As of early 2015, it’s approximately $3.00 per installed watt. The average sized solar panel system is 5,000 watts, so this brings the total cost to $15,000.That 15k figure is just an average amount.he large solar leasing companies are still charging $5.00 to $6.00 per installed watt or more, but their customers only see the lease payment. They simply have too much overhead, advertising costs, and investors seeking a good return on investment to offer a fair price on solar power.