Working safely and string vs micro inverters

Working on PV installations and safety

As mentioned before, we strongly recommend that you have a basic knowledge of electrical installations or get assistance from someone who does if you are a self-installer. It is not rocket science, but after all, we are working with high voltages and DC currents, solar panels do not have an on or off switch. You will also have to have your installation inspected, we work together with OCB for inspections.


Some important things regarding safety:


-Currents can only flow if the circuit is closed. So never work on a PV installation or the cabling with a closed circuit. Always switch off the inverter.

-Never simply pull out plugs while the installation is in operation to avoid an arc flash and damage.

-Ensure that the connections are technically sound, so use good quality materials.

-Do not forget to set the country setting of your inverter correctly.



A word of explanation about PV systems:

Series connection or string system: keep it simple, stupid?

A serially connected system is also called a string system. A serially connected system is traditionally the most commonly used system. Most solar panels only provide a limited voltage (approximately 30 to 40 volts). That is not enough to run a large inverter start up. On the other hand, the same panels give a fairly high current. This high current in combination with the low voltage, gives a lot of loss in the cabling or we have to use much thicker cables. A simple solution was to put the panels in series. The voltage adds up, the current remains the same.

The simplicity and the relatively low purchase price can be a great advantage in terms of profitability of your installation. The inverter is usually the weakest point technically, but it is easy to replace in case of a defect.

The main disadvantage is that in a series connection the weakest link affects the entire string. This means that if one solar panel produces less power than the others or becomes defective, they all suffer. If part, or even just one of the panels is in the shade for part of the day, a series-connected system may not be the best choice.
This problem can also be solved with optimizers and/or an inverter with multiple MPPTs, but this will of course result in a higher cost price.


Parallel connected system

A parallel connected system is a system with micro-inverters such as those from the Enphase brand.
Behind each solar panel you place a micro-inverter that converts the approximately 40 Volts of the solar panel directly into 230 Volts alternating current. You connect these micro-inverters parallel to each other on a collective cable that carries 230 Volts. The voltage remains the same, the current adds up with each new micro-inverter that you connect.

The advantage is that each panel can independently discharge its power. Shade, pollution or defects do not affect the rest of the system. If a panel breaks, the other panels continue to deliver maximum power. If an inverter breaks, the others simply continue to do their job.

The yield is typically higher than that of a serially connected system. In addition, micro inverters start at a lower voltage. In the morning, the system starts earlier and in the evening it goes out later.

In the monitoring app you have insight into the performance of the system, but also into the performance of each individual solar panel. A defect or problem is found so quickly.



Useful links:

-Enphase calculation module to determine whether and with which micro-inverter your PV panel is compatible:

https://enphase.com/en-in/installers/microinverters/calculator?_ga=2.66158695.872681191.1696105335-875767476.1696105335

-Calculation of profitability, cable losses etc. of your PV project:

https://www.sunnydesignweb.com/sdweb#/