Export of Solar Power & Import of Grid Power

Sounds like you need to hire a reputable engineering consultant. Ass, grass, or gas; no one rides for free.

Do your own homework.

How to Search the Internet Effectively | MediaSmarts

How to Search the Internet Effectively

Look at something like.....

http://www.sma.de/en/industrial-systems/commercial.html

If you delve around their site, like a busy dwarf, I am sure details of the configuration and control of a Solar system can be unearthed.

Briefly,

1. The 10 kWsystem at my local community centre has 40 panels which are in two strings of about 500V and 600V each with a DC isolator. The two strings feed into an inverter box, made by SMA which connects to 3 phase 400/230V building supply. It will work with one string isolated.
2. At night, the inverter recognises there is low DC voltage and opens an electromechanical contactor, isolating its main AC power circuit.
3. Import is measured by a meter in the connection to the street supply. Export is not measured, but the quantity generated is measured by another meter Mg. The SMA inverter also measures the kWh generated. Payment is made on the amount shown by Mg.
4. The metering does not tell us the export, even though the supply meter is capable of logging export - data sheet writes it can be programmed to display import and export. Consequently we no longer know building energy consumption!
5. Comparison with "before Solar system" suggests 80-85% of annual generation is exported.

Google and you get good number of articles on Solar energy. In US solar grids are in wide spread use.

Read the following link. you will get answer to all your questions.

http://www.ijera.com/papers/Vol3_issue2/EA32799805.pdf

A2) Solar power is not exported at night.