So for a project starting in the near future you can assume that the cost will be around $1.00: First Solar CEO: ‘By 2017, We’ll Be Under $1.00 per Watt Fully Installed’ . So a 1 megawatt solar farm will cost $1 million. You ask what the cost is to build a 1 MW solar farm. It is currently running a little over $5M. In other words, it's about $5/watt installed. If you build a bigger one, you can progressively drop that down to around $2 but that's usually only for the very largest plant sizes.