Which inverter is the best to work in low DC voltage?
There are many voltage values in a photovoltaic inverters parameter. One may be confused of what these voltage values accurately mean, what the correlation and functions are, in practical application, and which voltage value is worthiest of our attention. Today I will dive into these voltages in the photovoltaic inverter.
- Max DC input voltage:
The maximum voltage allowed by the DC input of the inverter refers to the highest of strings of DC input, not the sum of all string voltage. For example, if you have 20 panels, each one panel has an open circuit voltage of 40V. When you divide these panels into two strings, then 10 of a string, 10*40=400V. So your maximum voltage is 400V. If you divided these panels into four strings, then your maximum voltage is 5*40=200V. When the inverter detects the maximum voltage and exceeds the set allowable input voltage, it will not start to work.
2、MPPT voltage range:
MPPT voltage range means that the Mppt module of the inverter can operate normally only within the DC voltage range required by the equipment.
3、Rated grid output voltage
The AC output voltage should meet the requirement of the local power grid.
4、MPPT voltage range for full-load:
Within a certain voltage range, MPPT module can work with maximum efficiency.
5、The start-up voltage of inverter:
The inverter will start working when the highest voltage of DC input strings reaches the lowest starting voltage.
6、The shutdown voltage of inverter：
When the output current and voltage of DC input strings become weaker, which result in the output power of the inverter to be close to 0, then the inverter will stop working.
In the photovoltaic power generation system, the solar irradiance gradually increases from sunrise. The voltage generated by the power generation module also increases slowly. When the voltage reaches the working voltage of the inverter, the inverter starts to work and the whole system enters the power generation state. When the Photovoltaic panels voltage continues to rise and reaches the voltage operating range of the inverter MPPT, MPPT will adjust the voltage to the maximum power output point voltage, so that the strings of panels tracked by each MPPTs generates the maximum power. The situation remains the same from noon to evening. As the solar irradiance decreases, the voltage of the Photovoltaic panels decreases. When the voltage is lower than the lowest operating voltage of the inverter, the inverter stops running. The operating voltage range determines the start and stop time of the inverter in the day time. Similarly, the full load MPPT voltage range determines the full load operation time of MPPT. The wider the range, the higher the power generation efficiency of the inverter.
When you design the size of your photovoltaic system (that is, calculating the number of modules in series) in your home, two voltage values must be taken into account:
(1) The maximum DC voltage allowed on the DC input of the inverter
(2) Voltage range of MPPT
So how do the two parameters work together? Taking Australia as an example, we need to consider the DC input voltage and the following points should be noted:
- AS 4777.2 has stipulated, the DC voltage of the household system should be no higher than 600V.
- The mainstream photovoltaic panels maximum DC series voltage is 1000V, and with the development of technology, this value is constantly rising.
- The maximum DC voltage that can be carried by the DC wire.
- Maximum DC input voltage of the inverter
Only when the DC input voltage meets the above four requirements can it be included in the calculation of the number of Photovoltaic panels installing on your house.
So there are parameters that can easily to be ignored, the inverter start-up voltage and shut down voltage.
As mentioned above, the starting voltage is when the Photovoltaic panels reaches a certain voltage, which results in the power generation of the inverter, therefore inverters can start to work. When the MPPT starting voltage is not reached, the inverter can still generate electricity, but at this time it does not get the maximum power generation efficiency from the Photovoltaic panels. That is to say, the electronic energy grabbed from the photovoltaic panels to the inverters may have a certain “loss”, because the Photovoltaic panels did not work at the maximum power point!
But in the actual installation and application, our inverter is a very complex semiconductor electrical equipment. The installation is commissioned and tested. These works require a considerable amount of time and include labor costs. In the previous articles, we have mentioned that in developed countries, the installation of photovoltaic system needs to be finished by licensed electricians, and the labor cost is particularly high.
Therefore, a considerable brand of inverters needs a long time to adjust and connect to the network, because they do not have LCD screen and buttons to achieve adjustment, and their WIFI logger does not have Bluetooth. Under this condition, the installer needs to take 1-2 extra hours to complete the commissioning and testing, even spending an extra night until the sun rises to check that the inverter can start to work again before finishing the job. This may leave an impression that your teams are not professional.
“Why do you spend so long on installation and commissioning? Is the inverter not good?
On the other hand, the amount of power generated by solar power system is positively correlated with the grid-connected working time of system. Under the same conditions, the earlier the inverter starts up and connects to the grid, the higher the power generation. For example, in the same summer, one inverter can usually start up and be connected to the grid at around 05:00am, but another inverter may start later, or even 2-3 hours later than the other.
So let’s make a comparison of the start-up voltage and shut down voltage of mainstream inverter brands:
To sum it up, the start-up voltage and shut down voltage of the inverter, as well as the MPPT voltage range of the inverter play a crucial role in the working time and working performance of the inverter. Through the comparison, Each Energy has excellent performance. In the actual installation, Each Energy can start up at 40V and shut down at 30V, providing customers with more benefits, and for the installer to get more time to finish the installation, saving labor costs for the retailers or wholesalers. Meanwhile Each Energy has shown unparalleled flexibility when adapting to different types of roofs.