If frequent load shedding lasts each winter then there will be extended demand for grid-backup systems that can function with no grid for prolonged periods of time. Combining a battery inverter or a hybrid inverter along with a battery makes it possible to connect the energy from the PV system with that from the stored battery to power at least the essential loads in the property. The size of the battery required depends on the rating of the essential loads to be driven from it when no solar power is possible.

OFF-GRID SYSTEMS

Typically where no electricity is available, Island systems (off-grid systems) are recommended, which support a normal lifestyle without a grid connection. These systems are also called “off-grid”, although top-end inverters can utilize grid/generator power for backup. Under adverse weather conditions and at night, the system supplies power from batteries. High-quality components have been deliberately chosen to guarantee that the Island System achieves an extended service life despite the daily usage of its batteries. High-quality inverters ensure that the power generated by the Island System is more constant than that of generators, UPS’s, and even the national grid, allowing for longer service lives of your appliances.

Island Systems configuration allows for a single or three-phase power supply. Expanding an Island system can be done in a modular fashion and does not require you to discard equipment originally installed. Extra inverters are simply added and configured in order to accommodate the operation of multiple inverters on a single or three-phase power line.

GRID-TIE SYSTEMS

Typically, grid-connected PV systems (grid-tie systems) are utilized solely for energy cost reduction and self-consumption of green power. Unutilized power generated by the PV Grid-Tie system may be fed back into the utility network. This avoids green power being wasted as may be the case with an Island System, once batteries have been fully charged. This assures that your PV Grid-Tied system always operates at maximum capacity, yielding the lowest possible cost of generating green power per kWh. Also, as a result of this and the lack of battery storage, PV Grid-Tied systems have the shortest payback periods.

As these systems do not require any batteries, the necessary maintenance efforts are virtually negligible. PV Grid-Tied systems do not offer backup in case of grid failure. Grid systems can be expanded to AC coupled ESS systems at a later stage.

SMART GRID-TIED SYSTEMS

Unlike conventional grid-connected PV systems that feed power into an electrical grid and may feed excess power back to the utilities, smart grid systems are designed for optimizing self-consumption without any grid feedback. This process is achieved by acquiring regular weather forecasts and exchanging manageable loads to matching generation times.

In addition to load management, this system has the ability to throttle back the inverter’s generation to limit feedback of excess power to the national grid. These systems have online monitoring capabilities but do require internet connectivity, for daily weather forecasts as well as reporting.

As these systems do not require any batteries, the required maintenance efforts are negligible. Smart Grid PV Systems do not offer backup in case of grid collapse. Grid systems can be extended to AC-linked ESS systems at a later stage.

What is ESS?

ESS is short for Energy Storage System. It is a blend of conventional multipurpose Victron products, set up with an ESS configuration. In the system, there must at least be one inverter/charger and also the Color Control GX.

When to use ESS

Use in a self-consumption system, a backup system with solar, or a mixture of both: for example using the top 30% of the battery capacity for self-consumption, while keeping the other 70% available as a backup during a utility grid failure.

Self-consumption:
 At times when there is excess PV power, the PV energy is stored in the battery. That saved energy is then used to power the loads at times when there is a lack of PV power.

The percentage of battery capacity used for optimizing self-consumption is configurable: set it to 100% for (Western Europe / Germany). Or for locations with frequent, or even daily, grid failures, set the threshold to 80%.

Keep batteries charged:
 Besides using (part of) the battery for self-consumption, the system can also be configured to always keep the batteries charged. Failures of the utility grid are then the only moments when energy from the battery is used to power the loads (backup). Once the grid is restored, the batteries will be recharged with power from the grid, and of course, also solar when available.

When not to use ESS

• Off-grid systems;
• Marine systems;
• Automotive systems;
• Inverter priority, also known as intentional islanding or Ignore AC input systems.

With and without grid-meter

ESS can both be used with an external grid meter and without one.
 With a grid meter, a full or partial grid-parallel system.

Without grid-meter: All loads connected to AC-out. And in the case of PV Inverters, also connected to AC out.

Optional feed-in of MPPT Solar charger power

Power from an MPPT can be fed back to the grid, enabled/disabled by a user setting on the CCGX: Settings → ESS.

Fronius Zero feed-in option

By using the Power Reduction feature in Fronius grid-tie inverters, the system can automatically reduce the output of the PV Inverter as soon as feedback is detected; without switching and frequency shifting.

It is not possible to combine ESS with the Fronius Smart Meter; it is not necessary either, since ESS already has metering.
 With ESS, it is not possible to disable feed-in a system with other brands of grid-tie inverters.

A backup system with Solar

All loads are wired on the output of the inverter/charger. The ESS mode is configured to ‘Keep batteries charged’.
 When using a grid-tie inverter, it is connected to the output as well.
 While the mains is available, the battery will be charged with power from both the mains and PV. When feasible, loads are powered from PV.
 Feed-in is discretionary and can be enabled or disabled depending on local regulations.