Dallas sits at 32.7°N latitude with 234 sunny days per year. A south-facing roof produces approximately 1,400-1,600 kWh per kW of installed capacity annually. The average Dallas home uses 1,100-1,300 kWh per month, so a 6-8kW system covers most or all electricity production on an annual basis.
The math works because Dallas electricity costs are high. Between Oncor delivery charges and retail electric provider rates, Dallas homeowners pay an effective rate of $0.12-$0.16 per kWh. A 6kW system generating 8,400-9,600 kWh per year saves $1,000-$1,500 annually at current rates.