In this situation, the energy will go to the public grid which is not allowed in most of countries in EU.
So you have to avoid this situation.
1) Install current monitoring relay:
http://www.ev-power.eu/_d3376.html
http://www.ev-power.eu/_d4033.html
2) the power of solar system with gridfree have to be lower then your minimum consumption at your home.
Even for this case we recommend to instal Current monitoring relay.
Many information about Gridfree you can find also here:
http://gwl-power.tumblr.com/tagged/mcfaq
http://gwl-power.tumblr.com/tagged/GridFree
http://gwl-power.tumblr.com/tagged/MCInf