Solar Power

Choosing the inverter for your solar installation

What size inverter do I need?

When it comes to solar inverter sizing, three primary factors are considered: the size of your solar set, geography, and any site-specific conditions.

Size of the solar array

As a general rule of thumb, the size of your inverter should be similar to the direct current (DC) rating of your solar panel system; if you are installing a 6000 watt system, you can expect the proposed inverter to be around 6000 W (6kw), plus or minus a small percentage.

Inverter manufacturers typically list sizing guidelines for the array capacity their inverters can be paired with on their product spec sheets. If the size of the solar array paired with their inverter is outside of the stated guidelines, manufacturers may void their warranty offering.

Geographical location

Geography plays an important role in sizing your solar inverter due to its impact on the solar production. Solar irradiance increases in southern areas/regions/countries. This means that the same 6kw size solution in Spain would produce more power than a similarly sized system in north Germany.

This means that in areas with larger solar irradiance inverter should be sized close to the overall wattage of the solar panel output, so it could handle close to the maximum power output of the array at any given point of time. In other areas where it’s less likely to produce that maximum output defined by the DC rating then smaller sized inverter will get the job done.

Some site-specific factors

Direction and tilt of the solar array have the similar effect as geography. Also environmental factors like dust or trees play a large role in the DC output capabilities of the solar array. And again smaller sized inverter can be chosen.

So what size inverter to choose?

So all the above is nice and general – but what size to choose?

Typically it is ok to go with an inverter 10-15% of the size of your solar DC output. Typically for 6kw solar array a 5kw-5,5kw invereter is totally fine for any given location.

If the locational and site-specific factors are affecting the installation then up to 50% of the size of the inverter ca also be ok, i.e. for the same 6kw DC output system you choose 3kw inverter.

What happens if I overly downsize the inverter?

The situation where solar array system produces more than the inverter can handle. This is called clipping. Clipping in essence is not anything dangerous but you are simply losing some of the energy the solar array is producing.

Should I oversize the inverter?

No. You shouldn’t install a solar inverter that’s too big against the solar array because the inverter is going to be most efficient if it’s running close to its overall capacity. If the inverter is too large compared to the array, it will not produce the desired amount of electricity.

Summary

If location and site are favourable – choose the inverter 10-15% of the size of solar DC output – > 12kw solar output, 10kw inverter is ok.

In northern hemisphere, with solar panels facing for example east or west, with the roof tilt not the most favourable, with the 12kw solar output you are ok to choose 6kw inverter.