I can invest around 100k+ on equipments or hardware which are related to mining + free electricity I have
Then which coin is best to mine
Well,.. with $100K you can buy 122 Antminers T17 which will give you ~61000 Th/s.
With free energy this can be translated into $905/day acording to whattomine.com at current Bitcoin price of $8650.
Keep in mind that Bitcoin halving is near and this will translate into half of that after May 2020.
Since the halving is near, you can look at coins that already had it's halving i.e. Litecoin.
What is halving? and how it works?
already answered you (missed his reply).
Also if I mine ETH for $100k investing in Rigs and Cards which would then mine only ETH how much per day I can earn in terms of dollars.
Of course you can mine ethereum, but note that ETH will move to PoS (at least this is what they hope) and you won't be able to PoW mine Ethereum anymore. As a backup you should look after some other GPU mineable coins that are worth mining.
EDIT
Like
adaseb said mining is not that profitable if you put your money in the solar array and mining equipment. It will take years to recover your investment.
As an alternative, you can buy and hold Bitcoin - since the price will only increase with time.
Or if you want to have a weekly/monthly income, you can buy 1 or 2 Dash masternodes. (I don't know how much the 1.5 solar array costs but I assume is a lot of money, that's why I said 2 Dash masternodes).
Tip: These 2 alternatives will give you less headaches.