I would love to have solar devices on my roof with 20-30% "oversize", and I would definitately use it for mining coins. Unfortunately that investment here in The Netherlands is going to cost me a huge amount of money which I don't have now.

I'm not sure whether your idea is attractive to all people, but it is for people which are already into mining.  I think if you don't even know what Bitcoin is, or - even more difficult - how to mine, you don't want a rig in your house. The latter, you will just "sell" your energy.

With a (GPU) miner of 2000 watt I think you've got a hashrate between 3500/4000 khash/s. You can use http://www.coinwarz.com/cryptocurrency to see how many coins you can mine with this, and how many $ this is going to earn you.

(Use this direct URL and you will see how much you currently can earn with 4000 kh/s, without having electricity costs in mind: http://www.coinwarz.com/cryptocurrency/?sha256hr=1.00&sha256p=100.00&sha256pc=0.1000&scrypthr=4000&scryptp=2000&scryptpc=0.0&scryptnhr=450.00&scryptnp=500.00&scryptnpc=0.1000&sha256c=true&scryptc=true&e=Bitstamp)