It is not constant and varies slightly because of random facts like electricity cost etc. But someone surly created detailed 'ideal world mining' charts of Profitability vs. BTC Price.
for example the bitmain s9 (until the next diff inc.) generates ~0.01523574 BTC (~$9.9 at $650/btc) worth of revenue & consumes 32.76kw/day;
so if you pay sth like ¢10 a kwh, each day you'll make $9.9 & pay $3.278 in elec. bills. (again; this will change, mostly decrease, with every diff. change.)
that is for the s9 which is the latest tech & costs $2049 (without psu & shipping!!!)
i wonder why didn't the hashrate drop even more; of course many miners have dirt cheap elec. still i was expecting more of a drop in hashrate!
the next diff seems to be increasing as well!
btc demand is growing for sure but btc has to grow with the demand to accommodate more users;
right now what btc needs most is a resolve to it's scaling problems!
specially since the halving is well past & done, btc's at a point where it either starts growing or starts losing its edge being bottlenecked all the time!