Austin Energy Solar Rebate Program
You should visit the Austin Energy website for full details on their Solar Rebate Program. However, for the purposes of this calculator, here are the important numbers. They will pay $5.00 per watt of generating capacity up to $15,000, which represents 3000 watts. The wattage rating is after the inverter efficiency (typically 94%) is considered. Thus it might take 3000 divided by 0.94 = 3191 watts of solar panels to achieve the maximum rebate. Furthermore, they will not subsidize over 80% of the total cost of the system. The calculator accounts for this.

They will pay $6.50 per watt (instead of $5.00 per watt) if the solar panels are manufactured in Austin. However, I believe there are currently no such manufacturing facilities in Austin Texas.