Five Easy Steps to 3 Phase Solar Inverter Sizing

For the latest Techie Top Tip, we went straight to the experts, Huawei, world leaders in consumer electronics, telecommunications equipment and, of course, 3 phase inverters!

Choosing the size of an inverter is a simple task, however there are some considerations that must be kept in mind when doing this in order to design your system in a technical and cost effective manner:

1. Voltage Levels

Currently solar string inverters work with two types of DC voltage levels, 1000V and 1500V. Inverters for 1000V systems (normally 100kW and below) have an output AC voltage 300~500V and larger inverters for 1500V systems (normally 100kW and above) have outputs of AC voltage 600~800V. It is important to understand the characteristics of your installation before choosing the inverter. Inverters with higher output voltages are common on utility scale installations.

2. Space available

For large ground mounted system this is not a problem as there is always plenty of space on the mounting racks. However, in commercial or residential applications there are some cases where the inverters must be installed inside a room or in a place with limited space. In this case, you should keep in mind the dimensions of the inverters available and evaluate if it is better to have one large inverter or a couple of small ones. Also, it is necessary to respect the clearance between inverters and with their surroundings for cooling purposes.

3. Power density

The output power is not necessarily the best criteria to choose an inverter. Especially for commercial and residential applications, it is important to have an inverter with low weight and small dimensions so it is easy to handle and install in limited spaces. A good balance between power capacity, weight and volume if often desirable.

4. Cost

For large installations, regardless if it is a ground mounted system or a commercial rooftop, there will be always a cost benefit on choosing a larger inverter due to lower specific cost per kW. Moreover, inverters with high output voltage will help you reduce cable cost since these will have less output current and will allow you to select a cable with a smaller cross section.

5. DC/AC ratio

This value can vary depending on size of inverters. A high DC/AC ratio will normally bring high yield but a lower performance ratio (PR) your installation. It is very important to understand the purpose of the site before selecting this. If a generator is being paid a very good tariff per kWh generated then it could be justified to have a large DC/AC Oversizing on the installation. But in most of the projects it is desirable to optimize this value to a point where you have a good balance between Energy clipping due to too high DC/AC oversizing losses and the yield. The optimal DC/AC ratio will change depending on the location (meteorological data) and other design parameters like module power and string size.

Now you know how, check out three phase inverters here →