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In an off-grid energy system, you are completely disconnected from the electricity grid. You generate your own electricity, for example with solar panels. This energy is stored in batteries and you can use it when you need it. In practice, going off-grid in Western Europe is unrealistic because it would not be possible to generate enough electricity in the winter. That is why on-grid energy systems are often chosen, where the user remains connected to the electricity grid, and can always use it as a back-up.

Interested? Contact us for a custom-designed system

A smart grid is an intelligent network in which a private individual can also trade electricity. Previously, a power station supplied energy to your house, but since the advent of solar panels, that has changed. Energy suppliers and consumers can respond flexibly to each other. This ensures more efficient, sustainable electricity, which can smooth peaks in demand more effectively.  

"Active demand” is one of the most promising solutions, and part of a smart grid. In active demand, flexibility of energy consumption is used to change the control principle. The consumer has to adapt his energy consumption to the availability of wind and sun, and to the limitations of the electricity grid. So availability/production of energy takes priority over energy consumption. An example of this is the switching-on of domestic appliances (dishwasher, washing machine, water heater, ...) at the time when your home battery is charged and there is still a surplus of solar energy

The nominal capacity of Victron AGM and Gel Deep Cycle batteries relates to 20 hours of discharge, i.e.: discharge current of 0.05 C. The effective capacity reduces as the discharge current increases (see table). Bear in mind that the capacity reduction with a constant load, such as an inverter, will happen even faster.

Lithium batteries can be discharged 100% but in practice this will be more like 80 to 90%.

AGM (fibreglass mats): these batteries are ideally suited for supplying short periods of high current, e.g. for winches, bow thrusters, heavy inverters, etc. In addition, these batteries are cheaper than lithium or salt water batteries, for example.

Gel: these batteries have higher internal resistance making them particularly suitable for frequent discharges, 600 cycles of 50% discharge. These batteries are excellently suited to systems with many discharges down to a low level, where a long working life is desirable.

Lithium: An LFP battery does not need to be fully charged. The working life is even slightly longer if the battery is partly instead of fully charged. This is a great advantage of LFP in comparison with lead-acid. It makes these batteries ideal for use in solar systems.  
 
Other benefits are a wide range of operating temperatures, excellent cycle performance, low internal resistance and high efficiency. The energy-efficiency cycle (discharged from 100% to 0% and back to 100% charged) of the average lead-acid battery is 80%. The energy-efficiency cycle of an LFP battery is 92%. In addition, lithium batteries are as much as 70% lighter and save up to 70% of space. 
LFP batteries are expensive in comparison to lead-acid batteries. But in many applications, the high acquisition cost is more than compensated by the longer working life, superior reliability and excellent efficiency.

Salt water battery: Salt water technology is the safest, most environmentally-friendly way of storing electric energy. They were developed for years of trouble-free use in stationary applications. The negative aspect is that they are more expensive and heavier than other battery technologies and less efficient.

A temperature sensor must always be connected to the negative pole of the battery.

When multiple batteries are connected in parallel and / or series, the temperature sensor is only connected to the negative pole from which the battery cable departs.

If multiple devices (Multi, Quattro, ...) are connected in parallel or 3-phase, only one temperature sensor is connected to the master unit.

A connection in series is been made when the power, supplied to or taken from the batteries, becomes very high and resistance of the wiring could be a problem. For the correct functioning of the batteries connected in series it is very important that performances of the connected batteries are equal. This means the batteries have to be taken into service as a "set" of the same age and type. Mixing battery types causes trouble because the smaller one is overcharged and the bigger one is starved and will lose capacity.

For instance:

2 batteries 12V / 120Ah in series become a 24V / 120Ah system.

Schematic representation

When making a connection in parallel, special attention is needed for the cabling used. It is of the utmost importance that all the wires from terminal to the central conductor are of the same length. A difference in lenght means a difference in resistance which results in an undercharged battery on one end of the chain and an overcharged battery on the other end.

For instance:

2 batteries 12V / 120Ah in parallel become a 12V / 240Ah system.

Schematic representation

With a series/parallel connection 2 x 2 batteries are first connected in series.Then these 2 groups are connected in parallel.

4 batteries of 12V / 120Ah become a system of 24V / 240Ah.

A very important but often forgotten part in a series/parallel connection is the so-called compensation cable.
This cable, mounted between the series strings, takes care of voltage differences over both strings by equalisation. In an ideal situation, with 100% identical batteries, this cable is currentless.

Schematic representation

The wiring between battery and charger or inverter has to match the highest current possible. Thin cables get hot on high currents and cause a voltage loss. The voltage supplied to the battery is lower and charging takes more time.

The optimal diameter for the cable is:
charge or discharge current x 0,25 x metres cable

For example for a 50A charger with 2 metres of cable this is:
50 x 0,25 x 2 = 25mm².

When choosing between different standard diametres always take the thicker one.

This table gives an indication on the size of battery cables.

The best charging current lies between 10 and 20% of the C20 battery capacity. For a 12V 200Ah battery this is between 20A and 40A.

When charging batteries temperature of the battery and the environment is of importance.The gassing voltage and consequently the optimum absorption and float voltages are inversely proportional to temperature. This means that in case of a fixed charging voltage a cold battery will be insufficiently charged and a hot battery will be overcharged.
The charging voltage, as quoted by European battery manufacturers, applies at 20°C battery temperature and may be kept constant as long as the temperature of the battery remains reasonably constant (15°C to 25°C). Outside this temperature range temperature compensation is important, and must be implemented.

The function "Voltage Sense" on the Victron Energy chargers compensates the voltage drop in the cables / fuses /connection points. The wires should go straight from the charger to the battery.

Inverters and Multi's are safety class I products that are supplied with a ground terminal for safety purposes.

Its AC in- and output terminals and grounding point on the outside of the product must be provided with an uninterruptable grounding point for safety purposes.

  1. The Phoenix Inverter Compact has a free floating AC output. The grounding point located externally on the product must be used to ground the chassis. The neutral output wire must be connected to ground to ensure proper functioning of a GFCI (Ground Fault Circuit Interrupter).
  2. Phoenix Multi / MultiPlus Compact / Quattro: the output neutral wire will automatically be bonded to the chassis when no external AC source is available (backfeed / safety relay open and product running in inverter mode). When an external AC source is provided, the ground relay opens before closure of the backfeed / safety relay. Once closed, the backfeed / safety relay ensures that the neutral to ground bond is provided by the external AC source. This is to ensure proper functioning of a GFCI to be installed in the AC output of the Multi/MultiPlus.
  • In a fixed (for example terrestrial) installation an uninterrupted chassis ground may be provided by the AC input ground wire.
  • In case of a mobile installation (connection to input AC with a shore power cord), the ground connection is lost when the shore power cord is unplugged. In this case the chassis of the product or the on - board section of the input ground wire must be connected to the frame (of the vehicle) or the ground plate or hull (of a boat).
  • Marine applications: due to the potential for galvanic corrosion it is in general not acceptable to connect the shore side ground to the ground plate or hull of the boat. The proper and safe solution is to install an isolation transformer.

YES, up to 5 Phoenix Inverters 3000VA can be connected in parallel to increase the output power. "Small" inverters do not have this feature and will be damaged when connecting an AC source to the output.

Multi's and Quatrro's have a "Power Assist" function and synchronize their output to the shore and/or generator output; in this way up to 6 units can be connected in parallel with an inverter power of 45kW/54kVA and a charge current of 420A.

This is only possible with the same types of units, different types can not be paralleled.

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