I've imported 2x 300w mono panels from China about 6 years ago and mounted them on my east facing roof. Then added 2x 310w poly panels on my west facing roof. Their voltage specs were close enough as a match and I seem to get some good days between 600 and 800w at peak time. However, I would like to upgrade my panels to a higher watt and more efficient type as my panels are still of those old type. I would like to know what the dangers are of mixing those old panels with ones of higher watts. The logic behind this is to be completely sun reliant during the day with little or no use of the battery, keeping the battery fully charged for evening and night time loadshedding. Can someone lease advise? My battery is a Hubble AM5 5kva with mecer 5kva inverter.

11 minutes ago, erikvs said:

I've imported 2x 300w mono panels from China about 6 years ago and mounted them on my east facing roof. Then added 2x 310w poly panels on my west facing roof. Their voltage specs were close enough as a match and I seem to get some good days between 600 and 800w at peak time. However, I would like to upgrade my panels to a higher watt and more efficient type as my panels are still of those old type. I would like to know what the dangers are of mixing those old panels with ones of higher watts. The logic behind this is to be completely sun reliant during the day with little or no use of the battery, keeping the battery fully charged for evening and night time loadshedding. Can someone lease advise? My battery is a Hubble AM5 5kva with mecer 5kva inverter.

In order to assist provide the name and model of the inverter used as well as the Vmp and Imp of the current panels and we can help to explain. 

Also indicate how are they connected - series or parallel. 

The inverter is a mecer sol-i-ax-5m 5000va the panels are connected: east side pair in series, west facing side in series. Both sets in parallel into the inverter.

Max power voltage of the one brand panel is 36.2v and max amp current is 8.29A. other brand is: max power voltage 36.6 and max power current is 8.2A.

3 hours ago, erikvs said:

Max power voltage of the one brand panel is 36.2v and max amp current is 8.29A. other brand is: max power voltage 36.6 and max power current is 8.2A.

It appears if you can only fit up to 3000w in panels. You can confirm it on the sticker on the side of the inverter. This leaves you with 1800W to add in parallel with each set on east and west side. Stick to any size panels with a 36-37V Vmp. If you add larger panels with higher voltage for example 48V @ 9.5A for 455w you will loose 12VX9.5X2=227w of the 910w you add in parallel per side. Quite a high wastage for power paid for. 

I would rather look for the same voltage panel even if it mean adding 4 smaller panels per side. I assume your current panels are 60 cell panels. The current does not matter as long as you stick to around the 3000w level in total. 

This is my take on your question around mixing.