A lot of it is down to your hard work boab, and also because of continued traffic and cross linking. The Google bots are very cleverly designed and take into account all sorts of factors. As long as we keep the momentum going it will steadily up its rankings to the point where you may be approached to sell advertising space on the site.
This may be needed to keep it free or you are forced to take a fee to pay for bandwidth and space usage, it is a bridge all growing sites will have to cross. Bandwidth and space not free.