This article will cover various design aspects of OpenSolar, including inverter stringing, micro-inverters, and power optimizers. It will also touch on each of these in relation to the solar modeling software used to calculate output in OpenSolar (PV Watts and System Advisor Model)This article relates to the Project Zone> Design tab of the app.

Table of Contents

• String inverters
• Micro-inverters:
• Effect of Optimisers/Micro-inverters using PVWatts
• Effect of Optimisers/Micros using System Advisor Model (SAM)

String inverters

Currently, there are two modes: Manual and Auto stringing. We will review each option below:

Manual Stringing

Manual is the preferred method for stringing, giving you full control over how you want the system to be strung. To use the manual mode you want to go into the inverter tab or the design menu. From there, you want to select your inverter from the drop-down option. Once the inverter has been selected, you want to click on the + string button which will allow you to add your MPPTs and strings. 

To add the strings, you want to click and drag across the panels as shown below:

Auto String

• For auto-stringing, you want to select the inverter using the drop-down. Once this is selected, click on the "auto string" button. After a second, the system will be strung for you. 

Note: The default inverter modeling system can be changed in Control > Design & hardware > Setbacks & Design settings. From there edit or create a new template. Once in the template, you want to expand the Setbacks & Design Settings which will contain the "inverter modelling automation" field.

Micro-inverters:

When a micro-inverter is used, the system will automatically calculate the number of micro-inverters. 

Optimisers:

• Optimizers are added in Control > Design & Hardware > Other Components. This component must be created with the type set to “DC Optimiser”.
• Once you have optimizers in your list of components in your account then you can click on the “use DC optimizer” button in the panels section.

• The number of optimizers that are used in the system is determined by the panels that are used and the sizing constraints set on the optimizer.
• We can automatically determine whether the panel-to-optimiser ratio should be 1:1 or 2:1 etc. based on the specs of the panels and the optimizer (based on power, current, and voltage).

Effect of Optimisers/Micro-inverters using PVWatts

Using a micro-inverter or optimizer will change the mismatch loss to 0%

It will also apply a Shade mitigation factor (SMF) of 33%. So if there is any shading applied, the loss from that shading will be reduced by 33%.

Effect of Optimisers/Micros using System Advisor Model (SAM)

This will change the default losses:

If a string inverter is used with no optimizers then the losses will be:

Module mismatch = 2%

Diodes and connections = 0.5%

DC wiring = 2%

If an optimizer is used with a string inverter then the module mismatch will go to 0%, the DC wiring will go to 1% and the optimizer's efficiency will be used

If a micro-inverter is used the module mismatch will go to 0% and the DC wiring will go to 0.1%.

For shaded string inverter (no optimizer) systems, SAM will incorporate a validated data set to look up what the output will be based on the shading values calculated from OpenSolar 3D.

For shaded micro and optimizer systems, the shading values will have a direct relation with the output. So when the system is x% shaded, the output would also be reduced by x%.