Thanks for your help / advice guys... always better to hear other peoples views.
I am hopefully planning add 2 x AMD rigs to compliment our existing 580 rig...
and then start adding Nvidia rigs aswell to make a mini farm.
I have not looked into the 1660ti so I will do some research into these... but its looking likely I will have 1070 and 1660ti rigs going forward.
Do you guys mine to coinbase wallets and extract onto a Ledger Nano or sell/trade weekly/monthly?
Thanks
So... you're not really giving up on mining with $0.15 per kWh? With all the maintenance costs and this price of electricity, I'd recommend you to get your solar energy system completed before increasing the number of your rigs (that solar setup should be your priority IMO). I gave up on mining due to having the power valued at $0.12 per kWh (it didn't really look like being worth it even at that price), and it's interesting to see someone else trying to build up a mini mining farm with an electricity cost more than mine; I sort of appreciate that!
About the wallets, it totally depends upon what YOU are going to plan with your mining revenue. Do you plan on trading them? Or just HODLing them?