This calculator assumes your electricity rate is $0.12/kWh. To maximize accuracy, I recommend adding up all 12 monthly electricity bills for the year, divide them by 12, and the result will be your monthly average. This will factor in both your summer and winter electricity usage. Please note that solar system costs depend on the installer and equipment used.
Is the cost too high? The bulk of a solar system's cost is installation fees and 'soft costs', as explained by the DOE. They offer some tips for that.