Henry Dover answers:

If you average 9 hours per day of peak equivalent sunlight, and we assume that there are 30 days in a month,

9 h/day x 30 days x 1 kW = 270 kWh for a 1 kW array

and double that for a 2 kW array.

If you are in the US, do be aware that there is no state in the country that even comes close to 9 hours peak sunlight per day.

In Honolulu, due to high rebates and cost of electricity, you can get such a system put on at basically no cost, but you then pay the solar company for the electricity generated, at a rate that is generally lower than your normal bill. Or you can buy the system outright, and it will pay back in an average of 4 years.

As a reference, our house is in San Jose, California, and it takes 3 kW of panels to produce 500 kWh per month, about equal to our electricity usage.

With recent drops in panel prices, the cost of a system is now heavily influenced by installation cost. The best thing is to check with some local installers and get free quotes.