Every place is different based on laws, tax treatment, and incentives.  In no scenario where I live has producing more than I use to sell back to the utility making any sense. They buy back at the wholesale rate where I live so I am giving away power at a price way below it cost me to produce.  

So I would only size your solar for your own needs.  Also with the power hungry nature of mining you can really only hope to offset a small amount of power demand in a home setting.  So if you look at it from a perspective of reducing the cost per KWH for mining then maybe it can be used in that way.  

I have solar at my home that I built myself and the reality is that it really only offsets a tiny portion of my electric use.  That being said I did it for my own convictions and not from an economic value perspective and I will do it again when I move to my next home as well.  

Having solar, some sort of redundant power supply for emergencies, and even the ability to charge an electric car all are things that are quite appealing to me personally so would rather focus on those aspects more so than the mining side of it.  Quality of life sort of things.