Hybrid inverter selection

The main job of a PV inverter, also called an on-grid inverter, ’is to convert DC power generated from the PV array into usable AC power. Hybrid inverters go a step further and work with batteries to store excess power as well. The excess power stored in the batteries can then be used at night when no power is generated by the PV array. This reduces the energy taken from the grid supply - and thus your energy bill. The energy in the battery can also be used to provide AC power when the grid connection is down.

In the most extreme case, no energy is taken from the grid at all and all the power used is generated by the sun during the day, stored in the battery and  and used when needed. When this is done without any grid connection, this is called off-grid. All Deye hybrid inverters are capable of working both in a grid connected or off-grid scenario.

The difference between low voltage or high voltage hybrid inverter lies in the cable sizes needed to connect the battery to the inverter. When the inverter is producing power from the battery, all the power needs to come from the battery. The current that will be drawn from the battery can be calculated by dividing the power by the battery voltage.  ( Battery current = Power / Battery voltage )

As the power goes up, the current required will increase as well. The cables between the battery and the inverter need to be able to carry this current. The higher the current, the thicker the cables need to be. 

Low voltage batteries typically have an operating voltage between 44Vdc to 56Vdc. High voltage batteries have much higher voltages going up to 600Vdc or even 1000Vdc. The higher the battery voltage, the lower the current required from the battery to produce the same amount of power, and thus the smaller the cables can be. 

For example: 
if an inverter is providing 20kW of power, then the current required to do so from a low voltage battery is 20.000 W / 50 Vdc = 400 Ampere.
For a high voltage battery working at 500V for instance, this would be 20.000 W / 500 Vdc = 40 Ampere.

High voltages are more dangerous though so a balance needs to be found between safety and power requirements.  

As a rule of thumb, for installations up to 12~16kW, the required battery cable size is still practical and manageable and the use of low voltage battery and inverters is recommended. For power requirements above 12~16kW, the battery cables and required protection become harder to find, more expensive and more difficult to install. For higher power requirements it is thus recommended to use an inverter and battery voltage operating at a higher voltage.

Grid connected Application

In an On-grid scenario, the Deye hybrid inverter is connected to the main grid. In this scenario, you may want to achieve the following benefits:

Maximizing solar self-consumption: During the day, the PV system generates electricity which will be provided to the loads initially. Excess energy generated by the PV system will charge the battery via the Deye hybrid inverter. When solar generation drops off, due to cloud cover or setting of the sun, the stored energy in the battery can be released to power the loads as required.

Providing backup for critical loads: The Deye hybrid inverter has an independent critical load output port. It allows critical loads such as refrigerators, routers, lamps, computers and other critical appliances to be powered when the grid fails. The system can automatically switch to backup mode within 4 milliseconds. This automatic transfer time is very short and most critical loads will continue to work smoothly without a glitch.

Reducing your electricity bills: Thanks to 6 programmable time slots for battery charge and discharge, the Deye hybrid inverter allows you to charge the battery at the off-peak tariff and use the stored battery energy during peak times. The inverter also supports grid peak shaving function which can limit the Max. power drawn from grid, avoiding peak demand charges.

Typical system diagram

On grid system diagram

Operation Modes

When your systems is connected in an On-grid scenario as illustrated above, the Deye hybrid inverter allows you to choose the operational mode most suited for your situation:  

Sell First
This Mode allows the hybrid inverter to sell back any excess power produced by the solar panels to the grid. Depending on your preference, even the battery energy also can be sold into the grid. Otherwise, PV energy will be used to power the load and charge the battery first and then any excess energy will be sold back to the to grid.

Zero Export To Load
In this Mode, the hybrid inverter will only provide power to the backup load connection. The hybrid inverter will neither provide power to the home load nor sell power to grid. The built-in CT will detect power flowing back to the grid and will reduce the power of the inverter only to supply the backup load and charge the battery.

Zero Export To CT
The hybrid inverter will not only provide power to the backup load connected but also give power to the home load connected through the distribution board. An external CT will detect whether power is flowing back to the grid. The inverter will then reduce its output power to supply only the loads and charge the battery. If there is insufficient PV and battery power to power the loads, additional power will be taken from the grid. The hybrid inverter will not sell power to the grid.

Smart Gen/Load Port

The Deye hybrid inverters have a unique Smart Gen port which can be used to:

Connect a petrol or diesel generator
A dry contact is available on the Deye hybrid inverter which will be toggled when a grid failure has been detected and the inverter has gone into off-grid mode.  

Connect AC coupled solar
Either micro-inverters or string inverters can be connected to the Smart Gen input. This allows for easy retro-fit of existing solar systems. 

Connect to a so called 'Smart load'
When the Deye hybrid inverter is configured to have a 'smart load' connected, the GEN input will be used as an output instead. Smart loads or dump loads such a water heater can be connected to this port. These loads will be disconnected when the PV input power is low and the battery SoC is below a programmable value. The loads will be reconnected when sufficient solar power is available again and the battery is above a programmed SoC.

Typical Off-Grid Application

In an Off-grid application, the Deye hybrid inverter is not permanently connected to a grid. In such scenario, the main purpose of the system is to capture as much power from the solar array, provide power to local loads and store excess solar energy in the battery for later use.

Unbalanced loads
In off-grid mode, the Deye Hybrid inverter is capable of handling 100% unbalanced loads and maintain up to 50% of the total rated power of the inverter per phase. For instance, if a single phase on a 12kW, 3-phase inverter is not loaded at all, the remaining 2 phases will be able to product 50% of the inverter's rated power, or 6 kW per phase, producing the inverter's 12kW rated power in total.  

Peak power rating
All Deye hybrid inverters have a 2x peak power rating for 10 seconds. This peak power rating is important to start motors and other electrical machinery that have high in-rush or start-up currents.