Read an updated story from 2019 on inverter MPPT here.
By Roy Allen, technical sales support engineer at Power-One, a member of the ABB Group
MPPT is a four-letter acronym referenced in the solar industry by many, but understood by few. It’s important to understand the definition of MPPT and its functionality, because doing so can help a user improve the energy harvest of his photovoltaic installation, thereby increasing profitability.
What Is A MPPT?
MPPT stands for Maximum Power Point Tracker. It is a circuit (typically a DC to DC converter) employed in the majority of modern photovoltaic inverters. Its function is to maximize the energy available from the connected solar module arrays at any time during its operation.
Why Is A MPPT Necessary?
A solar module is a limited energy DC supply and has internal impedances that vary throughout the course of the day, depending primarily on the level of solar irradiance impinging on the module face and the cell temperature.
An inverter without an MPPT circuit would result in sub-par or non-optimal operating conditions between any PV module (or string of modules) and the inverter. Unless the inverter can match the strings to extract maximum power the result is a lower efficiency operation for the connected strings. The MPPT circuit constantly monitors the array voltage and current. It attempts to drive the operating point of the inverter to the maximum power point of the array, resulting in the highest energy harvest.
Dual vs. Single MPPT
Simply put, in the majority of applications with two strings or more, two MPPTs are better than one. To support this statement, review the table below.
|
Single Inverter Attribute |
Single MPPT |
Dual MPPT |
|
Allow connecting arrays with different solar azimuth angles |
No* |
Yes |
|
Allow connecting arrays with different solar tilt angles |
No* |
Yes |
|
Allow connecting arrays with different string lengths |
No* |
Yes |
|
Allow connecting strings of dissimilar modules |
No* |
Yes |
|
Allow connection more than two strings without combiner fusing |
No** |
Yes |
|
Provide better monitoring granularity |
No |
Yes |
|
* Can be done but results in low harvesting efficiency, lower harvested energy ** Violates NEC requirements. Dual MPPT provides two channels and code allows two strings per input without need for fusing |
||
Considering the entries in the table, an inverter with dual-MPPT functionality allows much greater system design flexibility, significant cost savings and higher levels of harvested energy.
Connecting two arrays with different solar azimuths or tilts, different string lengths (Voc) or different PV modules to a single-channel MPPT inverter would result in a highly inefficient system and, in some instances, an unsafe one.
By accommodating two arrays mounted at different azimuth and/or tilt angles, different string lengths –— even different modules –— into a single inverter increases the design options for installers because it eliminates the need for a second inverter in many situations.
The Maximum Power Point Tracking maximizes energy harvesting during different hours of the day, through changing weather conditions with altering roof pitches and different number of solar panels per string.
Additionally, even for PV systems with all strings facing the same direction, using the dual MPPT function is a better choice. Assume a system has four strings all on a flat roof. If a single MPPT channel is used to connect these to the inverter –— in addition to requiring an external combiner –— if one string is damaged or subjected to higher soiling rates or shading issues, this would affect the output of the entire array and result in a lower overall energy harvest.
Breaking the array into two segments on two MPPT channels will improve system harvesting, because if one string/array is damaged or soiled, the output power of the “good” array at the second MPPT will continue to provide full power, thus providing a higher yield than the single MPPT case. Furthermore, in systems requiring shade mitigation, one MPPT input could operate the shaded array with the other operating the unshaded array.
Historically, without dual-MPPT functionality, efficient interconnection of arrays on two different azimuths required two separate inverters, adding significant material and labor costs to the installation. Dual MPPT provides the installer with faster, less expensive system installation with the capability of handling large and small roof surfaces with different azimuths — all using a single inverter.
This is a great representation of the flexibility dual MPPT’s provide. These solar arrays face South East, and South West (two different Azimuths) and have a different number of solar panels per string. The triangle panels are 72W while the rectangular panels are 144W. Inverters with MPPT channels can accommodate such with optimized energy harvest for the lower installation and material cost than using a single inverter.
Combining up to four strings of PV modules to a single inverter without additional external combiner boxes saves time and materials. The exception of NEC section 690.9 allows connecting two PV strings to a single input of an inverter without a combiner fuse in each string. This is as long as the string wiring is sized properly and there are no other current sources that can back feed into the strings.
If an inverter has dual independent MPPT channels, then up to two strings may be connected per MPPT channel without combiner fuses in each string. Therefore, an inverter with dual-MPPT channels can have up to four strings connected without any external combining hardware.
Over the past few years, the output power rating of most PV modules available on the market has increased substantially such that today’s small residential systems don’t typically need more than two strings. Larger residential applications, however, typically require four strings. Commercial systems require a large number of strings and have historically used larger central inverters and external string combiners. But there is an industry trend of using a multiplicity of smaller inverters for these applications, so a dual MPPT inverter would be advantageous in these designs as well.
