In-Order to understand things, you need to understand your energy requirements, for that, I would
advice you to consult your Electricity Bills and number of units your consumed per month.
If you have consumed 600 units of electricity per month then those units represent Kilowatt Hr. of electricity consumed by you.
For Example, if your one energy saver is off 25 watts and you keep it on for 12 hours daily for next 30 days then that represents these many units of electricity per month.
Kilo Watt hr of electricity consumed by Energy saver per month: 25Watt * 12 hrs * 30days /1000 = 9 units.
Similarly, if you run your 2000Watt Air Conditioner for 6 hours daily for next 30 days then that will translate into these many units on electricity bill
Kilo Watt Hr. of Electricity consumed by Air Conditioner on above Condition: 2000 * 6 * 30 /1000 =360 units.
In Air Conditioner, a trick is, that compressor only runs for half the time, so actually you are running your AC for 12 hours in above case.
Now lets come to, that you want to reverse that electricity to national grid and get rid of those bills so in above example your total units becomes 369.
In Order to calculate that, we will assumed few parameters, simplify the data, so that it maybe as close to the reality as possible. We will consider 250 watt of solar panels with 6 hours of daily sunlight with continuous 600Watt/meter-square of solar radiations and 10 % losses.
Here are the formulas.
Daily Harvest in KWh = (Total Panels * Area of Each Panel) * (Assumed Solar Radiation Average) * (Total Assumed time interval of the day considered) * (Efficiency of the solar panels) * (losses as per assumed) * (Conversion into kw)
Month Harvest in kWh= Daily harvest * 30 days
Yearly harvest= Daily harvest * 365 days
Calculations:
Daily
Harvest in kWh= (10 * 1.48) * (600) * (6) * (17/100) * (90/100) *(1/1000)= 8.151 kWh/day
Monthly Harvest in kWh= 32.42 *30 = 244 kWh/month
So with Above calculations, you can see, with 10 solar panels, you would be able to
reverse 244units of electricity back to the national grid. In above calculations, you can increase number of solar panels to null to electricity bills after considering your consumer bill.