MPPT and String inverter is most common solar inverter in Australia market. They are features built into all grid-connected inverters. Of course, off-grid inverters do not mean that there is no MPPT. For example, the Growatt SPF 5000 ES has an MPPT. However, the AC Coupled inverter has no MPPT function, because it does not directly connect to the PV system, its main role is to link the battery system, so as to achieve the function of charging the battery.
What is the string inverter?
String inverter is also called central inverter. Most of solar system use string inverter because it can handle the power produced from several panels. It means you don’t need use micro inverter for each solar panel because micro inverter is more expensive.
Compared to micro inverter, string inverter can save on the upfront investment cost. But you should ensure your PV system will be installed in best location, otherwise it’s possible to affect performance results of the string inverter. As discussed in my article of how to design solar panels in rooftop, we have learned about some unfavorable factors such as shadows reducing capacity. So in here, a concept is that all solar panels in one string and connected to string inverter have to keep highest performing together.
What is the MPPT?
After understanding the concept of string inverter, then let us learn about MPPT. MPPT stands for Maximum Power Point Tracker, which employed in most of inverters today. It wides and maximises the power from the solar panels arrays connected in one string at any time in its operation.
MPPT is a device that regularly tracks characteristics of panels in the same string, and optimizes voltage and amperage accordingly for maximum power output.
Any inverters without MPPT circuit would cause non-optimal operation conditions between PV systems and inverters. Solar panels are mainly composed of cell modules, so DC supply mainly depends on the level of solar irradiance impinging on the panel face and the cell temperature. If panels sometimes are blocked by shadows, the whole string will be in low efficiency operation. At this point, MPPTs try to drive the operation point of the inverter to the maximum point or the other strings, keeping in the highest power collection.
Dual MPPTs are better than single MPPT, because many functions are not supported by one. For example, if your PV system is installed in different orientation roof, different tilt angles, different string length (means number of panels in a string) or different brand or modules, single MPPT won’t up to these jobs, but Dual MPPTs can. Furthermore, dual MPPTs can expand the design options for PV system and decrease the need for second inverters between two strings.
Similarly, one MPPT can operate one shaded string, while the other can operate unshaded ones. This is an advantage point for power collection because they break PV system into two MPPT channels.
It’s unsafe and inefficient system if you use a single MPPT to connect two stings with different angles, tilts, string lengths or modules. So, please don’t do that. And most of inverters today have dual MPPTs or more.
The more MPPTs & Strings, the better
The emergence of Multiple MPPTs & Strings inverter has solved the problem of poor performance to a certain extent. No matter single or several string facing the same direction, using multiple MPPTs instead of using single’s is always a better choice.
If one of strings in faulty or soiled, the others still works well, while MPPTs are always in monitor. It also means that the second or third MPPT will continue to provide full power, thus providing a higher yield than the single MPPT case.
We can’t stop the inverter, otherwise it can’t convert the DC to AC. It’s essential that Growatt inverter family both have multiple MPPTs and Strings, from Dual MPPTs to Three MPPTs, and always meet your home requirements.
Lots of cases in actual installation both meet 2 or even more rooftops, then panels are scattered on them. So, in Sunterra, we usually use two MPPTs inverters. Panel orientation and configuration is important. We use combination of series and parallel connections of the strings to have maximum output efficiency.
Growatt’s classic residential storage inverters
Growatt’s classic residential storage inverters – the SPH and TL-XH series, are not only compatible with growatt’s low-voltage or high-voltage batteries, but have dual MPPTs as well.
The battery inverter also has 2 MPPTs so that two independent strings can be connected. This property is particularly important if, for example, a part of your PV system is affected by shadows at certain times of the day. The non-impaired part of your system can continue to generate electricity with the maximum output.
MIN 5000TL-XH is a single phase hybrid inverter including dual MPPTs and strings.
Growatt's solar only inverters
MOD 10KTL3-X is a three phase solar inverter including 2 MPPTs and 3 strings. Two of strings can be designed in parallel connection. (The strings must be identical in terms of numbers of panels and model type when parallel connection to do so.)
MIN 10000TL-X is a single phase solar inverter including 3 MPPTs and 4 strings. Two of strings can be designed in parallel connection. (The strings must be identical in terms of numbers of panels and model type when parallel connection to do so.)