The simulator calculates a higher number of inverter than I expect

The simulator automatically calculates the module strings taking into account:

• The power limits of the inverters.
• The voltage limits per string.
• The number of MPPTs in each inverter.
• The orientation of the modules.

Although automatic calculations almost always produce expected results, you may occasionally encounter borderline cases with results that differ from what is expected. In this section you can see different ways to adjust the configuration to solve these borderline cases.

Parameters configurable from the Advanced tab

Maximum CC/CA ratio

If the tool calculates a higher number of inverters than expected, this is most likely due to the setting of the maximum DC/AC ratio.

The platform always respects this ratio so that, if necessary, it will add more inverters to avoid exceeding the defined limit. For example, if your installation uses 3 kWn inverters and you have made a design with 3.7 kWp modules:

• With a maximum DC/AC ratio of 1.2, 2 inverters will be needed, as with 1 inverter the maximum allowed DC power would be 3.6 kWp.
• With a maximum DC/AC ratio of 1.3 only 1 inverter will be needed, as the maximum allowed DC power would be 3.9 kWp.

Increasing this value will allow you to connect more DC power, reducing the number of inverters required in the installation.

Please note that this value represents the maximum ratio, i.e. the actual ratio after simulation will always be lower. This can affect the calculation of the number of inverters if you adjust this parameter too much. For example, if you use 100 kW inverters for a 380 kWp installation and set a maximum ratio of 1.3, in theory it should be possible to use 3 inverters (with a maximum of 390 kWp DC). However, if by string configuration it is only possible to connect 124 kWp or 132 kWp to one inverter (with no other values in between), then we can end up with a configuration of 124 kWp in the first inverter, 124 kWp in the second inverter and the remaining 132 kWp to be connected in the third inverter. When 132 kWp exceeds the maximum ratio of 1.3, a total of 4 inverters will be needed. To avoid this situation you can slightly increase the maximum DC/AC ratio. For example, with 1.35 it is already possible to connect 132 kWp to each inverter, so you could have 132 kWp in the first inverter, 132 kWp in the second inverter and the remaining 116 kWp in the third inverter.

Module grouping tolerance (°)

Another reason why the simulator may have selected more inverters than expected is the grouping of modules (°).

For correct operation of the system the simulator avoids connecting modules in different orientations on the same MPPT. It does this with a tolerance defined by this parameter. If the orientation of 2 modules differs by an angle greater than this tolerance, the simulator will require 2 different MPPTs (one for each orientation).

Although it is very rare, you might encounter a case where it is necessary to modify this parameter. For example, if you are working with an inverter with a single MPPT and two roofs that, despite having the same orientation, have a slightly different tilt (e.g. 5°). In cases like this you may want to increase the tolerance value to allow the modules of both decks to be connected to the same (and only MPPT), preventing the platform from calculating a need for 2 inverters for the installation.

Distribution of the number of incompatible modules

The calculation of the number of inverters does not only take into account DC and AC power, but also takes into account all module strings and the operating limits of MPPTs and inverters.

Sometimes, the configuration of modules and orientations can make string calculations impossible with a single inverter. These are very specific cases that are best analysed with an example.

Imagine that you have an installation that you want to build with an inverter with 2 MPPTs. The installation also has a gable roof with 2 orientations: east and west. You have calculated the power of the inverter so that it is possible to connect all the power of the modules without exceeding the maximum DC/AC ratio.

In principle there should be no problem with this configuration, as you are not going to exceed the power and you have 2 MPPTs for 2 orientations. But it turns out that the module distribution is as follows:

• 14 modules on the East roof
• 21 modules on the west roof

With the east cover there is no problem, as it calculates a single string of 14 modules, compatible with the MPPT operating limits.

With the west roof, however, there is a problem. Unfortunately 21 is complicated to handle: either you make 1 string of 21 modules or you make 3 strings of 7. In this case the platform has determined that 7 modules is too few for a string (it falls below the MPPT operating voltage range). On the other hand, it has also determined that 21 is above the number of modules that can be connected in series (exceeding the maximum input voltage of the MPPT according to the temperature history of the geolocation), so it also rules out that option. The only solution you have left is to add another inverter: this way you can connect 10 modules on one MPPT and 11 on another on the new inverter.

To solve this problem you can remove one module on the west roof, leaving a total number of modules of 20. You can also add one more module, as with a total of 22 modules it will calculate 2 strings of 11 modules that will go in parallel to the MPPT (assuming it has 2 inputs) 🚀.

Other parameters

Low-power modules

If the modules you are using do not have a high-enough peak power, the maximum DC power that you can connect to your inverter may be limited by the maximum input voltage per string.

For example, if you use a Sungrow SG110CX inverter paired with 300 W modules, and assuming that for the particular location the maximum number of those modules that you can connect in series is 16, then each inverter will be limited to:

• 9 MPPTs
• 2 inputs per MPPT (18 in total)
• 16 modules per input (288 in total)

So the total maximum number of modules that you can connect to the inverter is 288, or 86400 Wp, which is significantly bellow the nominal power of the inverter.

With this situation, a single 100 kWn inverter would not be sufficient for a 100 kWp installation.