At the moment I have a sofar on grid 3kw inverter with six 350w solar panels connected in series. As the cost of panels are coming down I would like to install additional panels. I understand I can't go above the  max operating voltage but can I use different wattage and voltage panels? Cheers for any help

With your Sofar inverter you are going to have to add panels in series with the existing ones.

 

New panels should be fairly close to the power output of your existing ones (we have 300W in series with 340W with no problems).

 

For panels in series, you should try to get additional ones with about the same or slightly higher Imp (max power current) as your existing ones. The string max current will be limited to whatever the lower Imp panels are. It rarely makes much difference as getting to that level is pretty rare even here.

 

For your voltage the sum of the Voc (open circuit voltage) of all the series panels must not exceed the maximum permitted input voltage of the MPPT. At least here we don't have to worry about cold weather (Voc goes up as the panels get cooler).

10 hours ago, zoolander said:

At the moment I have a sofar on grid 3kw inverter with six 350w solar panels connected in series.

Just replaced some of my 345w panels with 580w panels.

They work together in series just fine, but I lose a little because the older panels limit the current of the newer panels. Recon I'm getting 400w out of the 580w panels, but I'm also getting the advantages of the newer tech, and the much lower prices. These Rapid 580w are between 2,300bht and 2,100bht (with vouchers) inc delivery.

https://www.lazada.co.th/products/i5031706101-s21274917764.html