90 TH/s are also rookie numbers. You have 1 in around 83 thousand chance to find a block every day, and about 0.44% chance to find a block in one year. That's finding a block once every 227 years on average. The electricity cost is definitely noticeable, however. Electricity varies on location, but assuming kWh costs a conservative $0.20 in your place, and the miner burns 800 watt, you'll be paying $115 per month just for playing the lottery. Maybe if you're financially well, it's a fun game to play, but it's gambling $115/month is forbidden for most people.