How do you design a solar panel system?

Each solar energy system installation is unique. It can therefore be difficult chosing the right inverter for the right solar panels. We can provide you with the tools to make this decision more straightforward.

You will need:

  • Datasheet Inverter
  • Datasheet Solar Panel

When you need to determine what kind of installation is right for a specific location, it is usefull to first check the annual consumption. With this information it is possible to calculate which inverter and solar panels are most suitable for the system. A number of factors need to be taken into account:

  • Shadow:
  • Slope angle and orientation of the solar panels;
  • Correct configuration of the solar panels.

Slope angle and orientation of the solar panels

All solar panels that are connected in a single string must be set at the same angle and orientation. This is related with the voltage and current output of a solar panel. The voltage and current output need to match with all solar panels in the same string.

Why is this important for the inverter?
If the output differences between the solar panels vary too widely, the inverter will not be able to find the Maximum Power Point (the ideal point between voltage and current).

In the Netherlands, oversizing the inverter by 10% to 20% is generally the most effective way. This depends on the angle and orientation. The system will then curtail the output slightly in ideal circumstances, but it will perform much better in less than ideal circumstances (which, unfortunately, is often the case in the Netherlands). As a consequence, the output of the solar energy system is optimised.

Shadow

Check whether any shadows could cause problems. Shadows could come from other houses, trees, dormer windows, chimneys or even other solar panels (e.g. on many flat roof systems). If just one solar panel is in the shade, all other solar panels in the same string could be adversely affected by it. Therefore, make sure that the solar panels are in minimum shade. If there are no other options, then SolarEdge, for example, offers an excellent solution.

Correct configuration of solar panels

Example: a household uses 4500 kWh per year. You can choose to fit a 4500 kWp system. Overall, this will yield around 4100 kWh per year. In this sample calculation we will use the JA Solar Monocrystalline Percium 300WP and a Solis 4k single-phase inverter.

 

Overloading

With 15 solar panels JA Solar 300Wp we arrive at 4500Wp. This exactly matches the household’s consumption. The next step is to choose the number of strings that you want to connect. One of the key factors in this choice in the output voltage of solar panels. If the voltage is too high, it could blow the inverter. Caution: this would invalidate the guarantee because fitting has not been done according to specifications.

The maximum DC input voltage in the Solis 4k is 600 V. The JA Solar 300Wp panel has an open-circuit voltage of 39.85 V. Multiply the open-circuit voltage by the number of solar panels in the string: 15 x 39.85 = 597.75 V. This result implies that the solar panels can be fitted in a single string. However, the temperature coefficient will also need to be included in the calculation. The rule of thumb is to add 15% to the open-circuit voltage: 597.75 x 1.15 = 687.41 V. This number is well beyond the specifications of the inverter. The system must therefore be split between two strings. It is preferable to divide the strings equally where possible. In this case we would have a string of eight and a string of seven.

Start-up voltage

An inverter requires a minimum irradiation and voltage to start. The Solis 4k has a start-up voltage of 120 V. The inverter will start using the open-circuit voltage, but as soon as the inverter starts working, we need to work with the UMPP voltage. The shortest string in our example is 7 solar panels. This gives us 7 x 32.26 V (UMPP) = 225.82 V. Here too, the temperature coefficient will need to be taken into account because it affects the voltage. So this is 225.82 x 0.85 = 191.95 V, which is plenty for starting up the Solis 4k.

Extra tip

The inverter is the most vulnerable part of the system, so pay close attention to where you purchase it. Most manufacturers are from outside Europe and it is often not easy to get in touch with them if there are any problems. Libra Energy is certified to provide after-sales service on behalf of the manufacturer for every inverter that we sell. This means you can be assured of fast and excellent service.