To straighten things up from the start, I'm not advising OP to mine like this, I'm not telling anyone to do so because they might end up in court and with a fine or even with a prison sentence depending on the local laws there. But, to debate the mining aspect there is a dilemma :

You have free electricity but you need to be stealthy, so having low consumption gear might get you the stealthy aspect of going under the normal fluctuation in consumption and avoiding the noise, but at the same time doing so you won't be earning that much. Taking full opportunity of the cheap energy and plugging two generations old cheap hardware you can get for scrap metal price might earn you more with less investment but you're going to be in trouble for the consumption per penny earned. Putting too much money into a brand new efficient miner is also trouble since even with free electricity you might never ROI till you get caught because of the high acquisition prices for efficient gear.

So as Phil said, a below ~1kw miner might be the most advantageous choice, but are you ready to risk facing all those consequences for one dollar a day?