Reaching a Surplus in Solar Power

When more power is generated by a solar system than is need to run the house during the day, the surplus power is inserted into the grid, and the owner of the solar system is given credit for that power. During December, January, and February the days are short and the sun is low in the sky. This means that not a lot of power is generated by a solar system, and it is likely more power will be drawn from the grid than will be added to the grid. The opposite is true during the other months of the year, and it appears that an average of 20 Khw (solar power) each day of the month is needed for solar power to run my house during the day and to replace the power taken from the grid during the night. This value of 20 Khw will probably increase during the summer due to the use of central air conditioning and winter due to low power generation.