MPPT And Monitoring
Single MPPT channel inverters can only provide monitoring data at the entire array level. Whether one, two or four strings, data collection will be based on the overall array input. With independent dual MPPT channels, the inverter can provide monitoring information at the MPPT channel level. As a result, there is a finer granularity in the monitoring data, such as site status, energy production and troubleshooting data. This is important because, depending upon the system design, the loading of the two channels can be different. Therefore, for small systems (with one string per MPPT channel), data collection essentially happens at the string level. For larger residential systems (with up to two strings per MPPT channel), data collection is reported at the two-string level. Therefore, in addition to providing proper energy harvest values per channel, the user can understand what is happening at each input at any time. This can be helpful in troubleshooting abnormal conditions at a given inverter input.
Understanding all these aspects of MPPT can help provide better knowledge of how energy harvesting works and therefore help solar installations become more profitable.
For dual mppt inverter, it has 2 input ports but if i use single port with 12 modules of 330 wp and left the 2and input port with empty. Then what happens to generation and panels condition.
Is it possible to put 2 different power value on DC1 and DC2 in dual MPPT. I have 9x of 350 watts for DC1 and 4x 360 watts for DC2. thank you for the response.
Hi,
for an inverter with dual MPPTs and 2 DC inputs per MPPT, what will happen if only 1 of the inputs is use for both MPPTs? Ie 1 string connected to MPPT 1 and another string connected to MPPT 2.
hello just have a stupid question, i have hybrid deye inverter 5kw
PV Input Voltage (V) 370 (100~500)
MPPT Range (V) 125~425
Full Load DC Voltage Range (V) 240~425
Start-up Voltage (V) 150
PV Input Current (A) 13+13
my question is in the pv input voltage, the hybrid deye has 2 mppt, does the pv input voltage for single mppt or for 2 mppt?
hi, Asif here
dear my friend,
its for single string ( 240~425v),13A and other string also ( 240~425v) , 13A .
if you want to use double string then on one string voltage series is (240~425) and other string series range ( 240~425) and 13 amp
WHAT IS THE REQUIREMENT FOR 4KW SOLAR SYATEM SINGLE MPPT OR DUAL MPPT IVERTER ?
WHICH IS ADVISABLE ?
Sir; i am having an off grid system at my home, 10KW system with a 400w mono crystalline panels qty 10. they have wired up two parellal setup with 5 pannel each. working at 72V (6×12 V Bty) and the system work absolutely ok.
Now i want to know how the following :
1. can i work my same system during day time when sunlight is there with out battery back up ??
2. Can the system work off grid and at same time can my battery can charge and when sunlight is not there this bty can be used for inverter ??
3. how can i function the present system to work directly from solar panel with MPPT with out battery ?
4. How can i get my bty charged during the system work directly on utilities and the charged bty work when there is no power or no light. ??
My INV Device is 8kw on grid with 2 mppt. in that 1 mppt has 2 table string. I have the question why there are 2 strings in 1 mppt. What if the same pv module that I put in 1 chain instead of put in 2 series (voltage condition) ?? Please respond to your responses !! Best regards !!
To increase current strings were added
am having two 275watts solar panels,two 200Ah batteries and 12v/800watts inverter,what is the best solar mppt for this kind of arrangement?
What happens if use only one mppt of solar inverter and make second mppt inputs blank or not connect with pv strings? Does system performance decrease or noting happen to system? Please answer.
Nothing gonna happen
something definitely wrong. If I were you, I would isolate all panels on DC 2 and check voltage across each to identify if one of the panels has gone rogue (Voc, Isc) . If they are all ok, I would then check wire continuity (resistance). Step three would be checking the inverter by the manufacturer or authorized dealer.
What if you’ve got two identical arrays on the same azimuth angle, no shading etc. and the DC1 channel is yielding 324.7 volts, 4.3 amps whilst the DC2 channel is yielding 1.9 volts zero amps.. something wrong?
you probably have a bad connection somewhere along that string DC2. Need to check voltage at those panels for that string. Then see if you are getting the sum of those voltages further along. Best place to start is to check for the voltage at the disconnect of the trouble string first
“… whilst the DC2 channel is yielding 1.9 volts zero amps..”
A little bare (wire) will fix it! Stick with it!
I have recently installed a dual MPPT system at my house. It has 2 sets of panels in different azimuth roof positions. I had been wondering how the 2 arrays work. The explanation of the Dual MPPT system assisted me in understanding how my installation works. However when sun is in different positions the 2 panel sets must produce different outputs of power right? So how do I get aggregate power output of the installation? Is there a way I can monitor the 2 outputs atvany guven time?
Oh by the way I am an electrical engineer so I am technically interested in understanding these solar systems. Send me any data or websites I can get more technical information.
Regards
“[…] …the 2 panel sets must produce different outputs of power right? […]”
Not necessarily. You haven’t said whether your 2 panel sets are the same size or not. Just because they may be situated on different azimuths from each other doesn’t mean that their outputs must be different; plus the measuring of their individual outputs can vary at any given time which is like quoting a finagling-figure not dissimilar to 3/8ths of 13/27ths of 231/232nds ad infinitum.