts the AC power to DC power to charge
the battery modules (E). When the PV production
is lower than the consumption, the batteries will
then discharge to power the loads. The storage
system’s inverter (F) converts the DC power of
the battery modules (E) to AC power. The utility
meter (G), measures the power supplied to the
house and the power fed back to the grid (H) by
the PV array (if applicable). The storage system
will not discharge its batteries to the grid in
normal operation.
Time of use mode
This mode is very similar in function to self
consumption except that the storage system
will charge the batteries from the grid during
programmed time periods designated by the
operator selectable parameters. This mode is
often described as a “focused” self-consumption
in that the system is operating exactly as
described in the self consumption mode, but only
during a specific time period (user selectable).
Refer to the “Logging in to the sonnen eco”
section for instructions on how to change the time
periods. Check your local utility rate schedule
before making changes to these parameters.
Backup mode
Fig. 6 Backup mode
In backup mode, the storage system remains at
a high state of charge until there is a utility grid
failure. In the event of a grid failure, the house
is powered by the energy stored in the battery
modules and generated by the PV array. During
that time, the power from the PV array powers the
house or charges the battery modules, depending
on production and consumption levels. The
storage system can also turn the PV array off if
the battery modules become fully charged.
The storage unit will isolate the micro-grid from
the utility grid using a 200A automatic transfer
switch (ATS). A separate, external ATS is not
required. When this occurs, the storage unit will
produce grid-quality voltage and frequency so
that any grid-tied PV inverters in the micro-grid
will continue to operate.
The PV array will first power the loads on the
AC panel, with any excess energy charging the
batteries in the storage unit. If there is insufficient
PV to cover the loads, the storage unit will
discharge its batteries to meet demand.
To prevent battery overcharging while in backup
mode, the storage unit will perform a frequency
shift to 60.9 Hz (or 60.9-64.9Hz user defined
value depending on PV inverter operating range)
when its state of charge reaches 95 percent.
Because the PV inverter is still subject to UL1741
conditions, it will think that the “grid” is out of
spec for the frequency threshold (59.3 - 60.5 Hz)