If this is true, I would kill for this opportunity. If you truly have free electricity, it's a no brainer in my opinion.
I would probably invest in S7's, you get warranty, better GH/J, and more GH/m2.
If you are not limited by m2/squaremeters, and could get used S5+ from a trusted source, it would probably be a good idea to get some, as they probably give better GH/$.
Surely you have a limit on your free power? In that case I would go for the S7's.
Btw, if this real, I want in.

I do have a limit but it is huge i gotta have 50 s7 running at least to get to the point where the flat tariff we pay rises
Even then here electricity is 0,003$ kwh with no limits. And thats an industrial facility in an industrial zone we pay even less than 0,003 wich is almost paying nothing
ALSO in Venezuela there is a Currency Exchange strict control but there is a huge currency black market if u have any meanings to earn foreign currency you can live like a king here
Problem here is security but like i said it is a facility with guards and CCTV, alarms etc etc.
I was checking a lot of 16 SP20 fore sale what you guys thing of SP20 vs S5? he made me an offer of 16 SP20 with PSU included for 6072$ i made the calculations with a 8% difficulty increar only a monthly 2% raise of BTC price and i break even in 6 months and taking into consideration a halve of blocks in july i still can make 3000$ by january 2017
Im thinking of starting with a small investment of 15 or 20 Antminers S5 or make a big investment (At least for me) of 20 Antminers S7
PD: I would love in a future if i can run a succesful farm to host other ppl miners for a fee i have everything in place in that facility to do it easily thats how i got interested in bitcoin mining
I would start off smaller personally. To go from no miners to 20 of anything.... is a lot of growing pains. You will need proper electricity wiring, and cooling. I don't think a normal factory has been setup for bitcoin mining so you will need to make a area most likely if you have 20 miners going.
Is it 220/240? Do you need to wire the electricity? Add breakers or other things? Do you have PDU's the list goes on and on.
But try a few and see how it goes... then build up if it works good. Don't start with 20 with being new to mining.