Ok, for anyone that cares and is using a solar site with redundant links with Mikrotik router, here is what I'm doing to only switch the redundant links on when required..
On my upstream links I'm using /29's. e.g.
/ip address add address=172.16.1.188/29 interface=ether5-AF5X-MainBH-Trunk network=172.16.1.184
/ip route add comment="default gateway for main uplink" distance=179 gateway=172.16.1.185
/ip address add address=172.16.1.132/29 interface=vlan311-M5-ReserveBH network=172.16.1.128
/ip route add comment="default gateway for failover uplink" distance=180 gateway=172.16.1.129
(the static routes aren't necessary with OSPF but I'm using them as example)
I then create an IP address facing the netonix for my redundancy netwatch. e.g.
/ip address add address=172.31.1.185 comment=NetonixAF5Xwatchdog disabled=yes interface=ether2-netonix2-Mgmt
And associated netwatch script pointing at the next upstream hop IP (as it's /29 then it can only be seen over the primary upstream link)
/tool netwatch
add down-stript="/ip address enable [find address="\"172.31.1.185/32\"]" host=\172.16.1.185 interval=30s timeout=200ms up-script=\"/ip address disable [find address=\"172.31.1.185/32\"]"
Then I add the WATCHDOG on the netonix to switch on and off the redundant link as required.
You could combine with the POWER option to switch off the primary upstream link when voltage is low or at certain hours of the day when usage is low.
EDIT: In the above image, untick Notify on enable power (disable is fine) as they keep coming through if you have configured SMTP on the Netonix.