The answer to this question depends on where you live and how much space you have. We know that 1 unit of electricity is 1 kWh. Let us assume that you need 600 units a month. This is 20 kWh per day. Check your actual average usage using your electricity bill. The average solar in-sol-ation in Bangalore is 5 kWh/m2/day. If your solar panels were 4 m2 then simplistically speaking you would be receiving all the electricity you needed. Of course, there are losses and clouds and all the other predictable things. But the sun does give us 5 units/m2/day, on an average in Bangalore. It is for us to take advantage of this.